A03:
BUILDING ACOUSTICS

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0178

Development of measurement methods using sound intensity forevaluating top-of-wall joints
Wayland DONG1; John LOVERDE2; Chris KEZON3
1,2
3

Veneklasen Associates, USA

Western Electro-Acoustic Laboratory, USA

ABSTRACTIn the United States, there is no accepted procedure for characterizing the acoustical performance of narrowslits such as the joint at the top of a stud-framed wall. Such a method would allow for comparison of products
and methods, and calculation of the effect of joint performance on the overall isolation of the wall. The
differences due to changes in joint type can be difficult to evaluate with full-size walls, further complicatedby the reproducibility variations in laboratory testing. A test method similar to ISO 10140-1 Annex J wasdeveloped, which involved building small cassettes which only held the joint and measuring the transmission
loss per unit length of joint. This method was evaluated in a previous paper (Internoise 2020), and it was
shown that while the repeatability of the method was acceptable, the dynamic range was insufficient for the
products evaluated. In this paper, the authors develop and evaluate a modified cassette method using soundintensity to measure the transmission loss. Compared to the reverberant field measurement, using soundintensity appears to provide increased sensitivity and precision.
Keywords: Sound, Insulation, Gap, Top-of-wall

1. INTRODUCTION
It is well known that air leaks at the top of walls where they intersect with the structure cansignificantly degrade the airborne noise isolation. It is conventionally considered best practice toestablish an airtight seal at the top-of-wall joint using resilient caulking. Various products exist that
can take the place of a caulked joint from a fire safety perspective. However, in North America there
is no standardized or broadly accepted method for evaluating the acoustical effect of these products,
top-of-wall joint design, or any similar narrow element.
It may seem obvious that one could simply construct a wall in the lab with the proposed top -ofwall joint and compare this to a standard test of the same wall with the top fully sealed. This could
show equivalence to the traditional method of caulking or simply evaluate the wall’s acousticalinsulation. However, this method is impractical due to uncertainty in the measurement procedure. It
is common for different accredited laboratories to report differences in transmission loss on the samewall assembly that exceed 10 dB at the relevant mid- and high-frequency bands. (For example, theASTM reference assembly, despite being designed to minimize variation in construction, has a
reproducibility standard deviation of 3 dB or more at the upper frequencies. (1)) These uncertainties
make it impossible to use traditional acoustical test methods to determine by comparison whether thedifferences are due to the top-of-wall joint or to variability in the measurement.
Development of a robust methodology would have additional benefit beyond evaluating products.
While holes or cracks observed in separating construction rightly raises the suspicion of possible
sound leaks, these do not necessarily have a significant effect on the airborne sound isolation. Suchleaks and other workmanship issues are often blamed, when in practice equal or greater attention
should be placed on other possible causes such as flanking sound transmission. (2) The authors havepreviously documented how acoustical experts tend to automatically blame installation errors for
1
2

wdong@veneklasen.com
jloverde@veneklasen.com

lower than expected sound ratings of walls with resilient channels, when the actual problem wasinsufficient consideration of statistical variation of wall performance. (3) Similarly, top-of-wall leaks
are often blamed reflexively, even when (in hindsight) it is rather unlikely that they were the primaryissue or the potential cause of the actual performance limitation. Often, the “solutions” are wholesale
modifications of a variety of components of construction rather than focusing on the actual limitationsof the assembly. These failures are due to a lack of understanding in the limitations of the existingdata and test methods.
It is therefore valuable to develop a method for reliably and quantitatively evaluating the acoustical
performance of top-of-wall joints. This would give a means to investigate the effect of errors inconstruction.

2. REVERBERATION ROOM METHOD
2.1 Previous Results
In a previous study (4), the authors developed a test method based on ISO 10140-1 Annex J. (5)The standard states that this is applicable to “acoustic sealing of slits (with or without fillers)” as well
as gaskets and door or window seals. The test method is the same as typical measurement of soundreduction index, except calculated by length (per meter of the joint) rather than by area (per square
meter of the wall).
Testing was performed as described in ASTM E90 (6), except that Eq. (5) in that document is
modified to𝑙0 𝑙(1)𝑇𝐿(𝑓) = 𝐿𝑆 (𝑓) − 𝐿𝑅 (𝑓) + 10 log
𝐴𝑅 (𝑓)
where 𝑇𝐿 is transmission loss, equivalent to sound reduction index; 𝐿 is the average sound pressurelevel and 𝐴 is the acoustic absorption (in m 2) in the source (𝑆) and receive (𝑅) chambers, indicatedby subscripts; 𝑙 is the length of the specimen in meters, and 𝑙0 is the reference length of 1 m. We
refer to this as the reverberation room method.
Testing was performed at Western Electro-Acoustic Laboratory in Santa Clarita, California. WEAL
is NVLAP-accredited for ASTM E90, which defines airborne noise insulation measurements
analogous to ISO 10140-2. The dimensions of the receiving chamber were 6.3 x 4.5 x 5.2 m. The
opening between the chambers is nearly the entire common wall; a filler wall is built in the opening
to reduce the size of the test opening. The filler wall is constructed of double wood studs, 150 mm
and 200 mm deep (6 inch and 8 inch, nominal, respectively), with a 50 mm gap between the studs,
glass fiber batt insulation in the stud cavities, four layers of 16 mm (5/8-inch) type X gypsum wallboard on the source side and three layers on the receive side. The measured insulation of the filler
wall is STC 73 and R w (C; C tr) = 72 (-1; -4).
The cassettes were much thinner than the filler wall between the test chambers. The cassette wasmounted flush with the filler wall on the source room side and sloped in the vertical direction on thereceive side to avoid a deep tunnel or niche. This was accomplished by cutting the studs at an angle
in a manner that did not bridge the stud rows; this is shown in Figure 1.

Figure 1: Rendering (left) and photo (right) of test opening for cassette testing
2.2 Previous results
Here we summarize key findings from the previous study.
• The frequency range of the method was limited to frequencies above 500 Hz.
• The dynamic range of the method appeared to be insufficient to accurately measure thejoints under test. The measured isolation of the joints in that study differed from the
maximum TL by just 6 dB. The situation was not improved even when the length of thejoint was doubled, which should have increased the signal to noise ratio.
• The method was largely independent of the length of the joint, as desired.
• Full-scale testing of a wall with the joint under test was performed and compared with thecassette test of the joint. The TL of the cassette data was significantly lower than the fullscale wall, and using the cassette data would significantly underpredict the actual
performance of the wall in this case.

3. SOUND INTENSITY METHOD
3.1 Measurement Method
It seemed that the reverberation room method had insufficient sensitivity to accurately measure thejoints under test, and we suspected that this was due to flanking noise through the filler wall assembly,or the complexities of the coupling of a small source to a large reverberation room. Because soundintensity can directly measure the radiated sound power and can reject sound radiated from flanking
paths, it had the potential to be a better measurement method.
The filler wall and cassettes were constructed in the same manner as in the reverberation room
method. The transmission loss was measured using a sound intensity probe following the procedure
in ASTM E2249 (7). Acoustical absorption was added to the receiving chamber to create a sufficiently
absorptive receiving room.
3.2 Measurements
The cassettes were 1.25 m x 0.25 m high x 216 mm deep. A very short double stud wall wasconstructed in the cassettes, consisting of two sets of 64 mm (2.5 inch) steel studs with a 25 mm air
gap and insulation and two layers of 16 mm (5/8-inch) type X gypsum board on each side. The gypsum
board was cut to provide a defined gap at the top of the wall.
Several top-of-wall joint products were tested, including traditional caulk, with different sized gaps.
For each configuration of product and gap size, the cassette was installed and both measurement
methods were performed without disturbing or reinstalling the cassette.
3.3 Results
Some representative results are shown in the following figures. Figure 2 shows the reverberation

room method and Figure 3 shows the intensity method of the same products. The black and grey lines
are the traditional caulk, the light blue and light red lines are two products under evaluation, and thedark red line shows the gap with no product or sealant. (Note that this is not a clear gap because of
the presence of the solid top stud track.)
70

Sound Reduction Index (Rs), dB

65

60

55

50

45

5000

4000

3150

2500

2000

1600

1250

1000

800

630

500

400

315

40

Frequency, Hz

Figure 2: Transmission loss of cassettes measured using reverberation room method.
70

60

55

50

45

Frequency, Hz

Figure 3: Transmission loss of cassettes measured using intensity method

5000

4000

3150

2500

2000

1600

1250

1000

800

630

500

400

40

315

Intensity Transmission Loss (ITL), dB

65

As before, there were only significant differences observed above 500 Hz, and most strongly
between 1000 and 4000 Hz.
The reverberation room and intensity methods gave broadly consistent results. However, thereverberation room method showed limited dynamic range, similar to the previous results, with only
about 6 dB between the tested assemblies. The intensity method resulted in much higher transmission
loss values for the caulked joints, especially above 1000 Hz. The difference between the intensity
method and the reverberation room method increased with the performance of the joint. This suggeststhat the reverberation room method is being controlled by flanking or other paths, and that the intensity
method is successfully excluding these paths. With the intensity method, smaller differences between
the tested joints can be observed.
The joint with no sealing material (dark red curve) tested 2-3 dB higher with the intensity methodthan the reverberation room method. Similar biases between the reverberation room and intensity
methods are reported in the Appendix of ASTM E2249. Further investigation will be required todetermine whether this is due to flanking paths or inherent in the measurement method.

4. CONCLUSIONS
Acoustical testing of joints is needed to properly assess the effectiveness of the joint sealing
methods and the risk associated with the leak that may occur at these locations. Current measurement
methods do not provide enough information but require additional assessment for correlation,accuracy and meaning in terms of acoustical performance and effectiveness.
A small-scale cassette method patterned after ISO 10140-1 Annex J has been developed and used
to measured top-of-wall joint products and conditions. The difference between the joint types isobserved in the frequency range above 500 Hz. Measuring the transmission loss of the joint using
sound intensity gives significantly greater dynamic range compared to the reverberation room method.
The reverberation room method may be limited by flanking through the structure supporting thecassette.
Using the cassette mounting method and measuring the transmission loss with sound intensity is apromising method for measuring and comparing the performance of joints. Because sound intensity
is easily performed in the field as well as the laboratory, this method may also be suitable for in situ
measurements. Further investigation will determine whether the performance of full-scale walls withvarious top-of-wall joints can be predicted using this method.

ACKNOWLEDGEMENTS
The authors wish to thank their colleagues at Veneklasen Associates, Inc., for their support, and to
the staff at Western Electro-Acoustic Laboratory for their assistance. Partial funding for this project
was provided by the Paul S. Veneklasen Research Foundation.

REFERENCES
1. ASTM E1289-08, Standard Speciﬁcation for Reference Specimen for Sound Transmission Loss. ASTM
International, West Conshohocken, PA; 2016.
2. Hopkins C. Sound Insulation: Theory into Practice. Routledge; 2014.
3. LoVerde J, Dong W. Who pays? Defining construction defects and assigning blame in borderline
acoustical assemblies. J Acoust Soc Am. 2008 Oct 1;124(4):2441.
4. Dong W, LoVerde J, Kezon C. Investigation of methods to evaluate acoustical effects of top-of-wall joints.
In: Proc INTER_NOISE 2020. 2020.
5. ISO 10140-1 (2016), Acoustics - Laboratory measurement of sound insulation of building elements Part
1: Application rules for specific products. International Standards Organization; 2016.
6. ASTM E90, Standard Test Method for Laboratory Measurements of Airborne Sound Transmission Lossof Building Partitions and Elements. ASTM International, West Conshohocken, PA; 2016.
7. ASTM E2249-02, Standard Test Method for Laboratory Measurement of Airborne Transmission Loss of
Building Partitions and Elements Using Sound Intensity. ASTM International, West Conshohocken, PA;
2016.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0500

Acoustic beamforming applications in construction
José Carlos GINER1; Pedro do ESPÍRITO SANTO NETTO1; Murilo SOARES1; Bárbara FENGLER1;
Raquel ROSSATTO1; Luís Eduardo SOARES2
1
2

GINER, Brazil

Electro-Media Design, USA

ABSTRACTThis work aims to present the application of beamforming techniques for building acoustics. The main
purpose for applying this method in building acoustics consists in the qualitative characterization of soundtransmission through constructive elements, such as window frames, walls and doors, by checking criticalsound transmission and leakage spots. In the present work, tests were performed in buildings by using anomnidirectional sound source and an acoustic camera. Frames, walls and doors were analyzed, seeing thateach case addresses distinct goals. Evaluations were also performed with respect to the influence of soundleakage upon the acoustic insulation parameters used as reference in the Brazilian standard ABNT NBR
15575. Investigating the results obtained, it became possible to validate the effectiveness of employing the
beamform technique. It is possible to detect constructive failures in advance, preventing future problems, and,in a corrective manner, diagnosing sound leakage spots, allowing faster solutions to provide increased
acoustic insulation for a constructive element.
Keywords: Beamforming, Insulation, Transmission

1. INTRODUCTION
Due to the growing concern regarding acoustic comfort in buildings, new technologies must be
used to guarantee the sound insulation in a building. One practice which has become increasingly
widespread concerning the design of buildings is the development of acoustic projects capable ofestimating the insulation levels by using a simulation software.
However, simulations tend to work well in ideal scenarios, disregarding construction difficulties
and execution failures, which commonly occur in most construction sites. Because of that, to get the
expected results, the construction sector must take all the precautions rec ommended by the acoustic
project.
Despite that, there are many cases in which corrective actions must be taken to solve constructive
failures. In such cases, the more accurate the method when diagnosing problems, the more effective
solutions tend to be. One of the most advanced procedures in terms of acoustic measurements is theuse beamforming techniques. As per reference FONSECA (1), the beamforming method consists in atechnique for locating sound sources based on wave beam shaping, coming from a given direction or
region in space. The main purpose of applying this method in building acoustics is characterizing
sound transmission in a qualitative term, by means of constructive elements such as frames, walls anddoors while checking all the critical points for sound transmission and leakag es. Furthermore, it
becomes possible to spot possible flaws, either in the construction or installation of constructive
elements.
Studies addressing the application of such techniques are presented in this work, in order to solve
acoustic insulation and sound transmission problems in buildings.

2. MEASUREMENTS CONFIGURATION AND GOALS
The goal of such assessment, as reported in this work is to characterize sound transmission
1

lab@giner.com.brregarding constructive elements, as well as the identification of possible sound leakag e spots withinsuch elements. To that end, the following test rig was set up:

Figure 1 – Assay configuration
The purpose is creating a sound field in the source room as uniform as possible, covering the entire
extension of the partition under evaluation. Therefore, it becomes possible to carry out measurements
by means of an acoustic camera, capable of locating all the spots where major sound transmissions
levels take place within constructive elements.
Tests were carried out to obtain suitable configuration settings by varying sound sources of distinct
directivities as well as signal types and frequency ranges while also evaluating background noise
influence. The best configuration was found out to consist of an omnidirectional sound source
employing white noise as excitation signal, with a frequency range coverage of 3 to 10 kHz.

3. CASE STUDIESIn this section are presented practical case studies regarding the application of beamforming
techniques in construction works. Each case had a distinct goal which shall be described under eachsubsection.
3.1 Checking frame installation
The goal here was to check frame installation standardization at the construction site. To that end,
samples were taken from the same frame types on distinct floors. Tests were performed for each of
the samples, as shown in Figures 2 and 3.

Figure 2 – Results: Framing from the 3rd floorIn this case, as can be seen in Figure 2, there is no observable sound leakage from the frame.
Contrary to that, the frame shown in Figure 3, which presents identical composition to the first one,showed some sound leakage pointwise which became predominant at its uppermost edge.

Figure 3 – Results: Framing from 12th floor
After construction workers carried out an inspection to find out the causes for such leakage, it was
found out lack of mortar in the framing’s upper edge. In situations like that, it would not have beenpossible to spot this fault from visual inspection alone, given that the framing structure conceals sucharea. It demonstrates beamforming measurements effectiveness.
Another similar case was carried out over the balcony doors shown in Figure 3.

Figure 4 – Balcony doors

Once again, the study was carried out on samples from the same framing on different floors within
the building. The door under test, as shown in Figure 5, had been correctly installed, seeing that the
pointwise leakage detected in its upper central portion (panel junction) is due to framing configuration.
In Figure 6, which shows the tests for a door from another floor. One can notice a specific soundleakage, which is predominant in the upper portion of the door’s left panel.

Figure 5 – Results: Balcony Door from 5th floor

Figure 6 – Results: Balcony Door from 6th floor
By approaching the acoustic camera to the leakage area (Figure 7), it became possible to conclude
that sound was being transmitted through an existing gap between glass and sash, due to the lack of asealing element around its edge, as shown in Figure 8. Thanks to such assessment, the construction
team carried out an inspection on all the building’s doors, performing repairs as needed.

Figure 7 – Results: Door’s left panel in detail

Figure 8 – Lack of sealing element
3.2 Low acoustic insulation levels between office rooms
This specific case is a commercial building whose offices were already occupied. It is an office inwhich its users complained about the lack of privacy between adjacent rooms due to the low soundinsulation level of the partitions used. These partitions were made out of Drywalls and users suspectedthat their low acoustic performance was linked to constructive failures or the drillings mad e during
the equipment’s installation.
A beamforming assay was then performed by placing the omnidirectional sound source within asource room, while taking measurements from the acoustic camera in the adjacent room, the receivingroom. The goal is to determine how sound transmission was taking place in this partition. Test results
may be viewed in Figure 9.
Upon assessing the results, it became possible to notice that the predominating sound leakage camefrom the ceiling and not from the partition itself. After close investigation with those in charge of theconstruction, a peculiar characteristic of the building's air conditioning system was identified: there
were microperforations in the ceiling and the rooms got mutually connected, since the partition h eight
extended up to the ceiling only. Therefore, the sound emitted in one of the rooms would enter theceiling through these microperforations, reaching the adjacent room through the same path.
Due to the precise diagnosis provided by the beamforming assay, it became possible to act directly
upon the core of the problem by improving the sound insulation between rooms.

Figure 9 – Results: Ceiling-bound sound transmission
Measurements have also been carried out between one of the meeting rooms and the offi ce
reception. In this case, the door was identified as the weaker element, responsible for most of thesound transmission taking place. There was a large gap in this door’s upper portion thar would be hard
to be noticed visually due to ceiling placement. Nonetheless, it was detected after the beamforming
assay had been performed, as shown in Figure 10.

Figure 10 – Results: Door-bound sound transmission
3.3 Sound leakage between walls from distinct units
In this case, the goal consisted in determining the airborne sound insulation of a masonry partition
separating bedrooms from different units within a residential building, by determining the Weighted
Standardized Level Difference ( 𝐷n𝑇,w ) according to ISO 16283-1 standard (3). Such assay is
mandatory for new buildings in Brazil, which must follow the limits of acoustic performance
regarding constructive elements according to the ABNT NBR 15575 standard (2). In this specific case,the partition should present a value of 𝐷n𝑇,w = 45 dB.
Simultaneously to this, a beamforming assay was also carried out in order to characterize wall bound sound transmission.
Initially, the perception was that sound transmission took place smoothly all along the partition.
However, upon performing a full-wall scan, pointwise leaks were spotted from the electricalswitchboxes, according to the results shown in Figures 11 and 12.

Figure 11 – Results: Wall-bound sound transmission

Figure 12 – Results: Sound leakage on electrical switchboxes
Once the source of leakage had been identified, an immediate solution was used: fulfill the referredcavity with burlap. The effectiveness of such quick solution may be verified in Figure 1 3. Bycomparing Figures 11 and 13, one can notice that the specific sound leakage from the electricalswitchboxes ceased afterwards, leaving just the transmission of sound going through the wall itself.

Figure 13 – Results: Wall-bound transmission after leakage isolation
Acoustic insulation measurements were then carried out in order to determine the Weighted
Standardized Level Difference (𝐷n𝑇,w) for the partition, both with and without insulation fixes at theelectrical switchboxes. Figure 14 displays a comparison between both situations.

Figure 14 – Measured results for acoustic performance, shown both with and without solutions for the
leakage problem.
By assessing these results, it can be observed a 1dB increase in the 𝐷n𝑇,w value regarding thepartition, after the correction of the sound leakage spot. Such increase is quite significant, especiallyin those situations when acoustic insulation values are found to be very close to the acoustic
performance limit values set out by a specific standard.
3.4 Sound leakage in facade window frames
The standard for building performance in Brazil (2) specifies the acoustic insulation values forbuilding facades, according to the soundscape where these are located. Therefore, consideringbuildings located in very noisy environments, such standard specifies that the Weighted Standardized
Level Difference measured at a distance of 2 meters from the facade must be at least 30 dB(𝐷2m,n𝑇,w ≥ 30 dB).
The building addressed in the latter case fits the situation described above. In order to check
whether this building's facades would meet the minimum performance required by the standard,measurements in accordance to the ISO 16283-3 standard (4) were performed, to obtain the 𝐷2m,n𝑇,w
value. The results obtained showed that facade did not meet the mandatory requirement (𝐷2m,n𝑇,w ≥30 dB), having attained 𝐷2m,n𝑇,w ≥ 27 dB.
The main problem faced is that this situation was only detected when the construction work was
already concluded. Therefore, any solution found should be replicated for more than 300 existing
dormitories in the condominium, something that could generate extra costs, affecting directly the
project’s economic results.
Given the relevance of finding economically feasible solutions, beamforming measurements werecarried out for the facade. Figure 15 shows the environment under test. Our goal was to find the mostsensitive region along the facade and help the supplier in finding specific and simple solutions toachieve the minimum and mandatory results at the lowest costs possi ble.

Figure 15 – Measured room

The facade was made up of masonry; however, there was an area measuring approximately 0.4 m²
which had been covered with plasterboards only, to be found below the window line. This is a usual
practice which makes it possible for future users to install their air conditioning systems inside
bedrooms. Therefore, the first assessments aimed at checking the contributions from each constructive
element through transmission means, determining which of these would be more se nsitive from aninsulation standpoint. Figure 16 shows the results for this study. It becomes clear that soundtransmission takes place through the frame mostly.

Figure 16 – Result: Initial assessment of sound transmission through window frames
Therefore, we set out to determine which spots over the frame were the most sensitive ones. The
results showed that the upper corners had sound leakage due to existing cracks in the window frames.
The right corner displayed greater sound transmission range, and, for such a reason, it was the first
one upon which solutions were attempted. These results are shown in Figures 17 and 18.

Figure 17 – Results: Sound transmission level assessment through window frames

Figure 18 – Results: Approximate assessment of sound transmission by window frame
In order to seal the gap existing in this area, a fixed sealing element was added on the outer sideof the frame. Such element sealed the gap existing between rail and window frame, without impairing
frame movement. Figure 19 shows the solution already installed.

Figure 19 – Solution employed for sealing of main crevice
In order to check the effectiveness of such solution, another acoustic performance measurement
was carried out. Figure 20 shows a comparison of results, both before and after providing a solution.

Figure 20 – Measured results for acoustic facade insulation, both before and after a solution was fitted in.
When evaluating the results, one can notice that such solution significantly increased performanceby 5 dB, as the value found for 𝐷2m,n𝑇,w reached 32 dB. It is also noticeable the improved
performance from 1000 Hz upwards, caused by the crevice’s sound transmission characteristic.
Therefore, due to the precise diagnosis ensued by the beamforming assays, it became possible tocorrect a very unfavorable situation, by means of a simple and economically feasible solution.

4. CONCLUSIONS
After having assessed the results obtained under the most diverse situations and with distinct goals,
it was showed the relevance of acoustic measurements making use of the beamforming technic. It
allows the precise identification of all sound leakage spots, allowing for faster, more effective andcheaper solutions.

5. ACKNOWLEDGEMENTS
We wish to thank the staff at Giner and as well as all those who took part in this projec t, either
directly or otherwise, during the performance of measurements.

REFERENCES
1. Fonseca, William D’Andrea, “Beamforming Considering Acoustic Diffraction over Cylindrical Surfaces[tese] / William D'Andrea Fonseca ; orientador, Samir Nagi Yoursi Gerges ; co-orientador, Michael
Vorländer; co-orientador, Arcanjo Lenzi. - Florianópolis, SC, 2013. 340 p.
2. ABNT NBR 15575:2013 - Desempenho de edificações habitacionais
3. ISO 16283-1:2014 - Acoustics — Field measurement of sound insulation in buildings and of building
elements — Part 1: Airborne sound insulation.
4. ISO 16283-3:2016 - Acoustics — Field measurement of sound insulation in buildings and of building
elements — Part 3: Façade sound insulation

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0175

Measurement and estimation of the flanking impact soundtransmission in timber frame building constructions
Maximilian NEUSSER1; Thomas BEDNAR 2
1

Technische Universität Wien, Institute of Material Technology, Building Physics, and Building Ecology, Austria

ABSTRACTThe Kij vibration reduction index is the essential parameter for characterizing the flanking transmission of
impact sound in buildings. The calculation method according to EN ISO 12354-2 based on Kij has been
established for many years for heavy homogenous constructions. For timber frame constructions, thedetermination of the vibration reduction index is not, with sufficient accuracy, possible. The parameter used
for characterizing the flanking sound transmission in timber frame constructions to estimate the normalizedflanking impact sound pressure level Ln,f is the direction-averaged vibration level difference Dv,i,j. The paper
discusses the applicability of this method for timber frame constructions by comparing the measured and thepredicted normalized flanking impact sound pressure level Ln,f of a timber frame T-joint. The directionaveraged vibration level difference Dv,i,j was measured in a test facility in one T-joint configuration under
different loads on the joint. The measurement result was used to calculate Ln,f. The results are compared withthe measurement of the normalized flanking impact sound pressure level by shielding the direct transmission
path. The results show that with minor modifications of the measurement procedure, a satisfactory agreement
between the prediction model of the EN ISO 12354-2 and the measurement result can be achieved.
Keywords: Flanking Sound Transmission, Light weight constructions, Timber Frame Buildings

1. INTRODUCTION

An essential parameter in the planning of buildings and for predicting the flanking soundtransmission of impact and airborne sound in the EN ISO 12354 series of standards is the vibration
reduction index Kij . [1] This calculation method has been established for many years for solid mineral
constructions components and there are standardized prediction models for its input variables. The
Kij approach and the related measurement methods are only valid with the assumption of a diffuse
structural field. [2] Therefore, it is not useable to measure vibration reduction indices for joints inlightweight constructions (type B components according to EN ISO 10848-1). The revision of DIN
4109 “Sound Insulation in Buildings” use a prediction Model based on the measurement of theflanking sound pressure levels. [3] This model shows reliable calculation results but the measurementof the necessary input parameter D n,f,w is a labor-intensive and complex task. The parameter used in
EN ISO 12354-2 for the calculation of the standard flanking impact sound level is the normalized
direction averaged vibration level difference ��������
𝐷𝐷𝑣𝑣,𝚤𝚤𝚤𝚤,𝑛𝑛 . From the authors' point of view, the applicabilityof EN ISO 12354-2 in timber frame construction has not yet been confirmed and is currently one of
the current scientific issues. [4] In addition to the basic applicability, there are currently nostandardized calculation models for the prognosis of, the essential input parameters, for lightweighttimber construction. [5] The areas carried out in the paper put this applicability up for discussion bycomparing the measured normalized flanking impact sound pressure level Ln,f to the, in accordancewith EN ISO 12354-2, predicted Ln,f. For this purpose, the normalized direction averaged vibrationlevel difference of a T-Joint in timber frame construction was measured. For the same T-joint, thedirect sound transmission path was shielded and the resulting normalized flanking impact soundpressure level was measured and compared to the calculation result.

1
2

maximilian.neusser@tuwien.ac.at
thomas.bednar@tuwien.ac.at2. METHOD

The evaluation of the component and joint characteristics was carried out in accordance with thecurrently valid standards. The EN ISO 10848 series was used as the essential standard for measuring
the vibration level differences and the flanking sound pressure levels. The quantities to be determined
for the characterization of the joint are the normalized direction averaged vibration level difference
D v,ij,n and the normalized flanking impact sound pressure level Ln,f. Both parameters can be used inaccordance with ÖNORM EN ISO 12354-2 to calculate the normalized impact sound pressure level
L'n including the direct and the flanking sound transmission. The measurement of Ln,f requires a closed
recieving room and insulation of the flanking transmission path by shielding the direct soundtransmission path, which makes the test setup significantly more complex than for the determinationof D v,ij,n.
2.1 Measurement
The spatial averaging of the vibration levels was carried out per excitation position at fourmeasuring positions on the respective component surface. Structure-borne sound excitation takes
place at four positions per transmission direction. The vibration levels measured on both components
simultaneously perpendicular to the component surface are used to determine the vibration level
difference according to equation 1.
𝑀𝑀

𝑁𝑁

1
𝐷𝐷𝑣𝑣,𝑖𝑖𝑖𝑖 =� �(𝐷𝐷𝑣𝑣,𝑖𝑖𝑖𝑖 )𝑚𝑚𝑚𝑚
𝑀𝑀𝑀𝑀

(1)

𝑚𝑚=1 𝑛𝑛=1

In formula 1 M is the number of excitation points on component i, and N the number of measuring
positions at each component. The vibration level difference (𝐷𝐷𝑣𝑣,𝑖𝑖𝑖𝑖 )𝑚𝑚𝑚𝑚 is calculated for one excitation
point and a measurement position pair in dB. The excitation was carried out on the outside andunderside of the components by means of a small hammer mill "System Gössele". The hammer milluses a plunger to carry out a pulse-like excitation with a frequency of 10Hz. The nominal stroke hightof the 22g heavy hammer mass is around 5mm. According to EN ISO 10848-3:2018, the measurement
was carried out in both transmission directions. The measurement was carried out with a calibrated
measuring equipment of the type "Sinus Messtechnik Soundbook_octav with software SAMURAI
1.7.14, calibrated as a sound level meter of class 0.7". The vibration levels at the component surfaces
were measured with accelerometers of the type "ENDEVCO ISOTRON 65-10-Z". According to Figure
1, the accelerometers were attached to the measuring positions of the respective component by meansof beeswax.
1������
𝐷𝐷𝑣𝑣,𝚤𝚤𝚤𝚤 = �𝐷𝐷𝑣𝑣,𝑖𝑖𝑖𝑖 + 𝐷𝐷𝑣𝑣,𝑗𝑗𝑗𝑗 �2(2)

The normalized flanking impact sound pressure level Ln,f and the normalized impact sound pressurelevel L’n was determined by the spatial and temporal averaging of the sound level L2 in the receivingroom, which is generated by sound radiation of the wall and ceiling component of the T-joint. The
ceiling was excited on the top surface by a tapping machine. The bottom of the ceiling in the receivingroom was shielded for the measurement of Ln,f by a self-supporting suspended ceiling (80mm airspace
filled with mineral wool, 12.5mm gypsum fibreboard) in accordance with ÖNORM EN ISO 108481:2018. As a result, the direct sound transmission path is blocked and only the flanking soundtransmission contributes to the sound pressure field in the receiving room. This shielding wasdismantled again to determine L’ n. The measurement of L2 is carried out by averaging the soundpressure level determined at three measuring positions of the rotary microphone boom. The equivalent
absorption area A required for the calculation was determined by measuring the reverberation time in
the receiving room according to EN ISO 10140.
𝐿𝐿𝑛𝑛,𝑓𝑓 = 𝐿𝐿2 + 10𝑙𝑙𝑙𝑙

𝐴𝐴
𝐴𝐴0

(3)

Figure 1 - (left) Attachment of the accelerometer to the component surface; (right) Excitation of thecomponent by means of a small hammer mill "System Gössele"
The measurement of the normalized flanking impact sound pressure level Ln,f was carried out inaccordance with the EN ISO 10848 series of standards with calibrated measuring equipment of thetype "Norsonic Dual Channel Real Time Analyzer Type 830". The impact sound excitation was carriedout with a tapping machine of the type "Norsonic". The noise excitation for measuring thereverberation time was carried out with stationary, broadband noise. The measurement of the receiving
sound pressure levels was carried out with a calibrated 1/2" condenser microphone ("Brüel & Kjaer
Condenser Microphone Type 4165", "Brüel & Kjaer Preamplifier Type 2639" and "Brüel & Kjaer
Microphone Power Supply Type 2804"). Before each measurement, the measuring chain wascalibrated with a calibrated test sound source of the type "Norsonic Type 1251"; after eachmeasurement, the calibration was checked.

Figure 2 - (Left) Tapping machine on the wooden frame ceiling; (Right) Rotary boom microphone forsound pressure level measurement in the receiving room

2.2 Prediction Model
The calculation of the normalized flanking impact sound pressure level Ln,f is carried out according������
to EN ISO 12354-2:2017 from the direction averaged vibration level difference 𝐷𝐷
𝑣𝑣,𝚤𝚤𝚤𝚤 and thenormalized impact sound pressure level of the ceiling Ln,i. Furthermore, the two component surfacesof the ceiling S i and the wall S j are included in formula 4. All other variables in formula 4 can beneglected in this case. There are no additional layers (∆𝐿𝐿𝑖𝑖 = 0 𝑎𝑎𝑎𝑎𝑎𝑎 ∆𝑅𝑅𝑖𝑖 = 0), and the airborne sound
𝑅𝑅𝑖𝑖 −𝑅𝑅𝑗𝑗
insulation measure of both components are about the same size ( 2 ≈ 0) . Since the same
configuration of the components and component dimensions was used to determine ������
𝐷𝐷𝑣𝑣,𝚤𝚤𝚤𝚤 as well as������
����������
Ln,f the otherwise necessary conversion from 𝐷𝐷𝑣𝑣,𝚤𝚤𝚤𝚤 to 𝐷𝐷𝑣𝑣,𝚤𝚤𝚤𝚤,𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 is not necessary.
𝐿𝐿𝑛𝑛,𝑓𝑓 = 𝐿𝐿𝑛𝑛,𝑖𝑖 − ∆𝐿𝐿𝑖𝑖 +𝑅𝑅𝑖𝑖 − 𝑅𝑅𝑗𝑗
𝑆𝑆𝑖𝑖
− ∆𝑅𝑅𝑖𝑖 − ������
𝐷𝐷𝑣𝑣,𝚤𝚤𝚤𝚤 − 10lg �� �
2
𝑆𝑆𝑗𝑗

(4)

2.3 Test setup
The test setup was configured in accordance with the EN ISO 10848 series of standards. The test
setup consists of a wall element (2530 x 3100mm, timber frame construction, 12.5mm gypsum fiber
board, 160mm mineralwool/wooden beam, 12.5mm gypsum fiber board) and a ceiling element (3100
x 3550mmm timber frame construction, 18mm OSB board, 160mm mineralwool/wooden beam,
12.5mm gypsum fiber board). The edges of the test bench are decoupled from the load-bearing
elements by means of elastic interlayers. Therefore, the edges do not contribute to the soundtransmission behavior of the T-joint or the ceiling. The receiving room below the ceiling componentis spatially closed on both sides by hollow brick walls and on one side by a wooden frame construction
planked with gypsum fibers. This results in a receiving room volume of approx. 28 m³.

Figure 3 – Cross section of the investigated T-joint of timber a frame wall and a timber frame ceilingcomponent
In order to simulate the building load acting on the node, 20t were applied to the node during themeasurements. The attached 1200mm high wall stump in timber frame construction is primarily used
to distribute the load applied to the node by the hydraulic stamps. A measurement of the flanking
sound transmission wall-wall is not possible due to the small geometry and the resulting
inhomogeneous vibration fields in the wall stump.

Figure 4 - T-joint and closed receiving room
To measure the normalized flanking impact sound pressure level Ln,f, it is necessary to shield off
the direct impact sound transmission path through the ceiling so that only the sound pressure level inthe reception room resulting from the sound power radiated from the flanking building component ismeasured. Based on the recommendations in EN ISO 10848-1:2018, a self-supporting suspended
ceiling was installed below the ceiling construction. For this purpose, wooden beams (50mm x 80mm)
were mounted on the laterally receiving room walls. There is no mechanical connection between thesuspended ceiling and the ceiling construction. This wooden construction was planked with 12.5mm
thick gypsum fiber boards (m'=17kg/m²). The resulting cavity was dampened with mineral wool.

3. RESULTS��������
3.1 Normalized direction-averaged vibration level difference 𝑫𝑫
𝒗𝒗,𝒊𝒊𝒊𝒊,𝒏𝒏
The normalized direction-averaged vibration level difference calculated by means of the measured
vibration levels Lv (Figure 5a) is shown in Figure 5b. In the frequency range between 200Hz and
1250Hz, which is essential for the single-number evaluation, the curve with ±3dB runs horizontally,�������
which allows the use of the single number value Dv,ıȷ,n according to EN ISO 10848-1. The fluctuationsin the vibration levels may be caused to the modal vibration behavior of the components and theinhomogeneous vibration field in the different compartments.
Below and above this frequency range, the curve drops by about 7 dB. In the low frequency range,
this can be concluded from the greatly reduced signal-to-noise level ratio, which is <6dB at 50Hz.
Above 1250Hz, the velocity level difference decreases mainly due to the airborne noise caused in thereception room by small hammer mills. The ceiling, which is excited by means of a small hammer
mill, radiates sound power into the receiving room and thus causes the wall surface to vibrate
independently of the flanking transmission path. The structure-borne sound transmission is thus
influenced by airborne sound transmission. This can be seen in Figure 5a that the average velocity
level on the wall surface increases steeper from 1250Hz than that on the ceiling surface, when theceiling is excited and the measurement of the velocity levels of the wall surface were carried out
inside of the receiving room.

110
100
90
80
70
60
50

63 125 250 500 1000 2000 4000
Frequency in Hz
ceiling (C)wall (C)ceiling (W)wall (W)normalized direction-avaraged
vibration level difference Dv,ij,n indBavarage velocity level Lv in dB

(a)

120

25
20
15
10
5
0

(b)

Frequency in Hz

Figure 5 – (a) Frequency dependent trend of the average velocity levels on the building components
surfaces with excitation of the wall (W) and the ceiling (C); (b) Frequency dependent trend of the��������
normalized direction averaged vibration level difference 𝐷𝐷
𝑣𝑣,𝚤𝚤𝚤𝚤,𝑛𝑛 of the investigated T-joint in timber frame
construction for the ceiling-wall transmission path

Normalized impact sound pressure level L'n
in dB

3.2 Normalized impact sound pressure level L’n
Based on EN ISO 10140-3, the normalized impact sound pressure levels L’ n of the ceilingconstruction with and without self-supporting suspended ceiling were measured. With the assumptionthat with the shielded direct sound transmission path, sound power is only emitted by the flanking
building component, this impact sound pressure level reflects Ln,f .

90
80
70
60
Suspendedceiling
frei
tragende UD

50

keine
AD
No Suspended
ceiling

40
30
20

63

125

250 500 1000 2000 4000
Frequency in Hz

Figure 6 - Frequency dependent trend of the normalized impact sound pressure level L‘n of the wooden
frame ceiling with and without self-supporting suspended ceiling and with attached wooden frame wall

For the calculation of the normalized impact sound pressure level L’ n, according to ÖNORM EN
ISO 12354-2, it is assumed for the measurement without suspended ceiling that the flanking soundtransmission path to not have a significant influence on the overall impact sound pressure level andthus the measurement result can be regarded as the normalized impact sound pressure level Ln of theexamined ceiling construction.
The comparison of the two impact sound pressure levels in figure 6 shows an effectiveness of thesuspended ceiling construction beginning from 125Hz. Below this frequency, the impact soundpressure level for both ceiling constructions is almost the same and thus the suspended ceilingconstruction is ineffective. A comparison of the calculated and the measured flanking impact soundpressure levels is therefore not possible below 125Hz based on the measurement results shown.
3.3 Normalized flanking impact sound pressure level Ln,f
The comparison between the calculated and measured normalized flanking impact sound pressurelevel L'n,f in figure 7 shows that between 125Hz and 3150Hz a very good performance of the prediction
model of EN ISO 12354-2. Below 125Hz, the measurement of L'n,f was not possible (see section 3.2),
because the ineffectiveness of the shielding by the suspended ceiling. Therefore L'n,f is significantly
underestimated in the calculation. From 3150Hz, the problem is that the measured direction averaged
vibration level difference in this frequency range is influenced by the airborne sound induced in thereceiving room by the sound radiation of the excited building component (see section 3.1). This could
explain a deviation of the calculation result from the measurement result in this frequency range.

Normalized flanking impact sound pressure levelLn,f in dB

90
80
70
60
50
Gemessen

40

Berechnet nach EN12354-2

30
20
10
0

63

125

250
500 1000
Frequency in Hz

2000

4000

Figure 7 - Comparison between measured and calculated normalized flanking impact sound pressure level
L’n,f of a wall-ceiling T-joint in timber frame construction

4. CONCLUSIONS��������
It could be shown that for a by the normalized direction averaged vibration level difference 𝐷𝐷
𝑣𝑣,𝚤𝚤𝚤𝚤,𝑛𝑛characterized T-joint in timber frame construction, a calculation of the normalized flanking impact
sound pressure level L'n,f with the prediction model of the EN ISO 12354-2 with a sufficient accuracy(deviations <3dB) is possible. The calculation is limited by the accuracy of the measured input

parameters. The measurement needs to take place as unaffected as possible by other transmission��������
paths. A particular challenge in the measurement of 𝐷𝐷
𝑣𝑣,𝚤𝚤𝚤𝚤,𝑛𝑛 is the airborne sound transmission path
between ceiling and wall in the closed receiving room as well as the airborne sound power radiatedby the building components effecting the vibration level measurements inside the receiving room. An
improvement in the measurement accuracy is to be expected with the use of a “shaker” instead of thesmall hammer mill, whereby less airborne noise is induced in the receiving room, but the measuring
effort is significantly increased.

ACKNOWLEDGEMENTS

The authors acknowledge the support of all project partners of the research project“Schall.Holz.Bau II”. The project was funded by the "NÖ Wirtschafts- und Tourismusfonds" in thefunding track "Kooperation" under the number WST3-F2- 525823/007-2018.

REFERENCES

1. Neusser M., Bednar T. Construction details affecting flanking transmission in cross laminated timber
structures for multi-story housing. Internoise 2022, Glasgow, Scotland.
2. Villot. M., Guigou-Carter, C. Measurement methods adapted to wood frame lightweight
constructions. Build. Acoust. 2006, 13 pp. 189–198
3. Metzen A., Schumacher. Construction details affecting flanking transmission in cross laminated timber
structures for multi-story housing. Forum Acusticum 2005, Budapest, Hungar.
4. De Geetere L., Ingelaere B., Rychtarikova M. Vibration level difference measurements on atimber frame mock-up. Project AH+, part 3, Proc. Inter-Noise 2013, Innsbruck, Austria.
5. Schönwald S, Flanking sound transmission through lightweight framed double leaf walls; Prediction
using statistical energy analysis (SEA), Phd Thesis, Eindhoven, 2008
6. Schöpfer F., Mayr A., Schanda U. INTER-NOISE and NOISE-CON Congress and Conference
Proceedings, InterNoise16, Hamburg GERMANY, pages 2862-3857, pp. 2862-2871(10)PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0531

Junctions and their acoustical behaviour in high rise CLT buildings
Klas Hagberg 1; Delphine Bard 2; Erik Nilsson 3
1
2

Acouwood AB, Sweden

Kuster&Partner, Switzerland
3

Acouwood AB, Sweden

ABSTRACT
Cross-Laminated Timber (CLT) elements are interesting and exciting for use in multifamily buildings.
However, from an acoustic perspective it is rather complex. Firstly, CLT elements have relatively poor soundinsulation. Various number of layers and thicknesses of the layers in different panels creates specificdifficulties influencing the sound insulation properties. Secondly, due to the acoustical weaknesses of thepanels their connections in the junctions are yet another source of uncertainty. The junction behaviour varies
significantly due to floor plan, number of storeys (load), stabilizing walls and floors build-ups. To raise theknowledge regarding necessary measures to reduce flanking transmission through junctions, it is of greatinterest to follow up with extensive measurements in real buildings comprising real boundary conditions.
The measurement results can be used to refine prediction models for future The results from the field withreal boundary conditions are more reliable than measurements made in mock-ups. In this paper, someindicative results from measurements in real buildings are shown, with and without elastic layers aiming to
reduce flanking sound transmission between CLT elements. These results are very useful, to understandwhich frequencies that should be of highest priority to reduce between future dwellings with CLT structures.
Keywords: Sound, Insulation, Transmission, CLT, Junctions

1. INTRODUCTION

Over the past four years, Acouwood has made several sound insulation measurements in realbuildings both following the ISO standard ISO 16283-1 (1) and 2 (2) for building acoustics but alsodetailed measurements regarding vibration reduction through junctions following the standard ISO
10848 (3). In this paper we present only standard measurements and discuss the overall results from
that. Results related to vibration measurements will be presented separately, starting at Internoise
2022 in Glasgow, Nilsson (4).
For the measurements we have had access to several projects, amongst those one of the largest
CLT inner city projects in the world, Cedar Houses in Stockholm, Sweden. The project comprises four
separate buildings of which the highest one is 13 storeys (11 storeys of wood / CLT). Two of thebuildings are completed and moved in and two are still under construction, see Figure 1.
It is well known that CLT plates suffer from poor sound insulation itself, they need to besupplemented with other layers to fulfill normal legal requirements. The poor sound insulation of CLT
plates also imply that the elements normally should be separated to avoid severe flanking transmission.
Therefore, the acousticians want to separate the elements with elastic layers and isolated metallic
brackets that are connecting the plates, to reduce the flanking transmission. The elastic layers used isoften 25 mm thick. But when the building is 13 storey high and there is only CLT plates stabilizing
the building, the structural engineers struggle to keep strong connections. For these specific buildings,
the design team ended up in a compromise, namely one elastic layer of only 6 mm between the storeys
and ordinary steel brackets connecting the wall elements to the floor plate (on top of the floor plate),
see Figure 2. According to our calculations it will still be enough to fulfill the target values for thisproject which is:
Klas.hagberg@acouwood.com
Delphine.bard@kusterpartner.ch
3Erik.nilsson@acouwood.com
1
2

𝐷𝐷𝑛𝑛𝑛𝑛,𝑤𝑤 + 𝐶𝐶50−3150 ≥ 52 𝑑𝑑𝑑𝑑

𝐿𝐿´𝑛𝑛𝑛𝑛,𝑤𝑤 + 𝐶𝐶𝐼𝐼,50−2500 ≤ 52 𝑑𝑑𝑑𝑑

(1)
(2)

Figure 1 – Cedar houses, the first two buildings completed, Bologna 1 and 2.
In addition, we have had the opportunity to evaluate the effect of omitting the elastic layers
completely between a few storeys in one of the two buildings. The results from these initial tests
encouraged us to further investigate how many dB you gain by using elastic layers compared to asimplified solution with “wood to wood” in some other CLT multi-storey buildings.
There is of course a big interest from the developers in general if the acoustic requirements can befulfilled and provide sufficient sound insulation with solutions that simplify the prediction and in
addition provide static robust solutions. Therefore, we gained access to yet another building in the
Stockholm region with a building structure made up of CLT volume elements prefabricated in thefactory and then stacked together on site. In this case we simply evaluated the effect of replacing theelastic layer with wood pads, i.e. keeping the airspace between the volumes but omitting the resiliency.
We replaced the elastomers between the two storeys on the top of the building by wood layers andmeasured the differences in terms of airborne sound insulation. If any problems appear we could
simply remove the volumes and put back the elastic layers.
In this paper we present the overall results from measurements in these two projects but also some
important considerations regarding design of junctions.

2. DETAILS AND MEASUREMENTS
2.1 Structural build up, Cedar houses, project number 1
The floor structure is built up according to Figure 2 below. The concrete on top is not only due toacoustic requirements but also to reduce the wind induced vibrations. But it was shown to be a good
choice to fulfil the acoustic requirements for the building, see Equations 1 and 2 above. Combining
this floor structure with the junctions (see Figure 3) will arrive in a balanced results for the airborne
sound insulation and impact sound insulation between the residential units (5) arriving in very good
final results for sound insulation.

•Floor covering (parquet)•

80 mm concrete topping•

30 mm impact board

•

CLT

•

Ceiling (installation volume) covered by 2*13 mm
gypsum suspended by steel hangers

Figure 2 – Floor structure of Cedar houses
The floor structure in Figure 2 was connected to the bearing stabilizing CLT wall elements
according to the details in Figure 3. Some walls are of course covered with gypsum boards either
directly attached for fire protection or mounted on a separate timber stud wall for dwelling partitions
to fulfill sound requirements horizontally between dwellings, see Figure 4.

Steel brackets
Steel brackets

Xylofon 6 mm

Xylofon 6 mm

ScrewsScrewsFigure 3 – Junctions as designed in Cedar houses. Note that the real wall is supplemented with gypsum
boards for fire and / or acoustical treatment, see Figure 4. The floors are built up according to Figure 2
implying that the flanking sound reduces significantly horizontally.

15 fire gypsum
15 fire gypsum

CLT panel

13 gypsum

10 air space
70 wood studs + min.wool

CLT panel
13 gypsum

15 plywood

15 fire gypsum

15 fire gypsum

Figure 4 – Typical walls in Cedar houses. Left: Partitions between dwellings; Right: Stabilizing and bearing
walls inside dwellings. The facade walls are supplied with one layer of fire gypsum directly attached to the
CLT panel.
Between two storeys the elastic layers were completely removed. It was made after a common
agreement inside the project team for testing purposes, since calculations indicated that it might bepossible to still fulfill both the impact sound insulation and the airborne sound insulation without any
resilient layers between the storeys.
2.2 Structural build up, project number 2
In project number 2, the building was made of modular volume elements with CLT panels, implying
a large amount of flanking transmission, at least vertically. The volumes are separated horizontallywith an air space (including stone wool) large enough to fulfill the Swedish minimum requirement for
airborne sound insulation. Of course, there are some statical connection points to keep the volumes tostatically connected horizontally, so some margins for the wall itself are needed in the design phase.
Vertically, the various storeys were acoustically divided by 25 mm elastomer as the standard solution.
These elastic layers were replaced by 22 mm particle board on approximately 50 % of the wall lengths
on the top floor in one building. The volume elements and their connections were designed to fulfil
the Swedish minimum requirement both for airborne and impact sound insulation which means that
Equation 1 above should be fulfilled, but for Equation 2, 4 dB higher value is accepted, i.e. Equation
2 above should be equal or lower than 56 dB.
All in all, the large number of flanking panels in both Cedar houses and in project number 2 with
CLT volumes imply that the big challenge is to fulfill the airborne sound insulation. If only impact
sound insulation is considered, the elastic layers do not seem to be needed. However, resilient layers
make a difference on the airborne sound insulation at least compared to objective measures. Therefore,
we display mainly the effect of airborne sound insulation when replacing elastic layers with hardintermediate layers in this paper.

3. RESULTS

Measurements were carried out for two different cases in both buildings, with and without elastic
layers as described above. The results indicate that in those two cases it might be acceptable to either
completely remove elastic layers or, as was the case for the CLT volume element building, replace theelastic layers with 22 mm particle board (to still maintain the necessary distance between the volumes).
For both projects, the measurements were carried out prior to completion. The ceiling was not in place
for Cedar Houses during comparisons and for the volumes, mineral wool was missing between thevolumes vertically. That means that the single number values for the curves in Figure 4 and Figure 5
are not high enough in all cases to fulfill the minimum requirements in Sweden. However, bothbuildings were verified after completion and these measurements are higher than or equal to 52 dB

(see Equation 1), with a margin corresponding to 0–3 dB.

Figure 5 – Project no 1, Cedar Houses: Measured airborne sound insulation vertically between two different partitions with equal preconditions except that one is supplied with 6 mm elastomer, and one is without
elastomer. Red curve = partition with elastomer before mounting the ceiling; Green curve = partition without elastomer before mounting the ceiling; Blue curve = Without elastomer after ceiling is mounted.

Figure 6 – Volume elements in CLT: Measured airborne sound insulation vertically between two different
partitions with equal preconditions except that one is supplied with 25 mm elastomer, and one with noelastomer but 22 mm plywood instead. Red curve = partition with 25 mm elastomer; Green curve =partition with 22 mm plywood; Blue curve = 22 mm mineral wool with plywood.

One interesting thing in the comparison for project no 1, Cedar houses, is that the low frequency
performance is improved when omitting the elastomers and the single number ratings are shifting
place when the low frequency spectrum adaptation term is included. In Figure 5 the red curve equals
D nT,w (C50-3150 ) = 50 (-4) dB and the green curve DnT,w (C 50-3150 ) = 48(-1) dB, i.e. D nT,w is higher whenusing elastomer but D nT,w+C 50-3150 becomes lower. When project number 1 is supplied with ceiling,
the result changes to DnT,w(C 50-3150) = 54(-2) dB which fulfills the Swedish minimum requirements.
Same phenomena appear for the volumes, project number 2. In Figure 6 the red curve equals
DnT,w (C50-3150 ) = 52(-3) dB and the green curve D nT,w (C 50-3150) = 51(-1) dB, i.e. DnT,w is similar in thiscase which means that the number is higher when using elastomer but when low frequency spectrum
adaptation term is included, DnT,w+C50-3150 becomes lower compared to the wood layers. And the when
the case with wood layers is supplied with mineral wool between the modules, the result is DnT,w (C 503150 ) = 54(-2) dB which also fulfills the Swedish minimum requirements.

4. DISCUSSION

These two full scale tests, as presented in this paper, are made in two completely different types of
CLT buildings but they give the same indications. In the first building, they really wanted to remove
the elastic layers due to stability reasons. Nevertheless, the 6 mm layers were maintained since
additional measurements indicated that the margin to the requirement in Sweden increased by 1 to 2
dB by keeping the resilient layers and the structural engineers was supporting these thin layers.
However, it is not clarified that the perceived sound insulation is really improved. It is of great
importance to clarify annoyance due to airborne sound and verify in which frequencies dB:s are gained
and if it is worth the cost and the effort (5). For even higher wood buildings in the future, it is also
important to know when and if these layers should be supplied. This is of extra importance since inaddition to elastic layers, there are several other factors affecting the acoustic performance ofjunctions and the overall sound insulation between apartments. One technical aspect that is further
investigated by Acouwood in more detail is how the loading affects the sound insulation between
different floors. The initial results indicate that increased load has a negative effect on the airborne
sound insulation, however more thorough results are planned for publication shortly.
For the volume element manufacturer, the investigation was made to clarify if there is any way tosave money by reducing the elastic layers between the volumes. The elastic layers significantly affectthe overall costs. After several measurements in test mockups, it was decided to remove the elastic
layers and simply replace them with wood between the volumes in a real building and compensate inhigher frequencies by installing mineral wool in between the volume elements, see final result infigure 6.
The results can only be interpreted to the two typical structures shown in this paper. For any otherstructural components and connections, similar investigations or calculations must be undertaken.
Acouwood has also made vibration reduction index (𝐾𝐾𝑖𝑖𝑖𝑖 ) measurements, some results will be presented
at Internoise 2022 (4), and some results are planned to be published later this year in a journal article.

5. CONCLUSIONS

Junctions are crucial when it comes to acoustic design of CLT structures. It is not only the elastic
layers between the elements, but also how the elements are connected, either with angle brackets and/ or screws. Furthermore, the loading seems to have significant effect, the more load the lower airborne
sound insulation. Least but not less there are differences depending on the specific wall and floor
design and their mutual dependence. The examples shown in this paper are rather optimized in termsof wall thickness and floor height in respect of expected sound insulation in the finished building. The
requirements must always be discussed at an early stage in each project to arrive in the bestrequirement setup for securing high quality in terms of perceived sound insulation. Don´t focus toomuch on sound classes but make sure that the structural buildup fulfils the mandatory regulations but
also gives a building with overall a good acoustic quality.

ACKNOWLEDGEMENTS

Many thanks to all our clients providing access to the buildings. It has been of invaluable help forfuture understanding of acoustics in wood buildings.

REFERENCES

1. ISO 16283-1; Acoustics — Field measurement of sound insulation in buildings and of building elements— Part 1: Airborne sound insulation
2. ISO 16283-2; Acoustics — Field measurement of sound insulation in buildings and of building elements— Part 2: Impact sound insulation
3. ISO 10848 (all parts); Acoustics - Laboratory and field measurement of flanking transmission for
airborne, impact and building service equipment sound between adjoining rooms.
4. Nilsson, Erik; Menard, Sylvain; Bard, Delphine; Hagberg. Klas; Effect of Bearing Direction and Mounting
Techniques on Cross-Lami-nated Timber Elements in the Field. Internoise, 21 - 24 August, Glasgow 2022.
5. Hagberg K., Bard Delphine; Acoustic requirements for a sustainable future, CEES, 12 - 15 October 2021,
Coimbra, Portugal

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0625

Comparative analysis of vibroacoustic measurements in a CLT
building mock-up
Luca BARBARESI1; Antonino DI BELLA2; Vincenzo PETTONI POSSENTI3; Matteo
SALVALAGGIO4; Maria Rosa VALLUZZI5
1

Department of Industrial Engineering - University of Bologna, Italy2
3

Department of Industrial Engineering - University of Padova, Italy

Interdepartmental Centre for Industrial Research in Building and Construction - University of Bologna, Italy
4

Department of Cultural Heritage - University of Padova, Italy

5

Department of Cultural Heritage - University of Padova, Italy

ABSTRACT
Construction technology based on elements in Cross Laminated Timber (CLT) has assumed considerable
importance in the context of wooden buildings and is now widely consolidated. This construction system has
been extensively studied since its first appearance in the mid-1990s. The production of CLT elements is at anindustrial level, and the manufacturing and fixing techniques are now standardised, as are the structural
calculation methods and the prediction models for evaluating achievable performances. From an architectural
point of view, the current trend is to use CLT in buildings that increasingly go beyond the traditional patternsof wooden buildings to move towards typologies that have previously been the prerogative of otherconstruction systems, with tall buildings and considerable spans. Therefore, the need arises to deepen theknowledge of the acoustic behaviour of the joints between CLT elements in cases not currently considered in
the technical standards. This work shows the studies carried out on a CLT building mock-up made with twin
structures and subjected to structural, seismic and acoustic tests.
Keywords: CLT, Sound, Transmission

1. INTRODUCTION
Cross-laminated timber (CLT) is an industrial timber product at the basis of an articulated
construction system. The CLT has now become a technological reference system for constructing
wooden buildings. Its characteristics allow achieving particular structural performance, rationalisingsite management, and reducing construction time and cost. The growing diffusion of CLT has beenaccompanied by extensive research on the peculiar characteristics of this cons truction system, mainly
concerning its economic and environmental benefits, lifecycle, structural design, resistance to seismic
actions, fire protection, and energy efficiency. However, the study of the vibroacoustic characteristicsof this construction system has had great relevance only in the last decade [1-4]. As a result of theseresearch, the first models for the forecast calculation of CLT structures have been introduced in thereference standards [5].
12luca.barbaresi@unibo.it
antonino.dibella@unipd.it

vincenzo.pettoni2@unibo.it
matteo.salvalaggio@unipd.it
3
mariarosa.valluzzi@unipd.it
3
3

Despite this, many aspects still remain to be analysed. In particular, the aspects related to theimpact on the acoustic performance of particular measures aimed at improving structural or thermal
performance deserve to be studied in depth. Furthermore, there are numerous situations in which, inthe practice of building the architectural project on site, it is necessary to adapt the connection
techniques or the dimensions of the CLT elements.

2. DESCRIPTION OF THE CASE OF STUDY
2.1 CLT mock-up
Two twin CLT structures were built inside a shed (Figure 1). The structures have a concrete curbthat allows to simulate the real conditions of anchoring to the foundations. The test mock-up consistsof two sets of four rooms, placed side by side to form a "cross" junction in the centre of the building.
Both structures were subjected to mechanical actions to study the behaviour of the connections
under the effect of ordinary seismic actions that may occur during the life cycle of a building.
The only construction difference between the two structures is that the mock-up on the right ("Beta") resilient strips made of recycled SBR rubber granules and fibres were inserted between thejunctions to isolate the vertical and horizontal structural elements , while the mock-up on the left("Alpha α") did not.

Alpha

Beta

Alpha
Beta

(a)

(b)

(c)

Figure 1 – (a) Twin CLT buildings: "Alpha" on the left and "Beta" on the right. (b) Detail of “Alpha”. (c)Detail of “Beta”.
The ISO 12354-1 [5] standard considers CLT buildings belonging to type A because the panels intimber are generally continuous and size comparable to the partitions of a room, it is not difficult tofind walls or floors made with a single slab. However, among the various construction techniques that
use CLT panels, the use of modules with a pitch of 125 cm and a height equal to the room’s height isalso widespread. This construction technique is used, for example, in the experimental residentialbuilding which constitutes a permanent laboratory as part of the UNIZEB [6] project for the evaluationof indoor well-being in a nearly zero-emission building.
The small-sized modules (e.g. 125 × 300cm) are used for small to medium buildings where largespans are not required and with a reduced number of floors. The vertical connection between thepanels is ensured by a wooden board screwed and inserted in the special milling of the panels.
On the building in Figure 1, measurements were carried out to quantify the lateral transmission
and evaluate to which type (A or B) the construction elements could be attributed.
The study was done with three mounting configurations for floor panels for ea ch building: basic
configuration with separate panels (Conf. 0), connecting wooden boards (Conf. 1) and screws (Conf.
2).
Only three walls (“v”, “i” and “ii”) of both buildings with relative sound transmission paths (i-v,v-i; ii-v, v-ii; i-ii, ii-i) were analysed, as shown in Figure 2, because the two buildings havesymmetrical conformation.

ii

ii-v

v

i-ii

i-v
i

Figure 2 – Sound transmission path analysed: i-v, ii-v and i-ii.
2.2 Measurement instrumentation
The signal acquisition system consists of a computer, an acquisition unit and four accelerometers(Figure 3). An instrumented hammer was used to generate the signal [7]. The acquisition of thevelocity vibration levels starts after a few seconds from the start of hammer impact to ensure that thesource is in a steady state. All measurements were performed in compliance with ISO 10848 standard[8], finding the velocity level and structural reverberation time of the panels.

Figure 3 – Measurement setup.
2.3 Consideration about type A and B element
Before proceeding, the structural reverberation time the of “v” panel is compared in the threemounting configurations. This allows evaluating whether the structural reverberation time isinfluenced or not by the boundary conditions. As can be seen in Figure 4 the structural reverberation
time behaviour is similar between the three mounting configurations in the Alpha building andbetween the three mounting configurations in the Beta building. Therefore, the panel is not influenced
by the boundary conditions.
The propagation of the velocity level along the main direction of the “v” panel was also calculated(Figure 5). The difference of the velocity vibration levels was made between a point close to thesource (pt.27) and the other points on the panel. It turned out that the measuring points that are on thesame slab (pt.25, pt.26, pt.27) have similar behaviours while the points on the next slab (pt.28, pt.29,
pt.30) have similar behaviour to each other but with an attenuation of velocity level higher than 6 dB.
The same considerations can be made for panels “i” and “ii”. (Figure 6-7)

Structural reverberation time [s]

2,50

2,00

1,50

1,00

0,50

0,00
100

125

160

200

250

315

400

500

630

800

1000 1250 1600 2000 2500 3150

Third-octave band center frequencies [HzAlpha0Alpha1

Alpha2

Beta0

Beta1

Beta2

Figure 1. Comparison of structural reverberation time between configurations in “v” panel.

30
25
20
15

v

10
5
0

100

125

160

-5

200

250

315

400

500

630

800

1000 1250 1600 2000 2500 3150

Third-octave band center frequencies [Hz]
27-25

27-26

27-28

27-29

27-30

LIMITE 6 dB

Figure 2. on the left the direction of propagation (the red line is the junction), on the right the difference ofvibrations (orange line is the limit of 6 dB) in the “v” panel.

Figure 6. Comparison of structural reverberation time between configurations in “ii” panel.

Figure 7. Comparison of structural reverberation time between configurations in “ii” panel.
From these considerations the examined buildings are a type B. Therefore, it is more significant̅̅̅̅̅̅̅̅
̅̅̅̅̅̅̅̅
the normalized direction-averaged vibration level difference 𝐷𝑣,𝑖𝑗,𝑛 𝐷𝑣,𝑖𝑗,𝑛 compared to the vibration
reduction index 𝐾𝑖𝑗 .
The normalized direction-averaged level difference is found as in formula (1) and it does notdepend on the structural reverberation time:

𝐷𝑣,𝑖𝑗 + 𝐷𝑣,𝑗𝑖𝑙𝑖𝑗 𝑙0+ (10 𝑙𝑔
) [𝑑𝐵]
2√𝑆𝑚,𝑖 𝑆𝑚,𝑗̅̅̅̅̅̅̅̅
𝐷𝑣,𝑖𝑗,𝑛 =(1)

3. MEASUREMENT RESULTS

Average of normalized direction -average vibrationlevel difference D v,ij,n [dB]

The difference of the average (200-1250 Hz) of normalized direction-average vibration level̅̅̅̅̅̅̅̅
difference 𝐷𝑣,𝑖𝑗,𝑛 between Alpha (α) building and Beta () building is 5.4 dB for “i-v” path, 2.5 dB
for “ii-v” path and 2.2 dB for “i-ii” path (Figure ).
The use of resilient strips in the junctions reduces the flanking transmission of vibrations.
14,6

15

Alpha

14

Beta

13,4

12,9

12,7

13

12,4

12,0

12
11

11,8

10,3

12,2

10,1

10,0

10
8,7

9
8
7

8,9

8,8

8,6

7,9
7,4

6,9

6
i-v
i-v
i-v
Conf. 0 Conf. 1 Conf. 2

ii - v ii - v ii - v
Conf. 0 Conf. 1 Conf. 2i - iii - iii - iiConf. 0 Conf. 1 Conf. 2

Figure 8. Comparison between configurations (average 200-1250 Hz) of normalized direction-averagevibration level difference.

Normalized direction -averagevibration level difference D v,ij,n [dB]

30
25
20

Dv,i-v,n;Dv,i-v,n;Dv,i-v,n;Dv,i-v,n;Dv,i-v,n;Dv,i-v,n;

i-v

0
1
2
0
1
2

15
10
5
0

Third-octave band center frequencies [Hz]Figure 9. Comparison between configurations (i-v path) of normalized direction-average vibration level
difference.
Normalized direction -averagevibration level difference D v,ij,n [dB]

30
25
20

Dv,ii-v,n;Dv,ii-v,n;Dv,ii-v,n;Dv,ii-v,n;Dv,ii-v,n;Dv,ii-v,n;

0
1
2
0
1
2

15
10
5
0

Third-octave band center frequencies [Hz]Figure 10. Comparison between configurations (ii-v path) of normalized direction-average vibration level
difference.
Normalized direction -averagevibration level difference D v,ij,n [dB]

30
25
20

Dv,i-ii,n;Dv,i-ii,n;Dv,i-ii,n;Dv,i-ii,n;Dv,i-ii,n;Dv,i-ii,n;

0
1
2
0
1
2

15
10
5
0

Third-octave band center frequencies [Hz]Figure 11. Comparison between configurations (i-ii path) of normalized direction-average vibration level
difference.

4. CONCLUSIONS
The aim of this work was to investigate the flanking transmission in CLT buildings made withsmall wooden panels, for this reason, a couple of twin buildings were built. In one of the two mock ups (called alpha), the wooden panels were in direct contact, while in the other (called beta) elastic
strips of SRB rubber were inserted into the joint.
The measurements were also repeated with 3 different types of connections between the joints ofthe floor panels.
From the analysis of the results, the difference in levels exceeds 6 dB starting from the frequencyof 250 Hz at the change of the module, regardless of the type of junction. The structural reverberation
time of the panels, despite the different junctions, has remained substantially the same, further
confirming the belonging of the constructive solution to type B.
From the analysis of the data, it is therefore possible to state that the constructive solution underconsideration is of type B and that the lateral transmission must be expressed using the normalized̅̅̅̅̅̅̅̅
difference of the vibrations 𝐷𝑣,𝑖𝑗,𝑛 .

ACKNOWLEDGEMENTS
The authors wish to thank the company "Bozza s.r.l." of Padua (Italy) for the support of thisresearch.

REFERENCES
1. Di Bella, A., Mitrovic, M., Acoustic characteristics of cross-laminated timber systems, Sustainability,
2020, 12 (4), 5612, https://doi.org/10.3390/su12145612
2 Barbaresi, L., Morandi, F., Garai, M., Speranza, A. Experimental measurements of flanking transmissionin CLT structures (Open Access) (2016) Proceedings of Meetings on Acoustics, 28 (1), art. no.
015015 https://doi.org/10.1121/2.0000433
3 Morandi, F., Prato, A., Barbaresi, L., Schiavi, A. On the diffuseness of the vibrational field of a crosslaminated timber plate: Comparison between theoretical and experimental methods (2020) Applied
Acoustics, 159, art. no. 107104. https://doi.org/10.1016/j.apacoust.2019.107104
4 Santoni, A., Schoenwald, S., Fausti, P., Tröbs, H.-M. Modelling the radiation efficiency of orthotropic
cross-laminated timber plates with simply-supported boundaries (2019) Applied Acoustics, 143, pp.
112-124. https://doi.org/10.1016/j.apacoust.2018.08.022
5. ISO 12354-1:2017 Building acoustics — Estimation of acoustic performance of buildings from theperformance of elements — Part 1: Airborne sound insulation between rooms
6. https://unizeb.it/
7. Analysis on structure-borne sound transmission at junctions of solid wood double walls with continuous
floors,. S Schoenwald, B Zeitler, I Sabourin - Proceedings of 7th Forum Acusticum, Krakow, 2014 .
8. ISO 10848:2017 Acoustics — Laboratory and field measurement of flanking transmission for airborne,
impact and building service equipment sound between adjoining rooms — all parts

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0910

Sound insulation in cross laminated timber buildings and the effectof junction damping
Eli TOFTEMO 1; Anders LØVSTAD 2
1,2

Brekke & Strand Akustikk AS, Norway

ABSTRACTThe use of cross laminated timber (CLT) has surged over the last couple of decades and is used in increasingly
complex buildings. Despite increased knowledge and experience with CLT, considerable margins are neededin planning phases, which may be reduced if comparable laboratory or field data is available. This paper
reports on measurements of velocity level differences and sound insulation between floors employing various
elastic interlayers and fasteners for a full-scale CLT test building. Results show that all types of screw
fasteners generally reduce the dampening effect of the elastic interlayers significantly. The use of angle
brackets with elastic interlayer gave better results. Measurements of sound insulation with various floating
floors are reported on.
Keywords: Sound insulation, CLT, Junction damping

1. INTRODUCTION

In recent years an unprecedented increase in the use of cross laminated timber (CLT) in building
constructions has happened. CLT has been produced on an industrial scale for around 15 years, withsteadily increasing production volume (1). Not only has the sheer volume of CLT surged, butdevelopment, knowledge and experience of employing CLT in buildings have increased accordingly.
CLT is now considered and used in increasingly complex buildings with high sound insulation
requirements. The reasons for this development are diverse, but it is evident that there is a crossdisciplinary desire to work with and use CLT among authorities, property owners, architects andengineers as it is sustainable, enables rapid and efficient assembly, is light-weight, and possesses
several other desirable physical parameters as summarized by Di Bella et al (2).
National guidelines (3) and documentation of CLT floor and wall constructions have been
published in compliance with the development and complexity of its use. Maybe more so than othermaterials, the sound insulation achieved with CLT is highly dependent on junction assembly,
parameters and choice of resilient layers, linings, ceilings and floating floors, in addition to the qualityof mounting and assembly itself. Homb et al (4) collected and compared impact sound insulation for
typical floor assemblies in different European countries (and laboratories). Verdaxis et al (5) evaluatedairborne and impact sound insulation for CLT floors with additional layers in 12 configurations andfound that resilient layers and floating floors can exceed 20 and 30 dB improvement compared withthe 5-layered 180 mm CLT component alone for airborne and impact sound insulation, respectively.
Additional improvement may be obtained with suspended ceilings.
Laboratory data of sound insulation performance of slabs or walls alone form the basis ofconstruction designs, but field measurements can be significantly limited by flanking transmission (5),as extensively addressed by e.g. Hoeller et al (6). Morandi et al (7) performed flanking transmission
measurements of various CLT junctions and compared vibration reduction indices K ij . They found thatthe energy transmission through junctions is strongly related to the connectors.
In practice control of flanking transmission paths and mounting is paramount for CLT constructions,which further requires close cooperation with contractors, architects and construction designers.
Despite the surge in use of CLT, the overall experience with different CLT systems is not as developed
as with concrete slabs or even light-weight timber slabs. Laboratory data as reported in (4, 5) forms
1

2

eto@brekkestrand.noanl@brekkestrand.nothe basis of further construction details of flanking and mounting design. Commonly, at least in
Norway, there is a desire for CLT to be visible to as large extent as possible, which in turn questions
the need for linings and suspended ceilings. To a certain extent linings and suspended ceilings must
be included for sound insulation and/or absorption. However, in many cases it is questioned whether
they are needed to comply with minimum requirements, which frequently comes down to which
margin the project is comfortable with, and therein the specific experience of the constructors anddesigners.
Öqvist et al (8) reported on measurement uncertainty considering repeatability, measurement
direction and sound source time dependence for CLT constructions and found smaller variations for
prefabricated systems compared with on-site production. In a design phase large margins arecommonly included. Simmons (9) addressed which margins are needed when planning CLT buildings
when employing commonly used building acoustic software, comparing calculation results withmeasurements. He concluded that a safety margin of at least 8 dB should be used for CLT floors withlayered solutions on top of or below of the CLT slab, which may be reduced to 5 dB for constructions
where specific experiences of the same construction is available, such as junction and lining types.
These recommendations agree well with the authors experience from sound insulations measurements
on multiple constructions within the same buildings, where identical constructions in some cases vary
up to 8-10 dB due to e.g. mounting and assembly, room layout and furnishing. Thus, the uncertainty
in calculations, mounting and assembly and site variance is considerable, and is best addressed byfield measurements or other directly comparable measurements.
This paper addresses effects of employing various resilient interlayers and mounting methods onthe velocity level difference, Dv,ij . The measurements are carried out in designated test rooms basedon ISO 10848-1 (10) as explained below. Additionally, airborne and impact sound insulation aremeasured in compliance with ISO 16283-1 (11) and -2 (12), respectively. Measurements areintentionally done on building constructions that are comparable to those built in the field, whichenables a direct relation between the junction damping and sound insulation. Disadvantages of notcomplying fully with the ISO 10848-1 (10) are not having full control of all flanking transmission
paths and reduced measurement repeatability.

2. TEST AND MEASUREMENT SET-UP

The test set-up was built as a separate construction within an industrial warehouse with two rooms
on the ground floor and one room on the top floor, as shown in Figure 1. The ground floor and top
roof were 3-ply 120 mm thick CLT panels, while the horizontal slabs between the floors was 5-ply
160 mm CLT. All vertical CLT panels were 3-ply of 100 mm thickness. The test rig was deliveredfrom Splitkon AS, element strength classes T15 and T22. The density of the wood is 460 kg/m3 .
Room dimensions and layout are given in Figure 1 in addition to the CLT thicknesses. The top
floor could be lifted from the ground floor by hydraulic jacks as shown in Figure 2 to fit elastic
interlayers or mount angle brackets. This allowed for testing various profiles and fasteners in thejunctions between the floors. Additionally, wall linings, suspended ceilings and various floor
constructions were added and removed from the constructions to assess their impact on velocity level
difference and sound insulation.
b)

120

120
6400

120

160

160

100

100

100

160

100

100

2400

160

120

100

100

100

1880

120

100

a)

120

120
6400

Figure 1 – Vertical section drawings of the test set-up; a) length and b) width. All dimensions in mm.

Figure 2 – Test set-up shown in a) and b) corresponds to a) and b) in Figure 1. An elastic interlayer and thehydraulic jacks are seen in both a) and b), where the excerpt in b) shows a hydraulic jack specifically.
Measurement of velocity level difference was used to assess variations in damping across building
elements in the vertical direction. The velocity level difference is described in ISO 10848-1 (10).
Four measurement positions were employed on each panel/building element. Tests were carriedout employing three different sound sources; pink noise fed through a loudspeaker, a tapping machine
and hammer excitation. The results from hammer excitation have been left out since the excitation
proved difficult to control.
Velocity level differences show averaged values of two sets of sensor positions mounted on two
different walls, except for measurements with the floating floor, where only one set is included.

Figure 3 – Photo of sensor setup inside of the test rooms. Sensor positions indicated with white arrows.

3. MEASUREMENT RESULTS

Measurements of velocity level difference and sound insulation were done with various resilientinterlayers and fasteners between floors, as listed in Table 1. The configuration numbers in the firstcolumn are used for reference in the subsequent chapters.
Table 1 – Configuration of fasteners and elastic interlayers
Meas.

Screw

Centerthicknessdistance

Sylomer SR 28

8 mm

600 mmScrews partially threaded

None

6 mm

300 mm7

Screws p. threaded

Aladdin

8 mm

600 mm8

Screws p. threaded

Sylomer SR 28

6 mm

300 mm9

Screws p. threaded

Sylomer SR 28

8 mm

600 mm10

Screws p. threaded

Xylofon 35 shore

6 mm

300 mm11

Screws p. threaded

Xylofon 35 shore

8 mm

600 mm12

Angle brackets

Sylomer SR 28

1000 mm

GePi Connect 100

13

Angle brackets

Sylomer SR 28

1300 mm

GePi Connect 240

14

Angle brackets

Xylofon 35 shore

1000 mmTitan

15

Angle brackets

Xylofon 35 shore

1000 mm

Titan Silent

16

Angle brackets

Xylofon 35 shore

1000 mm

Titan Silent modified 3

Fastener

Elastic profile

1

None

None

2

None

Aladdin

3

None

Sylomer SR 28

4

None

Xylofon 35 shore

5

Screws fully threaded

6No.

Angle bracket

3.1 Junction damping using Sylomer as elastic interlayer
Measurements of velocity level difference between floors with Sylomer SR 28 as elastic interlayer
are shown in Figure 4. Tapping machine and loudspeaker were used as sound sources, and sensors
were mounted on walls in the top and bottom floor.
The results show that the choice of fastener is crucial to the resulting damping around the critical
middle frequencies. Measurements made with an elastic interlayer and screws as a fastener resulted
in marginally better damping than using no elastic interlayer and screws as fastener, while angle
brackets with elastic interlayer gave higher damping. As expected, the reference set-ups with nofasteners (beige line, no.3) and without an elastic interlayer (black line, no.1) gave the highest andlowest velocity level difference.

3

Titan modified bracket is a Titan silent bracket fitted with extra interlayer and steel fitting to decouple theattached wood elements.

b)

40

Frequency [Hz]

3
12
13
10
8
5
1

3150

2500

1600
2000

1250

800

1000

630

250
315
400
500

200

3150

2500

1600
2000

1250

800

1000

630

250
315
400
500

200

0

160

0

125

10

100

10

160

20

125

20

100

Dv,ij [dB]

30

50
63
80

Dv,ij [dB]

30

40

50
63
80

a)

Frequency [Hz]Damping obtained without fastener
GePi 100 angle brackets cc 1000 mm
GePi 240 angle brackets cc 1300 mm
8 mm partially threaded screws cc 600 mm
6 mm partially threaded screw cc 300
8 mm fully threaded screws cc 600 mm
6 mm screws cc 300 without elastic interlayer between floors

Figure 4 – Junction damping with Sylomer SR 28 as elastic interlayer between floors for various fasteners.
a) and b) show results obtained with tapping machine and loudspeaker as source, respectively.
3.2 Junction damping using Getzner and Rothoblaas elastic interlayers and fasteners
Velocity level differences with elastic interlayers and fasteners from Getzner and Rothoblaas areshown in Figure 5 Results from tapping machine and loudspeaker as source is shown in a) and b),
respectively. Sylomer SR28 (12 mm thickness) as the elastic interlayer between floors results inslightly higher damping than Xylofon 35 shore (thickness 6 mm) when fasteners are not applied. When
any type of screw fastener is applied, the damping performance becomes poor, regardless of what typeof elastic interlayer is applied. Angle brackets, however, results in higher damping around the crucial
middle frequencies.
b)

40

Frequency [Hz]

3
4
13
9
8
15
1

3150

2500

1600
2000

1250

1000

800

630

250
315
400
500

200

3150

2500

1600
2000

1250

1000

800

630

250
315
400
500

200

0

160

0

125

10

100

10

160

20

125

20

100

Dv,ij [dB]

30

50
63
80

Dv,ij [dB]

30

40

50
63
80

a)

Frequency [Hz]Damping obtained without fastener, Sylomer as elastic interlayer
Damping obtained without fastener, Xylofon as elastic interlayer
GePi 240 angle brackets cc 1300 mm, Sylomer as elastic interlayer
8 mm partially threaded screws cc 600 mm, Sylomer as elastic interlayer
8 mm partially threaded screw cc 600, Xylofon as elastic interlayer
Titan Silent angle brackets, Xylofon as elastic interlayer
6 mm screws cc 300 without elastic interlayer between floors

Figure 5 – Junction damping with elastic interlayers from Getzner and Rothoblaas for various fasteners. a)and b) show results obtained with tapping machine and loudspeaker as source, respectively.

3.3 Junction damping using angle brackets
Figure 6 shows velocity level difference with angle brackets with tapping machine and loudspeakeras source in a) and b), respectively. GePi connect angle brackets gives the highest damping followedby Titan Silent modified, then Titan Silent. The use of Titan angle brackets performs at about the samelevel as screw fasteners and with no elastic interlayer around the middle frequencies.
b)

40

Frequency [Hz]

3
12
13
14
16
15
1

3150

2500

1600
2000

1250

800

1000

630

250
315
400
500

200

3150

2500

1600
2000

1250

800

1000

630

250
315
400
500

200

0

160

0

125

10

100

10

160

20

125

20

100

Dv,ij [dB]

30

50
63
80

Dv,ij [dB]

30

40

50
63
80

a)

Frequency [Hz]Damping obtained without fastener, Sylomer as elastic interlayer
GePi 100 angle brackets cc 1300 mm, Sylomer as elastic interlayer
GePi 240 angle brackets cc 1300 mm, Sylomer as elastic interlayer
Titan angle brackets, Xylofon as elastic interlayer
Titan Silent modified angle brackets, Xylofon as elastic interlayer
Titan Silent angle brackets, Xylofon as elastic interlayer
6 mm screws cc 300 without elastic interlayer between floors

Figure 6 – Junction damping various angle brackets as fasteners. a) and b) show results obtained withtapping machine and loudspeaker as source, respectively.
3.4 Junction damping with and without heavy floating floor
Measured velocity level differences with and without heavy floating floor are shown in Figure 7.
Sylomer is used as elastic interlayer in both measurements, and GePi 240 as the fastener. The floating
floor construction consisted of 100 mm gravel laid directly onto the CLT floor, 40 mm mineral wool,
and 70 mm concrete on top. Adding the floating floor increases the velocity level difference by 6-12
dB around the middle frequencies. Somewhat better improvement is observed with a loudspeaker assound source, which is thought to be due to airborne sound transmission through the slab.
b)40

Frequency [Hz]

3150

2500

1600
2000

1250

1000

800

630

250
315
400
500

200

3150

2500

1600
2000

1250

1000

800

630

250
315
400
500

200

0

160

0

125

10

100

10

160

20

125

20

100

Dv,ij [dB]

30

50
63
80

Dv,ij [dB]

30

40

50
63
80

a)

Frequency [Hz]Figure 7 – Junction damping with sylomer SR 28 as elastic interlayer and GePi240 as fastener, where theblue and red lines show results without and with heavy floating floor. a) and b) show results obtained withtapping machine and loudspeaker as source, respectively.

3.5 Sound insulation measurements
Sound insulation measurements according to EN ISO 16283-1 (11) and EN ISO 16283-2 (12) weredone on various floors constructions. Measurements results are shown in Figure 8, where themeasurement numbers refer to the description of the upper floor constructions and resulting soundinsulation given in Table 2. Flanking sound was reduced by using separate wall linings in the bottom
floor consisting of 13 mm plasterboard on 70 mm isolated steel studs, total cavity depth 100 mm.
Suspended ceilings were not applied in the measurements shown.
b)

Apparent sound reduction index, R’ [dB]

60

40

20

0

50
63
80
100
125
160
200
250
315
400
500
630
800
1000
1250
1600
2000
2500
3150
4000
5000

Normalized impact sound pressure level, L’n [dB]

80

80

60

40

20

50
63
80
100
125
160
200
250
315
400
500
630
800
1000
1250
1600
2000
2500
3150
4000
5000

a)

Frequency [Hz]Frequency [Hz]Figure 8 – a) Vertical impact/structural sound insulation and b) airborne sound insulation. Beige (no.1), red(no.2), blue (no.3), green (no.4), and black lines (no.5) correspond to the measurement numbers in Table 2.
Results show that adding weight to a light floor construction improves the sound insulation
noticeably in the lower frequencies, as expected. Gravel added directly to the CLT floor gave
considerable improvement especially for impact sound insulation. The results indicate that the weightof the floating floor is not crucial if concrete is added directly to the CLT floor.
Table 2 – Description of upper floor and resulting sound insulation
Meas.

Description of top floorNo.

(from top to bottom)

1

2x22 mm chipboard, 40 mm mineral wool2

2x22 mm chipboard, 135 mm joists on 25 mm Sylomer.
100 mm isolation in the cavity

Airborne sound

Impact soundinsulation

insulation

R’w (C50-5000)

L’n,w (Cl50-2500)

53 (-2)57 (6)

54 (-2)55(5)58 (-1)52 (3)

2x22 mm chipboard, 135 mm joists on 25 mm Sylomer with3

100 mm isolation in the cavity, 50 mm thick concrete slabs
on CLT floor covering 30 % of the floor area

4

2x22 mm chip board, 40 mm mineral wool, 100 mm gravel61 (-3)44 (9)

570 mm concrete cast, 40 mm mineral wool, 100 mm gravel61 (-2)43 (7)

4. CONCLUSIONS

Velocity level difference has been measured on a full scale CLT model to assess the variation in
damping between various configurations of elastic interlayers and fasteners in junctions.
Measurements of sound insulation were done in parallel to the measurements of velocity level
differences. Results show that all type of screw fasteners reduce the damping effect significantly,
regardless of type of elastic interlayer. The use of elastic detached angle brackets proved to increase
the damping.
Velocity level differences were significantly increased when heavy floating floors were added onto
the CLT floor. Various upper floors were tested. Weight applied directly on to the CLT floor showed
an increase in low frequency sound insulation.

ACKNOWLEDGEMENTS

This project was initiated by Lars Strand, senior consultant at Brekke & Strand Akustikk AS, alongwith SplitkonAS. Contributors are Splitkon, Green Advisers, Brekke & Strand Akustikk,
Skogtiltakfondet, Innovasjon Norge, Christian Berner, Rothoblaas and others.

REFERENCES

1. Brandner R, Flatscher G, Ringhofer A, Schickhofer G, Thiel A, Cross laminated timber (CLT): overview
and development. Eur. J. Wood. Prod. 2016; 74:331-351.
2. Di Bella A, Mitrovic M, Acoustic Characteristics of Cross-Laminated Timber Systems, Sustainability,
2020, 12 (14),5612.
3. Homb A, Hveem S, Lydoverføring i byggesystemer med massivtreelementer, SINTEF Byggforsk, 2011,
80 (In Norwegian).
4. Homb A, Guigou-Carter C, Rabold A, Impact sound insulation of cross-laminated timber/massive woodfloor constructions: Collection of laboratory measurements and result evaluation, Building acoustics,
2017, 24(1):35-52.
5. Verdaxis N-G, Bard-Hagberg D, Dahlström J, Evaluating Laboratory Measurements for Sound Insulationof Cross-Laminated Timer (CLT) Floors: Configurations in Lightweight Buildings, Appl. Sci., 2022,
12,7642.
6. Hoeller C, Mahn J, Quirt D, Schoenwald S, Zeitler B, RR-335 Apparent Sound Insulation in CrossLaminated Timber Buildings, National Research Council Canada, 2017.
7. Morandi F, De Cesaris S, Garai M, Barbaresi L, Measurement of flanking transmission for thecharacterization and classification of cross laminated timber junctions, Applied Acoustics, 2018, 141:213222.
8. Öqvist R, Ljunggren F, Ågren A, On the uncertainty of building acoustic measurements – Case study ofa cross-laminated timber construction, Applied Acoustics, 2012, 73:904-912.
9. Simmons C, Can our standard digital tools predict the sound insulation in wooden buildings? A systematiccomparison with laboratory and field measurements on various floor constructions, Proc. Baltic-Nordic
Acoustics Meeting 2021; 3-5 May 2021; Oslo, Norway.
10. International Standardization Organisation, ISO 10848-1 Acoustics – Laboratory and field measurementof flanking transmission for airborne, impact and building service equipment sound between adjoining
rooms – Part 1: Frame document, 2017, Switzerland.
11. International Standardization Organisation, EN ISO 16283-1 Acoustics - Field measurement of soundinsulation in buildings and of building elements - Part 1: Airborne sound insulation, 2014, Switzerland.
12. International Standardization Organisation, EN ISO 16283-2 Acoustics - Field measurement of soundinsulation in buildings and of building elements - Part 2: Impact sound insulation, 2020, Switzerland

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0924

Measurement of the Vibration Reduction Index
for Cross-laminated Timber Walls in Canada

Jeffrey MAHN1; Markus MÜLLER-TRAPET and Iara B. CUNHA
National Research Council Canada

ABSTRACTThe National Research Council Canada has embarked on a study of the vibration reduction index of crosslaminated timber junctions with the aim of developing empirical models to estimate the values for the crosslaminated timber elements used in Canada. Changes to the fasteners including the use of resilient materials
will be examined. In addition, the vibration reduction index between cross-laminated timber floors andlightweight timber walls will be measured. This type of construction is popular in high rise mass timberbuildings in Canada where non-load bearing lightweight walls are used to reduce cost. The preliminary
results of the study will be presented.
Keywords: Apparent transmission loss, ASTC, Cross-laminated timber

1. INTRODUCTION
The 2015 edition of the National Building Code of Canada (NBCC) (1) describes different methods ofcalculating the apparent sound transmission class (ASTC) rating to demonstrate compliance with the acoustic
requirements of the Code. Depending on the type of building elements included in the building construction,
the ASTC rating can be determined by either following the calculation procedures described in the standard,
ISO 15712 (2) (the 2020 edition of the Code will reference ISO 12354 (3)) or based on level difference
measurements as described in the standard, ISO 10848 (4–6). To allow these standards to be used in a North
American context, the National Research Council of Canada (NRC) has published a series of research reports(7–10) which describe how to use the equations in the ISO standards, but with the metrics from the ASTM
standards which are used in North America.
One of these research reports is RR-335 The apparent sound insulation in mass timber buildings (10).
The report lists data for mass timber elements including cross-laminated timber (CLT) elements includingtransmission loss values, vibration reduction indices and improvements due to linings. The inclusion of themeasured data is important because the NBCC requires the use of measured transmission loss data andmeasured vibration reduction index data for mass timber elements for the calculation of the ASTC rating.
The use of empirical models for the vibration reduction index such as that found in Annex F of ISO 12354
for CLT elements or models to calculate the transmission loss are currently not permitted to be used todemonstrate compliance with the acoustic requirements of the NBCC. There are several reasons for thisexclusion including the large number of models available which give different results and that CLTs used in
Canada can have different constructions than those used in Europe, for example. Face laminated CLTs,
where there is adhesive applied between the layers of elements, but not between the individual elements arecommonly found in Canada. These are different than fully-bonded CLT elements which have adhesive
between the faces of the timber elements in adjacent layers as well as adhesive to bond the adjacent timberelements within a given layer. It is expected that the results between different CLT elements are notinterchangeable and the report, RR-335 includes warnings to this extent.
While the dependence on measured data allows for confidence in the data and it makes it easier to verify
compliance with the minimum acoustic compliance by those who do not have the technical background tojudge the merits of one theoretical model against another, it does limit the data that is available to that which
has been measured. To further expand that data that is available to builders, designers and architects, a1

jeffrey.mahn@nrc-cnrc.gc.ca

project is underway at the NRC to measure the vibration reduction index for a large number of junctions ofvarious elements and connections between them.

2. Mockup Junction Measurements
The mockup junctions currently being investigated include junctions between elements that have as large
a difference in their mass ratio as possible. This would include continuous 9-ply elements connected to
3-ply elements in both cross and T-junctions. An example of one of the cross junctions built in fullcompliance with ISO 10848 is shown in Figure 1.

Figure 1 - CLT cross-junction between a continuous 9-ply CLT and 3-ply CLTs.
The reason to focus on the mass ratio is to be able to observe the trends in the vibration reduction index
data with respect to the mass ratio. Most of the data collected by the NRC to date includes only small mass
ratios which is why the connection between the 9-ply and the 3-ply elements will be important for the future
development of empirical models for the vibration reduction index for CLTs produced in Canada.
The vibration reduction index is also dependent on the connectors between the CLT elements as well as
the spacing between the connectors as shown in Figure 2.

Figure 2 - Measured change in the mean vibration reduction index values for each path forthe cross-junction cases. From RR-335 (10).

For this project, brackets with and without resilient material, screws and combinations of both screws
and brackets are being evaluated with different spacings between the connectors. All of the findings will be
published in a new edition of RR-335 which is anticipated to be released in 2024 and in the web application
soundPATHS (11).

2. Combinations of CLT and lightweight framed elements
It is common practice in Canada to construct buildings with mass timber floors and façade elements, but
to use lightweight timber and steel stud walls as interior partitions between dwellings on each floor. The
reasons that lightweight framed elements are popular are cost and the ease of construction in terms material
handling, familiarity with the constructions and the installation of services such as electrical wiring,plumbing, etc. Little to no data is available regarding the ASTC ratings of these hybrid constructions and todate, the NRC has neither measured the vibration reduction index nor the level difference of the assemblies.
The new four room flanking facility at the NRC will be used to measure the transmission of structureborne vibration through these assemblies as modeled in Figure 3.

Figure 3 - The new four room flanking facility at the NRC with a hybrid building assembly
The walls are shown under construction in Figure 4.

Figure 4 - A hybrid assembly under construction in the four room flanking facility.

The new flanking facility was designed with the testing of these large elements as well as curtain walls
in mind and the overhead cranes makes it easier to construct the assemblies.

DISCUSSION AND CONCLUSIONS
The measurements underway at the NRC will help to calculate the ASTC rating of buildings constructedwith CLT elements both by increasing the existing library of vibration reduction index data available to the
public and the development of empirical models for the structure-borne noise through the assemblies of facelaminated CLTs. All of the data will be made publically available both in the publically available report,
RR-335 and in the web application soundPATHS which was developed by the NRC.

BIBLIOGRAPHY
1.
2.

3.

4.

5.

6.

7.

8.

9.

10.
11.

National Building Code of Canada. Codes Canada; 2015.
ISO 15712-1:2005 -- Building acoustics -- Estimation of acoustic performance of buildings from theperformance of elements -- Part 1: Airborne sound insulation between rooms. Geneva, Switzerland:International Standards Organization; 2005.
ISO 12354-1:2017 Building acoustics. Estimation of acoustic performance in buildings from theperformance of elements - Part 1: Airborne sound insulation between rooms. Geneva, Switzerland:International Organization for Standardization; 2017.
ISO 10848-2:2017 - Acoustics - Laboratory measurement of the flanking transmission of airborne
and impact sound between adjoining rooms - Part 2: Application to Type B elements when thejunction has a small influence. Geneva, Switzerland: International Standards Organization; 2017.
Report No.: ISO 10848-2:2017.
ISO 10848-3:2017 - Acoustics - Laboratory measurement of the flanking transmission of airborne
and impact sound between adjoining rooms - Part 3: Application to Type B elements when thejunction has a substantial influence. Geneva, Switzerland: International Standards Organization;2017. Report No.: ISO 10848-3:2017.
ISO 10848-4:2017 - Acoustics - Laboratory measurement of the flanking transmission of airborne
and impact sound between adjoining rooms - Part 4: Application to junctions with at least one TypeA element. Geneva, Switzerland: International Standards Organization; 2017. Report No.: ISO 108484:2017.
Mahn J, Quirt D, Cunha I, Müller-Trapet M. RR-331: Guide to Calculating Airborne Sound
Transmission in Buildings: 6th Edition. Ottawa, Canada: National Research Council Canada; 2022.
Report No.: RR-331.
Mahn J, Quirt D, Müller-Trapet M, Cunha IB. RR-333: Apparent Sound Insulation in Precast
Concrete Buildings: 2nd Edition. Ottawa, Canada: National Research Council Canada; 2022. Report
No.: RR-333.
Mahn J, Quirt D, Müller-Trapet M, Cunha IB. RR-334: Apparent Sound Insulation in Concrete Block
Masonry Buildings: 2nd Edition. Ottawa, Canada: National Research Council Canada; 2022. Report
No.: RR-334.
Mahn J, Quirt D, Mueller-Trapet M, Hoeller C. RR-335: Apparent Sound Insulation in Mass Timber
Buildings. Ottawa, Canada: National Research Council Canada; 2019 Mar. Report No.: RR-335.
soundPATHS Calculator [Internet]. [cited 2022 Aug 15]. Available from: https://soundpaths.nrccnrc.gc.ca/#/PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0944

Annoyance evaluation of impact sounds on timber floors in
different listening test setups
Sabrina SKODA1; Markus MÜLLER-TRAPET2; Young-Ji CHOI3; Iara BATISTA DA CUNHA2;
Jeffrey MAHN2
1

Institute of Sound and Vibration Engineering, Hochschule Düsseldorf University of Applied Sciences, Germany
2
3

Acoustics, National Research Council Canada, Canada

Architectural Acoustics Lab, Kangwon National University, Korea

ABSTRACTIn multi-residential buildings, impact noise from neighbors is one major cause of annoyance complaints
affecting residents’ quality of life. However, human perception of impact sounds is sometimes overlooked instandardized evaluation procedures in national building codes. Particularly for lightweight building
constructions with timber floors, established single number metrics show poor correlation with residents’
perceived annoyance of impact noise. Within this scope, a listening study was carried out as part of acollaborative research project between Canada, Korea and Germany. Participants rated the perceived
annoyance of different impact sounds (ball drops, footsteps, taps) on various timber floor-ceiling assemblies.
The effects of audio playback method and of visual stimuli on the perceived annoyance of impact sounds
were investigated in three different experimental lab settings: a headphone test, an Ambisonics loudspeakerarray and with a virtual living room presented via virtual reality glasses. Results showed an offset inannoyance ratings among experimental conditions, which can be explained by loudness mismatch andcognitive load theory. However, relative annoyance judgements of impact sources and floor-ceilingassemblies remained similar in all three experimental settings.
Keywords: Impact sound, timber floors, annoyance evaluation

1. INTRODUCTION

Noise from neighbors is one of the main sources of noise complaints in multi-unit residentialbuildings. Among the various types of sounds being transmitted from neighboring apartments, impact
noise coming from above is perceived as particularly annoying (1). Impact sounds easily attract
attention due to their impulsive noise characteristics, and with a significant amount of sound energy
in the low frequency range, reducing impact sound transmission through building structures poses achallenge. Housing in urban areas is densifying, with more people living in multi-residential buildings,
and at the same time, lightweight building methods using sustainable materials like timber are gaining
popularity. Compared with heavy concrete layers, wooden materials offer less sound insulation at very
low frequencies. Behind this background, acoustic comfort at home is becoming a more crucial factor.
International standards on impact sound were initially developed based on acoustic measurementsof heavyweight building materials (concrete, masonry) and therefore may not consider the full
frequency range needed to evaluate impact sound in lightweight timber floor constructions. Simmons
et al. showed, that residents in apartment buildings with timber joist floors and walls reported highannoyance due to impact noise, although standardized noise measurements indicated satisfying
acoustic performance (2). As a result, improved metrics with spectral adaption terms applied to awider frequency range have been proposed in recent years, however, these metrics still are not widelyused in national building codes. Besides this, studies showed that perceived annoyance of impact
sounds is not well enough explained by current standardized single number metrics (3, 4). Correlations
between standardized metrics and subjective annoyance ratings vary significantly, depending on thetype of impact source. For walking sounds, factors such as type of shoes, walking speed or spatial
distribution of the footsteps affect the annoyance ratings (5). To meet building residents’ demands on
acoustic comfort at home, and to improve building materials and methods regarding impact soundinsulation, standardized evaluation metrics in building codes need optimization with regards to humanperception.
Several listening studies on impact noise annoyance are being conducted as classic laboratory
experiments restricted to auditory perception. However, perception of an acoustic environment is not
only affected by acoustic factors and measurable physical characteristics of the sound. The listening
situation (including information from other sensory modalities), and other non-acoustic factors suchas a sound’s information content and the evaluation context affect the way a sound is perceived (6).
Also, personality traits of the listener, noise sensitivity, and attitude towards neighbors can have amoderating effect on impact sound perception. Therefore, subjective evaluations carried out in asensory-limited experimental setting often lack ecological validity. On the other hand, field surveys,
collecting annoyance judgments from residents at their own homes, are suitable to capture real life
situations, but they suffer from a high number of confounding variables that make it difficult tocompare results among different locations and to draw clear conclusions (7). In recent years, efforts
were made, to transfer everyday life conditions into controlled lab environments, by using audiovisual simulation methods and virtual reality (VR). Experimental settings on evaluation ofenvironmental sounds and complex acoustic environments are often designed with the aim of precise
spatial reproduction and localization of sound sources (8). However, the question arises, what kind ofexperimental setup best suits annoyance evaluations of impact sounds that are harder to localize andthus may require less detailed spatial reproduction, but need a realistic low-frequency soundreproduction.
In a collaborative research project, the National Research Council of Canada (NRC), the Kangwon
National University in Korea (KNU), and Hochschule Düsseldorf University of Applied Sciences(HSD) in Germany conducted series of listening experiments, to compare annoyance evaluations of
the same impact sounds among different countries. Based on the findings from previous experiments
in Canada and Korea, which were carried out as a loudspeaker experiment, a test with headphones andan online study, a question was raised about the effect of the test environment and the audio
reproduction method on the annoyance ratings of the same impact sounds. Regarding the evaluationof urban soundscapes, the replay method has an effect on factors such as perceived sound quality (9).
Besides this, different visual environments can moderate pleasantness and relaxation ratings of theperceived sound environment (10). However, impact noise is different in nature than environmental
sounds and draws attention to a greater extent. Hence, it was investigated, to what extent previous
findings from soundscape research can be transferred to impact sounds. A listening study using threedifferent experimental conditions was conducted at HSD in Germany.

2. EXPERIMENT
2.1 Test design
The listening study was designed as a between-subjects test, to avoid person-related confounding
variables like mere exposure effect and learning effects that are known to affect subjective ratings.
Therefore, different groups of participants were assigned to each experimental condition, to evaluate
the same impact sounds. Impact sounds from different sources and on different floor assemblies wereselected for evaluation, with the aim to offer a great variety in annoyance. To compare ratings fromdifferent audio reproduction methods, the first experimental condition was a headphone experimentwith audio stimuli only, and a multichannel loudspeaker setup was selected for the second
experimental condition. To investigate the effect of an additional visual stimulus within the sameacoustic environment, the loudspeaker experiment was repeated as a third experimental condition witha virtual living room presented via VR glasses. It was hypothesized that annoyance ratings will differ
between the headphone and the loudspeaker experiment, due to a different listening experience
induced by the loudspeaker setup. Furthermore, lower annoyance ratings were expected in the
loudspeaker setup with VR glasses compared with the setup without glasses, based on the expectationof higher cognitive load induced by the visual stimulus, which is associated with lower loudness
perception.
2.2 Experimental setups
The first listening experiment was conducted in the listening test studio of the Institute of Soundand Vibration Engineering (ISAVE) at HSD. The studio is a room-within-a-room (5.1m x 3.6m x 3.7m),
designed as a soundproof but natural listening environment suitable for listening experiments. The

background noise level in the room including ventilation noise was 25dB(A). In this experiment, thetest stimuli were presented to the participants via headphones, using open-back over-ear studio
headphones (AKG K702) and a RME Babyface. The output sound pressure level of the headphones
was adjusted based on calibration measurements with a dummy head (HEAD acoustics HMS II.3) inthe listener position, wearing the headphones.

Figure 1 – experimental setups: ISAVE listening studio (left) and VR lab (right)
The second and third experiment were both conducted in the ISAVE VR lab, a two-storey room
(8.7m x 7.3m x 7.6m) with sound-absorbing walls and a background noise level of 22.8 dB(A). The
test stimuli were played using an Ambisonics loudspeaker setup, which consisted of 8 active
loudspeakers (Genelec 8030C) and 4 subwoofers (2x Genelec 7040A, ME Geithain BASIS 1, ME
Geithain RL906 (studio monitor used as subwoofer)), connected within a Dante network system. The
crossover frequency between loudspeakers and subwoofers was 90Hz, with the two Geithain
subwoofers limited further to operate only below 45Hz. The listener position in the center of theloudspeaker setup was 1.60m above the floor, with a distance of 3.08m to four loudspeakers in thehorizontal plane (front-left, front-right, back-right, back-left), and with a distance of 2.40m to four
loudspeakers in the frontal plane (top-left, top-right, bottom-right, bottom-left). The four subwoofers
were distributed in the room to ensure sufficient low frequency sound pressure level at the listener
position, while minimizing interference effects. All loudspeakers and subwoofers were time-aligned
and equalized to obtain a flat frequency response between 20Hz and 12.5kHz. The spatial positionsof the loudspeakers and transfer functions measured between each loudspeaker and the listener
position were used to customize the playback. Calibration of absolute sound pressure levels was
performed using the HMS II.3 dummy head in the listener position.
A thin curtain was used to avoid visual distraction from the loudspeaker setup and to create a livingroom ambiance around the listener in the second experiment. All acoustic measurements were carriedout with the curtain in place. For the third experiment, the participants were placed in the same
experimental setup, but wearing VR glasses (HTC Vive Focus 3), so instead of the real setting, they
were seeing a virtual living room in Unity 3D while performing the listening experiment (see Fig. 2).
Both loudspeaker setup experiments were conducted in the same time period, randomly alternating
the experimental condition with and without VR glasses among participants.

Figure 2 – virtual living room as visual stimulus in third experimentIn all three experiments, participants used a Matlab-based interactive user interface, which enabled
them to operate the listening experiment on their own. In the experimental setup with VR glasses, theMatlab interface was streamed onto a screen object in the virtual living room with real-time remotecontrol via computer mouse.
2.3 Stimuli
All impact sounds were recorded in Canada at the NRC floor testing facility, which consists of two
vertically arranged reverberation chambers, separated by the floor-ceiling assembly under test. Impact
sources were operated in the upper chamber, and the corresponding sound recordings were carried out
in the lower chamber using a first-order Ambisonics microphone (Sennheiser AMBEO VR) and a
Brüel & Kjær Head-and-Torso-Simulator (HATS) Type 4128-C. The test stimuli were created fromthe microphone recordings, whereas the data from the HATS were used to calculate reference soundpressure levels for each test stimulus. During the sound recordings, the average reverberation time in
the receiving chamber was reduced to 0.6s by using absorbing materials, and the microphone position
was 0.6-0.7m below the floor-ceiling assembly, to simulate listening conditions in a real-life livingroom. The Ambisonics microphone recordings (A-format) were transformed into Ambisonics Bformat signals later, which were then further processed into headphone signals for the first experiment,
as well as into separate loudspeaker signals for the second and third experiment.
With the aim to present a wide range of sound pressure levels and impact sound characteristics inthis study, five different types of impact sources were operated on 12 different floor-ceiling assemblies.
Impact sources were: single taps of the standard tapping machine, the standard rubber ball dropped
from a height of 0.1m and 1.0m, and walking with shoes and with socks at a pace of about 1.5 steps/s.
Both, standardized and real life impact sources, were selected for evaluation in this study, to allow
for a comparison of annoyance ratings.
The 12 selected floor-ceiling assemblies consisted of either a cross-laminated timber (CLT) baseelement or a lightweight base element, which was a subfloor of oriented strand board (OSB) andengineered I-joists. These two types of base elements were then combined with various ceiling andtopping materials, resulting in a variety of impact sound transmission characteristics.
Impact sound recordings with a duration of 30-40s were made of each sound source on each floor
assembly, despite of the single taps, which were only recorded on six of the 12 assemblies. To obtainthe final listening test stimuli, singular sound events were extracted from the recordings and they wererearranged into sets depending on the type of impact source. For the ball drops and single taps, setsof three separate impacts with a time spacing of 1.25s were created. The walking sounds consisted ofseven consecutive steps with a time spacing of 0.75s. The final stimulus set contained 54 test sounds
and was the same for all three listening experiments.
2.4 Test procedure
Each participant completed the listening experiment in a single-person session. At the beginningof each session, the experimenter assessed the participants’ hearing by means of a pure-toneaudiometry. Then participants received written instructions on the test procedure and the evaluation
context. In all three experimental setups, instructions and experimental task were similar. The
experimental task was to imagine sitting in a quiet living room and hearing the following impact
sounds from the room above them. Participants were asked to rate the annoyance of the impact sounds
spontaneously, while being aware that there are no right or wrong answers.
The listening experiment took about 15 minutes to complete and it consisted of five parts, eachcontaining the stimuli representing one impact sound source. Before starting each experimental part,two sound examples of the respective impact sound source were presented to the participants. These
examples were the stimuli recorded from the best and worst performing floor-ceiling assembly, butthey were labelled neutrally as example A and B, to give an impression of the range of sounds without
leading the annoyance judgments. Participants could replay the examples multiple times and thesounds were not rated yet. In the experimental parts, each stimulus was replayed only once and theannoyance judgement was carried out immediately after replay, before proceeding to the next stimulus.
Participants rated the annoyance of each stimulus using a slider on a continuous scale with the endlabels ‘not annoying’ and ‘very annoying’. Slider positions were scaled within a numerical range of 0
(not annoying) to 100 (very annoying). Participants’ response times were tracked together with theannoyance ratings. The experimental parts and the stimuli within each part were presented to eachparticipant in randomized order.
After finishing the evaluation procedure, participants were asked to fill out a questionnaire.

Besides age and gender, the questionnaire addressed the participants’ housing situation, noise
sensitivity and coping strategies towards noise. Furthermore, participants had to evaluate theperceived authenticity of the sound environment and their sense of presence in the imagined livingroom situation using five-point rating scales. Eventually, a short feedback on the listening procedure
was requested. In the third experiment with VR glasses, participants were asked three additionalquestions, assessing the visual pleasantness of the virtual living room, comfort of the VR glasses, andusability of the rating interface within the VR environment.
2.5 Participants
The headphone test (HP) was completed by 30 participants (8 female), aged between 20 and 59
years (M = 37.2, SD = 12.2). In the loudspeaker setup (LS), a total of 20 persons (6 female), aged
between 20 and 68 years (M = 36.9, SD = 13.8) completed the experiment without VR glasses. The
third group (VR), conducting the listening experiment in the same loudspeaker setup but wearing VR
glasses, consisted of 30 persons (12 female), aged between 20 and 70 years (M = 34.8, SD = 13.6).
Participants were students and employees at HSD, and external volunteers recruited from theinstitute’s test person database.
Eight persons in the VR group had also participated in the headphone test previously. Therefore,
in order to rule out possible effects due to repeated exposure, the datasets from these persons were
excluded from the analyses. Their results were subject to separate analyses that are not reported inthis paper. In the LS group, ratings from two participants represented extreme outliers throughout the
test, which increased the variance in this group disproportionally. In order to ensure comparability
with the other experimental groups, these two datasets were excluded. In chapter 3, results are
therefore reported based on sample sizes of N(VR) = 22 and N(LS) = 18.
2.6 Statistical evaluation methods
Statistical data analysis was performed using Matlab R2021b and Jamovi 2.2 (11). Annoyance
ratings were compared among the three test setups by means of correlation analysis. To test theexperimental hypotheses, linear mixed-effects models were calculated including a random intercept
for each participant and using restricted maximum likelihood estimates of variance components andType III Analysis of Variance via Satterthwaite’s degrees of freedom method. One-way analysis ofvariance (ANOVA) was used to evaluate differences between the three test environments regarding
items assessed in the questionnaire after the listening experiment. For all analyses, the significancelevel α was set to .05.

3. RESULTS
3.1 Average annoyance ratings
Annoyance ratings of the test stimuli averaged across participants and floor-ceiling assemblies arepresented in figure 3. The figure shows arithmetic mean values for each impact source with 95%
confidence intervals (CI), and ratings from each test environment are depicted as separate lines.

Figure 3 – Average annoyance ratings for each impact source with 95%-CI, separated by test environment

While results from the headphone experiment (HP) and the loudspeaker setup with VR glasses(VR) show high similarity, the annoyance ratings from the loudspeaker setup without VR glasses (LS)are higher. An offset in mean values of approximately 10 scale points between the LS test and theother two experiments is visible for each of the five impact sources.
Among the different impact source types, ball drops from a height of 1.0m and the single taps fromthe standard tapping machine were rated as most annoying in all three experiments. On the annoyancescale ranging from 0 (not annoying) to 100 (very annoying), mean values for the high ball drops are
M ball_1.0(HP) = 60.6 and Mball_1.0(VR) = 66.2, and the mean value in the LS test is M ball_1.0(LS) = 78.7. The
single taps were rated in a similar range as the high ball drops, with mean values M s_taps (HP) = 65.9,
M s_taps (VR) = 59.6 and M s_taps (LS) = 74.3. The lower ball drops from a height of 0.1m received
medium annoyance ratings (Mball_0.1(HP) = 44.6, Mball_0.1(VR) = 50.0, Mball_0.1(LS) = 57.8). Annoyance
ratings of the walking sounds (with socks and shoes) are the lowest in this study, and the averagevalues of these two impact source types across all floor-ceiling assemblies are almost similar. Mean
annoyance values for walking with socks are M walk_so(HP) = 31.9, Mwalk_so(VR) = 33.1 andM walk_so(LS) = 41.5, and the walking sounds with shoes received the average values M walk_sh(HP) = 32.8,
M walk_sh(VR) = 35.6 and M walk_sh(LS) = 41.2. More distinct differences in annoyance occur between thetwo walking types, when separating source types and floor-ceiling assemblies in more detailed
analyses, which are not reported in this paper. As seen in figure 3, the annoyance rankings of the fiveimpact sound sources are similar in all three experiments.
Figure 4 shows annoyance ratings for each floor-ceiling assembly, averaged across participants
and impact sources. Like in the previous diagram, the results from the HP and the VR test are highly
similar regarding both, mean values for each floor-ceiling assembly, and annoyance rankings among
the assemblies. Again, results from the LS test show a quite even offset of about 10 scale points
towards higher annoyance ratings compared with the other two experiments. The difference in means
between tests is smaller for the worst rated assembly no. 7, which received the highest mean
annoyance values (M A7(HP) = 84.2, M A7(VR) = 88.6, M A7(LS) = 90.6). The ranking of the 12 floor-ceilingassemblies regarding the mean annoyance values remains the same across all three experiments.

Figure 4 – Average annoyance ratings for each floor-ceiling assembly with 95%-CI, separated by test
environment
3.2 Correlation of annoyance ratings among experiments
Annoyance ratings of all test stimuli, averaged over participants in each experimental group, showhigh positive correlations between results in the headphone experiment (HP) and both loudspeaker
experiments (LS and VR). Pearson’s correlation coefficients are r(54) = .957 for the HP and LS test,
and r(54) = .959 between HP and VR. Similarly, results from the two loudspeaker experiments are
positively correlated with Pearson’s r(54) = .973. All correlations are highly significant (p < .001).
3.3 Linear mixed-effects model
In the first step, the intraclass correlation coefficient (ICC) was calculated using a linear mixedeffects model (LMM) with only one random intercept for each participant (null model), with data fromthe three experiments merged into one dataset. The ICC is a measure to describe the amount ofvariance in annoyance ratings that is explained only by the participants performing the experiments,
without considering effects of the stimuli or the test environments. The model result shows that
person-related differences among participants explain 19.5% of variance in annoyance ratings in thisstudy (ICC = .195).
To test the experimental hypotheses, a linear mixed-effects model (LMM) was calculated withthree independent variables ‘test environment’, ‘impact source’ and ‘floor-ceiling assembly’, and one
random effect ‘participants’. This model explains 46% of variance in annoyance ratings (R²cond . = .636,
R² marg. = .455) and yields three significant main effects: ‘test environment’ (F(2,67) = 4.93, p = .010),‘impact source’ (F(4,3695) = 555.86, p < .001) and ‘floor-ceiling assembly’ (F(11,3695) = 203.73,
p < .001). Interactions among the variables were investigated as well. However, besides a ceiling
effect, that narrows the rating differences across test environments at the upper end of the annoyancescale for assembly no. 7, no relevant interaction effects can be concluded from the results depicted infigures 3 and 4. The average ratings show an even offset between the LS test and the other two
experiments across both, impact sources and floor-ceiling assemblies. Therefore, the model with main
effects only is considered further.
Post-hoc comparisons of the independent variable ‘test environment’ show, that average annoyance
ratings in the LS test were significantly higher than in the VR test (t(67) = 2.257, p = .027), and alsosignificantly higher than in the HP test (t(67) = 3.093, p = .003). However, there is no statisticallysignificant difference in ratings between the HP test and the VR test (t(67) = .730, p = .468).
Regarding the independent variable ‘impact source’, post-hoc comparisons reveal highly
significant differences among all sources (p < .001), except between the high ball drops and the single
taps (p = .594) and between the two walking types (p = .199).
Participants’ age, gender and self-reported noise sensitivity, which were tested in the model as
further explanatory variables, had no significant effect on the annoyance ratings in this study.
3.4 Evaluation of authenticity and presence
Ratings of perceived authenticity of the sound environment, and evaluations of the feeling ofpresence within the imagined living room situation were compared among the three experimental
conditions. Results from the one-way ANOVA showed, that neither the item authenticity(F(2,67) = 1.198, p = .308) nor the item presence (F(2,67) = 0.397, p = .674) showed any significant
differences in mean values among the three experimental conditions. Authenticity and presence ratings
showed significant positive correlation in the loudspeaker setup, with Pearson’s r LS = .544, p = .020,
and rVR = .463, p = .030. Correlation of these two items in the headphone test was not significant.
3.5 Effect of visual pleasantness
Visual pleasantness of the virtual living room was assessed only in the VR experiment. There wasno significant correlation of visual pleasantness ratings with annoyance ratings of the impact sounds(p = .459) in this experimental condition. However, visual pleasantness showed significant positive
correlations with authenticity (r = .507, p = .016) and with presence (r = .644, p = .001). Moreover,higher visual pleasantness was associated with higher comfort of the VR glasses (r = .655, p < .001).

4. DISCUSSION

Annoyance evaluations of the five different impact source types and the 12 floor-ceiling assemblies
showed an offset in ratings between the headphone (HP) setup and the loudspeaker (LS) playback. A
higher annoyance due to the impact sounds in the loudspeaker setup appears plausible. Although soundreproduction was calibrated in terms of sound pressure level and spectral distribution at the listener
position, the array of loudspeakers surrounding the participant still can create a different listening
experience compared with headphones. In literature, a loudness mismatch between headphones andloudspeakers, the “missing 6dB” (12), has been reported frequently. This loudness mismatch, which
is observed particularly at low frequencies and can be attributed to differences in room acoustics, canhave a significant effect on participants’ response behavior (13). As a result, higher annoyance ratings
due to higher perceived loudness occur in the loudspeaker setup. In contrast, the difference in ratings
between the LS and the setup with the VR glasses may be attributed to higher cognitive load which isinduced by the virtual living room presented via VR glasses, which acts as a distractor. Processing
information from different sensory modalities reduces focus of attention towards the soundenvironment, which can yield lower annoyance ratings (14). Besides that, the stereoscopic image
created by a head-mounted display triggers higher mental effort in the brain compared with natural

vision, which also increases cognitive load. It was interesting to observe, that both effects, of loudness
mismatch and of cognitive load, seemed to have similar effect sizes in this study, which resulted invery similar annoyance ratings in the HP and the VR setup, and thus yielded no significant differences
between these two experimental conditions.
The similar ratings of both, authenticity and presence, in the three experiments were somewhat
surprising, considering the different experimental conditions. The mean values of authenticity andpresence ratings were highest in the VR setup, however differences in means to the other experimental
conditions miss statistical significance. Therefore, an effect of the test setup on these two items could
not be confirmed in this study.
Compared with the impact sounds from the standard sources, the real life walking sounds wereperceived as significantly less annoying. The standard impact sounds covering a wide range of soundpressure levels, were perceived as more unfamiliar in the imagined living room situation and very
annoying. The observation that walking with shoes and walking with socks were rated in a similar
annoyance range can be attributed to the specific stimulus set in this study.

5. CONCLUSIONS

Results from this listening study showed an offset in annoyance ratings between the listening
experiment conducted with headphone playback and evaluations carried out in the Ambisonics
loudspeaker setup. Impact sounds were rated more annoying in the loudspeaker setup. However,preference rankings of the different impact sources and floor-ceiling assemblies did not differ amongexperimental conditions. Consequently, the experimental setup seems to affect impact sounds
consistently regarding absolute annoyance levels, but relative comparisons of the acoustic
performance among various lightweight building elements regarding perceived annoyance seem toremain stable.

REFERENCES

1. Frescura A, Lee PJ. Annoyance provoked by single and combined sound sources from neighbors inwooden residential buildings. Building and Environment 2021 Aug; 205:108248.
2. Simmons C, Hagberg K, Backman E. Acoustical performance of apartment buildings - resident's survey
and field measurements. Akulite Report 2011;2.2.
3. Spaeh M, Hagberg K, Bartlomé O, Weber L, Leistner P, Liebl A. Subjective and Objective Evaluation of
Impact Noise Sources in Wooden Buildings. Building Acoustics 2013; 20(3):193-214.
4. Høsøien C, Rindel J, Løvstad A, Klæboe R. Impact Sound Insulation and Perceived Sound Quality. Proc
Internoise 2016; 21-24 August 2016; Hamburg, Germany. p. 903-910.
5. Kylliäinen M, Hongisto V, Oliva D, Rekola L. Subjective and objective rating of impact sound instulationof a concrete floor with various coverings. Acta Acustica united with Acustica 2017; 103(2):236-251.
6. Rychtarikova M, Vermeier G, Vorländer M. Laboratory listening tests in room and building acoustics.
European symposium Harmonisation of European Sound Insulation Descriptors and Classification
Standards 2010; Florence, Italy.
7. Ljunggren F, Simmons C, Hagberg K. Correlation between sound insulation and occupants' perception Proposal of alternative single number rating of impact sound. Applied Acoustics 2014; 85:57-68.
8. Aspöck L, Mösch L, Stienen J, Vorländer M. Auralization of interactive virtual scenes containing
numerous sound sources. Proc ICA 2019; 9-13 September 2019; Aachen, Germany. p. 6401-6408.
9. Guastavino C, Katz B. Perceptual evaluation of multi-dimensional spatial audio reproduction. J Acoust
Soc Am 2004; 116(2):1105-1115.
10. Viollon S, Lavandier C, Drake C. Influence of visual setting on sound ratings in an urban environment.
Applied Acoustics 2002; 63:493-511.
11. The jamovi project, jamovi (version 2.2) [computer software], Retrieved from https://www.jamovi.org.
12. Munson WA, Wiener FM. In search of the missing 6 dB. J Acoust Soc Am 1952; 24:498-501.
13. Denk F, Kohnen M, Llorca-Bofi J, Vorländer M, Kollmeier B. The "Missing 6dB" Revisited: Influenceof Room Acoustics and Binaural Parameters on the Loudness Mismatch Between Headphones andLoudspeakers. Front Psychol 2021; 12:623670.
14 Steffens J, Müller F, Schulz M, Gibson S. The effect of inattention and cognitive load on unpleasantness
judgments of environmental sounds. Applied Acoustics 2020; 164:107278.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0993

Subjective Evaluation and Measurement of floor impact sound witha heavy and soft impact source
Hiroshi SATO1
1

National Institute of Advanced Industrial Science and Technology
1-1-1 Umezono, Tsukuba, Ibaraki 305-8566, Japan

ABSTRACTThis paper presents a summary of the relation between the subjective evaluation of floor impact soundmeasured with heavy and soft impact sources and physical indices with recorded floor impact sound of awood-frame test house. Subjective scores were obtained with a listening test with five scale judgment andpaired comparison test. The results presented that LiA,Fmax was well correlated with subjective scores.
Measurement results with different drooping heights are also reported.
Keywords: Floor impact sound, Subjective evaluation, Wood-frame construction, Soft and heavy impact
source1. INTRODUCTION
This study presents the relationship between subjective evaluation on floor impact sounds andphysical measures using published results by authors [1-3]. For the practical use of indicate insulation
performance of impact sound insulation performance, A-weighted maximum sound pressure level withtime constant Fast (L iA,Fmax) is discussed in this paper.
The first topic to be discussed is subjective evaluation of floor impact sound in different living
situation such as living room situation and bedroom situation. In this discussion, relationship between
L iA,Fmax and subjective evaluations are reported based on previous study[2].
The second topic just noticeable difference between is benefit of paired comparison test. The
previous study [3] reported that if detailed difference of floor structure, it is better to use paired
comparison test.
The third topic comparison of the subjective response between older listeners and younger listeners.
Basically, there is no difference between them, but possible difference will be found if the higher
frequency component contributes to the impression. For the discussion purpose, unpublished data ispresented but it is not well analyzed.
The last topic is effect of dropping height of the impact ball physica lly.

2. SUBJECTIVE EVALUATION OF FLOOR IMPACT SOUND
2.1 Five scale judgement
The detailed test method is already reported in the published paper [1]. The subjects rated theirannoyance (“KININARU” in Japanese) to 58 floor impact sounds presented in random order using
Japanese 5 category scale [4] with verb at each category; 1. MATTAKU-NAI (not annoy at all),
2.AMARI-NAI (not annoy), 3.TASHO (moderately annoying), 4. DAIBU (very annoying),
5.HIJOUNI (extremely annoying). Subjects were asked to image the situation; “Floor impact sounds
were heard from upper unit when you are reading book comfortably in your living room.” Measured
values were presented with two predictors of subjective rating named as “noticeable ratio of
annoyance” and “complain ratio of annoyance.”
Noticeable Ratio of Annoyance (NRA): This value is calculated as a ratio of sum of “moderately”
to “extremely” annoying to all responses.
Complain Ratio (CR): This value is calculated as a ratio of sum of “very” to “extremely” annoying
1sato.hiro@aist.go.jp

to all responses.
2.2 Constant method
The detailed test method is already reported in previous conference[ 3]. The procedure is same asconstant method but presentation of results are not as thresholds as usually the method utilized.
Subjects were asked to lie on the bed, to imagine the situation just before falling in asleep and to busha push button when he/she felt annoyance to the presented impact sound. Each subject responded 5
times to each stimulus and 85 responses were corrected for each stimulus.
Results of subjective evaluation

percent annoyance

2.3

100
90
80
70
60
50
40
30
20
10
0

Bedroom single
impactBedroom triple
impactLiving room(NRA)
Living room (CR)
Hamada (various
structure)

20

30

40

50
60
70
80
L iA,Fmax dB
Figure 1 Relationships between A-weighted maximum sound pressure levels and subjective
ratings[2,5]For all conditions and rating method for subjective evaluation presents more less the same curveas Figure 1 presents and each curve are shifted 5 to 10 dB interval. If a classification scheme is needed,
we have to think about situations, numbers of impact sound and criteria of judgement. It is found that
we human beings rate annoyance in the frame with the instruction when we listen the sound. Thistendency shall be considered to create classification scheme and shall not rely on only single result of
subjective study.

3. Just noticeable difference (JND) of floor impact sound
3.1 Sheffe’s paired comparison test
The previous study[3] employed LiA,Fmax as physical quantity and Sheffe’s paired comparison
method[6] to obtain subjective values. The purpose if the study was to find differences of detailed
floor-ceiling systems of wood-frame structure. The benefit of this subjective test is to get less scatteredresult and to get JND, which can present statistical difference of subjective judgement with connection
to physical number.
The experiment was done in a semi-anechoic room. Forty participants were asked to be seated andto look at 23” touch panel screen in front of the subject. participants were asked to rate the differences
for each pair in one of five categories. They did this by touching a number on the touch panel screenwith the following descriptions after listening to each pair of sentences:
1) Former is much more annoying than latter.
2) Former is more annoying than latter.
3) No difference is found on both sound4) Latter is more difficult than former.
5) Latter is much more difficult than former.

The categories were assigned scores of -2, -1, 0, 1, and 2 corresponding to the first to the fifth
responses in the list above, respectively. A total of 400 different pairs of impact sound conditions
including pairs of same stimuli were presented. Table 1 presents some of the floor-ceiling system usedin the test.
Table 1 – Specification of wood-frame floor-ceiling systems[3]A02

B01
Wood panel flooring,of birch, t=15 mm

Base floor
material

Typical wood panel
flooring, t=12 mm
Insulation mat t=12
mm

Base

Particle board, t=20mm

Base floor
material

Plywood, t=15mm

Floor joist

2x10, 235mm@455

Sound
absorber

GW24K-100mm

Ceilingjoist

2x6, 140mm@455

CeilingchannelNone

Ceiling
material

Doubled fire-resistant gypsum board, t=15 mm x 2

Floor code

Topping

B02

B03

Wood panel flooring, of birch, t=15 mm, bonded
to base floor material

Plywood of larch, t=28mm

Top layer
Base layer

improved
resilientchannel with lower
resonance frequency

Resilient channel

3.2 Test results and JND
Figure 2 presents relationship between physical measure of impact sounds and psychological scalevalue of impact sound. The variation ranges of impact sound with dropping height of 10 cm are

1.4

RC
B01
B02

A02
B03
A02
B01

B02

1.2

RC

B03

1.0
Phycological scale

10cm
1m(center)1m(corner)

10cm
1m(center)1m(corner)

RC
B01

0.8

B02

0.6

A02
B03

0.4
0.2

RC

A02
B01

0.0
-0.2

B03
B02

-0.4

-0.6
-0.8

6 7 8 9 10 11 12 13 14
Max loudness, dB re 1 sone

36 39 42 45 48 51 54 57 60 63 66

LiA,Fmax, dB

Figure 2 Relationship between L iA,Fmax of impact sounds and psychological scale value [3]narrower than that with dropping height 1m for both of psychological scale and physical scale.
Characters beside markers in Figure 2 presents different floor-ceiling system. “RC” means reinforced
concrete floor, which is used in a standard test chamber.
The Yardstick, which presents statistical difference of subjective value, was calculated to be 0.067(p<0.05) and 0.075 (p<0.01). If a difference of scores between stimuli would be larger than Yardstickof specific probability, each of them are statistically different in the specific probability. JND can beobtained with the Yardstick and slope of the regression line (0.09) as 0.74 dB (p<0.05) and 0.83
dB(p<0.01).

4. EFFECT OF AGEING ON ANNOYANCE TO FLOOR IMPACT SOUND
4.1 Result of listing test with 5 scale judgement
It is reported in published paper [1] that there was no statistical difference between younger andolder listener groups when the listening test was carried out with 5 scale judgement. Because of wide
variety of floors were used in the study, it is expected that personal variation would be significant
than ageing effect.
4.2 Result of listing test with Sheffe’s paired comparison test
The results presented in Section 3 was obtained same number of older and young adults [3]. The
comparison between both listers group is presented in Figure 3. There is no fundamental difference
between subject groups even though the test was carried out with paired comparison test.
1.4
1.2

Phycological scale (older)

1.0
0.8

y = 0.91x
R = 1.0

0.6

0.4
0.2
0.0
-0.2
-0.4

-0.6
-0.8
-1.0

-1.0-0.8-0.6-0.4-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Phycological scale (younger)
Figure 3 Relationship between psychological scale of younger listeners and that of older
listeners. Each plot corresponds to each stimulus [3].
Effect of ageing on annoyance to floor impact soundFigure 4 presents results of headphone listening test both with monaural (same sound presented
to both ears) and binaural conditions with dummy head recorded floor impact soun d [7]. Becauseof difficulty to invite participants to our laboratories, listening test procedure with headpho nes arebeing developed [8-10]. The experiment is currently being done with 5 scale judgement [7].
Because this experiment is ongoing and the result is not well analyzed, the discussion here is not
the final one. Thirty of older participants those are 65 years old and above and 15 of younger
participants from 20s to 50s were participated to listening tests and report their rating to each floor
impact sound twice. The difference is small but there is a possibility that younger listeners feeldifferently in some floor impact sound, but older listener feels less than younger listeners observed

4.3

scatters of plots between monaural and binaural conditions. It is generally said that ageing degrades
healing ability in higher frequency region,
spaciousness,Young
vs Older those depend on higher frequency
component, might heard differently both younger and older listeners.
100
for Youngery = 1.0x + 0.1
R = 0.98

90% Annyance (Binaural)80

for Oldery = 1.0x + 2.7
R = 0.99

70
60
50
40
30
20

Older
Younger

1000

10 20 30 40 50 60 70 80 90 100% Annoyance (Monaural)

Figure 4 Relationship between annoyance response to monaural (same sound presented to bothears) and binaural conditions (preliminary result from [7]).

5. EFFECT OF DORROPING HIGHT OF RUBBER BALL ON SOUND PRESSURE
LEVEL

dB
L A,Fmax @ different height(h),0.5, 1.2 m) dB
最大A特性音圧レベル(h=0.1,

Figure 5 presents the relationship between LA,Fmax measured with standard dropping height (1m)and different heights(h = 0.1 m, 0.5 m and 1.2 m) in wooden frame building where recording of floor

80

75
70

65
60
55

h=1.2 m50h=0.5 m45h=0.1 m

40
40

45

50

55

60

65

70

75

80

最大A特性音圧レベル(h=1.0m)，dB
LA,Fmax @ 1m, dB
Figure 5 Relationship between L A,Fmax measured with standard dropping height (1m) and different
heights(h = 0.1 m, 0.5 m and 1.2 m).

impact sound were carried out for listening tests[1-3]. Measurement results of lower dropping height
presents wider scatter than higher height because of difficulty of height control and weakness ofdropping force. Because the relationship between LA,Fmax from h=1.0m and others are liner, it ispossible to estimate floor impact sound from different height by that from standard height(h=1.0 m).

6. SUMMERYThis paper presents variety of factors to be considered when we will investigate effects of floor
impact sound with rubber ball. There are several social needs to create better indoor environment forsustainable development for growing ageing population and reasonable design and evaluation goals
to fit expectation of residents.

ACKNOWLEDGEMENTS
The author thanks to co-authors of previous studies. This study was partially supported by Japan
Two-by-Four Home Builders Association and Hokkaido Research Organization. The on-going study
is a part of the joint research project between NRC Canada and AIST Japan.
The author especially thanks to Prof. Ryu Jongkwan who had been working for this project to carryout the first experiment at AIST Japan for his Postdoctoral Fellowship term in Japan.

REFERENCES[1] Jongkwan Ryu, Hiroshi Sato, Kenji Kurakata, Atsuo Hiramitsu, Manabu Tanaka, and Tomohito Hirota,"Relation between annoyance and single-number quantities for rating heavy-weight floor impact soundinsulation in wooden houses," J. Acoust. Soc. Am. 129 (5), 3047-3055 (2011).
[2] Hiroshi Sato, Tomohito Hirota, Atsuo Hiramitsu, Manabu Tanaka,”Subjective evaluation of floor impact
sound of wood-frame construction dwellings in different living situation”, InterNoise2013, Innsbruck,
Austria, 6053-6059 (2013).
[3] Hiroshi Sato, Tomohito Hirota, Atsuo Hiramitsu, Manabu Tanaka, “ Subjective evaluation of floor impact
sound of wood-frame construction dwellings in different living situation”, InterNoise2014, Melbourne,
Australia, 4932-4937 (2014).
[4] T. Yano, J. Igarashi, J. Kaku, K. Kanda, T. Kaneko, S. Kuwano, Y. Nii, T. Sato, M. Sou, I. Yamaada, Y.
Yoshino, “International joint study on the measurement of community response to noise: construction ofnoise annoyance scale in Japanese,” J. Acoust. Soc. Jpn., 58(2), 101-110, (2002).
[5] Yukio Hamada, et. al, "Evaluation of heavy-weight floor impact sounds with maximum A-weighted soundpressure level," INTER-NOISE 2011(2011).
[6] H. Scheffe, ‘‘An analysis of variance for paired comparisons,’’ J. Am. Stat. Assoc. 47, 381–400 (1952).
[7] Susumu Hirakawa, Hayato Sato, Manabu Chikai, Atsuo Hiramitsu, Hiroshi Sato, Jeffrey Mahn, Markus
Mueller-Trapet, Iara Batista da Cunha, “Challenge for the subjective experiment using headphone”,
InterNoise 2022, Glasgow, UK, (2022).
[8] Jeffrey Mahn, Markus Mueller-Trapet, Iara Batista da Cunha, Hiroshi Sato, Susumu Hirakawa, Manabu
Chikai, “Impact noise annoyance amongst seniors aging in place”, InterNoise2020, Seoul, Korea, 12671270(2020).
[9] Hiroshi Sato, Susumu Hirakawa, Manabu Chikai, Jeffrey Mahn, Markus Mueller-Trapet, Iara Batista da
Cunha, “Effect of spatial distribution of floor impact sound on annoyance response for older and young
adults”, InterNoise2020, Seoul, Korea, 1263-1266 (2020).
[10] Markus Müller-Trapet, Iara Batista da Cunha, Jeffrey Mahn, “Subjective studies on impact sound intimes of a pandemic – a comparison between laboratory study and an online listening test”, InterNoise2021, Washington, D.C., USA, 4919-5918 (2021).

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0177

A modiﬁed impact testing method for simultaneously evaluating
multiple ﬂoor toppings
John LOVERDE1; Wayland DONG2
1,2

Veneklasen Associates, USA

ABSTRACT
Materials such as floor coverings, screeds, and resilient matting are commonly applied on top of a floorceiling assembly to improve the impact noise insulation. Such toppings involve multiple parameters (finish
floor, screed thickness, resilient mat thickness), which much be tested on multiple structural assemblies, andeven within a manufacturer or product line, the number of permutations is so large that it is infeasible to test
each one. Theory and experience indicate that the improvement in impact insulation due to floor toppings islimited to the frequency range above the natural frequency of the resilient materials. In order to reduce thenumber of tests required to characterize floor toppings, the authors are developing a modified method wheremultiple top-side assemblies could be installed on the same structural assembly. The expectation is thatairborne and low-frequency impact insulation would be consistent since the base assembly is unchanged, but
high-frequency impact insulation would provide the same result as a full-scale test. Data supporting thismethod was previously presented at ICA 2019. Additional laboratory data and comparisons to conventional
testing are presented.
Keywords: Low-frequency, High-frequency, Impact, Airborne, Insulation

1. INTRODUCTION
Floor coverings are materials applied on top of the base floor-ceiling assembly that are not used tomeet structural or fire resistance requirements. Floor coverings primarily include finish floors, screeds,
and resilient materials designed for impact noise isolation, but also include materials for thermal
control, waterproofing, leveling, etc. A common class of product for improving impact insulation isresilient matting installed either below the finish flooring or below a gypsum concrete screed. Many
products can be installed with a wide variety of finish floors and structural syste ms, and the productmust be tested in the laboratory with multiple finish floors and on all of the structural assembly types
that may be encountered. The number of combinations quickly rises to unmanageable quantities.
Here we begin development of a modified test method in which the floor surface is divided into
zones, enabling testing of multiple floor toppings on the same structural assembly. This will
significantly reduce the time and cost required to assembly the necessary data , with the supposition
that the results will provide the same information. In this paper, we explain why the modified method
is expected to yield similar results as full floor testing, and begin testing to validate the method.

2. ANALYSIS
It is well documented that the improvement in impact insulation due to floor coverings isapproximately zero below the resonance frequency of the floor covering, and increases with frequency
above the resonance frequency (1–3). In other words, there are two frequency domains that are
relevant to the impact insulation of an assembly. At low frequencies (b elow the resonance frequencyof the floor covering), the isolation is determined by the properties of the structural system and thefloor covering can largely be ignored. At high frequencies, the minimum level of isolation isdetermined by the base assembly, but the impact insulation is determined largely by the properties ofthe floor covering.
1
2

jloverde@veneklasen.com
wdong@veneklasen.com

Because the low and high frequency domains are due to different physical processes, the testing
program can be optimized to obtain the desired acoustical information with increased efficiency.
2.1 Rating for low-frequency impact noise
The authors have shown that the low-frequency impact isolation can be characterized by the levelsin the 50, 63 and 80 Hz bands generated by the standard tapping machine (4,5). The rating formeasuring low-frequency impact isolation in the field called Low-frequency Impact Rating (LIR) andthe rating for laboratory testing is named Low-frequency Impact Insulation Class (LIIC). These ratings
are defined in ASTM E3207 (6) and are calculated by the formula
𝐿𝐼𝐼𝐶 = 190 − 2𝐿50−80(1)where 𝐿50−80 refers to the energetic sum of the impact sound pressure levels in the 50, 63, and 80
Hz third-octave bands.
For assemblies controlled at low frequencies, LIR is well correlated with 𝐿′𝑛𝑇,𝑤 + 𝐶𝐼,50−2500 , whichis the recommended metric in the COST Action (7), and the recommended classification schemes for
the LIR are also consistent with the COST Action guidelines (8).
The measurement uncertainty increases at low frequencies, and the reproducibility between
laboratories at those frequencies is expected to be poor. The statistics of LIIC have been investigated(9). Important conclusions from the previous study include confirming that the finish flooring did notappear to have any effect on the LIIC rating, and measuring the standard deviation of LIIC in the samechamber to be around 2–4 points (depending on the assembly). While this variation is sizable, thestudy also confirmed that by averaging a sufficient number of tests, even small differences bet ween
assemblies (on the order of a few dB) could be accurately measured.
2.2 Rating for high-frequency impact noise
Impact noise at high frequencies depends strongly on the local compliance of the surface that is
struck by the falling hammer (10). The resultant behavior is that the improvement in impact insulationlevel (Δ𝐿𝑛 ) due to floor coverings is
Δ𝐿𝑛 = 𝐾 lg

𝑓
𝑓0

(2)

where 𝑓 is the frequency, 𝑓0 is the resonance frequency of the floor covering, and K is a constant(typically 30 or 40) that depends on the type of covering and how it is coupled to the structure (1–3).
The resonant frequencies of available floor coverings varies widely, but the authors have shown that
evaluation of the high-frequency impact isolation can be evaluated by including the bands from 400
Hz and above (4). Even for materials that have resonance frequencies below 400 Hz, the improvementin those bands is small compared to higher frequency bands. Ratings such as IIC and 𝐿𝑛,𝑤 become
controlled by lower frequency bands, and therefore do not accurately describe the amount of highfrequency isolation that the assembly provides. (11)The authors have therefore proposed a new family of high-frequency impact ratings that are
intended to accurately portray the effect of floor coverings. The calculation procedure is the same as
the IIC rating, except that the frequency range is from 400–3150 Hz, and the 8 dB rule is not
implemented. There is a high-frequency version of each of the existing ratings, and these ratings haverecently been published as ASTM E3222 (12). The laboratory rating is called High-frequency Impact
Insulation Class (HIIC).
For most floors with ratings below IIC 55 (𝐿𝑛,𝑤 above about 55), the HIIC and the IIC are usually
very close. For high-performing floors with high-performing floor coverings (i.e., with low resonancefrequencies), however, the HIIC can greatly exceed the IIC.
2.3 Rationale
Based on this behavior, we consider the feasibility that installing multiple floor coverings on thesame structural assembly would result in the same low and high -frequency impact ratings as the fullinstallation.
For low frequency measurements, the floor covering has minimal effect. If multiple floor coverings
are installed on the same assembly, measurement of the low frequency impact insulation should yield
the same result when measured on any of them. This is complicated by several factors. The uncertainty
in measurement of LIIC is large, so that only the average of several tests is meaningful. Further, thenoise level can vary with tapping machine location, and the loc ations will in general be different with

multiple floor coverings as opposed to a single covering. Since the result is averaged over tapping
machine positions, however, the low frequency rating on average should be the same whether
measured over single or multiple floor coverings.
For high frequency measurements, for “locally reacting” floor coverings, the specimen size is notimportant by definition. For floating floor coverings, the specimen needs to be of sufficient size thatthe response to the tapping machine is the same as the full floor installation. For example, it isgenerally assumed that the laboratory (full floor) installation of approximately 10 m 2 is representativeof field conditions where the floor area may be much larger. ISO 10140-1 (13) Annex H allows floor
covering measurements to be made on 3 or more small specimens (large enough only for a single
tapping machine position), and 10140-5 (14) Annex G allows lightweight wood floor mock-up that is
2.0 x 2.6 m (5.2 m 2). However, it remains for experiment to determine the differences between fullfloor installations and smaller areas.
For airborne isolation, the floor covering would be expected to have an effect if it changes themass of the assembly. If multiple floor coverings are tested simultaneously, the airborne isolation
should be similar to the full floor installation if each covering has similar mass. In other words, all
the floor coverings installed should be of the same type.

3. PROPOSED METHOD
The proposed method is internally referred to as “Floor Zone”. The structural assembly is built andinstalled in the test opening in the usual fashion. The top surface of the structural assembly is divided
into zones. Multiple configurations are possible; here we consider dividing the floor into 4 equal zones(quadrants).
The laboratory in which this was tested has total specimen area of 10.98 m 2. The zones are
separated by 2x4 lumber (approximate dimensions 38 x 89 mm). The lumber borders are lined withperimeter isolation material in the same manner as the perimeter of the specimen. The size of theresultant zones is 1473 mm x 1778 mm (2.62 m 2 ). See Figure 1.
Four impact tests are performed, with four tapping machine positions on each zone. The tapping
machine positions are as defined in ASTM E492 (15), except oriented based on the center of eachzone rather than the center of the entire floor area. The receiving room microphone posit ions andmeasurement procedure is the same as for a full floor installation. Airborne testing is also performedin the same manner as if the installation were the full floor.

Figure 1 – A picture of the top surface of the assembly divided into 4 Floor Zones. A different floor topping
will be installed in each Floor Zone.

4. EVALUATION
Previous work presented results on open-web wood truss assemblies (16). Here a testing program
based on CLT structure is presented. The quadrant assemblies are shown in Table 1 and Figure 2. For
this program, the same finish flooring was installed on all quadrants. Twelve finish floors were tested
including the bare slab.

Q1

Table 1 – Quadrant Assemblies
Q2

Finish floor

Q3

Q4

Varies44 mm gypsum

44 mm gypsum

44 mm gypsum

44 mm gypsum

concreteconcreteconcreteconcrete

Sound mat

Underlayment 1

Underlayment 2

Underlayment 3

Underlayment 4

Radiant Tubing

StapledStapledPlastic screed panel

Plastic screed panel

Topping slab

Structure

CLT, no suspended ceiling

Figure 2 – Picture of assembly being constructed before the gypsum concrete topping was poured. The four
quadrants are clearly visible, as are the different methods of securing the radiant tubing.
4.1 Airborne Noise Insulation
The transmission loss spectra for all finish flooring are graphed in Figure 3. The average rating
was STC 47.
There are one clearly anomalous result and a second that is considerably lower than the others in
the mid-frequencies. We have observed similar anomalies before, but the reason for this behavior is
not known. Aside from these two floors, the remaining floors had a rating of STC 47 or 48.

Figure 3 – Transmission loss spectra for all finish flooring
4.2 Impact Noise Insulation
Figure 4 shows the impact spectra for each quadrant, averaged over all finish floors. The single
number ratings are shown in Table 2.

Figure 4 – Impact sound pressure level spectra by quadrant, averaged over all finish flooringTable 2 – Single Number Ratings, averaged over all finish flooring
IIC
LIIC
HIIC
Q1

43

60

46

Q2

43

60

49

Q3

53

55

62

Q4

51

52

64

The differences between the quadrants with the stapled radiant tubing (1 and 2) and the quadrants
with the tubing in the modular screed panels (3 and 4) is apparent. The LIIC rating was higher in thefloors with the staples. This behavior was consistent across all finish floors. The reason for thisbehavior is not known, and needs to be replicated in full sized testing to verify whether it is a propertyof the assembly or an artifact of the measurement.
Figure 5 shows the spectra from all of the finish floors on a single quadrant (quadrant 4; remaining
quadrants not shown but are similar). The IIC ratings vary from 47-56, while the HIIC ratings varyfrom 45–80. This clearly illustrates the benefit of using the high frequency ratings to evaluate theassembly and to compare floor coverings. The IIC ratings are controlled at the lower frequencies
which are similar for all finish floors. Some floors have the same IIC rating but differ by 11 HIIC
points. The low frequency behavior for all floors does not vary significantly for a given quadrant.

Figure 5 – Impact sound spectra for Quadrant 1 for all finish flooring

5. SUMMARY
A method, named Floor Zone, has been developed to measure multiple floor coverings on the sameassembly. The method has been used here to compare not only finish flooring but also the resilient
underlayment and radiant tubing attachment method. The differences between the quadrants wereconsistent with all finish flooring and clearly showed the effect of staples short-circuiting the resilient
underlayment.
The quadrants showed differences in low-frequency rating (LIIC) that were greater than expected
between the floors with and without staples. These may be actual differences due to the staples causing
greater coupling between the topping slab and the CLT slab. However this has not been confirmed.
The rank order and relative differences between finish flooring was consistent between quadrants.

This confirms that the high frequency impact behavior the floors is mostly independent of thestructural assembly. As expected on theoretical grounds, the local compliance of the floor is theprimary factor affecting high frequency impact noise.
This investigation shows that the Floor Zone method provides a faster and more efficient way tocompare the performance of assemblies, and does not appear to have significantly worse measurement
uncertainties than the full size tests. Further investigations on different assembly types are underway.

ACKNOWLEDGEMENTS
The authors wish to acknowledge the assistance of Shaw Industries Group in the gathering of thisdata. Some funding was provided by the Paul S. Veneklasen Research Foundation. The authors thanktheir colleagues at Veneklasen Associates, Inc., for their continued assistance.

REFERENCES
1. Vér IL. Impact Noise Isolation of Composite Floors. J Acoust Soc Am. 1971 Oct 1;50(4A):1043–50.
2. ISO 12354-2. Building acoustics - Estimation of acoustic performance of buildings from the performanceof elements Part 2: Impact sound insulation between rooms.
3. Rindel JH. Sound Insulation in Buildings. In CRC Press; 2018.
4. LoVerde JJ, Dong DW. A dual-rating method for evaluating impact noise isolation of floor-ceilingassemblies. J Acoust Soc Am. 2017 Jan 1;141(1):428–40.
5. LoVerde J, Dong W. The low-frequency limit of proposed ratings for quantifying low-frequency impact
insulation. Proc Meet Acoust. 2018 Nov 5;35(1):015003.
6. ASTM E3207-21, Standard Classification for Determination of Low-frequency Impact Noise Ratings.
ASTM International; 2021.
7. Rasmussen B, Machimbarrena M. COST Action TU0901 - Building acoustics throughout Europe. Volume
1: Towards a common framework in building acoustics throughout Europe. COST Office Action TU0901;
2014.
8. LoVerde J, Dong W. Developing classifications using a dual-rating method of evaluating impact noise.
In: Proc INTER-NOISE 2018. Chicago, IL; 2018.
9. LoVerde J, Dong W. Laboratory measurement of low-frequency impact sound. In: Proc ICSV25.
Hiroshima; 2018.
10. Watters BG. Impact-Noise Characteristics of Female Hard-Heeled Foot Traffic. J Acoust Soc Am.
1965;37(4):619–30.
11. Lo Verde J, Dong W, Rawlings S. New ASTM Ratings for Impact Noise Insulation. In: Proc
INTER_NOISE 2022. 2022.
12. ASTM E3222-20, Standard Classification for Determination of High-frequency Impact Sound Ratings.
ASTM International; 2020.
13. ISO 10140-1 (2016), Acoustics - Laboratory measurement of sound insulation of building elements Part
1: Application rules for specific products. International Standards Organization; 2016.
14. ISO 10140-5, Acoustics - Laboratory measurement of sound insulation of building elements Part 5:
Requirements for tests facilities and equipment. International Standards Organization; 2010.
15. ASTM Standard E492, “Standard Test Method for Laboratory Measurement of Impact Sound
Transmission Through Floor-Ceiling Assemblies Using the Tapping Machine.” ASTM International; 2009.
16. Loverde J, Dong W. Development of a modiﬁed impact testing method for simultaneously evaluating
multiple ﬂoor toppings. In: Proc ICA 2019. 2019.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022, in Gyeongju, Korea
Extended abstractABS-0203

Spatial audio reproduction of floor impact noises for auditory
demonstrations
Youngmin KWON1; Daewook JUNG2
1

Samsung C&T, S. Korea

2Riverway ENG, S. Korea

ABSTRACT
Floor impact noise in the typical apartment buildings in S. Korea has become a major social issue in their
daily lives. The national housing authority recently amended the floor impact noise evaluation method in
consideration of the acoustic characteristics of the actual impact sources in real life. On the other hand human
auditory perception is yet subjective. This study explored spatial audio reproduction of floor impact noises
for auditory demonstrations to the laypersons at a brand new floor impact noise test-bed. In a typicalapartment structure type of the test-bed, the impact-borne noises generated both by the standard impact
sources that are used in evaluation and by a few actual impact sources including walking and jumping wererecorded. The various types of microphones such as directional, omni-directional and contact were employedto pick up the impact-borne noises. Their sound levels and the reverberation times of the room were alsomeasured for reference. A multi-channel audio system engaging front/rear/ceiling speakers with sub-woofers
was implemented to reproduce the impact-borne noises. The system was optimized to create the sound close
to the one in the above room and designed to demonstrate it at different sound levels in reference to theimpact noise criteria.
Keywords: Impact-borne, Reproduction, Audio, Demonstration

1. INTRODUCTION
The floor impact noise occurred in the typical high-rise apartment buildings in S. Korea has becomea major issue for a length of time. Physical proximity of the apartment units horizontally resided
between demising walls and vertically stacked within a typical floor-to-floor height of 2.9-3.0m (or afloor-to-ceiling height of 2.5m) for each unit would cause a quick transfer of impact sound to theneighbors. A large amount of impact sound energy is transmitted through the building structure suchas floors, walls and columns in terms of structure-borne vibration at low-frequencies and is released
air-borne in the neighborhood.
Such floor impact sound insulation in buildings in S. Korea is to be measured and evaluated with
two types of standard impact sources: light impact one and heavy impact one. The standard light
impact source is characterized across the low through mid-frequency bands from 125 to 2k Hz,
representing hard but light impact sources in real life such as walking in high heels or dropping ofgolf balls on the hard floor surfaces. Tapping Machine is used as the standard light one. Equivalentsound pressure levels (L eq ) are measured for evaluation on light impact sound insulation performance.
Then, the levels are corrected with the effect of background noise and room sound absorption power.
On the other hand, the standard heavy impact source is characterized across the low-frequency bands
from 63 to 500Hz, representing soft but heavy impact sources such as jumping barefoot by children
or walking barefoot by adults. Bang Machine and Rubber Ball are used as the standard heavy one.
Maximum sound pressure levels (L Fmax) are measured for evaluation on heavy impact sound insulation
performance. Plus, the levels are corrected with the effect of background noise. These measurement
frequency ranges and evaluation method are to be in effect for the apartment construction projects
approved before August 4, 2022 when the amended evaluation method and new criteria for floor
impact sound insulation were released.
1

iam0min.kwon@samsung.com

In the meanwhile, auditory perception of floor impact sound has remained subjective and arguableagainst the classification and criteria set out for floor impact sound insulation in S. Korea. Floor
impact sound varies in perception according to the impact sources which differ in their tonal colors
or textures when exciting a floor surface, not to mention sound intensity and frequency contents. Asa matter of fact, the floor impact sound can be varied not only by the impact sources but also by thephysical properties of building structure such as structure types, density and thickness of reinforced
concrete (RC) slabs, slab span between solid walls, floor components on the concrete slabs, etc.
Such sounds excited by some various floor impact sources were recorded at the apartment units
with typical structure types in a brand new floor impact sound test-bed and reproduced for auditory
demonstrations. The test-bed is named “RAEMIAN Goyoan Laboratory (G-Lab),” which was
designed primarily to study how to mitigate floor impact sound transmission. In addition to research
purpose, the G-Lab facilitates a comprehensive understanding of key aspects of floor impact soundaddressed by a technical gallery engaging an auditory demonstration room. In this regard, the impactborne sounds generated by the standard impact sources that are used in evaluation of floor impact
sound insulation as well as by a few actual impact sources in our daily life were attained in favor of
auditory demonstrations for the laypersons. The latter ones include jumping barefoot lightly andwalking barefoot by an adult male. A multi-channel audio system engaging a total of seven (7)loudspeakers – five distributed ceiling loudspeakers with two sub-woofers – was integrated to createa sound field in a fifteen square meter (15m2 ) space identical to a typical small living room. Allocationof the loudspeakers enables reproduction of the floor impact sounds realistically as audible in anapartment unit, which are transmitted down from the one above.

2. FEATURES OF TEST-BED AND DEMO ROOM
2.1 Floor Impact Sound Insulation Test-bed
The floor impact sound insulation test-bed called “G-Lab” consists of a total of ten (10) apartment
units in combination with four (4) typical apartment structure types found in S. Korea and four (4)RC slabs different in thickness. Those structure types are 1) wall structure; 2) column structure; 3)wall-column hybrid structure; and 4) Rahmen structure with shallow beams classified according toload-bearing internal structural elements. The first three structure types are made up of flat slabs on
top without beams. The slabs vary in thickness across 210, 250, 210-250 hybrid and 300mm.

(a) Wall Structure(b) Column Structure(c) Wall-Column Hybrid Structure(d) Rahmen Structure

Figure 1 – Typical apartment structure types in S. Korea

The wall structure type accounts for the majority of the structure types, which employed in theapartment buildings built from the 1990s in S. Korea, and it became known relatively vulnerable toimpact-borne sound transmission among other structure types. More recently however the apartmentbuildings incorporating wall-column hybrid structure type are on the rise, taking advantage of building
sustainability as well as sound transmission loss, though it may not lead to an intelligible differencein auditory perception.
2.2 Auditory Demonstration RoomThe G-Lab provides a unique experience for either the general public or the prospective customers(apartment buyers or developers) as they can take an opportunity to understand better about themechanisms of both transmission and insulation of floor impact sound. In this context, a technicalgallery was designed and inset into a hallway and a test apartment unit of the G-Lab. Refer to Figure
2. The gallery consists of PR, Tech and Ex Zones, accommodating an auditory demonstration setting.
The demonstration room was created with a multi-channel audio reproduction system in the livingroom, where people spend most of their time at home while awake. On some occasions, an auditory
demonstration can be made in real time by setting off the standard impact sources on the floor above.
People can hear live impact-borne sound along with reproduced ones.

Figure 2 – G-Lab technical gallery with an auditory demonstration room

3. METHOD AND PROCESS OF SOUND REPRODUCTION
In the first step, either equivalent or maximum sound pressure levels denoted respectively as Leq
or LFmax were measured in the living rooms of the test apartment units in the G -Lab. The sound levels
were taken across octave band frequencies of interest for the types of floor impact sources while
excited on the floor of another living room right above. The background noise levels and reverberation
times in the receiving room were also measured for the sound levels to be corrected and normalized.
Next, the impact-borne sounds were recorded by a multi-track recording system. The various typesof microphones including omnidirectional, unidirectional (cardioid) and piezoelectric contact ones
were employed to pick up the impact-borne sound propagation from the surfaces in the room. The
recordings were then sampled, filtered to eliminate any intruded disparate noise in signals andenhanced in quality by DSP-based post audio processing.
Then, the sound levels of the playback at the listening position in the middle of the auditory
demonstration room were aligned with those actually measured across octave band frequencies. The
sound level was tuned up within plus-minus (±) 2 dB at each of octave band frequencies of interest.
Finally, the impact-borne sound recordings can be reproduced in the auditory demonstration room
by a multi-channel audio system integrating seven (7) loudspeakers total. In particular, five distributed
loudspeakers allotted in the upper volume of the demonstration room enable an efficient conveyanceof impact-borne sound energy downward from the above as if the listeners reside in a real apartment
unit and perceive the sound coming from the upper floor.

4. MEASUREMENT AND RECORDING OF IMPACT-BORNE SOUNDS
4.1 Acoustic Data Acquisition for Floor Impact-borne Sounds
Above all, the data of sound pressure levels were obtained across octave band frequencies fromacoustic measurements in the living rooms (receiving rooms) of the test apartment units while excitedby the impact sources on the floor in other living rooms (source rooms) adjacent vertically above .
Those impact sources include the standard impact sources used for evaluation of floor impact soundinsulation as shown in Figure 3 and a few actual impact sources outstanding in real life. Equivalentsound pressure levels (L eq ) were taken at the low through mid-frequency bands up to 2k Hz for Tapping
Machine that is served as the standard light impact source. Whereas, maximum sound pressure levels(LFmax) were taken at the low-frequency bands up to 500 Hz for Bang Machine and Rubber Ball thatare served as the standard heavy impact sources as well as for jumping barefoot lightly and walking
barefoot performed by a trained male adult.
Next, the room background noise levels and the reverberation times that affect the perceived
loudness to be variable were obtained in the receiving rooms. The former is applicable for correctionof the sound levels measured with both standard light and heavy impact sources, while the latter is tobe applicable for correction of those measured with the standard light impact source only. The soundlevels measured with the standard light impact source came to be finally normalized across thefrequency bands of interest in regard to room sound absorption power computed from thereverberation times, resulting in normalized impact sound pressure levels (L'n). Whereas, thosemeasured with the standard heavy impact source after correction came to result in maximum impact
sound pressure levels (L i,Fmax). These resulted sound level data became the basis of sound levelalignment of the audio signals to be reproduced in the auditory demonstration room.

(a) Tapping Machine(b) Bang Machine(c) Rubber Ball

Figure 3 – Standard impact sources setting off on the floor above
4.2 Audio Recording of Floor Impact-borne Sounds
The impact-borne sounds of the standard impact sources and the actual impact sources including
walking and jumping barefoot as in the scope of work were recorded via a multi-track audio systemfor digital recording. The various types of microphones according to sound pickup patterns wereencompassed. Refer to Figure 4. An omnidirectional microphone was located in the middle of thereceiving room to pick up the room sound built with sound energy radiated from all the structuralelements and surfaces. Another omnidirectional one was accommodated in an isolation box tominimize the effect of sound buildup by reflections in such a small room volume (approximately 40m 3 )of the receiving room. Five cardioid unidirectional ones were located up in the air near the ceiling at
each corner of the room as well as in the center to pick up the direct sound radiation from the ceilingsurface. Furthermore, a piezoelectric contact microphone was employed to capture structure-boneresonance within the low but audible frequency range above the lower hearing limit.
In this way, acoustic signature and other information on the properties of floor impact-borne sounds
would be encased well in the recorded signals. In addition to sound intensity or loudness, thoseacoustic signature and sonic information kept in the signals are to be dissimilar each other in frequency
contents, tonal colors or textures and thus would draw varied auditory perception.

(a) Audio Interface with Various Microphones(b) Piezo Contact Microphone

Figure 4 – Audio recording with acoustic transducers in different pickup attributes

5. SOUND REPRODUCTION FOR AUDITORY DEMONSTRATIONS
5.1 Spatial Audio Reproduction
An auditory demonstration room was designed to create the same acoustic environment as theliving room in an apartment unit with a moderate level of reverberation. Within the room, therecordings of the floor impact-borne sounds are to be reproduced in the sound field formed by a multichannel playback system integrating an array of seven (7) distributed loudspeakers. Among them, a2-way premium conical loudspeaker with an 8˝ driver mounted in the central ceiling enough to cover
the frequencies from 60Hz takes a role in creating a sound image up in the air. And four distributed
ceiling loudspeakers at the corners of the demonstration room do their role in conveying impact-borne
sound transmitted through the ceiling and upper wall surfaces. To increase the efficacy of structure borne sound radiation more naturally in the room, these four loudspeakers were made up standmounted, facing toward the ceiling surface to help indirectly generating widely spread inbound soundenergy as if the sound comes from the whole surface above the listener. In addition, two subwoofers
cover the impact-borne sound performance at lower frequencies than 80Hz. Refer to Figures 5 & 6.
In the case of floor impact-borne sound recordings of the standard impact sources, they can be
reproduced in tune with the floor impact sound insulation ratings or classes as set forth by law in S.
Korea, so that the listener can take chances to hear and compare the reproduced samples with eachother. Note that the single number ratings of floor impact sound insulation are categorized into four(4) classes: Class 1 through Class 4 according to level of insulation performance.

Figure 5 – Sound reproduction scheme for auditory demonstrations

Figure 6 – Auditory demonstration room with a sophisticatedly designed
audio reproduction system
5.2 Live Demonstration
The auditory demonstration room facilitates live presentations that can be performed with thestandard impact sources on the floor above. People can hear live sound in the demonstration room,
watching the live stream on TV airing the upper floor through a CCTV network. Refer to Figure 5.

REFERENCES
1. Walker R. Equalisation of room acoustics and adaptive systems in the equalisation of small room acoustics.
Criteria for noise and vibration in buildings and communities. Proceedings of The AES 15th International
Conference; 31 October-2 November 1998; Copenhagen, Denmark 1998. p. 32-40.
2. Zacharov N. An overview of multichannel level alignment. Proceedings of The AES 15th International
Conference; 31 October-2 November 1998; Copenhagen, Denmark 1998. p. 174-186.
3. Davis G, Jones R. Sound Reinforcement Handbook. 2nd ed. Milwaukee, Wisconsin, USA: Hal Leonard;
1989.
4. Jeong J. Background noise, noise sensitivity, and attitudes towards neighbours, and a subjective
experiment using a rubber ball impact sound. Int. J. Environmental Research and Public Health
2021;18(14): 7569; https://doi.org/10.3390/ijerph18147569
5. ISO 10140-3:2010 Acoustics - Laboratory measurement of sound insulation of building elements - Part
3: Measurement of impact sound insulation. International Organization for Standardization; Geneva,
Switzerland 2010.
6. ISO 16283-2:2015 Acoustics - Field measurement of sound insulation in buildings and of building
elements - Part 2: Impact sound insulation. International Organization for Standardization; Geneva,
Switzerland 2015.
7. ISO 717-2:2020 Acoustics - Rating of sound insulation in buildings and of building elements - Part 2:
Impact sound insulation. International Organization for Standardization; Geneva, Switzerland 2020.
8. KS F 2810-1:2015 Field measurement of impact sound insulation of floors - Part 1: Method using standard
light impact source. Korean Agency for Technology and Standards; Eumseong, Chungcheongbuk-do, S.
Korea 2020.
9. KS F 2810-2:2012 Field measurement of impact sound insulation of floors - Part 2: Method using standard
heavy impact source. Korean Agency for Technology and Standards; Eumseong, Chungcheongbuk-do, S.
Korea 2017.
10. KS F 2863-1:2017 Rating of floor impact sound insulation for impact source in buildings and of building
elements - Part 1: Floor impact sound insulation against standard light impact source. Korean Agency forTechnology and Standards; Eumseong, Chungcheongbuk-do, S. Korea 2017.
11. KS F 2863-2:2017 Rating of floor impact sound insulation for impact source in buildings and of building
elements - Part 2: Floor impact sound insulation against standard heavy impact source. Korean Agency
for Technology and Standards; Eumseong, Chungcheongbuk-do, S. Korea 2017.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0319

Experimental and theoretical study on transfer force characteristics
of support legs of dry-type double floor system
Da CAO1; Yu AIDA2; Naohisa INOUE3; Tetsuya SAKUMA4
1

The University of Tokyo, Japan2

3

Haseko Corporation, Japan

Maebashi Institute of Technology, Japan
4

The University of Tokyo, Japan

ABSTRACTThe dry-type double floor system, which is popularly installed for apartment buildings in Japan, has anegative aspect that it generally causes deterioration of heavy-weight floor impact sound insulation. To
predict the effect of the double floor, all the components of the vibro-acoustic system need to be modeled
precisely. In this paper, an experimental and theoretical study is conducted to investigate the transfer force
characteristics of support legs of the double floor. In the experiment, a small specimen with four support legs
is impacted by the standard rubber ball, and the transfer force is measured under the legs, where changing
the fall height of the impact source, the mass of upper flooring, the type and adhesive condition of support
legs. A simple theoretical model is introduced for the double floor system, and the viscoelastic properties forsupport leg and rubber ball are estimated from the experimental results. Finally, this approach is validated byusing a 2-DOF system, showing that it can well simulate the transfer force characteristics of support legs.
Keywords: Floor impact sound, Dry-type double floor system, Transfer force characteristics

1. INTRODUCTION
The dry-type double floor system is a floor finishing structure mainly composed of floor panels
and support legs, and widely installed for apartment buildings and offices in Japan. However, it iswell known that the dry-type double floor system can decrease the heavy floor impact insulation
performance [1]. On the other hand, different impact sources can result in different floor impact soundlevel reductions of dry-type double floor systems because of the nonlinearity of the double floor
system [2]. In order to establish an effective numerical model of floor impact sounds for the double
floor system, it is important to understand the transfer force characteristics of the support legs andthen establish a modeling method for support legs.
Several previous studies were conducted related to support legs. Ishimaru [3] made a single-DOF
specimen composed of a mass and three support legs, and the relationship between dynamic spring
constants and impact forces were found by dynamic experiments. Asakura [4] conducted theexperimental modal analysis of a mass supported by one support leg and calculated the spring constantof the support leg from the first eigenfrequency. In these previous studies, although the dynamic spring
constants were obtained, the experiment conditions were limited, and the quantitative analysis oftransfer force characteristics were not conducted.
In this paper, a test specimen is made, and experiments about the transfer force characteristics ofsupport legs under different conditions are conducted, where the specimen is impacted by the standard
heavy impact source (rubber ball) [5]. Then, a lumped-parameter model for support legs is establishedbased on experimental results. By comparing the calculated results with the experimental results, thetransfer force characteristics of support legs are analyzed quantitatively.
1

dcao@g.ecc.u-tokyo.ac.jp
Yu_Aida@haseko.co.jp
3inoue@maebashi-it.ac.jp
4
sakuma@arch1.t.u-tokyo.ac.jp
22. EXPERIMENTAL METHOD
Four types of support legs are included in the experiments. They are A1 without adhesive, A2 withoutadhesive, A1 with adhesive and A2 with adhesive. The support leg is composed of a steel support bolt andan anti-vibration rubber. A1 has a soft rubber whose Shore hardness is 65A and A2 has a relatively harderrubber whose Shore hardness is 70A. In addition, the anti-vibration rubber of A1 and A2 have different shapes
as shown in Figure 1. The polyurethane adhesives are spread between the support legs and experimental
instruments to stick them together, which is considered as the with adhesive condition. On the other hand,
the without adhesive condition means that support legs are directly put on the experimental instruments.
Firstly, the static spring constants of support legs are measured by unconfined compression test. Then, thedynamic experiments are conducted. The test specimen and dynamic experimental method is shown in Figure
2. The specimen is composed of four same support legs and a square particle board whose length of one sideand thickness is 250 mm and 20 mm respectively. The mass of the specimen is adjusted by changing thenumber of iron plates put on the particle board. The transfer forces of support legs and displacements aremeasured by the impact force sensor (Rion PF-10) and laser displacement meter respectively. The distance
between the bottom of the particle board and the impact force sensor is 100 mm.
As the conditions of the dynamic experiment, the rubber ball is dropped from the height 100 cm, 50 cm
and 20 cm. The mass of the specimen is varied with the number of iron plate, 5.78 kg (1 iron plate), 15.54 kg(3 iron plates), 25.3 kg (5 iron plates). Here, when the mass of the specimen is 25.3 kg, the loading condition
6.34 kg/leg realizes the loading condition of the usual double floor system whose mass of floor panels is 23.2
kg/m2 and the number of support legs is 3.66 leg/m2.
[mm]

Impact source
Iron plates

m1

Particle board

30.5

A1

[mm]

26

Figure 1 – Support legs

c1

k1
Supportlegs

Displacement
sensor

m2
k2

13.7

A2

35

c2

Impact force sensor

Figure 2 – The test specimen and dynamic
experimental method

Figure 3 – The 2-DOF system

3. EXPERIMENTAL RESULTS
3.1 Static Experiment
The results of static experiments are shown in Figure 4. When the support legs are without adhesive,
A1 can be considered as a linear spring whose compression force is proportional to the displacement.
The compression force for A2 without adhesive rises sharply when the displacement exceeds 4 mm,
which shows A2 has the nonlinear characteristics. When the support legs are with adhesive, theexperimental results show the similar tendency, but the slope of A2 increases while the slope of A1
remains almost the same. Table 1 shows the static spring constants of A1 and A2 calculated by linear
regression over the linear range of experimental results.
10
A2, with adhesive
A2, w/o adhesive

Force [kN]8
6
4

A1, with adhesive
A1, w/o adhesive

2
0

0

2

4

6

8

10

Displacement[mm]Figure 4 – Relationship between loads and displacements in static experiments

Table 1 – Experimental results of static spring constants
kN/m

A1

A2

w/o adhesive

112

276

With adhesive

120

361

3.2 Dynamic Experiment
The relationship between transfer forces and displacements in dynamic experiments is shown in
Figure 5. The dynamic spring constants of support legs are calculated from the ratio between the
maximum transfer forces and the maximum displacements within the impact time. The average valueof the dynamic spring constant for each supporting leg is shown in Table 2.
Table 2 – Experimental results of dynamic spring constants
kN/m

A1

A2

w/o adhesive

162

432

with adhesive

255

962

Since the calculated dynamic spring constants of A1 without adhesive show good agreement under
different experiment conditions, the linear characteristics of A1 can be confirmed. For A2 withoutadhesive, the deviation due to mass in the relationship between transfer forces and displacements is
relatively large. Further, there is a tendency that the larger the mass of the specimen is, the larger the
dynamic spring constant is calculated. For A1 and A2 with adhesive, the dynamic spring constants aremuch higher than those without adhesive, and the deviation is also larger.
3
2.5

15.54 kg2

25.3 kg

1.5
1
0.5
0

2
5.78 kg

25.3 kg

1
0.5

0

3

1

2

3

0

4

0

1

2

3

4

Displacement [mm]3

A1, with adhesive

2.5

A2, with adhesive

2.5

Transfer force [kN]

Transfer force [kN]

15.54 kg

1.5

Displacement [mm]

2
1.5
1

5.78 kg
15.54 kg

0.5
0A2, w/o adhesive

2.5

5.78 kgTransfer force [kN]

Transfer force [kN]3

A1, w/o adhesive

1

2

3

Displacement [mm]5.78 kg

1.5

15.54 kg
25.3 kg1
0.5

25.3 kg

0

2

4

0

0

1

2

3

Displacement [mm]Figure 5 – Relationship between transfer forces and displacements in dynamic experiments

44. THEORETICAL ANALYSIS
4.1 Theoretical Model
The rubber ball and test specimens in previous experiments is modeled by the Kelvin-Voigt model
where a spring and a damper are in parallel. The calculation model of the 2-DOF system is shown
Figure 3, where 𝑚𝑖 is the mass, 𝑘𝑖 is the spring constant and 𝑐𝑖 is the damping coefficient. Subscripts
1 and 2 denote the rubber ball and the test specimen, respectively.
The theoretical analysis is performed in two steps. In the first step when the impact force of therubber ball is acting on the specimen, the calculation is performed as a 2-DOF system by Equation 1,
where 𝑔 is the gravitational acceleration. After the rubber ball bounces, the calculation is performed
as a single-DOF system by Equation 2.
𝑚1
[0

𝑐1
0 𝑢̈1
𝑚2 ] [𝑢̈2 ] + [−𝑐1

−𝑐1
𝑢̇1
𝑘1
𝑐1 + 𝑐2 ] [𝑢̇2 ] + [−𝑘1

𝑢1
−𝑘1
𝑚1 𝑔
𝑘1 + 𝑘2 ] [𝑢2 ] = [ 0 ]

(1)
(2)

𝑚2 𝑢̈2 + 𝑐2 𝑢̇2 + 𝑘2 𝑢2 = 0

4.2 Parameters of the Theoretical Model
The rubber ball is modeled by the method proposed by Nagurka [6]. Here, 𝑘1 and 𝑐1 are calculated
by Equation 3 and Equation 4, respectively.
𝑚
𝑘1 = 12 [𝜋 2 + (ln 𝑒)2 ](3)𝛥𝑇
𝑐1 = −

2𝑚1⋅ ln 𝑒𝛥𝑇(4)

The impact time 𝛥𝑇 is measured on a rigid floor, and the coefficient of restitution 𝑒 is 0.8 whichis the specified catalog value of the rubber ball. The parameters of the rubber ball calculated at
different fall heights ℎ is shown in Table 3. The measured and calculated results of impact forces on
the rigid floor is shown in Figure 6. Although the calculated results tend to deviate slightly in thesecond half of the impact time compared with the measured results, since the maximum values are ingood agreement, the effectiveness of the present model is confirmed.
Table 3 – Parameters of the rubber ballh [cm]

k1 [kN/m]c1 [Ns/m]

100

68.2

58.5

50

66.1

57.6

20

60.6

55.1

Impact Force [N]2000

100 cm, calc.
100 cm, meas.
50 cm, calc.
50 cm, meas.
20 cm, calc.
20 cm, meas.

1500
1000
500
0

0

5

10

Time [ms]15

20

Figure 6 – Calculated and measured results of impact forces
Experimental values shown in Table 2 are used for the spring constants 𝑘2 of test specimens. The mass
𝑚2 is 5.78 kg, 15.54 kg, and 25.3 kg which is the same as the experiment condition. The damping ratio 𝜁 is
set to 0.1 and the damping coefficient 𝑐2 is calculated by 𝑐2 = 2𝜁 √𝑘2 𝑚2 .

5. RESULTS AND DISCUSSIONS
5.1 Validation of the Model
As the initial condition for the calculation, the initial velocity 𝑣 of the rubber ball is given by 𝑣 =√2𝑔ℎ, and the transient analysis is calculated by the Newmark-β method (γ=0.5, β=0.25).
The comparison between calculated results and experimental results is shown in Figure 7. There isa slight error in the maximum value of the transfer forces, where the setting of damping coefficients𝑐2 could be the cause. Since the shapes of the calculated waves and the durations of the transfer forces
under different conditions correspond well with the experimental results, it can be concluded that thepresent model is effective to simulate the transfer force characteristics of the support legs.
w/o adhesive

50 cm
1000

20 cm
0

10

20

30

100 cm

2000

50 cm
1000

20 cm
0

0

10

20

30

2000

50 cm

1000

0

20 cm
0

10

20

0

10

30

20

30

Time [ms](b)A1, Meas.
A2, Meas.
A1, Calc.
A2, Calc.

100 cm

50 cm
1000

20 cm
0

10

20

30

Time [ms]3000

A1, Meas.
A2, Meas.
A1, Calc.
A2, Calc.

(c) 100 cm

20 cm

2000

0

Time [ms]

3000

50 cm

1000

3000

A1, Meas.
A2, Meas.
A1, Calc.
A2, Calc.

Transfer force [N](b)A1, Meas.
A2, Meas.
A1, Calc.
A2, Calc.

100 cm2000

0Time [ms]3000Transfer force [N](a)A1, Meas.
A2, Meas.
A1, Calc.
A2, Calc.

2000

0Transfer force [N]

100 cmTransfer force [N](a)with adhesive

3000

Transfer force [N]Transfer force [N]3000

A1, Meas.
A2, Meas.
A1, Calc.
A2, Calc.

100 cm

(c)
2000

50 cm
1000

0

20 cm
0

10

20

30

Time [ms]Time [ms]Figure 7 – Calculated and measured transfer forces for A1 and A2:(a) 𝑚2 =5.78 kg, (b) 𝑚2 =15.54 kg, (c) 𝑚2 =25.3 kg

5.2 Discussions
Using the present model, the relationship between natural frequencies of the test specimens andthe maximum value of transfer forces as well as the durations of transfer forces are discussed. The
results of the relationship discussions are shown in Figure 8 under the condition that the impact ballis dropped at the height 100 cm. The results in Figure are discussed theoretically in following
paragraphs combined with Figure 7.

cb a

2000

1000
A1, w/o adhesive

0
100

10

1

cb a

3000

Impact Force
Transfer Force

Maximum Force [N]Maximum Force [N]3000

Impact Force
Transfer Force

2000

1000

0
100

2

10

cb a

1000
A1, with adhesive

Maximum Force [N]Maximum Force [N]

2000

1

Impact Force
Transfer Force

2000

1000

0
100

2

10

cb a

3000

Impact Force
Transfer Force

0
100

10

a

26
24
22
20
18
10

A1, w/o adhesive12

Impact Force
Transfer Force

26
24
22
20
18

A2, w/o adhesive
1

10

10

a

Impact Force
Transfer Force

26
24
22
20
18
101

A1, with adhesive

102

Natural frequency [Hz]102Natural frequency [Hz]c b

Maximum Time [ms]Maximum Time [ms]

c b

a

28

Natural frequency [Hz]
28

102

10

c b
Impact Force
Transfer Force

Maximum Time [ms]Maximum Time [ms]c b

A2, with adhesive
1

Natural frequency [Hz]Natural frequency [Hz]
28

102

10

Natural frequency [Hz]Natural frequency [Hz]3000

A2, w/o adhesive
1

a

28

Impact Force
Transfer Force

26
24
22
20
18
101

A2, with adhesive

102

Natural frequency [Hz]Figure 8 –Maximum value and duration of transfer forces vs. natural frequency of test specimen
For A1 without adhesive, when the mass of the test specimen is increased from 5.78 kg to 25.3 kg,
the durations of transfer forces are extended, which is caused by the decrease of the natural frequenciesof the specimen. On the other hand, due to the experiment condition of the specimen mass is near the
resonant frequency, it can be found that the maximum value of the transfer forces does not movesignificantly with mass. Similar quantitative discussions can also be made for A1 with adhesive.
For A2, regardless of whether the support leg is with or without adhesive, the duration of transfer
forces remains almost unchanged as mass varies. The reason is that the natural frequency of the test
specimen with A2 is much higher than with A1 so that the upper limit of the duration of transfer forcesis determined by the impact frequency of the rubber ball. Contrast to A1, the maximum values oftransfer forces for A2 clearly tend to increase as the mass increases, which is the result of theresonance caused by the decrease of the natural frequency. In addition, two peaks can be found for A2
with adhesive when the specimen mass is 5.88 kg in Figure 7(a). This phenomenon is caused by thehigh natural frequency of the specimen compared with the impact frequency.

6. CONCLUSIONSIn this paper, experimental and theoretical investigations of transfer force characteristics of support
legs of dry-type double floor system are conducted. From the experimental and calculated results, themain findings in this paper are as follows:•

The static spring constants of A1 (Shore hardness 65A) have linear characteristics, but thestatic spring constants of A2 (Shore hardness 70A) show strong nonlinear characteristics.

•

When the rubber ball is used as the impact source, the maximum transfer forces of support legs
for both A1 and A2 are generally proportional to the maximum displacements, which can beconsidered as linear characteristics.

•

It is confirmed that the coupling between the impact source and support legs can be considered
as a 2-DOF system, and both of the impact ball and the specimen can be modeled by the KelvinVoigt model where the spring and the damper are in parallel.

In the future, more experimental and theoretical study will be conducted to find out the effect ofdifferent impact sources to transfer force characteristics of support legs. Then, the present modelling
method for support legs will be included into the finite element analysis of dry type double floor
system to simulate the floor impact sound insulation performance.

ACKNOWLEDGEMENTS
This work has been supported by JST SPRING, Grant Number JPMJSP2108.

REFERENCES
1. Architectural Institute of Japan. Guidance for evaluation and design of sound insulation in apartment
houses. Maruzen Publishing, Tokyo, Japan;2006.
2. Masuda K, and Tanaka H. Difference of impact sound level reduction by a double floor using different
heavy impact sources -Nonlinear model calculation-. Proc. Autumn Meet. (Acoust. Soc. Jpn.) 2017;9991000.
3. Ishimaru T, Kume S, and Yamashita Y. Consideration concerning transmission force characteristic of supp
ort leg rubber of dry double floorings with standard heavy weight impact source. Proc. Annual Meet.,
Environ. Eng. 1 (Archit. Inst. Jpn.), 2008;181-182.
4. Asakura T. Prediction of vibroacoustic transmission characteristics through double-plate floor structuresby using finite-difference time-domain analysis, Acoust Sci. Tech. 2019;40(5): 344-356.
5. JIS A 1418-2:2000. Acoustics−Measurement of floor impact sound insulation of buildings−Part 2:
Method using standard heavy impact sources.
6 Nagurka M, and Huang S. A mass-spring-damper model of a bouncing ball, Int. J. Engng. Ed. 2006;22(2):393-401.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0390

Consideration of floor impact sound by heavy impact source of thebox floor structure due to holes on the side of box
Ryuta TOMITA1; Kyoko ABE2
1

College of Science and Technology, Nihon University, Japan
2

College of Art, Nihon University, Japan

ABSTRACT
We investigated reduction of transmitted impact sound by heavy impact source of the box structure in areinforced concrete wall construction testing device. The size of the box is 1200 × 600 mm, and ten bodies
are connected to the box. There are two cavities of size 560 × 570 mm, and PVC resin sound insulation sheets
are tightly packed in them. The anti-vibration pad used in this study is an ether-based polyurethane foamelastomer. Two 25mm thick sheets are stacked and installed under the box. In addition, the anti-vibration pad
and the box are simply loaded and not glued. The total thickness of the box floor is about 125 mm. In thisreport, the experiment was conducted under the condition that the air layer under the box was closed. Multiple
holes were provided on the sides of the connected BOX, and the effect on floor impact sound and vibrationof the slab was examined. As a result, it may be possible to reduce heavy-weight floor impact sound bycreating holes on the side surface of the box based on the volume of the air layer on the box and the size andnumber of through-holes.
Keywords: Impact, Sound, Transmission

1. INTRODUCTION
Since the enactment of the “Comprehensive Support System for Children and Child-rearing” (1)in April 2015, authorized small-scale childcare facilities are anticipated to serve as a trump card inurban areas for resolving the issue of children on waiting lists, and as a new childcare structur e
template in regional areas during this era of depopulation. Thus, opening a small-scale nursery schoolfor children aged 0–2 years, with a capacity of 6–19 children, has become possible. As these smallscale nursery schools are becoming licensed, the number of nursery schools that use vacant rooms inapartments and buildings is increasing.
In a previous study (2), we examined practical countermeasures for floor impact sound in small scale nursery schools. By implementing anti-vibration and sound insulation measures on storage
furniture using tatami emphasizing low-price, workability, and storage, we conducted a practicalinvestigation on measures against heavy-weight floor impact sound. In another previous study (3), we
examined the application of these measures in actual buildings b y constructing an area ofapproximately four and half tatami mats (7.2 m 2 ), where the storage furniture with tatami wasconnected to the actual RC structure building. Consequently, the performance improved from Lr-60
to Lr-50 during the car-tire source with impact force characteristics (1) as specified in JIS A 1418 -2(4) excitation.
Applying the results of these studies, we conducted an experimental study and proposed a floor
finishing structure that is highly effective against heavy-weight floor impact sound (5). It is consideredthat this can be used for floor finishing structure of apartment houses. Further, it can also be used fortransforming offices into apartments or childcare facilities. If the commercially available storage
furniture with tatami used in the previous studies [2] is employed, the height from the floor will be 365
mm or more. When applying it to the floor finishing structure, it will be very useful if the height isreduced to approximately 150 mm, thus blocking heavy-weight floor impact sound. Therefore,
utilizing a plane size of 1200 × 600 mm, which was effective for the storage furniture with tatami, as
1
2

tomita.ryuta@nihon-u.ac.jp
abe.kyoko@nihon-u.ac.jp

the base, we conducted an experimental study to keep the size at 150 mm or less. In a previous study[5], we used a connected plane having a size of 1200×1200 mm 2 . With the air around the anti-vibration
pad sealed, an effect of 8–11 dB was obtained in the 63 Hz band, except for some specifications. It
was found that, even if the floor height is maintained at approximately 125 mm due to thespecifications, it can be a useful countermeasure against heavy-weight floor impact sound.
In the previous study (6), we conducted a basic investigation on the reduction in the heavy-weightfloor impact sound level of the box floor structure in the wall-type construction testing laboratory. As
a result, it was confirmed that in the construction of the box floor, the performance improves byapproximately 5 dB in the 63 Hz band, even when the edge is sealed. The result was obtained when
16 sound insulation sheets were used to reduce the weight. Based on the results of our previous study(6), herein, we investigated the reduction of transmitted heavy-weight floor impact sound level of thebox floor structure in the wall-type reinforced concrete laboratory. When the end air space was sealed,holes was made in the side of the box floor. With the air coming out to the adjacent box floor, we
examined heavy-weight floor impact sound based on the presence and absence of holes and the numberof holes.

2. EXPERIMENTAL METHOD
2.1 Experimental Facility
The reduction of transmitted heavy-weight floor impact sound level was measured at the wall-type
reinforced concrete laboratory. Fig. 1 shows the plan view of the laboratory. Measurements were
performed on a slab of 200 mm.
S1

S2

S5

2,800

S3

2,800

S4

3,600

3,600

Frame
Sound source room
(200mm slab)

L1,140cm

Sound source room
(150mm slab)

L4,200cm

L3,180cm
L2,120cm

L5,100cm

Sound receiving room(200 mm slab)

Sound receiving room(150 mm slab)

Figure 1 – Plan view of sound source room and sound receiving room
2.2 Outline of the Box Floor Structure
Figs. 2 and 3 show the plan and cross-sectional views of the box floor structure. The size of thebox floor is 1200 × 600 mm 2 , and ten bodies are connected to the box floor. As shown in Fig. 3, antivibration pads are installed under the legs of the dry double floor on the outer circumference. The box
floor considered in this study is the same as that considered in the previous report (6) and the area ofthe plane is 1200 × 600 mm 2 . There are two cavities of size 560 × 570 mm 2 , and PVC resin soundinsulation sheets are tightly packed in them. In addition, to connect boxes to one another, two places

200(both ends) are fastened with screws on each side (560 or 570 mm) of the hollow part. The soundinsulation sheet has an area density of 2.0 kg/m 2 and a thickness of 1.2 mm. The two cavities are
separated using a 20-mm partition plate. The anti-vibration pad used in this study is an ether-based
polyurethane foam elastomer (0.16 g/cm 3 ). Two 25-mm-thick sheets are stacked and installed underthe box floor.

600

2,400
2,800

600

600

Box floor
1200×600×125mm

Anti-vibration pad

600

300

300

Vibrationmeasurement
point

1,200

600
3,000
3,600

300

200

Periphery
1,200
300

Figure 2 – Plan view of the box floor structure

Sealed with tape

300
1ch

2ch

3ch

System joist
Anti-vibration pad t25×50×50
Anti-vibration pad t25×100×100 (2 sheets)
Steel plate t3.2
Lower part of box floor t40
Particle board t20
Plywood t12

Figure 3 – Cross-sectional view of the box floor structure
In addition, the anti-vibration pad and the box floor are simply loaded and not glued. The total
thickness of the box floor is ~125 mm. There is an air layer of 50-mm thickness between the antivibration rubbers supporting the box floor. The particleboard was manufactured for each test piece,
and the plywood on the upper surface was installed on the central part of the box floor structure toconnect the test pieces and outer peripheral parts.
The experiment was performed with seven patterns (Table 1). The number of mass -added soundinsulation sheets differed between test pieces B and C; the number of sound insulation sheets waschanged to 16 and 6 for each type, respectively. Four anti-vibration pads were considered for each test
piece. Experiment No. 0 was used as a reference, and Experiment Nos. 5 and 7 were the same as thosepreviously reported (6). The outer peripheral parts of test pieces B and C were removed. In ExperimentNos. 5 and 7, air was sealed, and the finish of the box floor structure was up to the particleboard withthe plywood removed. Experiment No. 5 + sp and No. 7 + sp are the specifications of Experiment No.
5 and No. 7, and through holes were created on the side surface of the box floor. As shown in Fig. 4,
two φ12 through-holes were created on both side surfaces of the 600-mm-wide the lower part of box
floor at a distance of 200 mm from the boundary of the side surface. The height was 20 mm from the
top of the lower part of box floor 40mm. In Experiment Nos. 5 + bp and 7 + bp, three additional
through-holes were created according to Experiment Nos. 5 + sp and 7 + sp. As shown in Fig. 4, three
additional through-holes were created on the side surface of the 600-mm-wide BOX, so that there
would be five holes at a pitch of 100 mm from the end. The height was 15 mm from the top of thelower part of box floor 40mm. No through-hole was created on the side surface of the ten box floor
structures facing the outer peripheral portion.
Table 1 – Outline of experimental patterns

5+sp
7+sp
5+bp
7+bp

-

-

-

1200×1200×75

125

30.6

20.9

1200×1200×75

125

30.6

4.8

1200×1200×75

125

30.6

20.9

1200×1200×75

125

30.6

4.8

1200×1200×75

125

30.6

20.9

1200×1200×75

125

30.6

4.8

100
25

40

100

Through hole on Total mass
the side of the of box floor
box floor(kg)-

Finished
surface

16 soundinsulation sheets
6 sound insulation
sheets16 soundinsulation sheets
6 sound insulation
sheets16 soundinsulation sheets
6 sound insulation
sheetsMass persquare meter(kg/m2 )-Linking-The
Air under
outer
box
periphery-

Particle board

None

51.5

71.5

Yes

None

SealedParticle board

None

35.4

49.2

Yes

None

Sealed

51.5

71.5

Yes

None

Sealed

35.4

49.2

Yes

None

Sealed

51.5

71.5

Yes

None

Sealed

35.4

49.2

Yes

None

Sealeddiameter φ 12×2
/ 1 per side
diameter φ 12×2
/ 1 per side
diameter φ 12×5
/ 1 per side
diameter φ 12×5
/ 1 per side

Particle board
Particle board
Particle board
Particle board

100

100

100

100
25

7

None
Specimentype B
Specimentype CSpecimentype B
Specimentype CSpecimentype B
Specimentype C

Mass additionmaterial

20

5Size (mm)

25

0

Mass
addition(kg)-

Design floor Box mass
height (mm)
(kg)

20

Experim Specimenent No.
type

600

Figure 4 – Through holes on the side of the lower part of box floor
2.3 Measurement Method
The reduction of transmitted heavy-weight floor impact sound level was measured in accordancewith JIS A 1440-2 (7). The car-tire source with impact force characteristics (1) of JIS A 1418 -2 (4)was used to apply the vibration. The five points shown in Figure 1 were vibrated and were considered
to be the sound receiving points. The reduction of transmitted heavy-weight floor impact sound level
was calculated by subtracting the floor impact sound level of the box floor structure from that of thebare concrete slab surface.
For vibration measurement, piezoelectric accelerometers (RION, PV-91CH) were mounted on thetop, bottom of the box floor, and the concrete slab, and the vibration acceleration during S2 (Fig. 1)
was measured using the car-tire source. The measurement positions are shown in Figs. 2 and 3.
Vibration acceleration was simultaneously recorded for three channels with a data recorder (RION,
DA-21). The recorded waveform was analyzed in the 1/3 octave band with a time constant of 10 ms.

3. EXPERIMENTAL RESULTS AND DISCUSSION
3.1 Reduction of Transmitted Heavy-weight Floor Impact Sound Level
Fig. 5 shows the reduction of transmitted heavy-weight floor impact sound level. No significant
change was observed in No. 7. In particular, the difference was <1 dB in the 63 Hz band. In contrast,
in No. 5 with a large mass addition, the effect was observed at >125 Hz when there were two through holes. In addition, when there were five through-holes, the effect was observed in the 63 Hz band.
In the case of No. 5, the number of sound insulation sheets is higher and the thickness of the airlayer in the box floor is thinner compared to those of No. 7. Therefore, it is inferred that the internalsound pressure generated in the box floor during floor impact has reduced owing to the movement of
air to the other box floors through the through-holes.
As described above, it is assumed that sound pressure depends on the volume of the air layer on
the box floor and the size and number of through-holes; however, it was found that a hole on the sideof the box floor can counter the heavy-weight floor impact sound. It is necessary to study conditions
under which the effect will be significant.

20

Reduction of floor impact sound pressure level (dB)

Reduction of floor impact sound pressure level (dB)

20

15
10
5
0
-5
-10
-15

No.5-Specimen type B-20

No.5+sp-φ12×2
-25

15
10

5
0
-5
-10
-15

No.7-Specimen type C-20

No.7+sp-φ12×2-25

No.5+bp-φ12×5

No.7+bp-φ12×5

-30

-30

63

125

250

500

63

Octave band center frequency (Hz)

125

250

500

Octave band center frequency (Hz)Figure 5 –Reduction of transmitted heavy-weight floor impact sound level
3.2 Vibration Acceleration Level of the Box Floor and the Concrete SlabFigs. 6 and 7 show the vibration acceleration level of the lower part of the box floor (bottom
surface) and the concrete slab.
The trend observed in the concrete slab results (Figs. 6 and 7, right) is relatively similar to thatobserved in the sound results (Fig. 5).
In No. 7 (Fig. 7), no significant change was observed depending on the presence and number ofthrough-holes. Results indicated that for the 50–80 Hz band, the vibration acceleration level decreasedin the order of Experiment No. 7 + sp > Experiment No. 7 > Experiment No. 7 + bp.
In No. 5 (Fig. 6) with a large mass addition, the effect was observed at >100 Hz when there were
two through-holes. In addition, when there were five through-holes, the effect was observed in the 40
Hz band. In particular, the vibration reduction effect was large in the 50 –80 Hz band, namely the 63
Hz band, where the effect was also observed in the sound, and the sound results exhibited adequate
correspondence with this effect.
3ch : Concrete slab

110

90

1/3 Octave band center frequency (Hz)No.5-Specimen type B
No.5+bp-φ 12×5

No.5+sp-φ 12×2

1/3 Octave band center frequency (Hz)No.5-Specimen type B
No.5+bp-φ 12×5

No.5+sp-φ 12×2
No.0-None

Figure 6 – Vibration acceleration level measurement results (No.5)

630

500

400

315

250

200

160

125

80

100

63

630

500

400

315

250

200

160

125

80

100

63

50
50

70
40

60

25

80

50

70

40

90

80

25

100

31.5

Vibration acceleration level (dB)

100

31.5

Vibration acceleration level (dB)

2ch : Bottom surface of box floor
1203ch : Concrete slab

110

90

1/3 Octave band center frequency (Hz)No.7-Specimen type C
No.7+bp-φ 12×5

No.7+sp-φ 12×2

630

500

400

315

250

200

160

125

80

100

63

630

500

400

315

250

200

160

125

80

100

63

50
50

70
40

60

25

80

50

70

40

90

80

25

100

31.5

Vibration acceleration level (dB)

100

31.5

Vibration acceleration level (dB)

2ch : Bottom surface of box floor120

1/3 Octave band center frequency (Hz)No.7-Specimen type C
No.7+bp-φ 12×5

No.7+sp-φ 12×2
No.0-None

Figure 7 – Vibration acceleration level measurement results (No.7)

4. CONCLUSIONS
We conducted an experimental study on the reduction of transmitted heavy-weight floor impact
sound level of the box floor structure when the end air space was sealed and when the effect of athrough-hole on the side surface of a box floor was considered. As a result, it may be possible toreduce heavy-weight floor impact sound by creating holes on the side surface of the box floor basedon the volume of the air layer on the box floor and the size and number of through-holes.

ACKNOWLEDGEMENTS
Part of this study was supported by a project research grant from the College of Science andTechnology, Nihon University.

REFERENCES
1. National Small-Scale Childcare Facilities Committee, Small-Scale Childcare Facilities White Paper 2016
Edition, 2016. (in Japanese)
2. Ryuta T, Takuya O, Yuta O, Kyoko A. Experimental study on practical control of floor impact sound fornursery schools. Proceedings of INTER-NOISE 2019 June 2019; Madrid 2019.
3. Ryuta T, Takuya O. Kyoko A. Application of storage furniture with tatami to actual building andpsychological evaluation experiment - A study on floor impact sound by heavy impact source of smallscale nursery facilities. ASJ-Architectural Acoustics Study Group Materials January 2020. (in Japanese)
4. JIS A 1418-2:2019. Acoustics – Measurement of floor impact sound insulation of buildings – Part 2:
Method using standard heavy impact sources, 2019. (in Japanese)
5. Ryuta T, Takuya O, Kyoko A. Countermeasure against floor impact sound by heavy impact source of box
floor structure. Proceedings of INTER-NOISE 2020 August 2020; Seoul 2020.
6. Ryuta T, Kyoko A. Countermeasures against floor impact sound by heavy impact source of a box floor
structure in a reinforced concrete wall construction testing device. Proceedings of INTER-NOISE 2021
August 2021; Washington, DC 2021.
7. JIS A 1440-2:2007, Acoustics – Laboratory measurements of the reduction of transmitted impact soundby floor coverings on a solid standard floor – Part 2: Method using standard heavy impact sources, 2007.
(in Japanese)

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0577

Acoustical characteristics of impact sound on upper and lower floors
by a rubber ball excitation in apartment
Chunwon Eom1; Songmi Lee1; Jeonghun Kim1; Jongkwan Ryu2
1

Architectural & Civil Engineering, Chonnam National University, Korea
2

School of Architecture, Chonnam National University, Korea

ABSTRACTThe purpose of this study is to investigate how the floor impact sound generated from a specific floor istransmitted not only to the floor directly below it but also to other neighboring floors. For this purpose, thefloor impact sound by a rubber ball excitation was measured at two excitation and sound receiving positionin three units each on the upper and lower floors of the floor impact excitation floor for six apartmentbuildings. As a result of the measurement, the floor impact sound pressure level (SPL) decreased by up to 16
dB to 19 dB in L'iA,Fmax. Although there is a floor impact SPL difference in the floor directly below excitation
floor among apartment buildings, the finally attenuated floor impact SPL was found to be similar. It was
found that the floor impact SPL in the 125 Hz band was attenuated the most and that in the 500 Hz band was
the least attenuated. Overall, there was a difference in the amount of floor impact sound attenuation dependingon the excitation and the sound receiving position, and such characteristics were found to be varied by theoctave band.
Keywords: Floor impact sound, Propagation characteristics, Excitation and Receiving position

1. INTRODUCTION
In Korea, complaints about floor impact noise are increasing year by year, and there were manycases where the floor impact noise occurred in several upper and lower floors, not directly above thefloor. Accordingly, it is necessary to accurately identify the location of the floor impact noise. In thebox-frame structure, which is the main structural form of Korean apartments, the walls connected tothe upper and lower floors become the main path for vibration and noise propagation. Accordingly,
the floor impact noise should consider the floor impact noise of several floors above and below aswell as the floor directly above it. In addition, it is necessary to measure at various excitation andsound receiving positions considering the floor impact noise, which is dominated by low frequencies.
Chung et al. [1] confirmed that when the floor impact sound was measured at the apartment site, thefloor impact sound was transmitted to the floor below four floors and directly above it. In the studyof Kwak et al. [2], it was found that the floor impact SPL (L' i,Fmax ) of the five upper and lower floorsof the excitation floor was about 23 dB lower than that of the floor directly below it. Lee et al. [3]compared the propagation characteristics of the floor impact sound according to the sound receiving
position when it was divided into the center and corners in the upper 5 and lower five layers of theexcitation floor. As a result, it was reported that the floor impact sound attenuation (maximum 30 dB
in L'iA,Fmax ) at the corner sound receiving point was greater than at th e center point (maximum 20 dB
in L' iA,Fmax ), and the lower floor had greater attenuation than the upper floor. However, since theprevious studies [1-3] were conducted for one apartment building, additional measurements areneeded in various types of apartments. In addition, the propagation characteristics of the floor impact
sound according to the excitation position as well as the effect of the sound receiving position are
required. In this study, the propagation characteristics of the floor impact sound by a rubber ball were
explored by measuring floor impact sound for a total of six buildings. The field measurements wereconducted at two excitation and sound receiving points in three units each on the upper and lower
1
2

ucw1472@naver.com
jkryu@jnu.ac.kr

floors of the floor impact excitation floor. The floor impact sound level for each floor and the floor
impact sound attenuation level according to the excitation and sound receiving points werecomparatively analyzed.

2. MEASUREMENT METHOD
2.1 Site
Floor impact sound in a total of 30 units in 5 apartments of box-frame reinforced concrete (RC)structure with different areas were measured for each of 6 units (3 upper floors, 3 lower floors). Table
1 shows the indoor specifications of the apartment to be measured. The composition of floor was 210
mm of concrete slab, 40 mm of lightweight aerated concrete, 30 mm of resilient material (EPS), 40
mm of cement mortar, and wooden flooring
2.2 Measurement and analysis methods
For the measurement of floor impact sound in each unit, referring to the ISO 10052 [4] survey
method, the excitation and sound receiving point was located at the center and the corner. As shownin Figures 1 and 2, the sound recording was simultaneously performed on three the upper and lower
floors of the excitation floor using a sound level meter (RION NL-52). The impact source was a rubberball and sound by free fall from a floor height of 100 cm was recorded. The floor impact sound wasrecorded for 20 seconds at a height of 1.2 m above the floor. The sound source editing started from 1
second before the start point of sound source, and the length of a sound source was edited to be 8
seconds including 3 individual impact sounds. The sound source was analyzed using AS-70 (RION),
to obtain sound pressure level of 1/3 octave band and a single number quantity (SNQ, L'iA,Fmax ) of
floor impact sound on the basis of ISO 717-2 [5].
Table 1 – Specification of room and floor impact sound insulation in unit
Site Bldg.
A

B

Area

Area of living room (W*D)

a

59 m

8.52 m (3.77 * 2.26)

51 dB

b

72 m2

16.14 m2 (4.72 * 3.42)

50 dB

c

76 m

2

84 m

2

d
e

123 m

2

2

SNQ of floor impact SPL

2

2

50 dB

2

52 dB

2

50 dB

20.62 m (5.62 * 3.67)
20.04 m (5.22 * 3.84)
22.85 m (5.52 * 4.14)

Figure 1 – Rubber ball excitation and microphone receiving position (A corner microphone position for themeasurement was selected on each apartment building)Figure 2 – Microphone positions on each floor

3. RESULTS
3.1 SNQ of floor impact sound pressure level on each floor
As shown in Figure 3 (a), in the case of center excitation position and the center sound receiving
position, the floor impact SPL (SNQ, L' iA,Fmax ) on a floor (L1F) directly below the excitation floor
was 50 dB, and it on the three upper floors (U3F) and lower floors (L3F) was 31 dB and 34 dB,
respectively. From the three-floor propagation process, 16 to 19 dB of SNQ of floor impact SPL
attenuation occurred. In the case of corner sound receiving position, the SNQ on L1F was 51 dB, andit on the U3F and L3F was 32 and 36 dB, respectively, indicating that attenuation of 15 to 19 dB
occurred. As shown in Figure 3 (b), in the case of the corner excitation and center sound receiving
position, the SNQ on L1F was 48 dB, and it on the U3F and L3F was 29 dB and 32 dB, respectively,
showing attenuation of 16 to 19 dB. In the corner sound receiving position, the SNQ on L1F was 50
dB, and it on the U3F and L3F were 34 and 35 dB, respectively, resulting in attenuation of 15 to 16
dB. In the center excitation, a maximum of 19 dB was attenuated regardless of the sound receiving
position, whereas in the corner excitation, the SNQ in corner sound receiving position was lessattenuated by about 3 dB at a maximum of 16 dB than center sound receiving position.

Figure 3 – Floor impact SPL (SNQ: L'iA,Fmax) on each floor for each excitation and sound receiving position

3.2 Octave band SPL of floor impact sound on each floor
Figure 4 shows the octave band SPL of the floor impact sound on each floor for each excitation andsound receiving position. The SPL in the corner sound receiving position was higher than that of thecenter sound in the 63 Hz band due to the effect of the room mode, whereas the SPL in the center
position was higher than that of corner position in the 125 to 500 Hz band. Overall, the SPL decreased
as the distance from the excitation floor increased, and the difference in the SPL among floors was
small in the 500 Hz band.

(1) Center excitation(2) Corner excitation

Figure 4 – Octave band spectrum of floor impact sound on each floor for each excitation and sound receiving
position (BGN: background noise, U: upper floor, L: lower floor)

3.3 Attenuation of octave band SPL on each floor
Figure 5 shows the attenuation (ΔL'i,Fmax : floor directly below the excitation floor – the target floor)of octave band SPL at each sound receiving position on each floor compared to the floor directly
below excitation floor (excitation position: center). In the 63 Hz band, the attenuation of the cornersound receiving point was higher than that of the center sound receiving point, but in the rest of theoctave band, the attenuation of the center sound receiving point was relatively high. As shown in
Figure 5 (c), the band with the largest difference in attenuation between the sound receiving points
was the 250 Hz band, which showed about attenuation of 4 to 5 dB for each floor. In addition, themaximum attenuation of the sound pressure level to the upper and lower floor was the largest in the
125 Hz band, while the attenuation in the 500 Hz band was relatively small.
Figure 6 shows the attenuation of octave band SPL at each excitation position on each floor
compared to the floor directly below excitation floor (sound receiving position: center). The
attenuation in corner excitation position was mostly smaller than that of the center excitation position
except for 250 Hz octave band in Figure 6 (c).

Figure 5 – Attenuation of octave band SPL at each sound receiving position on each floor compared to thefloor directly below excitation floor (excitation position: center)

Figure 6 – Attenuation of octave band SPL at each excitation position on each floor compared to the floor
directly below excitation floor (sound receiving position: center)4. CONCLUSION
In this study, the field measurements were conducted to explore the propagation characteristics ofthe floor impact sound by a rubber ball. Measurements of floor impact sound for a total of six
apartment buildings were conducted at two excitation and sound receiving points in three units eachon the upper and lower floors of the floor impact excitation floor. As a result of the measurement, thefloor impact SPL (SNQ, L'iA,Fmax ) decreased by up to 16 dB to 19 dB. Although there is a differencein the floor impact SPL on the floor directly below excitation floor between apartment buildings, thefinally attenuated floor impact SPL is similar. It was found that the floor impact SPL attenuated themost in the 125 Hz band and the least in the 500 Hz band. In general, there is a difference in theamount of floor impact sound attenuation depending on the excitation point and the sound receiving
point, and this characteristic was found to be varied with octave band.

ACKNOWLEDGEMENTS
This work is supported by Chonnam National University (Grant number: 2020-3742 ) and the Korean
Agency for Infrastructure Technology Advancement (KAIA) grant funded by the Ministry of Land,
Infrastructure and Transport (Grant 21CTAP-C163631-01).

REFERENCES[1] Chung, J. Y., Lim, J. B. and Lee, S. C., 2013, Propagation characteristics of floor impact sound fromneighboring households, Proceedings of Acoustical Society of Korea, pp.116~117.
[2] Kwak, Y. S., Lee, S. Y., Park, J. W., Hwang, D. Y., Jeon, J. Y. and Park, J. H., 2017, Effect of the static
compressive load on vibration propagation in multistory buildings and resulting heavyweight floor impact
sounds, The Journal of the Acoustical Society of America, Vol. 142, No. 1, pp. 308~316.
[3] Lee, S. M., Kim, J. H., Kim, S. H., Song, H. S. and Ryu, J. K., 2021, Floor Impact Sound Level
Distribution in Upper and Lower Units of an Apartment Based on Flanking Transmission by the Impactof a Rubber Ball, Transactions of the Korean Society for Noise and Vibration Engineering, Vol 31, No. 5,
pp.574~581.
[4] International Organization for Standardization, 2021, ISO 10052 Acoustics — Field Measurements ofAirborne and Impact Sound Insulation and of Service Equipment Sound — Survey method.
[5] International Organization for Standardization, 2020, ISO 717-2 Acoustics — Rating of Sound Insulationin Buildings and of Building Elements — Part 2: Impact Sound Insulation.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0647

Influence of ducts on the impact sound insulation of floating
screeds
Debby WUYTS1; Charlotte CRISPIN2; Arne DIJCKMANS3
123

Belgian Building Research Institute, Belgium

ABSTRACT
Cementitious floating screeds are commonly used in Belgian residential buildings to meet the national
standard criteria for impact sound insulation. Reliable data for the improvement of impact sound insulationof these floating floors are an essential prerequisite for a correct estimation of the achievable performance insitu. Laboratory measurements according to ISO 10140-3 are commonly performed for this purpose, albeit
on assemblies that are not always in line with common practice. For instance, floating screeds usually containducts and pipes, such as for plumbing or electricity, which are completely lacking from laboratory test setups.
The influence of these pipes on the improvement of impact sound insulation is investigated in a large
measurement campaign at the BBRI acoustics laboratory. Different possible influence parameters are
examined such as the number, diameter and embedding of the pipes, and this for different types of resilient
underlays and levelling screeds. The research results should allow design and implementation guidelines tobe developed that consider the acoustic impact of pipes in floating screeds. The paper summarizes the mostrecent findings of the study in progress.
Keywords: ducts, impact noise, floating screed

1. INTRODUCTION
In order to meet both the acoustic and thermal criteria, partition floors between dwellings areusually fitted with a floating screed on top of a thick thermal layer which at the same time can levelout partly or fully the present ducts on the supporting floor. A prediction model that takes into accountthe standing wave formation in this thermal levelling screed is currently being developed by Crispin
et al. (1). The influence of ducts in the levelling screed has not been investigated so far.
The effect of different duct configurations was investigated for different types of thermal screeds
and resilient underlays by means of laboratory measurements to determine the reduction in impact
sound pressure level ΔL according to ISO 10140-3 and the corresponding single number value ΔLw
according to ISO 717-2 (2,3). A total of 6 different floating assemblies and 12 different ductconfigurations were investigated. In order to save time and costs, the set-ups were built up in half test
sections of 2.20m x 2.60m. The size effect was estimated beforehand on the basis of comparative
measurements and literature study (4). A number of set-ups were built up and tested repeatedly inorder to identify the standard deviation for reproducibility and to examine the relevance of the effectof the ducts. A selection of the measurement results is presented with the most important findings todate.

2. MEASUREMENT RESULTS
2.1 Complexes without ducts
The studied floating screeds are systematically composed of a cement screed, a resilient underlay
1

debby.wuyts@bbri.becharlotte.crispin@bbri.be
3
arne.dijckmans@bbri.be2and a thermal levelling layer. The characteristics of the materials involved are listed in Table 1. A
significant spread in density of the bulk materials was observed over the different mounting series.
Therefore, the effect of the ducts was mainly studied on complexes built up within the same series. In
addition, an uncertainty on the effective thickness of the bulk materials was found, even within thesame mounting series. The examined combinations of resilient underlay and thermal levelling layer
are shown in Table 2. The resilient underlay is systematically applied between the thermal layer andthe finishing screed.
Table 1 – Measured thickness, density and stiffness of the materials concerned (*manufacturer's data)
Description
Finishing screed
EPS-mortar
Cement foam
PU-foamResilient underlay “S”
Resilient underlay “F”

Fibre reinforced sandcement mixture
Mixture of polystyrene
beads with cement
Mixture of cement andair bubbles
Projected polyurethane
foam
Extruded polyethylene
foamComplex of polyolefin
foam and polyester felt

Thickness
[mm]
50-60

Density[kg/m³]1782 - 2119

E
[Pa]
-

s’dyn
[N/m³]-

50

224 - 346

7.51e+06-

50

596 - 611

1.68e+08-

50

37 - 40

3.71e+07

-

6

30*

-

6.88e+07

6

37*

-

8.0e+06*

Table 2 – Overview of the examined combinations of thermal layer and resilient underlay
Complex 1
Complex 2
Complex 3
Complex 4

Thermal levelling screed
EPS-mortar
EPS-mortar
Cement foam
PU-foamResilient underlay
“S”
“F”
“S”
“S”

The measured reductions of impact sound pressure level and the corresponding weighted value
ΔLw for the complexes without ducts are shown in Figure 1. Each complex is characterised by adecrease in impact sound reduction in the zone 63Hz -200 Hz due to the resonance of the screed on
the underlying springy complex of thermal layer and resilient underlay. The frequency around which
this resonance occurs is referred to as the resonance frequency f0 . In the zone above 500 Hz, a second
drop in acoustic performance occurs which can be attributed to a phenomenon of standing wave
formation in the thickness of the thermal layer. These thickness resonances are typical for complexes
containing thick layers and are characterised by the resonance frequency fr,1 i.e. the frequency at which
the first thickness resonance occurs.
A computational model for the prediction of the reduction in impact sound pressure level ofmultilayer floating screeds subjected to thickness resonances is currently being developed by Crispin,
Dijckmans and Schiavi (5). The resonance frequency f0 is determined by the equivalent stiffness s' eq[N/m³] of the complex 'thermal layer + resilient underlay' and the surface mass of the cementitious
screed M [kg/m²], according to formula (1). The first thickness resonance fr,1 for a simple complex
can be calculated from formula (2) and depends on the thickness d [m], the density ρ [kg/m³] and thestiffness modulus E [N/m²] of the thick layer. However, this formula does not take the influence ofthe resilient underlay into account and is the subject of ongoing research.
𝑓
𝑓,

𝑠′

𝑀

2𝜋

(1)

𝐸. 𝜌

2𝑑

(2)

60
Complex 1 ‐‐ ΔLw = 22.7 dB
50

Complex 2 ‐‐ ΔLw = 26.9 dB

40

Complex 3 ‐‐ ΔLw = 20.7 dB

ΔL [dB]

Complex 4 ‐‐ ΔLw = 21.4 dB
30
20
10

‐10

5000

3150

2000

1250

800

500

315

200

125

80

50

0

f [Hz]

Figure 1 – Measurement values for the studied complexes without ducts
2.2 Protruding and embedded ducts
Initially, the effect of PVC ducts with a diameter of 50 mm and a centre-to-centre distance ofapproximately 400 mm was investigated. In a first configuration, the ducts were placed on small
blocks, and therefor protruding about 30 mm above the thermal levelling layer, into the cement screed(Figure 2, left). In the second configuration, the ducts were placed directly on the supporting floor
and fully embedded in the levelling layer (Figure 2, right). In both cases, the resilient underlay runs
continuously above the ducts.

Figure 2 – Schematic representations and pictures of the studied duct configurations. Left : Configuration 1
with elevated ducts, placed on 30 mm high blocks. Right : Configuration 2 with ducts laid directly on the
supporting floor (pictures taken before mounting of the thermal layer)

60

60

complex 1

complex 2+0.5 dB+1.6 dB
ΔL [dB]

30

40

20

0

0
‐10

f [Hz]

70

40

60
50

f [Hz]

45

complex 3

35+2.5 dB+0.5 dB

30

complex 4+2.7 dB+5.1 dB

25

ΔL [dB]40

ΔL [dB]

20
10

‐10

+1.1 dB+‐1.1 dB

30

10

50
80
125
200
315
500
800
1250
2000
3150
5000

ΔL [dB]

40

50

50
80
125
200
315
500
800
1250
2000
3150
5000

50

30

20
15

20

10

10

5

50
80
125
200
315
500
800
1250
2000
3150
5000

‐10

f [Hz]

‐5
‐10

50
80
125
200
315
500
800
1250
2000
3150
5000

0
0

f [Hz]

Figure 3 – Measurement values for the complexes without ducts (black dotted line), with duct configuration
1 (red triangle line) and duct configuration 2 (blue bullet line)
For duct configuration 1 (protruding, elevated ducts), an overall positive effect on the single
number value ΔLw, determined from the performances between 100 Hz and 3150 Hz according to EN
ISO 717-2, is recorded for the four complexes ((Figure 3, indicated values on the graphs). The overall
effect for duct configuration 2 (embedded pipes) varies from slightly negative (-1.1 dB) to strongly
positive (+5.1 dB). For strongly rising spectra, the low-frequency performance is the most determining
for this parameter.
For the protruding ducts (configuration 1), we observe a shift of the resonance frequency f0 towards
the lower frequencies, mainly for the stiffer complexes with PU foam and cement foam (complexes 3
and 4). This leads to a non-negligible gain in acoustic performance in the zone above 100 Hz. For thecomplexes with EPS mortar (complexes 1 and 2), the resonance frequency f0 is somewhat lower andthe shift is less pronounced. An important shift of the thickness resonance frequency fr,1 towards lower
frequencies occurs mainly in complexes with pronounced thickness resonances in the midfrequency
zone (complexes 1 and 4) leading to a non-negligible loss of performance between 500 Hz and 2000
Hz.

For the heavy, rigid cement foam (complex 3) with relatively low-frequency thickness resonances,
the influence of the ducts at the resonance frequency fr,1 is limited and the shift of the resonancefrequency f0 generates an overall positive effect over the entire spectrum. Compared to complex 1,
the thickness resonances in complex 2 with a more resilient underlay “F” appear to spread out over alarger mid- and high-frequency zone, despite the same thermal layer (EPS mortar). This shows that
formula (2) cannot be applied to multilayer floating systems, as the resilient underlay also influences
the thickness resonances. The negative effect due to the shift of fr,1 is smaller here, but spreads out
over a larger frequency range.
For the embedded ducts (configuration 2), the influence at the resonance frequency f0 seems almost
negligible for all complexes, except for the light PU foam (complex 4) where the ducts seem togenerate a considerably high low-frequency attenuation. At the first thickness resonance fr,1 for the
EPS mortar and the PU foam (complex 1 and complex 4)we again observe a clear shift towards lower
frequencies, albeit with a more limited negative effect than for the protruding ducts (configuration 1).
For the EPS mortar with more resilient underlay “F” (complex 2), a similar shift of the zone of
thickness resonances is observed as for the protruding ducts (configuration 1). However, lowfrequency gain at the resonance frequency f0 is not observed, resulting in an overall limited negative
effect of -1.1 dB.
2.3 Relevance of the effect
In order to estimate the relevance of the observed effects, the measurement results for 3
reproductions within different mounting series of the 50 mm EPS mortar with standard resilient
underlay “S” (complex 1), with and without ducts (configurations 1 and 2) were studied. The
dispersion appears to be greatest for the complex without ducts, resulting in large differences in ΔLw
values (Figure 4, left). The large spread in results is probably mainly due to variations in thickness
and density of the EPS mortar, which strongly determine the resonance frequencies f0 and fr,1. The
dispersion on the measurement results with protruding ducts (configuration 1) appears to be much
more limited (Figure 7, centre). This probably indicates a strong determining role of this ductconfiguration for the expressing of the resonance frequencies f0 and fr,1.

40

30

30

30

f [Hz]
f [Hz]

50

3150

1600

800

400

200

‐10

100

50

3150

‐10

1600

0

800

0
400

0
200

10

100

10

50

10

‐10

3150

20

1600

20

800

ΔL [dB]40
ΔL [dB]40

20

ΔLw = 21.8 à 25.7 dB

50

400

50

200

ΔLw = 24.4 à 25.3 dB

100

ΔLw = 20.4 à 25.5 dB

50

ΔL [dB]

60

60

60

f [dB]

Figure 4 – Measurement values for different reproductions of complex 1: without ducts (left), withprotruding ducts configuration 1 (middle) and with embedded duct configuration 2 (right)
From the average measured reductions of impact sound pressure level, we again observe a shift(which may not be coincidental) of the resonance frequencies f0 and fr,1 towards lower frequencies forduct configuration 1 (Figure 5, left). The associated low- and mid-frequency gains and losses also
appear to be relevant with respect to the standard deviations for the complex without ducts (Figure 5,
right). For duct configuration 2, the observed average differences are smaller. Yet, a negative effectin the mid-frequency region at the shifted thickness resonance is again difficult to refute.

60.0

6.0

50.0

4.0
2.0

40.0

Δ(ΔL)

20.0

‐2.0
‐4.0

10.0

‐6.0

0.0

‐8.0
50
80
125
200
315
500
800
1250
2000
3150
5000

ΔL [dB]

0.0
30.0

‐10.0

‐10.0

f [Hz]

f [Hz]

Figure 5 – Left : Mean measured values for complex 1 without ducts (black dotted line), with ductconfiguration 1 (red triangles) and with duct configuration 2 (blue dots). Right : Mean measured effect forduct configuration 1 (black bars) and duct configuration 2 (white bars) with respect to the standard
deviation for complex 1 without ducts

2.4 Large number of ducts
Next, an extremely high concentration of 50 mm PVC ducts with a centre-to-centre distance ofapproximately 100 mm was studied for complex 1 (Figure 6). For the protruding duct configuration,a significant shift of the resonance frequencies f0 and fr,1 was found, resulting in an overall gain of 5.7
dB (compared to mean values). For the embedded duct configuration, the shift of the resonancefrequency f0 is smaller, despite an almost identical shift of the thickness resonance fr,1 . In both cases
there is a strong broadening of the thickness resonance zone.
60+5.7 dB+1.7 dB

50

ΔL [dB]

40
30
20
10

5000

3150

2000

1250

800

500

315

200

125

80

50

0
‐10

f [Hz]

Figure 6 – Measurement values for complex 1, without ducts (dotted line, mean values) and with highly
concentrated protruding (red triangles) and embedded ducts (blue dots).

2.5 Protruding ducts, directly laid on the supporting floor
Finally, the effect of protruding ducts laid directly on the supporting floor was examined. The
protrusion was realised on the one hand with larger ducts (diameter 90 mm), and on the other handwith 50 mm ducts with punctually crossing duct sections (Figure 7). At the mass-spring-mass
resonance f0 , the effect of the ducts seams limited. In both cases the first thickness resonance spreads
to the lower frequencies over a larger frequency area. The overall gain is limited due to the limited
low-frequency gain, similar to the effect seen for the embedded ducts, which were also directly laidon the supporting floor.

ΔL [dB]6050+ 1.4 dB40

+ 0.6 dB

30
20
10

5000

3150

2000

800

500

315

200

80

1250

‐10

125

50

0

f [Hz]

Figure 7 – Measurement values for complex 1, without ducts (dotted line, mean values), with 90 mm ducts(solid line) and with 50 mm pipes with punctual protrusions (dashed line)

3. DISCUSSION OF RESULTS
A clear influence of the ducts was observed on the thickness resonances in the thermal levelling
layer for all studied duct configurations and floating screed complexes. From the results for the 50
mm thick thermal layers, a shift of the first thickness resonance fr,1 to lower frequencies is invariably
observed, which could be explained by a decrease of the 'equivalent stiffness' of the complex'resilient underlay + thermal layer’. The shift seems to be more pronounced for light thermal layerswith relatively high thickness resonance frequency (f r,1 > 1000 Hz). For protruding ducts, an extensionof the zone of thickness resonances is also observed, regardless of the contact with the supporting
floor, which may be related to the irregular increase in layer thickness. The shift seems to be lesspronounced for heavier layers with relatively low fr,1 or complexes with more high-performance
resilient underlays characterised by a broad plateau of thickness resonances. The resonance frequency
fr,1 is of course also strongly influenced by thickness variations in the thermal layer, which are difficult
to control even within the same mounting series. Especially in the case of sprayed PU foam, thisappears to be a difficult parameter to control.
In case of a pronounced shift towards lower frequencies, the performance decreases in the zone
below the original fr,1 . Nevertheless, in most cases an overall positive effect of the ducts was observed
due to an increase of the reduction in impact sound pressure level in the low frequencies, albeit oftenvery limited. A pronounced low frequency gain can usually be attributed to a shift of the resonancefrequency f0 and was mainly observed for relatively stiff complexes (f0 > 100 Hz) with elevated ducts(not laid directly on the supporting floor). A shift of the resonance frequency f0 towards lower
frequencies would imply a higher resilience of the complex with ducts. When the ducts are laid
directly on the floor, only a limited shift occurs around the resonance frequency. Since the ducts
locally replace the thermal layer and establish a direct connection between the resilient underlay andthe supporting floor, in principle a shift of the resonance frequency f0 to higher frequencies could also
occur in the case of relatively stiff ducts or flexible thermal layers.

4. CONCLUSIONS
From the measurement results, the overall effect of ducts on the weighted reduction in the impact
sound pressure level ΔLw of floating screeds seems mostly positive or slightly negative. Punctually
supported ducts would potentially have the most favourable effect, especially in the case of relatively
rigid complexes due to a considerable shift of the resonance frequency f0. On the other hand, the riskof an overall negative effect is greatest when the ducts are laid directly on the supporting floor. For
thermal layers with pronounced thickness resonances in the zone above 1000 Hz, the performance canbe further affected by a shift of the thickness resonance frequency fr,1 , especially in the case of
protruding pipes where the zone of thickness resonances tends to broaden.
Further research is necessary to confirm these tendencies and to gain insight into the underlying
working mechanisms, whereby other duct configurations (e.g. punctually supported pipes without
protrusion) and combinations with other resilient underlays and thermal layers should be investigated.
There is a need to examine more closely the standard deviations under reproducibility conditions forfloating screeds, as the standard ISO 12999-1 (6) does not currently provide for this. The uncertainties
due to deviations on material properties and mounting conditions of bulk products should be
investigated in particular. In the end, the confirmed tendencies have to be validated on full-scale test
plates. Finally, the relevance of the effects found in laboratory should be examined under real in situ
conditions to evaluate the need for adaptation of the acoustic characterisation of floating screeds oralternative mounting guidelines.

ACKNOWLEDGEMENTS
The authors would like to acknowledge the Belgian Federal Public Service Finance for financial
support. Special thanks goes to Carro-bel Group, CDM-Stravitec and EVA-International for theirimplication and logistic support for part of the research campaign.

REFERENCES
1. Crispin C, Wuyts D, Dijckmans A. Thickness-resonance waves in underlays of floating screed. Proc InterNoise 2021; 1-5 August 2021; Washington, D.C., USA. p. 2949-3943.
2. NBN EN ISO 10140-3:2021. Acoustics - Laboratory measurement of sound insulation of building
elements - Part 3: Measurement of impact sound insulation (ISO 10140-3:2021)
3. NBN EN ISO 717-2:2021. Acoustics - Rating of sound insulation in buildings and of building elements Part 2: Impact sound insulation (ISO 717-2:2020)
4. Miškinis K, Dikavičius V, Ramanauskas J, Norvaišienė R. Dependence between reduction of weighted
impact sound pressure level and specimen size of floating floor construction. Materials Science(Medžiagotyra). Vol. 18, No. 1. 2012. p. 93-97.
5. Crispin C, Dijckmans A, Schiavi A. The accurate estimation of impact sound insulation in floating floors;
thickness-resonance wave effects in multi-component systems. Applied Acoustics (article underpreparation).
6. NBN EN ISO 12999-1:2020. Acoustics - Determination and application of measurement uncertainties inbuilding acoustics - Part 1: Sound insulation (ISO 12999-1:2020).

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0817

Classification of the source unit of the floor impact sound in anapartment building using AI
Jeonghun Kim1; Chunwon Eom2 and Jongkwan Ryu3
Architecture, Chonnam National University, Korea

ABSTRACTIn Korea, noise complaints are occurring about floor impact sound generated not only
from the floor just above, but also from other floors. Accordingly, it is necessary to identify
the location of the floor impact sound in order to resolve the conflict by themisunderstanding between neighbors. Therefore, in this study, AI was used to classify thesource unit generating floor impact sound in apartment under various conditions (plan,slab, finishing materials, and so on). Recordings of floor impact sounds like a child’s
jumping sound were conducted on the three upper and lower floors than excitation floor.
Temporal and spatial parameters were analyzed to investigate the acoustic characteristicsof floor impact sound on each floor. The source unit of the floor impact sound inapartment was classified through machine learning based on various parameters andimage-based deep learning.
Keywords: Floor impact sound, Classification, Artificial intelligent (AI)

1. INTRODUCTION
In Korea, floor impact sound is a major noise source causing noise problems. Currently,
a regulation on noise generated from the upper floors [1] are being implemented, but
complaint from floor impact sounds from other floors is occurring. Accordingly, it isnecessary to identify the source unit in which the floor impact sound is generated in orderto resolve the conflict of the floor impact sound caused by the misunderstanding between
neighbors about the origin. An AI-based floor impact sound classification model [2]classified type of sound sources including floor impact sound recorded from the upper
floor, and a study [3] was conducted on the classification of the types and locations offive noise sources in a three-story university building. However, there has been no study
examining the classification of the source unit generating the floor impact sound sourcein various apartment houses, and it is difficult to classify the location of the noise source

wjdgns9752@naver.com
ucw1472@naver.com
3
jkryu@jnu.ac.kr
1
2

with the current architectural acoustics methodology. Therefore, in this study, AI was used
to classify the source unit of floor impact sound generated in apartment houses undervarious conditions.

2. METHOD

2.1

DATASETIn this study, measurements were conducted in 6 apartment buildings before
completion in Korea. As shown in Figure 1, measurements were made on the three upperand lower floors (total of six units) in each building. By referring to the ISO 10052 simple
method [4] , the rubber ball (standard impact source) at the heigh of 20 cm and 120 cm
and the actual floor impact sounds (adult jumping and adult running), which are major
source of complaints, were excited at two points (center and corner of the living room) inan excitation floor.

Figure 1 – Floor impact sound recording on each floor by rubber ball dropping in a floor
As shown in Figure 2, in order to extract spatial, temporal, and psychoacoustic
parameters for each sound receiving floor, measurements were made using a sound level
meter (NL-52), a head torso (HATS), and an ambisonic microphone at the same location
as the excitation point.

Figure 2 – Microphone installation of sound level meter (left) and HATS and ambisonicmicrophone (right)

2.2

ACOUSTICAL FEATURE AND CLASSIFICATION

Each sound source on the floor was recorded for 20 s, and all sound sources were
finally edited into 2 s using Adobe audition software. Spatial and temporal parameters foreach sound receiving floor were then extracted. In addition,, sound features (mfcc, mel
spectrogram, and so on) were extracted through librosa.
Classification of source unit where floor impact sound is generated was performed
using machine learning algorithm (SVM, ANN, and so on) based on various acousticalfeatures and deep learning (CNN, CRNN, etc.) based on images.

Figure 3 –Mel spectrograms of rubber ball sound on each floor

3. RESULT AND SUMMARY
In this study, the classification of source unit generating floor impact sound was
performed through machine learning using various acoustic parameters and image -based
deep learning. The accuracy of image-based deep learning was higher than that ofmachine learning through acoustical features for each sound receiving floor. Based on the
results of this study, it is shown that complaints related to the source location of floor
impact sound can be resolved by classifying the source unit of the floor impact sound in
an apartment building. In the future, feature-base machine and image-based deeplearning using psycho-acoustic parameters will be performed and compared with resultsof this study.

ACKNOWLEDGEMENTS
This work is supported by the Korean Agency for Infrastructure Technology Advancement (KAIA) grant
funded by the Ministry of Land, Infrastructure and Transport (Grant 21CTAP-C163631-01).

REFERENCES[1] Ministry of Land and Transportation and Ministry of the Environment in Korea, Regulation of the Scope
and Criteria of Noise Between Floors in an Apartment (2014).
[2] Shin, H. K., Park, S. H., & Kim, K. W. (2020). Inter-floor noise classification using convolutional neuralnetwork. Plos one, 15(12), e0243758.

[3] Choi, H., Yang, H., Lee, S., & Seong, W. (2019). Classification of inter-floor noise type/position via
convolutional neural network-based supervised learning. Applied Sciences, 9(18), 3735.
[4] ISO 10052:2021. Acoustics — Field measurements of airborne and impact sound insulation and of service
equipment sound — Survey method. International Organization for Standardization: Geneva, Switzerland.

ABS-0172

Experimental study of open to closed pore ratio on acoustic absorption of
porous materials
Zenong CAI(1) , Vicente Cutanda HENRIQUEZ(1) , Frieder LUCKLUM(1)(1) Centre for Acoustic-Mechanical Microsystems (CAMM), Department of Electrical and Photonics Engineering, Technical

University of Denmark (DTU), DK-2800, Kongens Lyngby, Denmark, zenca@dtu.dk

ABSTRACTIn this study, we investigate and discuss the influence of different proportions of open porosity to total porosity
on the acoustic behavior based on measurements. Four kinds of porous polymer materials are analyzed in termsof their basic physical properties, including surface density, flow resistivity, mean pore size, and geometricstructure. Sound absorption, impedance and transmission loss curves of these samples are measured, and theresults are discussed combined with basic parameters mentioned above.

Keywords: Porous material, Sound absorption, Transmission loss

1

INTRODUCTION

Porous materials used in the noise reduction are usually open-cell structures, which is due to the general belief
that the energy dissipation caused by viscous and thermal effects in the open cells has a dominant effect onsound absorption [1]. However, increasing the proportion of closed pores is beneficial to the mechanical properties of the whole structure [2]. Especially for noise and vibration control inside millimeter-scale devices, suchas hearing aids and hearables, both the acoustic and mechanical performances are significant. Therefore, theinvestigation of how the open pore ratio affects the porous material behavior is meaningful.
For the investigation of sound absorption of porous materials, Biot’s theory [3] [4] and equivalent fluid models [5] [6] [7] [8] [9] are the two main approaches. Biot’s theory is more focused on wave propagation in
porous media from a macroscopic perspective, which does not provide a link between micro-geometry parameters and acoustic parameters. Although equivalent fluid models include micro-geometry parameters, they aremostly focused on open-cell structures. Many different models predicting sound absorption of porous materials
only use the open porosity. Therefore, sound absorption due to mechanical resonances, which can be especiallyrelevant for closed pores, is not included in the calculation.
Because of the complex structure of porous materials, research on sound insulation of porous materials is
mostly from a macroscopic point of view [10], targeting the composite structure in combination with othermaterials [11] [12] [13], while research on individual porous materials from their microscopic geometry is moredifficult and has not been extensively investigated in the literature.
In this study, four materials with different open porosity rates are selected and experimentally studied in bothsound absorption and sound insulation. In the second section, the parameters of the selected materials aredescribed, followed by the introduction of the measurement system. The third section discusses the experimentally measured sound absorption coefficients, acoustic impedance curves, and transmission loss curves in three
separate sub-sections.

2

MATERIAL AND METHOD

2.1 Materials for experiments
This section describes the basic parameters of the materials used for the experiments, as shown in the Table 1.

The geometric parameters are measured from microscopic images, and the data of flow resistivity is measured
by flowmeter (nor1517A, Norsonic AS), according to ISO 9053-2. From the different structures, the four materials can be classified into four types A to D. Among them, the microscopic images of types A,B, C are shownby Figure 1(a) to Figure 1(c) . D is a special material with internal pores like type C, but the skeleton iselastic, and the outer two surfaces are wrapped by membranes, as shown in the Figure 1(d). All the skeletonsof four samples are polymer materials.
Table 1. Parameters of Materials
Flow Resistivity(Pa · s/m2 )Average poresize (mm)Thickness(mm)

Surface density(kg/m2 )

12580

0.5

9

0.27

1

669

1

9

0.22

C Closed pores

02970609

0.3

9

0.39

D Nitrile sponge0265808

0.5

24

1.25

Type

Open Porosity Ratio

A Bubble-like pores

0.5

B Reticulated structure(a) Type A Bubble-like pores(b) Type B Reticulated structure(c) Type C Closed pores(d) Type D Nitrile sponge

Figure 1. Photos of samples for the tests. (a) (b) (c) are micrographs of pores type A, B and C, respectively.
(d) is the photo of type D. Since D differs from C in the two sides of the membranes, a macroscopic photo of
D is used instead of a micrograph.

2.2 Test system
In this study, as shown in the Figure 2, we use the impedance tube (AcoustiTube DN100, AED), amplifier(D3020, NAD), and data acquisition (Symphonie, 01dB). The inner diameter of the tube is 100 mm. The

distances between microphone 1 and 2, 3 and 4 are 75 mm. Plane waves are generated in the tube using abroadband signal from a noise source, which is 1 Vrms white noise.
The sound absorption tests are based on ISO 10534-2, using the transfer function of the two microphones tocalculate sound absorption coefficients and sound impedance data. The termination is a sound hard boundary.
The transmission loss tests are based on ASTM E2611-17, calculated by the transfer functions of the four
microphones, based on the transfer matrix method. The two kinds of termination are sound hard boundary andanechoic boundary.

(a) Sound absorption test system(b) Transmission loss test system(c) Physical figure of the test system(d) Four samples, diameter 100 mm

Figure 2. Test system and samples used in this research
As can be seen in the Figure 2(d), the edge of the specimens is not smooth. It is because of the limitationof cutting approach (the round samples were cut from large samples by knife). The cutting diameter was chosen
1mm larger than the tube diameter to avoid leakage at the edges. This causes the edges to be slightly squeezed
when the samples are placed in the tube, which will slightly increase the porosity of the sample. However,because of the flexible, porous structure, only the edge parts are affected significantly, and the central parts
are affected negligibly. For experiments conducted by the impedance tube, the central parts are much more
important than edge parts. Therefore the tiny squeeze on the edge has little effect on the experimental results.

3

RESULT AND DISCUSSION

3.1 Sound absorption
Figure 3 shows the measured data of normal incidence absorption curves of the four samples. The frequency
range is from 100 Hz to 1600 Hz. For reference, the absorption measured in an empty tube is also plotted in
Figure 3.

Figure 3. Normal sound absorption measured by the impedance tube.
As it is demonstrated in Figure 3, nitrile sponge D has a different sound absorption mechanism than the others.
The peak value hapends at 1044 Hz. From the next section we can know that it is a resonance peak, and D
is a resonant absorbing structure. Although both C and D have closed pores and very high flow resistivity, C
only has very low sound absorption similar to empty tube data. Besides, reticulated structure B also has quite
low sound absorption behavior, due to its low flow resistivity which is related to its large mean pore size. The
curve of A shows low sound absorption performance at low frequency, which is a typical trend for the soundabsorption of thin porous materials with open pores.
3.2 Acoustic impedance
In order to further illustrate the difference between C and D, the specific sound impedance of C and D areplotted, shown as Figure 4. The frequency range is from 100 Hz to 1600 Hz.
From the impedance matching principle, the sound resistance should be similar to the characteristic impedanceof air (about 415 Pa · s/m) if the porous material is desired to have good sound absorption performance. According to Figure 4(a), after 600 Hz the real part becomes quite low, which is lower than the air characteristic
impedance, and the value becomes lower and lower as the frequency increases. Besides, after about 100 Hz, theimaginary part becomes negative, and up to 1600 Hz the absolute value are still high (beyond 1000 Pa · s/m).
This means that there is no acoustic energy stored inside the material to be released. The above properties of
acoustic resistance and acoustic reactance explain the reason why the sound absorption coefficient of C is very
low. While from Figure 4(b), both the real part and imaginary part are positive. The two curves cross at 1044
Hz, which is the peak of the absorption curve. This figure clearly demonstrates that D is a resonant acoustic
structure. At 1044 Hz, the value of real part is 1040 Pa · s/m, higher than the characteristic impedance of air,so the peak absorption value in Figure 3 is just around 0.5. It means that the structure of D still needs to be(a) Sound impedance of C: Closed pores(b) Sound impedance of D: Nitrile sponge

Figure 4. Specific sound impedance of C and D.
optimized on impedance matching to get higher sound absorption performance.
3.3 Sound insulation
Figure 5 shows the measured transmission loss data from the four kinds of samples. The frequency range isfrom 100 Hz to 1600 Hz.

Figure 5. Transmission Loss measured by the impedance tube.
According to Figure 5, samples with open porosity (A and B) have very low sound insulation ability. Especiallyfor the reticulated structure, the sound almost goes through the whole structure without any loss. Besides,
samples with closed pores (C and D) have higher transmission loss than others. Especially for C, which has
the same shape and similar surface density as A and B. This can indicate that the internal pores can improve
the sound insulation performance of closed-cell materials. Moreover, for C and D, the resonance region canbe seen at low frequency (220 Hz and 430 Hz, respectively), due to the mechanical resonance occurring at

lower order natural frequencies. This indicates that they perform more similar to plates. Moreover, in thecase of C, the measured results reduce at higher frequencies than 1400 Hz, and the curves of other cases also
don’t increase with frequency, which means they don’t really depend on the mass-law. This behavior will be
investigated in further studies, including measurements at higher frequencies using smaller impedance tubes aswell as comparison with different modeling approaches.

4

CONCLUSION

Based on the measurements of sound absorption curves and transmission loss of four porous materials withdifferent open-pores rates, the following conclusions are obtained:• Closed-cell materials with elastic skeletons have the similar properties of resonant sound-absorbing materials, which can be useful for dealing with low and specific frequency noise problems.
• Compared to open-cell materials, closed-cell materials have better performance in sound insulation.
In addition to the study shown in this paper, we also investigate the vibroacoustic dynamics behavior of thesame group of porous materials. Combined with another related research on mechanical performance of porous
material in vibroacoustic measurements, this research provide the basis for our work on design and optimizationof porous materials for microacoustic and vibroacoustic applications in millimeter scale.

REFERENCES[1] Allard, J, Atalla, N. Propagation of sound in porous media: modelling sound absorbing materials, John
Wiley Sons, 2nd edition, 2009.
[2] Coussy, O. Mechanics and physics of porous solids. John Wiley & Sons, 2011.
[3] Biot, MA. Theory of propagation of elastic waves in a fluid saturated porous solid. I Low frequency range.
The Journal of the Acoustical Society of America, 28, 1956, 168–178.
[4] Biot, MA. Theory of propagation of elastic waves in a fluid saturated porous solid. II Higher frequency
range. The Journal of the Acoustical Society of America, 28, 1956, 179–191.
[5] Zwikker, C, Kosten, CW. Sound absorbing materials. Elsevier publishing company, 1949.
[6] Delany, ME, Bazley, EN. Acoustical properties of fibrous absorbent materials. Applied Acoustics, 3(2),1970, 105-116.
[7] Johnson, DL, Koplik, J, Dashen, R. Theory of dynamic permeability and tortuosity in fluid-saturated porous
media. Journal of fluid mechanics, 176, 1987, 379-402.
[8] Champoux, Y, Allard, J-F. Dynamic tortuosity and bulk modulus in air-saturated porous media. Journal of
applied physics, 70(4), 1991, 1975-1979.
[9] Lafarge, D, Lemarinier, P, Allard, J-F, Tarnow, V. Dynamic compressibility of air in porous structures at
audible frequencies. The Journal of the Acoustical Society of America, 102(4), 1997, 1995-2006.
[10] Bolton, JS, Shiau, NM, Kang, YJ. Sound transmission through multi-panel structures lined with elastic
porous materials. Journal of sound and vibration, 191(3), 1996, 317-347.
[11] Lee, JH, Kim, J, and Kim, HJ. Simplified method to solve sound transmission through structures linedwith elastic porous material. The Journal of the Acoustical Society of America, 110(5), 2001, 2282-2294.
[12] Zhou, J, Bhaskar, A, Zhang, X. The effect of external mean flow on sound transmission through doublewalled cylindrical shells lined with poroelastic material. Journal of Sound and Vibration, 333(7), 2014,
1972-1990.

[13] Golzari, M, Jafari, AA. Effect of poroelastic material on vibroacoustic behavior of truncated conical shells.
Aerospace Science and Technology, 118, 2021, 106982.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0512

Effects of a winding neck extension structure ona resonant frequency of sound absorption by
3D-printed thin square resonators
Shinsuke NAKANISHI1
1

Hiroshima Institute of Technology, Japan

ABSTRACT
Thin acoustic resonators can be tuned at low frequency by building a long neck extension in its surface panel.
Author has studied effects of a winding neck extension on resonant frequency and absorption coefficient of
3D-printed resonators. Thin tile-like resonator with multiple opening holes requires quite small opening holeand long neck extension designed for tuning at a low frequency, that are built in a quite thin surface panel.
However, 3D-printed resonators by a fused deposition modeling (FDM) causes that a measured peakfrequency of sound absorption shift from a designed resonant frequency. The maximum frequency shift with
1/4.6 octave shows at measured 172 Hz from designed 200 Hz of a sound absorption peak caused by aresonator having 2.4 mm x 2.4 mm square holes. These shifts are caused by two mechanism that are a shrinkof opening hole size at process of 3D-printing with a fused deposition modeling and reduction of air volume
in a winding neck extension built in a surface panel. This study discusses effects of a winding neck extension
structure having multiple turn backs on the resonant frequency and suggests its prediction formula modified
by considering reduction of air volume depending on multiple turn backs.
Keywords: Sound Absorption, Resonator, Additive Manufacturing

1. INTRODUCTION
The author proposes to apply a resonator to the sound absorption mechanism with the aim ofrealizing a thin sound-absorbing structure with high sound absorption in the low frequency range [13]. A resonator is a sound absorption mechanism in which the mass of the air in the neck and the air
spring due to a small cavity form a single resonant system and has high sound absorption around theresonant frequency. Since the sound absorption characteristics are determined by the shape anddimensions of the cavity, the opening hole, and the neck part, the resonance frequency can be adjusted
to a low frequency by lengthening the neck of the perforated plate.
The structure of the resonator's neck that extends and protrudes into the cavity is an example ofwhat Brüel[4] used for the conference room of the Technical University of Denmark. It has various
cavity volumes and neck lengths, so that it can be tuned from 91 Hz to 300 Hz. Although Brüel does
not mention protruding the neck into the cavity, the figure shown in the reference 9 indicates that theneck was also extended behind to smooth the interior walls.
Iwase et al. [5-6] propose a method of equivalently increasing the thickness of the perforated plateby attaching a small extension part to the back side of the opening hole without changing the thicknessof the perforated plate. As a result of measuring the normal incident sound absorption coefficient [5],it was confirmed that the peak of the sound absorption coefficient moved to the low frequency range
according to the diameter and length. It was also suggested that the peak value of the sound absorption
coefficient increased as the inner diameter of the additional part became elongated, due to the increase
in resistance on the inner wall surface. Although the length of the straight extension to be adjusted forthe resonance frequency is limited up to the thickness of the cavity, the bending extension can beextended longer than the straight extension even if in the same cavity. Iwase et al. [6] indicates thatthe bending neck extension gives the same frequency characteristics of the sound absorption
coefficient of the perforated plate as one by attaching the same length of straight neck extension.
In addition, in order to realize a thin sound-absorbing structure that can be applied to small spaces,
1s.nakanishi.9a@cc.it-hiroshima.ac.jp

Kaneko et al.[7] apply numerical analysis using the finite difference time domain method to the soundabsorption of the Helmholtz resonator. And, they discuss the influence of the difference between the
structure in which the neck is repeatedly bent rectangularly along the inner wall in the cavity and thestructure that bends by winding in it. As a result of the analysis of a Helmholtz resonator with a square
opening of 20 mm square in a cuboid cavity, the peak of the sound absorption coefficient shifted to
the low frequency according to the length of the neck part. Even if both shapes of the bending neckextension differ each other as mentioned above, the peak frequency of the sound absorption coefficientof the two indicate no influence on the sound absorption characteristic due to the bending method.
However, since the bending path of the neck extension in these studies starts forward normal
direction to the surface of the sound-absorbing structure, these structures have a limitation in reducing
the thickness of the entire sound-absorbing structure, as shown in Figure 1. In contrast, the author has
proposed a Helmholtz resonator with a flatter cavity by bending the neck extension parallel to thesurface of the sound-absorbing structure in the previous studies [1-3].

Figure1 – Comparison of the bending neck extension of the Helmholtz resonator. Left resonator’sneck path is normal to the surface and right resonator’s neck path is parallel to the surface.
The author [3] measured and discussed sound absorption of thin resonator tuned at a low frequency,
which have various neck extensions built in a surface panel and 10 mm or 15 mm total thickness ofresonators. The previous paper focuses effects of opening size of the resonator, path length, numberof turns of the winding neck extension and cavity volume on the sound absorption of the thin resonator.
Thirty of the thirty-six specimens, which have square opening holes with a side of 3.0 mm or 3.6 mm,
cause the peak of the sound absorption coefficient at 209 Hz although these are designed to have aresonant frequency at 200 Hz.
In the previous studies [1-3], the specimen was made by 3D printer with a fused deposition
modeling (FDM). In order to smooth the surface, the gap between the injection head and the build
table is narrowed to about 0.04 mm. As the result, it is because that the filament fixed in the build
table is crushed to narrow the opening or the specimens generally cool down and shrinks after output.
This study measures the opening dimensions of a thin resonator made by a 3D printer and discusses
the effect on the peak frequency of the sound absorption coefficient. As the results, it was suggested
that the peak frequency depends on the number of turn backs of the winding neck extension.
Furthermore, the author proposes a modified prediction formula of the resonant frequency in the soundabsorption of the resonator, by considering reduction of volume of the reciprocating air motion in thewinding neck extension depending on multiple turn backs when caused the resonance.

2. MEASUREMENT
2.1 Procedure
A normal incident sound absorption coefficient is measured in accordance with ISO 10534-2:1998(Acoustics - Determination of sound absorption coefficient and impedance in impedance tubes - Part
2: Transfer-function method). A self-made impedance tube with a 500 mm-length acoustic tube has asquare cross section with inner dimensions 100 mm x 100 mm. The impedance tube used formeasurement shown in Figure 2 is assembled four 10 mm thick polycarbonate plates with a solventbased adhesive to ensure airtightness. On the bottom surface of the acoustic tube on which thespecimen is installed, a 3 mm thick stainless-steel plate is fixed with epoxy putty, and the space behindit (120 mm×120 mm×90 mm) is filled with clay. The measured sound absorption coefficient of thebottom surface of this impedance tube is uniformly approximately 3 % at frequencies below 1200 Hz
with a half wavelength of 144 mm diagonal of the inner dimension of the square cross section.

Figure 2 – A self-made impedance tube with a square cross section.
2.2 Structures of test thin square resonator
A specimen is modeled with Google SketchUp and made by a FDM 3D printer (MakerBot,
Replicator 2) with polylactic acid plastic (PLA) filaments. Figure 3 shows that the specimen is asquare plane of 120 mm × 120 mm with a thickness of 15 mm. The neck is bent 90 degrees at the
opening to be parallel to the surface, and then the neck extensions have 180 degrees turn backs
repeated until the end leads to the cavity. The square opening has three types of sides of 2.4 mm, 3.0mm, and 3.6 mm. The neck length is 80 mm as the trajectory of the cross-sectional center, and thenumber of turn backs is 2, 4, 6, and 8. The number of openings was determined by obtaining the total
opening area from equation (1) with a resonance frequency of 200 Hz. One side of the aperture was
2.4 mm, 3.0 mm, and 3.6 mm, respectively, and the number of the opening holes was 30, 18, and 12.
𝑓!"# =𝑐𝑆&
2𝜋 𝑉(𝑙 + 0.8 𝑑′)

[Hz]

(1)

Here, 𝑐 is a speed of sound in the air [m/s], 𝑆 is sum of areas of opening square holes [m$ ], 𝑉 isa volume of the cavity [m% ], and 𝑙 is the length of the neck [m], 𝑑′ is the diameter [m] of the circle
with an area equal to the area of the opening.

Figure 3 – 3D model sample of a test square resonator having multi-opening hole and bending neck.

3. RESULTS AND DISCUSSION
3.1 Frequency characteristics of absorption coefficient
Figure 4 shows the measurement result of the normal incident sound absorption coefficient. For
each size of square opening hole, a peak of the sound absorption coefficient can be seen around thedesigned 200 Hz, indicating the specific sound absorption characteristics of the resonator. On theother hand, a sharp peak also appears around 800 Hz to 1000 Hz and coincides a single peak of soundabsorption characteristics measured for specimens with the same dimension without holes. This isprobably the peak of panel-type sound absorption due to the resonance of a finite square panel.
In Figure 5, blue circles and solid lines indicate a tendency for the peak frequency to increase as
the number of turn backs of winding neck extension increases. If this change is due to narrowing of
the square opening hole or heat shrinkage when the specimen is made by a 3D printer, it is assumed
that a degree of the narrowing or heat shrinkage depends on the number of the turn backs.
Therefore, the dimensions and area of the opening of the specimen surface were measured with amicroscope. Figure 6 shows the area ratio of measured square opening hole of surface to designed
opening area. When one side of the square hole is 2.4 mm, the area ratio is smaller than that of 3.0
mm or 3.6 mm for all turn backs.
In addition, when we focus on the dimensions of each square opening hole with 4, 6, and 8 turnbacks, it can be said that the actual area of the square opening hole of the specimen is almost constantFigure 4 – Results of absorption coefficient of resonators with multi-opening hole and bending neck.

Figure 5 – Measured peak frequency of absorption coefficient and predicted resonant frequencies ofresonators having multi-opening hole and bending neck.

Figure 6 – Area ratio of measured square opening hole of surface to designed opening area.
regardless of the number of turn backs. Furthermore, the area ratio with one side of the square openingof 3.0 mm and 3.6 mm are the same. This is probably because the height of the injection head of the
3D printer from the building table were adjusted after printed out specimens with one side of thesquare opening hole of 2.4 mm. However, the peak frequency of the sound absorption coefficient
shown in Figure 5 increases as the number of turn backs increases, even if the area ratio of the openingis almost equal.
The red triangle and solid line in Figure 5 show the result of predicting the resonant frequency byapplied the actual measured opening area to Equation (1). The predicted resonant frequency is lower
than the measured peak frequency, especially when one side of the square opening is 2.4 mm and 3.6mm, the frequency difference between the predicted and measured value increases as the number ofturn backs increases. Therefore, even if a resonator is made by using a stereolithography 3D printerwith higher accuracy for actual opening hole with the same dimension to the designed model, it issuggested that the peak frequency of the sound absorption coefficient depends on the number of turnbacks in the winding neck extension.
3.2 Modified formula of a resonant frequency
In Figure 5, it has been suggested that number of the turn backs in the winding neck extension
dominates the difference between the measured peak frequency of the resonators with the winding

neck extension and the resonance frequency predicted from Equation (1). When the geometric volumeof the air contained in the neck extension is constant, the mass in the single resonant system of theresonator is constant regardless of the number of turn backs. Therefore, it is necessary to estimate thisreciprocating air volume and its mass in the winding neck extension when resonance is caused.
When the winding neck extension is regarded as a repetition of a rectangular flow path with a sharp
turn of 180 degrees, the numerical analysis of turbulent flow in a square duct with one roughened wallby Sugiyama et al. [8] are helpful although the constant air flow with one direction. Figure 6 showsthat the numerical analysis of turbulent flow well matches the measurement by Nakayama et al. [9].
The air flows after turning around the inner wall end generates a flow separated from the tip and goesback to the tip along the inner wall as the turbulent flow. Also, the air flow from upstream into theturn changes the direction of the flow rapidly at a rectangular entering corner, and it causes a vortex
staying at the corner.

Figure 6 – Comparison of stream-wise velocity vectors between the measurement and the numericalanalysis of turbulent flow in a square duct with one roughened wall by Sugiyama et al. [8].
In this study, when the resonance causes, the air flow in the winding neck extension is inreciprocating motion. The reciprocating air motion alternately pushes away the area of the turbulent
flow near the tip of the inner wall, but the vortex at the rectangular entering corner is fixed andseparated from the reciprocating air flow. As the result, it is suggested that reduction of the air volume
due to the vortex becomes mass reduction in the single resonant system of the resonator. When the air
volume reciprocating in the winding neck extension is represented as 𝜉 𝑆 (𝑙 + 0.8 𝑑′) referred toEquation 1, the coefficient 𝜉 is defined as a volume ratio of the reciprocating air flow to thegeometrical air volume in the winding neck extension and is called “volume reduction index” in thispaper. Equation 1 on the prediction formula of the resonant frequency is modified as follows:𝑓!"#,'"() =𝑐
𝑆&
2𝜋 𝑉 𝜉 (𝑙 + 0.8 𝑑′)

[Hz]

(2)

The volume reduction index 𝜉 is also represented by combining Equations 1 and 2, as follows:𝑓!"#,'"() =

𝑓!"#
:𝜉

⇒

𝜉=

𝑓!"# $
𝑓!"#,'"() $(3)

Furthermore, the volume reduction index 𝜉 can be defined as a function of the total number of therectangular corners which are summed two corners for each turn back and one corner for each opening
hole on the front of the resonator and bordering to the cavity. For each resonator specimen, themeasured peak frequency indicated by the blue circle and solid line of Figure 5 is given to 𝑓!"#,'"()
of Equation 3, and the resonant frequency calculated from Equation 1 indicated by the red triangle
and solid line of Figure 5 is given to 𝑓!"# .
Figure 7 shows that the volume reduction index 𝜉 decreases as the total number of corners in thewinding neck extension increases. As the results, the measured peak frequency shown in Figure 5 isFigure 7 – A volume reduction index 𝜉 for a bending neck extension as a function of number ofcorners.

Figure 8 – Measured peak frequency of absorption coefficient and predicted resonant frequencies
modified with a volume loss factor 𝜉.

higher than the resonant frequency predicted by Equation 1, due to the smaller mass of thesingleresonant system of the resonator given by smaller volume of the reciprocating air flow, when
the number of turn backs becomes larger.
Here, a liner regression is applied to each scatter diagram in Figure 7 by giving an intercept inwhich the total number of corners 𝑛* is 0 and 𝜉 = 1 as shown in the dotted line in Figure 7. And, thevolume reduction index is approximately obtained as a function of the total number of corners 𝑛* asfollows:(4𝑎)𝜉$.,-- = 1 − 0.0128 𝑛*
𝜉%..-- = 1 − 0.0106 𝑛*(4𝑏)𝜉%./-- = 1 − 0.0109 𝑛*(4𝑐)

It can be said that the predicted resonant frequency by Equation 2 with the volume reduction index
𝜉 given by Equation 4 as a function of the total number of corners 𝑛* is in good agreement with themeasured peak frequency, as shown in Figure 8.

4. CONCLUSIONSThis study considered the effect of heat shrink of the opening of a thin resonator made by a 3D
printer while cooling down on the peak frequency of the sound absorption coefficient. In addition,
since it was suggested that the peak frequency depends on the number of turn backs of the winding
neck extension, the author confirms that the modified prediction formula of the resonant frequency inthe sound absorption characteristics of the resonator, by considering reduction of air volume
depending on multiple turn backs, gives a good agreement to the predicted resonant frequency withthe measured peak frequency.

REFERENCES
1. Nakansihi S, "A pilot study of acoustic absorption by a perforated panel with bending tube extension built
in the panel," Proceedings in DVD-ROM on internoise2015 (2015, San Francisco, CA), 10p (2015).
2. Nakansihi S, "Sound absorption of Helmholtz resonator included a winding built-in neck extension,"
Proceedings in DVD-ROM on internoise2016 (2016, Hamburg, Germany), 8p (2016).
3. Nakanishi S, “Sound Absorption of Thin Resonators Including a Winding Neck Extension in Surface
Panel,” Proceedings of the 23rd International Congress on Acoustics (2019, Aachen, Germany), 23202326 (2019)
4. Brüel Per V., Sound Insulation and Room Acoustics (Chapman & Hall Ltd., London, 1951), pp112-113.
5. Iwase T, Shirahata K, Igarashi A, Sugie S, Okada Y, “Shortening Helmholtz resonator by subsided neckand appli-cation to perforated plate structure for low frequency sound resonance,” Proceedings in DVDROM on internoise2012 (2012, New York, NY), 12p (2012).
6. Iwase T, Sugie S, Abe M, Kurono H, Nishimura S, Okada Y and Yoshihisa K, "Modeling and verificationof perforated plate structure for high sound absorption at low frequency with extending parts behind holes
into shallow air space," Proceedings in DVD-ROM on internoise2015 (2015, San Francisco, CA), 12p(2015).
7. Kaneko Y, Kawakami T, Kawaguchi T and Fujimoto K, “Thin absorptive structure in low frequency byextending the neck of Helmholtz resonator,” Journal of Architecture and Urban Design, Kyushu
University, No.24, p.73~ 7 (2013.7) (in Japanese).
8. Sugiyama H, Tanaka T and Mukai H, "Numerical analysis of turbulent flow separation in a rectangularduct with a sharp 180‐degree turn by algebraic Reynolds stress model," International Journal for
Numerical Methods in Fluids, 56(12), 2207–2228
9. Nakayama H, Hirota M, Fujita H, Yamada T and Koide Y, “Flow characteristics in rectangular ducts witha sharp 180-degree turn,” Transactions of the JSME 2003; 69-681:1171–1179 (2003) (in Japanese).

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022in Gyeongju, Korea

ABS-0544

Sustainable Acoustic Material Investigation Using Fruit Seeds
DamlaTarman1;ZühreSü Gül1
1

Department of Architecture
Architecture,Bilkent University, Turkey

ABSTRACT
In order to reduce the carbon footprint due to currently applied sound absorptive materials in the building
construction industry, alternative sustainable systems are investigated in this research. By re
re-using the waste
fruit seeds that are abundant in the Central Anatolia region of Tu
Turkey,rkey, a composite panel system is developed
to be applied in buildings as a fine finish surface, like a wall or ceiling panel. The raw material is composed ofvarious fruit seeds including cherry, watermelon, olive, etc. As a natural adhesive, the wood res
resin iscombined with wood fire ash. The efficacy of the adhesive property is the subject of natural adhesive research
Wood glue is utilized as an alternative to other adhesive materials; it is regarded to be more efficient inmaterial production due to its practicality and accessibility. The varied combinations of seeds, tree resin andtree glue has been tested through impedance tube measurements and sound absorption coefficient data are
acquired. The results indicate that the panels out of seeds joined with proper adhesives have a potential to be
applied as sound absorptive decorative systems in interior spaces. The study is ongoing to alternative porous
adhesives.
Keywords: Sound absorption, impedance tube, sustainable materials, acoustic panel, fruit sseeds

1. INTRODUCTION
Through the use of ecologically harmful materials in the modern world, the limit of sustainability
has been exceeded, and as a result, the world has been propelled into an unavoidable catastrophe.
Consequently, each year the demand for green technologies has expanded considerably. To
comprehend the sustainability of a substance, its effects on the environment, human health, and social
justice must be evaluated. In addition, in order to ensure the sustainability of the resources, theproductionn process should create the least amount of trash feasible, or waste products should be able tofind a second life. In this aspect, renewable energy is favored over nonrenewable resources [1].
Therefore, it is essential to utilize eco
eco-friendly and biodegradable
dable products wherever feasible. The
most prevalent materials for sound absorption include perforated wood panels, perforated gypsum
board, wood wool, and melamine foam. Traditional acoustic soundsound-absorbing
absorbing materials forarchitectural uses are often backe
backed up (perforated panels or fabric-finishedfinished panels) with mineral or
glass wool. As these materials are breathable and emit tiny particles, even in small amounts, they may
pose future health risks to the workers in this industry. In addition, their high manufacturing
manuf
costs
result in significant carbon footprints and severe environmental implications [2,3].
[2,3].Exposure to dust is
estimated to provide
rovide an average health risk [4[4]] based on an evaluation of the situation as a whole.
Different research groups have inves
investigatedtigated organic materials such as coconut husks
husk and palm oilflower spikes based on their sound absorption and reflection characteristics. In these cases, after
testing the materials' qualities, researchers found that organic materials have promising poten
potential to be
used
ed in acoustical applications [5,6[5,6]. On the other hand, the recovery of bioactive substances from fruit
seeds is a research movement that attempts to minimize trash production and satisfy the public's highdemand for organic matter, which is believed to offer health-promoting
promoting and disease-preventive
diseaseproperties against
ainst chronic conditions [7[7]. Due to this, we believe that sound-absorbing
soundpanelsproduced from eco-friendly
friendly fruit seeds are less hazardous to human health. On the other hand, fruit
consumption
sumption rises with global population growth. As a result, more waste fruit seeds haveaccumulated. Some previous work has investigated the production of sound-absorbing
absorbing materials ofvarying thicknesses from collected
ted fruit seeds (cherry, olive, apricot, and peach). According to thesestudies,, the distinct shapes and sizes of fruit stones result in different sound absorption properties [8,9].
Peach-like
like stones with a rougher and more porous surface absorb significantly more sound. The
1

damla.tarman@bilkent.edu.tr

behavior of tiny seeds, notably cherry seed samples, results in greater sound absorption coefficients[9].
Various species of fruit are cultivated in Turkey, which has vastly varying ecological circumstancesand geographical features. A substantial percentage of Turkey's fruit production comprises stone fruits,
the majority of which are waste stone fruits. This study is motivated by the widespread cultivation ofcherries in the Turkish province of Konya, in the Central Anatolian area, and the dumping of cherry
seeds from this region as waste. Seeds are employed as raw materials in this study of acoustic materials,
and wood glue and resin are used to bind the seeds together. Various combinations of seed types withvarying sizes are evaluated in an impedance tube to determine the sound absorption coefficient. As
basic criteria for the selection of seeds, it is considered that they should belong to fruit species that areabundant in Turkey and that their sizes are appropriate for the sound-absorbing panel production thatis intended to be produced. First, two examples are produced by combining cherry seeds from distinct
batches with resin and wood glue. In addition to cherry seeds, olive and watermelon seeds aresubsequently employed to broaden the variety of available materials. Since acoustic panels areintended for indoor application, the degree to which the seeds are resistant to fire is also a focus ofstudy. Some material samples are coated with fire-resistant nano-composite paint-based coatings [10]to examine their influence on the acoustic performance of the material samples. Cherry seeds, which
are the focus of this research, are colored in order to enhance fire resistance since the paint includes
numerous compounds and is projected to promote fire resistance. This study intends to expand
material combinations by mixing diverse seeds and to contribute to the literature in this regard bystudying the influence of seed diversity on the sound absorption performance of different material
compositions. The objective is to expand the possible use of local waste fruit seeds in architectural
applications in order to improve acoustic comfort in interior spaces and contribute to the reuse ofnatural resources. The following sections introduce the methodology and results of this study.

2. METHODOLOGY
2.1 Sample Preparation
In order to gain maximal sustainability and recyclability from the sound-absorbing materials
proposed for production, the collection of fruit seeds is one of the most important procedures in thisstudy. Seasonal availability aided the gathering of cherry, olive, and watermelon seeds to be formed
into sound absorbing panel samples. The waste seeds after collection are exposed to the sun for one
month to totally dehydrate and dry. Fig. 1 depicts fruit seeds, which will be the raw material for thesound-absorbing panel to be formed.

abcdFigure 1 –Raw materials: a) Cherry seeds b) Large olive seeds c) Small olive seeds d) Watermelon
seeds
To identify the most optimal variant, nine sorts of samples are prepared. As the impedance tube isa cylinder (in two different diameters), circular-shaped samples having a diameter of 100 mm and 28
mm are prepared for each of the nine samples with a thickness of 20 mm. These nine samples havedifferent compositions in terms of ingredients (Table 1). Tree resin and wood glue are employed in the
research as binding materials. First, wood resin -an organic binder (sweet gum resin, Fig. 2a, 2b)- isheated to a moderate temperature, and then wood ash is added to improve the resin's stickiness anddensity. Next, the mixture of resin and wood ash is combined with cherry seeds to produce the firstmaterial sample (A). Wood glue (Fig. 2c), another substance employed as a binder in the research, islater on favored owing to its practical use, and is used in the next eight samples.

abc
Figure 2 –Adhesive
Adhesive materials: a) Sweet gum resin b) Heated tree resresin c) Wood glue
The production phases of Material I are illustrated in Fig. 3. As seen in Figure 2c, wood glue iswhite in liquid form and becomes transparent upon drying. In the last material sample (I), cherry seeds
coated with red spray paint and wood glue are combined, and the influence of the paint on thematerial's sound absorption coefficient is investigated.
Table 1: Contents of material samples A, B, C, D, E, F, G, H, and I

a
b
c
d
e
Figure 3 – Preparation steps of Material II: a) Painted cherry seeds b) Addition of tree gluec) Mixing tree glue and red cherry seeds d) The prepared mixture in the mold e) Mixture upondrying
2.2 Tube Measurements
Impedance tube measurements are performed with S.C.S. Kundt Tube. 'Kundt Tube' configuration
represents the basic, standard system set up for absorption coefficient and acoustic impeda
impedancemeasurements (2 microphones-transfer
transfer function method), according to ISO 10534-2:1998
10534[11,12].
The
he double tube configuration for measuring sound absorption contains both small and large tubes. For
measurements in the low frequency range (50 Hz to 1200 Hz), 100 mm tubes are used, whereas 28 mm
tubes are used for measurements in the high frequency rang
rangee (1200 Hz to 8000 Hz). All samples placedin tubes A, B, C, D, E, F, G, H, and I (Figure 4) are 20 mm thick and measured with a 30 mm air gap.
C, D, E, F, G, and H are also measured without an air gap behind.

Figure 4 – Photographs of the material samples casted within tube ring.
Fig. 5 depicts the impedance tube setup and the placement of Sample C within the tube. To
verify the accuracy of the data, each composition is tested multiple times, and the mean values of these
repeated tests are utilized in the analysis, omitting any outlier.

abcFigure 5 – During the measurement of proposed products,a) Tube set-up b) Sample C in the large tube c) Sample D in the small tube

3. RESULTS
In this section, sound absorption coefficient measurement results of samples A, B, C, D, E, F, G, H,
and I are presented. Fig.6 depicts the samples tested with 30 mm air gap for samples A and B, which
are formed by changing the binder. Accordingly, sample A, whose binder is resin, has absorption
efficiency in a greater frequency range 500 to 2000 Hz in comparison to B, whose binder is wood glue.
As shown on the graph, sample A's alpha value reaches its maximum (0.7) at 800 Hz. At low
frequencies (below 250 Hz), the measurement findings for these two materials demonstrate aremarkably similar pattern, and low sound absorption. This can easily be related to the thickness of the
air gap. If the thickness of the air gap is increased, the effective frequency range can move towards
lower octave bands for both samples.

Figure 6 – Sound absorption coefficients over frequency spectrum from 50 Hz to 5000 Hz obtained
for samples A and B with a 30 mm air gap backing
Fig. 7 depicts the sound absorption coefficient mea
measurement
surement results conducted forfo 20 mm thick B,
C, D, E, F, G and H samples with a 30 mm air gap backing. When the results are analyzed, it isobserved that all seven samples exhibit greater sound absorption between 500 Hz and 2000 Hz. The
sound absorption coefficientsoefficients over octave bands from 125 Hzz to 4000 Hz for A, B, C, D, E, F, G, H, andI are also presented in Table 2. According to Fig. 7 and Table 2, sample
sampless H and C have the highest
sound absorption performance in their effective ranges; with sound absor
absorption
ption coefficients reaching up
to 0.70 at mid frequencies. On thehe other hand, samples B and I have comparatively much lower soundabsorption coefficient values over the measured frequency range. While samples B and I include solely
cherry seeds, sample H has cherry, large
large-small
small olive, and watermelon seeds; therefore, it can beconcluded that the material's ability to absorb sound rises as the diversity of seeds (with different
diameters) within the sample increases.

Figure 7 – Sound absorption coefficients over frequency spectrum from 50 Hz to 5000 Hz obtained
for samples B, C, D, E, F, G, H and I with a 30 mm air gap behind.
Table 2: Sound absorption coefficient
coefficients over 1/1 octave bands (Hz) obtained from impedance
tube test for samples A, B, C, D, E, F, G, H, and I

Fig. 8 depicts the measurement results for samples C, D, E, F, G, and H with no air gap behind. The
range of speech tones is 500 Hz to 2000 Hz differs within the range. Without an air gap, the effective
sound absorption of the samples is in between 2000 Hz–4000 Hz, indicating high frequencies. In orderto provide effective sound absorption, especially considering the intended speech frequencies forindoor custom environments, it is recommended that the panels to be applied with minimum a 30 mm
air gap behind. This can be readily provided with a supporting bracket for hanging the panels on walls.

Figure 8 – Sound absorption coefficients over frequency spectrum from 50 Hz to 5000 Hz obtained
for samplesC, D, E, F, G, and H without air gap behind.
By maintaining the same composition with material sample B (cherry seeds), material sample I isformed only by an additional spray-painting on to increase the fire resistance of the panel. Although
the primary function of paint is to enhance fire resistance, the influence of paint on the material's soundabsorption is investigated. According to Fig. 9, the paint shifted the effective frequency range from1000 Hz to higher frequencies, 1600 Hz–5000 Hz. At 1600 Hz, the maximum sound absorption
coefficient of painted sample is 0.42. Application of paint to other samples should be tested in the
future to derive a better conclusion of the effective frequency range of samples that are painted for fire
resistance.

Figure 9 – Sound absorption coefficients over frequency spectrum from 50 Hz to 5000 Hz obtained
for samples B and I with a 30 mm air gap behind.

4. CONCLUSIONSThe purpose of this research is to investigate reusable and biodegradable waste materials in order toprovide a potential solution for sound absorptive materials to be applied in indoor spaces. This paper
uses fruit seeds that are vastly trashed in the region, with a focus on cherry seeds of Central Anatolia.
In the experimental set-up, nine distinct composite samples are tested to specify their sound absorption
performance. The material sample containing tree resin, as a binder, is observed to be superior to thatof the material sample with wood glue binder. When the numbers of seed types, thus the seed sizes, arevaried the sound absorption performances of the samples are improved. The use of waste fruit seeds(cherry, olive, and watermelon) in the design and production of sound absorptive acoustic panels
indicates considerable promise. Another outcome is that the spray-on paint application to increase thefire resistance of one sample panel, has shifted the effective frequency range towards higher octaves.
To sum up, the developed panel systems, can find different grounds of application in indoor spaces
where control of speech sound and absorption is critical, such as open-plan offices, meeting rooms,
living rooms, or public places such as cafés, restaurants, etc. Further research is necessary toinvestigate more biodegradable binder types, as well as to observe the effects of different paints overdifferent material samples.

ACKNOWLEDGEMENTS
The authors gratefully acknowledge Mezzo Stüdyo Ltd., Ankara for providing the laboratory
opportunities for impedance tube measurements.

REFERENCES
1. Santoni, A., Bonfiglio, P., Fausti, P., Marescotti, C., Mazzanti, V., Mollica, F., &Pompoli, F. Improving
the sound absorption performance of sustainable thermal insulation materials: Natural hemp fibres.
Applied Acoustics, 150, 279–289 (2019).
2. Buratti, C., Belloni, E., Lascaro, E. & Giovanna, L. Sustainable Panels with Recycled Materials for
Building Applications: Environmental and Acoustic Characterization. Energy Procedia, 101, 972–979(2016).
3. Saldana-Mendoza, S. A., Ascacio-Valdes, J. A., Palacios-Ponce, A. S. et al. Use of wastes from the tea
and coffee industries for the production of cellulases using fungi isolated from the Western Ghats ofIndia. Systems Microbiology and Biomanufacturing, 1, 33–41 (2021).
4. Kupczewska-Dobecka, M., Konieczko, K., &Czerczak, S. Occupational risk resulting from exposure tomineral wool when installing insulation in buildings. International Journal of Occupational Medicine
and Environmental Health, 33(6), 757–769 (2020).
5. Rimantho, D., YuliantiHidayah, N., & Pane, E. Utilization of the organic and inorganic solid waste as
acoustic material. Journal of Engineering and Applied Sciences, 14(8), 1502–1506 (2019).
6. Masrol, S. R., Rosdin, M. & Ibrahim, M. Sound absorption characteristics of palm oil male flower spikes
fiber reinforced composite. (2013).
7. Cheok, C. Y., MohdAdzahan, N., Abdul Rahman, R., Zainal Abedin, N. H., Hussain, N., Sulaiman, R., &Chong, G. H. Current trends of tropical fruit waste utilization. Critical Reviews in Food Science andNutrition, 1–27 (2016).
8. Sanchis, E. J., Alcaraz, J. S., Belda, I. M., & Borrell, J. G. Sustainable multiple resonator soundabsorbers made from fruit stones and air gap. Alexandria Engineering Journal, 61(12),10219–10231(2022).
9. Gadea Borrell, J., Juliá Sanchis, E., Segura Alcaraz, J., & Montava Belda, I. Sustainable sound absorbers
from fruit stones waste. Applied Acoustics, 161, 107174. (2020).
10. Sethurajaperumal, A., Manohar, A., Banerjee, A., Varrla, E., Wang, H., &Ostrikov, K. K. A thermallyinsulating vermiculite nanosheet–epoxy nanocomposite paint as a fire-resistant wood coating.
Nanoscale Advances, 3(14), (2021).
11.International Organization for Standardization, Acoustics – Determination of Sound Absorption
Coefficient and Impedance in Impedance Tubes – Part 2: Transfer- Function Method, 1998.
12. Yazıcı, B. & Gül, Z. Biomimetic metamaterial design simulation and evaluation for building acoustics
by impedance measurements. Journal of Testing and Evaluation, 49, (2021).

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022, in Gyeongju, Korea
Extended abstractABS-0681

Modelling and optimisation of nanofibers with porous substrate
Victor CHEN1,2; Ignacio PEREZ PABLOS3; Jer-Ming CHEN1
1

Singapore University of Technology and Design, Singapore
23

Dyson Operations Pte Ltd, Singapore

Dyson Technology Limited, Malmesbury, UK

ABSTRACTIn this study we present the prediction of enhanced acoustic absorption of nanofiber-porous systems, forporous media overlaid with nanofiber weave. Assuming the nanofiber layer to be a resistive screen of
identical cylindrical perforations, normal incidence surface impedance measurements of nanofiber weave
over an air gap were used to estimate equivalent fluid parameters and bulk properties of dynamic mass densityand bulk modulus using the JCA model, as well as the impedance for a lumped element model. Using bothmodels in a transfer matrix to calculate absorption coefficient of nanofiber-porous systems gave good
agreement between prediction and measurement, with the lumped element model having the advantage of
not requiring nanofiber layer thickness measurement and the associated uncertainty. A regression model forthe real and imaginary components of the nanofiber lumped impedance versus areal density was established,creating a single parameter prediction tool for optimisation of nanofiber-porous systems with high acoustic
absorption at target frequencies without prior characterisation of the nanofiber layer.
Keywords: Nanofiber, composite, modelling

1. INTRODUCTION
The higher acoustic absorption of a porous substrate when overlaid with nanofiber layers to form
a nanofiber-porous system has been demonstrated(1–3) and increases with nanofiber areal density(4).
Nanofibers were acoustically characterised as a bulk material (5) using the Johnson-Champux-Allard(JCA) model with limp-frame assumption, suggesting that bulk properties can potentially be used intransfer matrix models of multi-layer configurations. Flow resistance as a means of predicting lumped
acoustic impedance was investigated(6,7), highlighting disparities between physical measurement andacoustic characterization. Other efforts to create a design tool include statistical optimisation using
multi-criteria decision analysis(8) and artificial neural networks(9).
In this work, two acoustic models for the nanofiber layer are explored – equivalent fluid andlumped element. A characterisation methodology for resistive screens was applied to nanofibers overan air gap in an impedance tube to inversely derive JCA parameters and a lumped acoustic impedancefrom A relationship with nanofiber physical properties was then obtained using regression.

2. MATERIALS AND METHODS
Nanofibers were electrospun using needle-collector configurations with PA6, PVA and PVB
precursors in varying concentrations, giving different diameter distributions measured using
DiameterJ(10) to analyse SEM images while longer electrospinning duration gave higher areal density
ρA. Layer thickness was measured using a Hanatek FT3 Precision Thickness Gauge as per ISO 9073 2:1995 with foot pressure of 0.5kPa. Static flow resistance was measured using a TexTest F3300,
extrapolating down to 0.5mm/s where necessary. A PP non-woven substrate selected for negligible
contribution to flow resistance was used to support the nanofibers and its’ thickness was subtracted
from the overall measurements.

1

victor_chen@mymail.sutd.edu.sg

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022, in Gyeongju, Korea
Extended abstract

Figure 1: Sample mounting for (top)resistive screen characterisation and (below)
nanofiber-porous system

Figure 2: Absorption coefficient for 10mm thicknanofiber-porous

systemsof

areal

densityincreasing from (a)-(d), prediction vs measurement.

For measurement of normal incidence surface impedance, the nanofiber samples were mounted inannular Mylar frames (see Figure 1) for consistency. Simplifying the nanofiber layer as identical,
parallel cylindrical perforations(11), JCA parameters were obtained using the resistive screens
methodology(12). The lumped acoustic impedance was derived from circuit analogy expressions(13)by subtracting the analytical solution for surface impedance of the air gap from the samemeasurements. The melamine foam substrate was characterised using the two thickness method (14).

3. RESULTS & DISCUSSION
Transfer matrices were used to model the absorption coefficient of nanofiber-porous systems basedon JCA and lumped element models. The predictions were generally similar between the two methods,
with the latter not having the uncertainty(6) of thickness measurements and requiring less parameters.
Results for the lumped element model are shown in Figure 2, exhibiting good agreement between
measurement and prediction.

Figure 3: Regression fit for (a) real and (b) imaginary component of lumped acoustic impedance.
To facilitate design of nanofiber-porous systems directly from the nanofiber physical parameters,
regression fits were used to identify strong relationships between areal density and the real andimaginary components of lumped acoustic impedance as per Figure 3. This allows parameterisationfor optimised application of nanofiber-porous systems in complex acoustic networks, accounting forsource characteristics and upstream/downstream impedances.

ACKNOWLEDGEMENTS
This research was supported by the Economic Development Board of Singapore under the
Industrial Postgraduate Programme (IGIPDYSON1802).

REFERENCES
1.

Xiang H fan, Tan S xia, Yu X lan, Long Y hua, Zhang X li, Zhao N, et al. Sound absorption behaviorof electrospun polyacrylonitrile nanofibrous membranes. Chin J Polym Sci. 2011 Aug;29(6):650–7.
2.

Rabbi A, Bahrambeygi H, Mousavi Shoushtari A, Nasouri K. Incorporation of Nanofiber Layers in

Nonwoven Materials for Improving Their Acoustic Properties. In: Journal of Engineered Fibers and Fabrics.
SAGE Publications; 2013. p. 155892501300800.
3.

Ulrich T, Arenas JP. Sound Absorption of Sustainable Polymer Nanofibrous Thin Membranes Bonded

to a Bulk Porous Material. Sustainability. 2020 Mar;12(6):2361.
4.

Özkal A, Çallıoğlu FC. Effect of nanofiber spinning duration on the sound absorption capacity of

nonwovens produced from recycled polyethylene terephthalate fibers. Appl Acoust. 2020 Dec;169:107468.
5.

Akasaka S, Kato T, Azuma K, Konosu Y, Matsumoto H, Asai S. Structure-sound absorption property

relationships of electrospun thin silica fiber sheets: Quantitative analysis based on acoustic models. Appl
Acoust. 2019 Sep;152:13–20.
6.

Horoshenkov K, Hurrell A, Jiao M, Pelegrinis M. WHAT IS THE ACTUAL INFLUENCE OF A

NANO-FIBROUS MEMBRANE ON THE ACOUSTICAL PROPERTY OF POROUS SUBSTRATE? 2
NANO-FIBROUS MEMBRANES 2.1 Structure. In: The Journal of the Acoustical Society of America.
Acoustical Society of America (ASA); 2018. p. 1755–1755.
7.

Hurrell A, Horoshenkov KV, King SG, Stolojon V. On the relationship of the observed acoustical andrelated non-acoustical behaviours of nanofibers membranes using Biot- and Darcy-type models. Appl Acoust.
2021 Aug;179:108075.
8.

Kucukali-Ozturk M, Nergis B, Candan C. Design of layered structure with nanofibrous resonant

membrane for acoustic applications. J Ind Text. 2018 May;47(7):1739–56.
9.

Ciaburro G, Iannace G, Passaro J, Bifulco A, Marano D, Guida M, et al. Artificial neural network-

based models for predicting the sound absorption coefficient of electrospun poly(vinyl pyrrolidone)/silica
composite. Appl Acoust. 2020 Dec;169:107472.
10.

Hotaling NA, Bharti K, Kriel H, Simon CG. DiameterJ: A validated open source nanofiber diametermeasurement tool. Biomaterials. 2015;61:327–38.
11.

Atalla N, Sgard F. Modeling of perforated plates and screens using rigid frame porous models. J Sound

Vib. 2007;303(1):195–208.
12.

Jaouen L, Bécot FX. Acoustical characterization of perforated facings. J Acoust Soc Am. 2011 Mar

1;129(3):1400–6.
13.

Pieren R. Sound absorption modeling of thin woven fabrics backed by an air cavity. Text Res J. 2012

Mar;82(9):864–74.
14.

Smith CD, Parrott TL. Comparison of three methods for measuring acoustic properties of bulk

materials. J Acoust Soc Am. 1983;74(5):1577–82.

ABS-0746

Studies on the sound absorption properties of wood-based pulp
fibre foams
Jose Cucharero(1,2) , Sara Ceccherini(3) , Muhammad Awais(3) , Kari Kammiovirta(1) , Thaddeus
Maloney(3) , Lauri Rautkari(3) , Tapio Lokki(2) , Tuomas Hänninen(1) ,(1) Lumir Oy, 01260 Vantaa, Finland. jose.cuchareromoya@lumir.fi(2) Dept. of Signal Processing and Acoustics, School of Electrical Engr., Aalto University, Finland(3) Dept. of Bioproducts and Biosystems, School of Chemical Engr., Aalto University, Finland

ABSTRACT
Acoustic behaviour of wood fibres depends on material properties on different hierarchical structural levels, including molecular, microscopic, and macroscopic. In this paper, we present comprehensive studies on
the effect of the hierarchical structure of wood pulp fibres on acoustical properties. In the molecular level,
structural polymers of wood and their arrangement in the cell wall are crucial in determining the material
properties of the fibres. In the microscopic level, wood fibres are characterised by an irregular morphology
and present average fibre lengths and widths ranging from 0.4 – 6 mm and 10 – 50 µm, respectively. In themacroscopic level, the porous structure of a 3D-fibre network formed by means of foam-forming techniquedepends on the raw fibres as well as on the foam forming procedure used. The studied pulp fibre foams
achieve comparable sound absorption properties to those of conventional synthetic porous materials. Increasing use of wood based materials in buildings contribute to reduce CO2 from the atmosphere by binding CO2
into the building structure for decades.

Keywords: Sound, Insulation, Transmission

1.

INTRODUCTION

The current market of porous sound absorbing materials is dominated by mineral wool and plastic
based products. Emissions from the production processes of these materials have been reduced during
the last years by means of a more sustainable use of energy as well as the use of recycled raw materials fortheir production. However, their production processes are still highly energy intensive which aggravateenvironmental degradation of the planet. Thus, use of acoustic materials with low-carbon emissions isneeded to reverse the current role of buildings and mitigate climate change. In this study, we propose
wood-based pulp fibre foams to be used as sound absorbing building materials. The production processes
of wood based pulp fibres are highly efficient and release low emissions of CO2 (1). Additionally,wood based pulp fibres are carbon negative raw materials as wood fibres sequester more CO2 from theatmosphere than their production processes release.
Sound absorption properties of wood fibres depend on material properties on different hierarchicalstructural levels, including molecular, microscopic, and macroscopic. In the molecular level, structuralpolymers of wood fibres and their arrangement in the cell wall are crucial in determining the material
properties of the fibres. Furthermore, mechanical properties of wood fibres, flexibility among others,change with varying moisture content. This is mainly attributed to rearrangement of structural polymers
as moisture gets into wood fibres, as well as variation in the dimensions of the fibres due to swelling.
As reported in (2), at low frequencies, the ability to dissipate sound energy of fibrous materials is
sensitive to fibre flexibility. In contrast, at high frequencies, the movement of fibres is null, and therefore
sound absorption due to fibre flexibility can be neglected. It should also be considered that in fibrous
porous materials, fibre contact and bonding influences the flexibility of fibres and freedom of movement,
and thus, they also influence the ability of the material to dissipate sound energy. Moreover, dislocations,microcompressions, curling, crimps, and kinks are induced during the pulping process. All these artefacts
tend to increase the flexibility of pulp fibres (3). In the microscopic level, wood fibres are characterisedFigure 1 The hierarchichal structure of wood at multiple scales. a) The cell wall consists of the lumen(the void space in the middle of the cell), the primary wall and the secondary wall, which, in turns,
is divided in three sublayers: S1, S2 and S3. Cellulose, hemicellulose and lignin are the three main
components that form the cell wall. b) The cross- and longitudinal sections of cells show that microfibrills(MFCs) are embedded in a matrix of hemicellulose and lignin. The figure also shows that microfibrils
contain crystalline (highly ordered) and amorphous (disordered) regions. Adapted from (6).
by their irregular morphology, and their length and width vary considerably with species. Average length
and width of softwood fibres range between 2–6 mm and 20–50 µm, respectively. Whereas length andwidth of hardwoods range between 0.4–1.4 mm and 10–40 µm (10–300 µm for vessel elements) (4).
Three biopolymers are the main components of wood fibres: cellulose, hemicellulose and lignin. The
proportion of these biopolymers in wood fibres depends on tree species. In general, the cellulose content
of hardwoods is 40% - 50 %, hemicellulose content 23% - 40%, lignin is 19% - 23%, and extractives
around 5% - 10% extractives. Whereas, for softwoods, cellulose content is 40%, hemicellulose 23% 30%, lignin 27% - 33%, and extractive 5% - 10% (4). The main elements of wood fibres are cellulose
microfibrils (CMF) which are formed by the aggregation of cellulose chains that are bonded by hydrogenbonds and Van der Wall forces. The width of CMF is 3-4 nm whereas the length is in the micro-scale,although it strongly depends on the tree species. The walls of wood fibres consist of CMFs embedded
in a matrix of hemicelluloses and lignin, where lignin acts as the cementing component (4). Figure 1
presents an illustration of the hierarchical structure of wood at multiple scales.
To be able to utilise wood fibres they need to be isolated from wood. The methods to separate wood
fibres are classified into mechanical or chemical pulping. Among all the existing methods, the kraft
process (chemical pulping) is the most popular. The kraft process aims to completely eliminate lignin
from the cell wall (4).
In this study, foam forming technique (5) was used to produce porous sound absorbers from softwoodand hardwood pulp fibres with varying chemical composition and ultrastructural properties. The soundabsorption coefficients of the produced materials were measured using an impedance tube. We studied
the influence of pulp fibre dimensions and chemical composition on the acoustic behaviour of the produced foams. In addition, this study also presents results on the influence of moisture on the mechanicalproperties of pulp fibres, and in turn, on the acoustical properties of the foams. The results provide
valuable insight for the optimization of bio-based sound absorbing materials.

2.

MATERIAL AND METHODS

2.1
Materials
Industrial hardwood (HW) and softwood (SW) kraft and dissolving pulps were provided by Finnish
mills. Kraft pulp samples were obtained from three different stages of the pulping and bleaching process:before and after oxygen delignification, and after bleaching. The pulps were either used as never-driedor as machine-dried.
2.2
Preparation of sound absorbing foam samples
Sound absorbing foams samples were prepared using foam-forming technique following the method
described in (5). Pulp, water and sodium dodecyl sulphate (SDS) were axially agitated at a rotational
speed ca. 3000 rpm in a cylindrical container of dimensions 67 cm length and 27 cm diameter. The mixer
was built according to (7). A variation of fibre consistencies were used (2.5 % and 3.5 %) to achievefoams with varying densities. The dosage of SDS was 0.5 g/L. The dry pulps were soaked in 10 L of
tap-water for 1 day at room temperature. Before the addition of SDS, the suspension of pulp in water was
mixed for 5 minutes to disperse fibres. Then SDS was added and the foaming continued until the initial
volume of the mixture doubled. The fibre foam was poured in a square mould of dimensions 40 cm x
40 cm x 50 cm with two stainless steel nets located at the bottom, and then left to gravity drain for over
15 minutes. The top net had an opening mesh of 0.16 mm, while the net below had a mesh openingof 5 mm. The latter served as a support for the top net to avoid curvature of the bottom surface of thesamples being produced. The foams was dried with heated air flow at 40 - 50 C◦ for three days.
Circular samples were cut from the produced foamed materials with the help of a bench drill. The
produced samples had variable inner density, with a higher density at the bottom. In order to attain morehomogeneous samples in terms of density, layers of fibres were removed from both sides of the samples
with the help of a sharp blade.
2.3
Determination of carbohydrates and lignin
Pulp carbohydrates and lignin were determined according to standard NREL/TP-510-42618. The
content of cellulose and hemicelluloses were determined applying the Janson formula (8). Soluble lignin
was measured in a UV-Visible spectrophotometer (UV-2550, Shimadzu).
2.4
Fibre morphological properties
Morphological properties of the different pulp fibres were characterized using a Kajaani FiberLab optical fibre analyser (Metso automation, Finland). The following properties were measured: fibre length,
width, curl (degree of non-straightness of fibre), kink (degree of sharp bends along the fibre), fines (small
particles detached from pulp fibres), fibres per unit weight, and cell wall thickness (CWT).
2.5
Handsheets and fibre mechanical properties
Handsheets were prepared according to ISO 5269-1. Tensile strength, stiffness, and stretch indicesas well as modulus of elasticity were measured in the longitudinal direction according to ISO 1924-2
with the help of a L&W tensile tester with fracture toughness SE 064. The results are given by theaverage results of ten test pieces obtained from four different handsheets. Grammage of handsheets
was determined and their thickness was measured according to ISO 534 using a thickness tester L&W
micrometer SE 250d. Handsheets were conditioned for one day at 50% relative humidity and 23 C◦ . The
conditioning was kept throughout the test.
The elastic modulus of well-bonded handsheets of long straight fibres is governed by the propertiesof the fibres as described by Eq. (1) (9).
1
Ep = φ E f(1)
3
Where E p is the sheet elastic modulus, E f is fibre modulus, and φ describes the efficiency of the fibre
to transfer stress in a sheet (φ = 1 for sheets of long, well-bonded fibres). For lower bonding degrees
or for shorter fibres, the sheet modulus is smaller than that given by Eq. (1) because of the inefficiencyof stress transfer along the fibre length. Nevertheless, the effect of fibre length on sheet modulus is only
relevant at very low densities (10). The density of the ordinary sheets prepared in this study is sufficient
to make a very high number of inter-fiber bonds, thus only a small fraction of the total fibre length does
not transfer stress.

2.6
Dynamic vapor sorption (DVS)
Water sorption was measured with an automated sorption apparatus (DVS intrinsic, Surface Measurement Systems, UK). Pulp samples were placed on the sample chamber at a constant temperatureof 25 C◦ . A constant nigrogen flow (grade 5.0, B 3 ppm H2O) of 200 sccm was used to control theRH within the sample chamber. Sorption isotherms were measured starting from the dry state with 10
distinct relative humidity steps (0, 5, 15, 25, 35, 45, 55, 65, 75, 85 and 95%). Each relative humidity step
was maintained until the sample equilibrium moisture content (EMC) was reached with a mass change
per minute (dm/dt) less than 0.0005 over a period of 10 min. The slope in a 10 min window was used to
calculate the change in mass with respect to time (dm/dt).
2.7
Measurements of sound absorption coefficients
The normal incidence sound absorption coefficients of the samples were determined using the impedance
tube transfer-function method defined in ISO 10534-2. The impedance tube used was a Brüel & Kjaer
type 4206. To study the effect of moisture on the sound absorption properties of wood-based pulp fibre foams, foams samples of varying density were prepared and they were exposed to varying relative
humidities (0%, 10%, 32%, 75% and 99%) for two days. This period of time was sufficient for the samples to reach equilibrium moisture content. The different relative humidity conditions were created by
preparing salt solutions and pouring them into sealed containers. The prepared aqueous salt solutions andexpected relative humidities were: NaOH 50 wt%, MgCl2 35.2 wt%, and NaCl 26.5 wt% to create 10 %,32 % and 75 % RH. Temperature was 20◦ - 25◦ . 99 % RH conditions were created by adding water tothe sealed box (11). Samples were first dried overnight at 80◦ and their sound absorption properties were
measured after drying. Immediately after taking sound absorption measurements the samples were exposed to 10% relative humidity for two days, and then they were measured in impedance tube. The sameprocess was repeated for all the relative humidities. It is noted that samples were outside the desired
humidity conditions only for 1-2 minutes maximum, the time it took to conduct the sound absorption
measurements.
The dimensions of the foam samples used to study the influence of moisture on the sound absorption
properties of wood-based pulp fibre foams were 100 mm diameter and 60 mm thickness. This size ofsamples allowed measurements of sound absorption coefficients in the frequency range 50 Hz - 1600
Hz. The dimensions of the samples used to study the influence of pulp fibre dimension and chemicalcomposition on sound absorption were 29 mm diameter and 40 mm thickness. This size of samples
allowed measurements of sound absorption coefficients in the frequency range 500 Hz - 6000 Hz.

3.

Results and Discussions

3.1

Chemical composition and morphological properties of fibres

Table 1 Chemical composition and morphological properties of pulp fibres.
Pulp

Fib/mg(pcs/mg)

Length
(mm)

Width
(µm)

Kink
(m−1 )

Curl
(%)

Fines
(%)

CWT
(µm)

Cellulose(%)

Hemicellulose(%)

Lignin(%)

HWunblch
HWox
HWblch
HWdissSWunblch
SWox
SWblch
SWdiss

12600
14400
12600
19700
5300
5800
5400
5900

0.96
0.86
0.80
0.73
2.11
1.88
1.97
1.73

20.03
20.28
20.71
16.32
28.31
27.49
25.36
23.83

602
1258
1702
2409
432
881
984
1440

7.8
12.9
17.1
17.7
9.3
14.5
15.4
18.8

1.5
1.2
2.1
1.6
2.4
3.1
3.3
2.3

6.27
5.97
6.02
4.05
8.51
7.98
7.03
6.38

67.0
68.8
70.2
93.9
73.7
76.4
82.7
92.5

29.3
28.9
28.8
5.4
18.7
19.9
16.5
6.7

3.7
2.3
1.0
0.7
7.6
3.8
0.9
0.8

The chemical composition and morphology of the wood-based pulp fibres are presented in Table 1.
As expected, the proportion of cellulose and hemicelluloses differs between hardwoods and softwoods
fibres, having hardwoods greater content in hemicelluloses. Lignin content is very low in both typesof pulp fibres and it further decreases in each of the stages of the bleaching process. This is because
the kraft process aims maximising the removal of lignin while minimising removal of cellulose andhemicelluloses. As can be observed from Table 1, the main difference between dissolving and bleachedkraft pulps is the content in cellulose and hemicelluloses. The main objective of dissolving pulp is theremoval of hemicelluloses, and thus, dissolving pulps are pulps of high cellulose content (>90%). The
differences in chemical composition between the two types of fibres make them suitable for different
applications. For example, dissolving pulp are preferred in the textile industry whereas bleached kraft
pulp is more used for paper applications.
It can be seen (Table 1) that softwoods are considerably longer and wider fibres than hardwoods.
Within the group of hardwood pulp fibres, cell wall thickness, fibre length and width generally decrease
with removal of lignin and hemicelluloses. The same trend is seen for softwood fibres. Differences
within the hardwood pulps and the softwood pulps are rather small, being fibre width between bleachedand dissolving fibres the most significant difference.
3.2

Dynamic vapor sorption (DVS)
HW
DPHW
SW
DPSW
Glasswool
Rockwool

20

15

Moisture Content (%)

15

Moisture Content (%)

HW
DPHW
SW
DPSW
Glasswool
Rockwool

20

10

10

5

5

0

0

0

10

20

30

40

50

60

Relative Humidity (%)

(a)

70

80

90

100

0

10

20

30

40

50

60

70

80

90

100

Relative Humidity (%)(b)

Figure 2 (2a) Dynamic vapor sorption measurements of kraft bleached and dissolving hardwood andsoftwood pulps. Glasswood and rockwool were also measured as reference sound absorbing materials;(2b) Moisture content measured from samples used in sound absorption measurements.
Figure 2 presents the sorption isotherms measured for bleached and dissolving hardwoods/softwood
fibres. The vapor sorption isotherms describe the relationship between relative humidity of the environment and total moisture content in wood fibres at constant temperature. Sorption isotherms of glasswool
and rockwool fibres were also measured as reference materials. It can be seen from Figure 2 that the interaction of water with synthetic fibres, glasswool and rockwool, is much lower than that of pulp fibres.
Rockwool and glasswool fibres begin to take some moisture at relative humidities above 60% and 85%,
respectively. On the other hand, moisture sorption by pulp fibres immediately begins as relative humidity
increases over 0%. Moisture uptake by pulp fibres is mainly due to the number of accessible hydroxyl
groups, however, also additional mechanisms may exercise control over water uptake (12). The greater
the degree of crystallinity of the fibres, the lower the number of accessible hydroxyl groups, which leads
to lower moisture uptake. The degree of crystallinity of cellulose is significantly higher than that ofhemicelluloses, which implies that hemicelluloses can adsorb more water than cellulose. Thus, dissolving pulp fibres take less moisture because they are more crystalline than bleached fibres as dissolving
pulp fibres contain much more celluloses and less hemicelluloses than bleached fibres.
3.3
Handsheet and fibre mechanical properties
Table 2 presents the measured mechanical properties of the handsheets and calculated fibre Youngmodulus, both in the longitudinal direction. As can be seen from the table, hemicellulose content is a
critical factor determining the mechanical properties of the handsheets. The tensile index and stiffnessof hardwoods and softwoods decrease with decrease in hemicellulose content of the fibres. The Youngmodulus of the different pulp fibres has been calculated according to Eq. (1) and they are shown in Table
2. It is concluded that bleached hardwood pulp fibres are the stiffest ones whereas dissolving pulp fibres
show the lowest stiffness. These results are in accordance with those reported in (4).

Table 2 Handsheet and calculated fibre properties.
Handsheet properties
Pulps
HWblch, M
HWdissSWblch, M
SWdiss3.4

Fibre properties

Density[Kg/m3 ]Elongation(%)

Young mod.
[Gpa]

Stiffness Ind[kNm/g]Tensile Ind[Nm/g]

Fibre Youngmod. [Gpa]

491
402
429
386

1.69
1.47
2.73
2.45

1.56
0.75
1.13
0.92

3.17
1.86
2.63
2.37

17.13
9.58
16.76
15.21

4.68
2.25
3.39
2.76

Sound absorption

3.4.1 Influence of fibre dimensions and chemical composition on sound absorption
The influence of pulp fibre dimensions, mainly fibre length and width, and chemical composition on
sound absorption has been reported in a previous study (13). The study concluded that dissolving hardwood pulp fibres provide the greatest absorption. The authors resported that further processed, shorterand thinner fibres move the first peak of the sound absorption curves towards lower frequencies. The
effect was attributed to the increase in the number of fibres needed to fill a unit volume as the dimensionsof the fibre decreases. Increasing the number of fibres per unit volume results in more tortuous paths
and surfaces for sound energy to dissipate within the materials. These results were in agreement with theresults reported in earlier studies (14).
3.4.2 Influence of moisture on sound absorption properties of wood-based pulp fibre foams
The increase in moisture content was controlled for the samples exposed at varying relative humidities
and the results are shown in Figure 2a. As can be observed, the results from Figure 2b resemble muchthose shown in Figure 2a which confirms that the exposition of materials to varying humidities was
performed correctly and that the samples reached moisture equilibrium before absorption measurements.
It is noted that DVS measurements were taken from fibres that did not go through foam-forming process,whereas the sound absorbing foam samples went through foam-forming and drying process. Foamforming may cause rearrangement of hemicelluloses in the cell wall (13), whereas drying may cause
further hornification of fibres (15), i.e., further closure of pores withing the fibres. This may explainsome of the differences found between 2a and 2b.
Figure 3 shows the sound absorption coeff. of bleached and dissolving hardwood and softwood pulp
fibres measured at the two extreme relative humidity conditions, 0% and 100%. The results show how
the sound absorption of pulp fibres improve at low-mid frequencies with increasing moisture content.
Moreover, the increase in absorption properties tend to be slightly greater for denser samples. As expected, glasswool and rockwool fibres did not show changes in their sound absorption at varying relative
humidity conditions. This is mainly due to the inherent hygrophobicity of these materials.
In an attempt to explain the influence of moisture on the sound absorption properties of wood fibres
we suggest two theories, changes in the mechanical properties of pulp fibres and structural changes offibres with increasing moisture content. Variations in relative humidity conditions result in changes in
the water content of pulps fibres which, in turn, leads to changes in the mechanical properties. A wellknown effect of moisture on the mechanical properties of pulp fibres is the decrease of the fibre modulus
with increasing moisture content, i.e., fibres become more flexible as moisture content increases (16).
The main reason why pulp fibres become more flexible with increasing moisture content is that watermolecules get into the fibre matrix and weaken the interfibrillar hydroxyl bondings (17). The increase infibre flexibility is suggested to be one of the parameters that improve the absorption properties of pulp
fibres at low-mid frequencies. This is in agreement with the results reported in (2).
Moisture uptake by wood fibres also causes structural changes in the microfibril bundles that forms
the cell wall. Two main structural changes have been suggested to occur at different moisture contents(17, 18). At low moisture content, 0% - 10%, microfibril bundles release stresses and adopt higher
degrees of crystallinity. At around 10% - 15% moisture content, water begins to dominate the space
between microfibrils and the matrix softens. As the matrix softens it can deform more easily, which

RH: 100%

1

0.8

0.8

0.6

0.6

DPHW

0.4

DPSW

3

0.4

:14 kg/m3:23 kg/m3

0.2:24 kg/m3:13 kg/m

0.2
0

0
125

Sound absorption,

RH: 0%

1

250

500

1000

1600

125

1

1

0.8

0.8

0.6

0.2

500

0.6

HW

0.4

250

1000

SW

:16 kg/m

3

0.4:13 kg/m3:24 kg/m

3

0.2:25 kg/m3

0

1600

0
125

250

500

1000

1600

125

1

1

0.8

0.8

0.6

0.6

0.4

GW

0.2

:90 kg/m

3

0

250

500

1000

0.4

RW

0.2

:20 kg/m3

1600

0
125

250

500

1000

1600

125

250

500

1000

1600

Frequency [Hz]Figure 3 Sound absorption coeff. in third-octave bands measured from bleached and dissolving hardwood and softwood pulp fibres-based foams. Glass- and rockwool were also measured as referencematerials. The results are averages of the sound absorption coeff. measured from the two sides of thesamples. Dashed and continuous lines represent denser and less dense foams, respectively. Black andmagenta colors are used to represents dry foams and foams exposed to 100 % RH, respectively. The
thickness of all the samples was 6 cm except for glasswool whose thickness was 4 cm.
leads to expands water channels between microfibrils and swelling of fibril bundles (18). This swellingof fibrils results in increasing width dimensions of pulp fibres which, in turn, modify the porous structureof pulp fibre based samples. The increase in fibre width is suggested to be a second parameter that may
influence the sound absorption properties of pulp fibres based foams. The increase in width experienced
by pulp fibres with varying moisture content will be studied in future research. Nevertheless, someauthors have already reported some results on this question (17, 19, 20). Pulp fibres expanded in widthfrom 2 - 4.5% (depending on the chemical composition of the pulp) after fibre exposure to 75% relative
humidity (19). Other authors reported increase in lateral dimensions of pulp fibres up to approx. 20%
over the range of relative humidities from 0% to 100% (20).
Pulp fibres, and wood in general, is in constant interaction with the moisture in the surrounding air,i.e., at higher relative humidities wood uptakes water and the uptaked moisture is released when thesurrounding air is dryer. This inherent property of wood is convenient to control changes in relative
humidity indoors. Additionally, wood fibres do not create problems for indoor air quality, and offer
excellent acoustic properties while reducing CO2 from the atmosphere by binding CO2 into the building
structure during the material operating life.

4.

CONCLUSIONSIn this paper, we presented studies on the different ultrastructural properties of pulp fibres that affect the sound absorption properties of wood-based pulp fibre foams. It was demonstrated that further

processed pulp fibres of smaller dimensions contribute to greater sound absorption. Moisture was also
shown to affect the sound absorption properties of pulp fibres. The absorption properties of the pulp
fibres increased at low-mid frequencies as they were exposed to higher relative humidities. This phenomenon has been attributed to two mechanisms, increasing flexibility and width of pulp fibres withincreasing moisture content. However, further research is needed to confirm these results.

ACKNOWLEDGEMENTS
The authors gratefully acknowledge support from Lumir Oy (Finland), and cooperation of Lumir personnel Marko Makkonen and Hannes Hynninen. The authors express their gratitude to Puunjalostusinsinöörit for funding part of the travel expenses of this event.

REFERENCES
1. Lipiäinen S, Kuparinen K, Sermyagina E, Vakkilainen E. Pulp and paper industry in energy transition: Towards energy-efficient and low carbon operation in Finland and Sweden. Sustainable
Production and Consumption. 2022;29:421-31.
2. Attenborough K. The influence of microstructure on propagation in porous fibrous absorbents. J
Sound Vib. 1971;16(3):419 442.
3. Page D, DH P, RS S. The elastic modulus of paper. II: The importance of fiber modulus, bonding,and fiber length. Tappi J. 1980;63(10):99-102.
4. Sixta H. Handbook of paper and board. Wiley-VCH; 2006.
5. Pöhler T, Jetsu P, Isomoisio H. Benchmarking new wood fibre–based sound absorbing material madewith a foam-forming technique. Build Acoust. 2016;23(3-4):131-43.
6. Chen C, Kuang Y, Zhu S, Burgert I, Keplinger T, Gong A, et al. Structure–property–function relationships of natural and engineered wood. Nat Rev Mater. 2020:1-25.
7. Lappalainen T, Lehmonen J. PAPER PHYSICS: Determinations of bubble size distribution of foamfibre mixture using circular hough transform. Nord Pulp Pap Res J. 2012;27(5):930-9.
8. Janson J, et al. Calculation of the polysaccharide composition of wood and pulp. Paperi ja puu.
1970;52(5):323-9.
9. Seth R, Page D. The stress-strain curve of paper. The role of fundamental research in paper making.
1981;1:421-52.
10. Niskanen K. Kraft fibers in paper–Effect of beating. In: Cellulosic Pulps, Fibres and Materials.
Elsevier; 2000. p. 249-60.
11. O’Brien FE. The control of humidity by saturated salt solutions. Journal of Scientific Instruments.
1948;25(3):73.
12. Rautkari L, Hill CA, Curling S, Jalaludin Z, Ormondroyd G. What is the role of the accessibility of wood hydroxyl groups in controlling moisture content? Journal of Materials Science.
2013;48(18):6352-6.
13. Cucharero J, Ceccherini S, Maloney T, Lokki T, Hänninen T. Sound absorption properties of woodbased pulp fibre foams. Cellulose. 2021;28(7):4267-79.
14. Arenas JP, Asdrubali F. Eco-Materials with Noise Reduction Properties. In: Martínez LMT,
Kharissova OV, Kharisov BI, editors. Handbook of Ecomaterials. Cham: Springer; 2018. p. 3031-56.
15. Lovikka VA, Khanjani P, Väisänen S, Vuorinen T, Maloney TC. Porosity of wood pulp fibers in the
wet and highly open dry state. Micropor Mesopor Mat J. 2016;234:326-35.
16. Rhim JW. Effect of moisture content on tensile properties of paper-based food packaging materials.
Food Science and Biotechnology. 2010;19(1):243-7.
17. Lindner M. Factors affecting the hygroexpansion of paper. Journal of Materials Science.
2018;53(1):1-26.
18. Paajanen A, Zitting A, Rautkari L, Ketoja JA, Penttilä PA. Nanoscale Mechanism of MoistureInduced Swelling in Wood Microfibril Bundles. Nano Letters. 2022.
19. Lee JM, Pawlak JJ, Heitmann JA. Dimensional and hygroexpansive behaviors of cellulose microfibrils (MFs) from kraft pulp-based fibers as a function of relative humidity. Holzforschung.
2012;66(8):1001-8.
20. Alava M, Niskanen K. The physics of paper. Reports on progress in physics. 2006;69(3):669.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0769

Application of sound absorber using bubble wrap
for nursery facilities
Emi TOYODA 1; Satoshi SUGIE2
1, 2

Kobayasi Institute of Physical Research, Japan

ABSTRACTIn Japan, the sound environment of nursery facilities tends to be too noisy and too reverberant due toinsufficient sound absorption properties. The current situation should be improved as soon as possible for thechildren in the hearing development. However, it is not easy to add sound absorbers to ceilings and walls ofnursery rooms that are already in operation. Therefore, we consider that the artworks made as the children’s
craft activities can be used as sound absorbers to improve the sound environment in nursery rooms. Namely,
if the sound absorbers can be made using familiar materials that nursery teachers and children make together,
it is easy to install those in the nursery rooms. In this study, we have made the sound absorber of cloths andbubble wrap and investigated the sound absorption performance. Furthermore, we installed the absorbers inan actual nursery room and conducted the field experiments of reverberation time.
Keywords: Craft activity, Reverberation time, Field experiment

1. INTRODUCTION

Several studies (1, 2) have reported the effect of sound absorption on mitigating the noisy soundenvironment of nursery facilities over the last decade. However, in Japan, there are still many nursery
facilities in which the sound environments are very noisy and reverberant due to insufficient soundabsorption. To develop a comfortable sound environment for children, it is thought that soundengineers need to inform people concerned in nursery facilities, such as nursery teachers and parents,
about the importance of sound absorption in the facilities. In addition, it is also important to installsound absorbers easily for early treatment of the noisy sound environment.
This article introduces sound absorbers that anyone can easily make using familiar materials, which
nursery teachers and children make together as a part of craft activities. Therefore, displaying theirartworks (sound absorbers) in the nursery room improves the sound environment. Namely, it is“Killing two birds with stone”. We have made the sound absorbers using cloths and bubble wrap andinvestigated the sound absorption performance. Furthermore, we measured the reverberation time
before and after the sound absorbers were installed in an actual nursery room to verify theireffectiveness.

2. OVERVIEW OF SOUND ABSORBER USING BUBBLE WRAP

We designed the lightweight sound absorber, which anyone can easily make using familiar
materials. That is because the lightweight thing is safe for children when nursery rooms are decorated
with the sound absorbers. Figure 1 shows the vertical cross-section and the photographs of the soundabsorber. The round-shaped sound absorber has a surface layer made from a cloth cover. To reduce
the weight, we made it with an internal cavity. The surface layer consists of six spindle-shaped parts
like a beach ball, as shown in Fig 1(a). These spindle-shaped parts are formed in a bag by arranging
two layers of thin cloth, and familiar porous materials, such as stuffing cotton for handcrafts, are filledin the bag, as shown in Fig.1(b). In this study, polyester wool was filled inside the spindle-shaped
1

toyoda@kobayasi-riken.or.jp

Filled withporous materials
Filled with
Bubble wrap
Diameter
×6

Vertical cross-section(a) Surface layer consistsof six spindle-shaped parts(b)
Spindle-shaped part

Figure 1 – Vertical section and photographs of the BW absorber made using cloth and bubble wrap
parts as porous material. However, the sound absorber cannot maintain a round shape because thesurface layer is flexible. So, it is necessary to fill the inside with light materials. Therefore, we usedbubble wrap (BW) as a lightweight material. It is familiar to nursery teachers and children because it
is widely used for packing products. In this article, the sound absorber will be called the BW absorber.

3. MEASUREMENT OF THE SOUND ABSORPTION PERFORMANCE
3.1 Specimens structure and experimental method
The sound absorption performance of the BW absorber is expected to depend on the diameter andthe amount of BW. Thus, we measured the sound absorption performance of six specimens of different
diameters and various BW’s weights, as shown in Table 1. The diameter of the BW absorbers was two
types. Nos.1 to 3 had an approximate diameter of 28 cm and were named Type S. Nos.4 to 6 had anapproximate diameter of 35 cm and were named Type L. Incidentally, the BW absorber is not a perfectsphere. For each diameter, the weight of BW filled inside varied in three steps: empty, 50 g, and 100 g.
The empty specimen, Nos. 1 and 4, have a prolate spherical shape like a rugby ball; however, the otherspecimens have a nearly spherical shape. In all cases, the total weight of polyester wool filled in all
six spindle-shaped parts was 90 g. Furthermore, the weight of the cloth cover was approximately 100 g
for Type S and 150 g for Type L. The total weights of each specimen were 190 to 440 g, theapproximate sum of cloth cover, polyester wool, and BW, as shown in Table 1.
The measurements of the equivalent sound absorption area per object Aobj in a reverberation room
were carried out based on JIS A 1409 (ISO 354:1985 compatible) as the sound absorption performanceof the BW absorber. The reverberation room has a volume of 513 m3 and a surface area of 382 m2 .
Twelve units of the BW absorbers were suspended at intervals of 900 mm, and at the height of 400 mm,
as shown in Fig. 2(a). This setting condition assumes that the floor corresponds to a ceiling in an
actual room. The only specimens of Type L-BW100(No. 5) were also set directly on the floor, as
shown in Fig.2(b), assuming they were mounted directly on the wall or the ceiling.

1

Table 1 – Structure of the specimen under investigation
Weight of BW
Total weight, gSpecimen
Diameter, cm
filled inside, gType S-empty
28
190

2

Type S-BW50

28

50

240

3

Type S-BW100

28

100

290

4

Type L-empty

35

-

240

5

Type L-BW100

35

100

340

6

Type L-BW200

35

200

440

No.

400 mm

900 mm(a) Suspending condition for spesimens of Nos. 1 to 6

900 mm

900 mm(b) Directly on the floor for only specimen of No.5
Figure 2 – Photographs of the BW absorbers set in the reverberation room
3.2 Experimental results
The measurement results of A obj versus the amounts of BW for Type S and Type L are shown in
Fig. 3 and Fig 4, respectively. In both types, the results of A obj improved by increasing the amount of
BW in the middle and high frequency range; moreover, the results of A obj became almost flat at
frequencies above the midrange. As comparing Figs. 3 and 4, Type L provided a higher performanceof A obj than Type S in the whole frequency region.
Figure 5 compares the measurement results of A obj under two different setting conditions when thespecimen is L-BW100(No. 5). When the BW absorbers were set directly on the floor, an increase in
A obj appeared at frequencies below 630 Hz. However, at frequencies above 1 kHz, the suspending
condition was higher in Aobj than the condition set on the floor. Those results indicate that soundabsorption performance can be improved at lower frequencies by mounting on the boundary of a room,such as a wall and a ceiling.

Equivalent sound absorption
area per object Aobj, m2

1/3 octave band center frequency, Hz
Figure 3 – Comparison of the equivalent sound absorption area per object for different amounts of BW

Equivalent sound absorption
area per object Aobj, m2

filled in Type S (Nos.1 to 3) with suspending condition

1/3 octave band center frequency, Hz
Figure 4 – Comparison of the equivalent sound absorption area per object for different amounts of BW

Equivalent sound absorption
area per object Aobj, m2

filled in Type L (Nos.4 to 6) with suspending condition

Suspending condition

1/3 octave band center frequency, Hz
Figure 5 – Comparison of the equivalent sound absorption area per object of L-BW100(No. 5) under
different setting conditions

4. Field experiment

To verify the effect of the BW absorber, we carried out the measurements of reverberation time(RT) in the actual nursery room where the BW absorbers were installed. Table 2 shows the
specifications of the surveyed nursery room. Twenty children aged four are usually cared for in thisroom; however, the values of RT were measured without children using the interrupted noise method.
Figure 6 shows the arrangement of the sound source and five microphone positions in the surveyed
nursery room.
We measured the values of RT by a survey method using the Origami impulse source (3) to estimate
the sound absorption performance of this nursery room beforehand because we needed to make therequired number of the BW absorber to reduce the values of RT adequately. From the measurement,
the value of RT before installing the BW absorber was expected to be approximately 0.7 s averaging
the measured results in the octave bands of 500 Hz and 1 kHz, and the average absorption coefficient
𝛼𝛼 was estimated as 0.17. According to the academic guidelines proposed by the Architectural Instituteof Japan (4), the recommended values averaged at 500 Hz and 1 kHz are 0.4 s and 0.25, in RT and 𝛼𝛼,
respectively. The required value of the equivalent sound absorption area A was calculated as 14.3 m2
in the surveyed nursery room to satisfy 0.25 as this recommended value of 𝛼𝛼. Therefore, for adjusting
to 14.3 m2 of the required A, we determined the required number of BW absorbers as follows.
Two types of BW absorbers, Type S-BW100(No.3) and Type L-BW100(No.6), were installed in
the room. Here, they are called Type S and Type L, respectively. The value averaging A obj at
frequencies from 400 Hz to 1.25 kHz in the 1/3 octave band was calculated from the measurement
results in section 3. The average values for Type S in the suspending condition and Type L set directlyon the floor were 0.28 and 0.39, respectively. From those results, A for Type S with 18 units installed
was 5.04 m2 (0.28×18 units) and A for Type L with 26 units installed was 10.14 m 2 (0.39×26 units).
The total A was 15.18 m2 to satisfy the room’s required A of 14.3 m2 .
The BW absorbers were installed in the nursery room, as shown in Fig.7. The units of Type S weresuspended 400 mm from the ceiling. The units of Type L were installed at 700 mm spacing on the wallnear the ceiling. Figure 8 compares the results of RT before and after the BW absorbers are installed.
The effect of the BW absorbers was particularly significant at frequencies above 500 Hz; consequently,
the value of RT decreased by more than 0.2 s after installing them. Figure 9 shows the estimatedresults of 𝛼𝛼 from the measured results of RT. The values of 𝛼𝛼 at 500 Hz and 1 kHz satisfied
approximately 0.25 of the recommended values. These results indicate that the BW absorbers
effectively improve the sound environment in nursery rooms.
Table 2 – Specifications of the surveyed nursery room
Volume (m3)131.8

Surface (m2)

178.7

Floor area (m2)

51.2

7.6 m

Corridor

Glass
Window

6.1 m
Furniture

Source position (Height:1.5 m)
8.2 m

Ceiling height:2.6 m

Microphone position (Height:1.0 m)

Figure 6 – Arrangement for the measurement of reverberation timeType SType L

Reverberation time, sFigure 7 – Installation of the BW absorbers

Octave band center frequency, Hz

Average absorption coefficient 𝛼𝛼Figure 8 – The results of reverberation time before and after the BW absorber are installed

Octave band center frequency, Hz
Figure 9 – The average absorption coefficient estimated from the result of reverberation time

5. CONCLUSIONSIn this study, we proposed the BW absorbers made using familiar materials to add easily soundabsorption in nursery facilities. The larger the diameter and the greater the amount of BW, the higher
the sound absorption performance, even at lower frequencies. The BW absorber can offer reasonable
absorptivity at frequencies above the midrange. Moreover, in an actual reverberant nursery room, theaverage sound absorption coefficient of the room could be adjusted to satisfy the recommended values
by using the BW absorbers. These results indicate that even a simple sound absorber using familiar
materials, such as the BW absorber, can improve the sound environment of nursery facilities.
It is not easy to conduct acoustical renovations while already operating nursery rooms. However,sound absorption can be easily added even in the rooms by making the sound absorber as a part ofcraft activities. Therefore, it will be helpful as one of the immediate actions for promoting a
comfortable acoustic environment in nursery facilities.

ACKNOWLEDGEMENTS

We would like to thank Nakano Uchikoshi Hoikuen, the nursery facility in Tokyo, for thecooperation to carry out our research.

REFERENCES

1. K. Kawai et al. Mitigation of noise in nursery school classrooms by sound absorption. Part 1-3. Proc.
Inter-noise 2011-2013.
2. K. Kawai et al. Overview of acoustic environment of nursery facilities in Japan -Present situation andrecent studies. Proc. Forum Acusticum 2014.
3. E. Toyoda and J. Yoshimura. Characteristics of "Origami impulse source". Proc. Inter-noise 2009.
4. Architectural Institute of Japan. AIJES-S0001-2020: Standard and Design Guidelines for Sound
Environment in School Buildings. (in Japanese)

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0895

Study on sound absorption characteristics of porous clay bricks
Kana Ikeda1; Reiji Tomiku2; Noriko Okamoto2; Toru Otsuru2; Arisa Tabaru1; Siwat Lawanwadeekul3;
1

Graduate School of Engineering, Oita University, 700 Dannoharu, Oita, 870-1192 Japan

2

Faculty of Science and Technology, Oita University, 700 Dannoharu, Oita, 870-1192 Japan

3

Faculty of Industrial Technology, Lampang Rajabhat University, Lampang 52100 Thailand

ABSTRACT
Porous clay brick（PCB）is the low-cost material under development in Thailand as one of the alternative
materials used to solve thermal and noise pollution. This paper reports focus on sound absorption coefficientsof PCBs measured by the impedance tube method, the reverberation room method, and an in-situ
measurement method using ensemble averaging technique, or EA method. First, measurements for PCB
under three mounting conditions are carried out by the impedance tube method, the condition that Oil clay
filled the gap around the circumference of the specimen (clay) showed the smallest variation of all measurements
for all samples. Next, measurements for PCBs with different shapes are carried out by the EA method andthe shape of the measurement sample and the position of the sound receiving point is investigated. Finally,
the reverberation absorption coefficient of PCBs is measured and compared with the statistical soundabsorption coefficients by the impedance tube method and EA method. The results indicated that the gaps
between samples caused by the different shapes of each sample affect the sound absorption characteristics inaddition to the inherent sound absorption characteristics of PCBs.
Keywords: Clay bricks, Sound absorption coefficient, EApu method, and statistical sound absorption coefficient

1. INTRODUCTION
To predict and control the indoor sound field, it is important to understand the sound absorption
characteristics of building materials. The characteristics are generally measured by the reverberation room
method [1, 2] and the impedance tube method [3, 4] regulated by JIS and ISO. On the other hand, the authors
have recently proposed the in-situ measurement method using the ensemble averaging technique (EA method)[5-7]. the EA method is a simple and efficient in-situ measurement method of the surface normal impedance ofmaterials at random incidence.
Also, in the history of the development of construction materials, brick has been an essential primarybuilding material because of its low cost. Numerous studies have attempted to add waste to bricks and fire themat a high temperature to produce porous clay bricks (PCBs) [8, 9]. Nonthaphong and Sakdipown [10] focusedon producing porous clay brick and the PCB uses local clay from Chiang Mai, Thailand, with charcoal added
to the brick. Siwat et al. [11, 12] also studied the production of bricks in Lampang, Thailand, intending to
produce bricks that meet the Thai industrial standard (TIS 77-2545) [13] and the optimization of PCBs was
examined by testing the physical, mechanical, and thermal properties of clay bricks that were prepared using
three different sizes of ground corncobs as additives. In addition, Siwat et al. [14, 15] applied the EA method
to understand the sound absorption characteristics of PCBs on a trial basis, and the repeatability andapplicability of the measurement in the predetermined measurement point have been presented. However, PCBs
have uneven surface and edge caused by the irregular shrinkage for each sample when it manufactures the PCBs,
and they are required to examine not only the EA method but also even other methods to evaluate thecharacteristics of PCBs.
In this study, based on the results of previous studies [14, 15], sound absorption characteristics of newly
manufactured PCBs are measured by three methods, i.e., EA method, impedance tube method, and1

v21e5002@oita-u.ac.jp,

reverberation room method, to clarify the sound absorption characteristics of PCBs. Moreover, PCBs used inthis study are manufactured by adding charcoal with a grain diameter of 2 mm to clay, mixing it with water,
forming it in a hydraulic press, firing it at 1100 °C for 12 hours, and then cooling it naturally to room
temperature. The surface of the manufactured PCB has numerous pores, the size, and quantity of which can be
adjusted by the charcoal additive, but not the position. The irregular expansion of the additive during production
causes differences in the physical properties of the PCBs.

2. MATERIALS AND METHODS
2.1

Impedance tube method
As the specimens, cylindrical PCBs with a size that enables smooth insertion of the specimen into thesample holder of the impedance tube are used. Table 1 shows the three physical properties (bulk density,
apparent porosity, and water absorption) of the four PCBs (Sample C1 to C4) measured according to ASTMC
373-88 [16].
Table 1 Physical properties of cylindrical PCBs.
Sample
C1
C2
C3
C4

Bulk density (g/cm3)
0.90
0.90
0.95
0.91

Apparent porosity (%)
42.00
39.04
40.91
39.51

Water absorption (%)
41.69
38.87
37.81
39.17

Measurements of the normal acoustics impedance were performed using an impedance tube according to
JIS 1405-2:2007 [2], and the normal incidence sound absorption coefficients were calculated. The impedance
tube (NOE AIT100) with an inner diameter of 100 mm was used. A loudspeaker radiating incoherent white
noises was placed on one side of the impedance tube. Two 1/4-inch microphones (B&K 2670 type) wereused as sensors. The transfer function between two positions were calculated. The frequency resolution of
FFT was set to 3.125 Hz and linear averaging was performed 150 times using the Hanning window.
In this measurement, the authors set the following four specimens’ mounting conditions referring to JIS
1405-2:2007 [2].
・With the gap around the circumference of the sample and without adhesion to the rear rigid wall. (non)・With the gap around the circumference of the sample and adhesion to the rear rigid wall. (tape)・Without the gap around the circumference of the sample by filling the gap with the oil clay and withoutadhesion to the rear rigid wall. (clay)
Figure 1 shows photographs of each mounting condition after being mounted on the holder.
Measurements were performed six times for each sample of each mounting condition. After eachmeasurement, the specimen was removed from the cell and reinstalled. The values were averaged in thefrequency domain of the 1/3-octave band, and the average of the six times was used for the following
comparisons.

(a) Non(b) Tape(c) Clay

Figure 1 Photographs of sample surface and cross sections of installation conditions on the impedance tube:(a) Non, (b) Tape, (c) Clay.
2.2 EApu method
Figure 2 shows a block diagram of the EApu method, which is the EA method using particle velocity
sensor (pu sensor). The pu sensor (PU-Regular, Microflown technologies) is placed at 10 mm fromthe sample surface, and the specific acoustic impedance is obtained from the measured transfer function toFigure 2 Block diagram of the measurement setup in EApu method.
calculate the sound absorption coefficient.
The three PCB shapes used in the EApu method are shown in Figure 3 (a)-(c) and their dimensions
are shown in Table 2. The cylindrical PCB used in the tube method was combined with the PCB Frame,
and its combination of the PCBs approximates the surface area of the rectangular PCB. A gap of
approximately 0.3 cm existed between the cylindrical PCB and the PCB frame.
The measurement was carried out in the irregularly shaped reverberation room with diffusers(room volume: 168 m3). To make the incidence condition closer to random, six loudspeakers radiating
incoherent pink noises were moved manually. In the measurement, a pu sensor was located at theupside of the center of the material.
Figure 4 (a)-(b) shows the two types of installation conditions of the specimen: combo 3, in which
the frame was combined with a cylindrical PCB, and eight rectangular PCBs were placed around it,
based on a previous report [15]; and rect. 9, in which only rectangular PCBs were used. Four samples
are measured in each installation condition. In each installation condition, the sound receiving points
were the center of the sample and two points 10 mm away from the center, and measurements werecarried out three times for each sound receiving point. The measurement frequency, evaluation method,
and FFT were the same as the impedance tube method.

(a) Cylindrical(b) Frame(c) Rectangular

Figure 3 PCBs using EApu method: (a) Cylindrical, (b) Frame, (c) Rectangular.
Table 2 Sample dimensions for measurement.
ShapesCylindrical
Frame
RectangularDimensions
Φ 99 ×40 mm3
190 ×280 ×40 mm3
190 ×280 ×40 mm3

Unit [mm](a) Combo 3(b) Rect. 9

Figure 4 PCBs setup and receiving points in EApu method: (a) Combo 3, (b) Rect. 9.

To clarify the relationship between the gap of each rectangular PCB for rect. 9 and the measured soundabsorption characteristics of the PCB, the sound receiving points were set and measured as shown in Figure
5 for the installation condition of rect. 9. The receiving points were set from the center of the sample to thelong side, short side, and the vertex of the sample as line A to line C, respectively, and each line has eight
points: four points from the center and four points from the gap between the rectangular PCBs for 10 mm
intervals. The receiving points are numbered RP1-8 from the center of the sample to the edge of the sample,
in that order.

Figure 5 Position of the sound receiving point of rect. 9 in the study on the effect of gap between
the rectangular PCBs.
2.3

Reverberation room method
Measurements of the reverberation absorption coefficient were performed and calculated using JIS
1409: 1998[4]. Figure 6 shows the diagram of the installation conditions of the specimen and thepositions of the sound source and sound receiving point. As the measurement samples, the PCBs of
the three shapes are used as shown in Figure 3. Since the uneven surface and edge of each specimen,
the width of each gap is different. The total size of the specimen was 9.48 m2 .
The measurements were performed in the same reverberation room as in the previous section. An
integrated impulse response method was applied to measure the reverberation time of the sound field
with/without the specimen. The number of microphone positions was six, and the number of source positions
is one: the number of microphone and loudspeaker positions is six. Arithmetic averaging of six reverberation
times at each band, which is 1/3 octave band, was performed.

(a) Location of sound receiving points and sound sources(b) Installation pattern of materials

Figure 6 Measurement settings of reverberation room method :(a) Location of sound receiving points
and sound sources, (b) Installation pattern of materials.

3. RESULTS AND DISCUSSION
3.1

Examination of the setting condition by the impedance tube and EApu method
In Figure 7, the data showed the maximum, the minimum, and the mean of the sound absorption
coefficient measured by the impedance tube and EApu method for each installation condition and all samples.
Regarding the impedance tube method, clay showed the smallest variation of six times

measurements for all mounting conditions and all samples in the frequency range above 400 Hz. The
sound absorption coefficient varied depending on the presence or absence of the gap around thecircumference of the sample, the peak of the sound absorption coefficient increases and moves to higher
frequencies under the mounting conditions where the gap was present. Since PCBs have different shapes ofthe sample due to uneven shrinkage, we consider that the gap filling with oil clay is effective. Regarding the
EApu method, the magnitudes of the variation of nine times measurements for each installation condition
were broadly similar. However, the sound absorption coefficient of combo 3, which is measured at the points
closer to the gap around the circumference of the specimen, is higher than that of rect. 9 in the frequency
range above 500 Hz.
Comparing the impedance tube and the EApu method, the absorption coefficient of clay measured
using the impedance tube method is similar to that of rect. 9 measured using the EApu method, andthat of non and tape measured using the impedance tube method are similar to that of combo 3
measured using the EApu method. However, the peak of sound absorption coefficient measured using
the impedance tube method is broadly larger than the EApu method.

0.8
0.6

1.0

Non
Tape
Clay

Absorption coefficient

Absorption coefficient

1.0

0.4
0.2
0.0
100

Frequency [Hz]

1000

0.8
0.6
0.4
0.2
0.0
100

1600

Combo 3
Rect. 9(a) Impedance tube method

Frequency [Hz]

1000

1600

(b) EApu method

Figure 7 Comparisons of sound absorption coefficients at all installation conditions and all samples: (a)impedance tube method, (b) EApu method.
Figure 8 (a) shows the sound absorption coefficients of RP1 positioned at the center and RP4 positioned
30 mm away from the center for each line shown in Figure 5. It was confirmed that the variation of themeasured values near the center of the sample was small. Figure 8 (b) shows the sound absorption coefficientsof RP5 positioned 30 mm away from the gap and RP8 positioned on the gap for each line. the soundabsorption coefficient increases throughout the frequency range from 100 Hz to 1.6 kHz as the receiving
point approached the gap. The peak of the sound absorption coefficient at RP8 for line A and line B is around
400 Hz. In contrast, it is around 800 Hz for line C. The sound absorption coefficient on the gap of eachrectangular PCB for rect. 9 is higher in this paper, but the effect is less pronounced at 100 mm or more fromthe gap, and stable measurement values can be expected near the center of the PCB.

0.8

RP1 of Line A
RP1 of Line B
RP1 of Line C

1.0

RP4 of Line A
RP4 of Line B
RP4 of Line C

Absorption coefficient

Absorption coefficient

1.0

0.6
0.4
0.2
0.0
100

Frequency [Hz](a) Near the center

1000

1600

0.8

RP5 of Line A
RP5 of Line B
RP5 of Line C

RP8 of Line A
RP8 of Line B
RP8 of Line C

0.6
0.4
0.2
0.0
100

Frequency [Hz]

1000

1600

(b) Near the gap

Figure 8 Sound absorption coefficient at each receiving point located on line A, line B, and line C: (a) Near
the center, (b) Near the gap.

3.2

Comparison of sound absorption coefficient by the three methods
Figure 9 shows the reverberant sound absorption coefficient with the statistical absorption coefficients
calculated from clay measured using the impedance tube method, rect. 9 measured at the three points near
the center, and rect. 9 measured on the gap using the EApu method. The statistical absorption coefficient canbe theoretically calculated by averaging the absorption coefficient across all incidence angles for a planewave, and it is given by [17]. The reverberant sound absorption coefficient was higher than that measured by
the impedance tube and the EApu method throughout the frequency range from 100 Hz to 3kHz. Also, thestatistical absorption coefficient measured on the gap of rectangular PCB by the EApu method was the best
approximation to the reverberant sound absorption coefficient in the frequency range above 300 Hz. From
the results of the previous chapters, it is assumed that the effect of the gap is more significant than theabsorption characteristics of the PCB itself.

Absorption coefficient

1.0
0.8
0.6
0.4

Reverberant absorption coefficient
Statistical value of clay
Statistical value of rect. 9 near the center
Statistical value of rect. 9 on the gap

0.2
0.0
100

1000
Frequency [Hz]3150

Figure 9 Reverberant absorption coefficient and the statistical absorption coefficients calculated from theimpedance tube method and EApu method using the London equation.

4. CONCLUSIONSIn this study, to clarify the sound absorption characteristics of porous clay brick (PCB), the soundabsorption coefficient at the normal incidence, the sound absorption coefficient using the ensemble
average method (EApu method), and the reverberant sound absorption coefficient were applied. The
measurements of the sound absorption coefficient of PCB are difficult to determine because PCB isnot considered to be an isotropic material and it is difficult to create a large area of material andprecisely control the shape of the material. The results show the gap of each rectangular PCB for rect.
9 caused by the different shapes of each sample affects the sound absorption characteristics in addition
to the inherent sound absorption characteristics of PCB.

ACKNOWLEDGEMENTS
This study was partly supported by JSPS KAKENHI Grant No. 19H02298. The authors would liketo thank graduate students at Oita University, for their continuous contribution to this research.

REFERENCES[1] ISO 10534-2:1998. Acoustics – Determination of sound absorption coefficient and impedance in
impedance tubes-Part 2: Transfer-function method.
[2] JIS 1405-2:2007. Determination of sound absorption coefficient and impedance in impedance tubes-Part
2: Transfer-function method.
[3] ISO 354:2003. Acoustics – Measurement of sound absorption in a reverberation room.
[4] JIS A 1409:1998. Measurement of sound absorption in a reverberation room.
[5] Takahashi Y, et al., In situ measurements of surface impedance and absorption coefficients of porous
materials using two microphones and ambient noise, Applied Acoustics, 66(7), pp. 845-865, 2005.
[6] Otsuru T, et al., Ensemble averaged surface normal impedance of material using an in-situ technique:
Preliminary study using boundary element method, J. Acoust. Soc. Am., 125(6), pp. 3784-3791, 2009.
[7] Din N. B. C, et al., Reproducibility and applicability of ensemble averaged surface normal impedance ofmaterials using an in-situ technique, Accost. Australia., 41(3), pp. 207-212, 2013.
[8] Zhang L, Production of bricks from waste materials-A review. Construction and Building Materials, 47,
pp.643-655, 2013.
[9] Bories C, et al., Development of eco-friendly porous red clay bricks using pore-forming agents: A review,
Journal of Environmental Management, 143, pp.186-196, 2014.
[10] Phonphuak N, Thiansem S, Effect of charcoal on physical and mechanical properties of fired test
briquettes, 37(2), pp.120-124, 2011.
[11] Lawanwadeekul S, Bunma M, Effect of grinding and firing temperatures on physical and mechanicalproperties of common bricks from Ban San Bun Reung Community Enterprise Group Lampang
Province, Ind Technol Lampang Rajabhat Univ J, pp.70-78, 2015.
[12] Lawanwadeekul S, et al., Production and characterization of porous insulating fired clay bricks withcorn cobs admixture, KKU Eng J, 4(S1), pp. 4-9, 2016.
[13] TIS 77-2545, Building brick Thai Industrial Standards Institute, Ministry of Industry, 2002.
[14] Lawanwadeekul S, et al., Thermal-acoustic clay brick production with added charcoal for use in
Thailand, Construction and Building Materials, 255, 119376, 2020.
[15] Lawanwadeekul S, et al., Applying the ensemble averaging method with a pressure–velocity sensor tomeasure sound absorption characteristics of porous clay bricks, Applied Acoustics, 164, 107250, 2020.
[16] ASTM C373–88, Standard test method for water absorption, bulk density, apparent density and apparent
specific gravity of fired white wares products, ASTM International, West Conshohocken, PA, 2002.
[17] London A, The determination of reverberant sound absorption coefficients from acoustic impedance
measurements, The Journal of the Acoustical Society of America, 22, pp. 263-269, 1950.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0542

A Study on the Measurement of Elevator Noise according to the
Rise of Residential Buildings
Min-Woo KANG1 and Yang-Ki OH2
1

Mokpo National University, Department of Architecture, Muan-gun, Jeollanam-do, Republic of Korea.

2

Mokpo National University, Department of Architecture, Muan-gun, Jeollanam-do, Republic of Korea.

ABSTRACTIn high-rise buildings, elevators are very important equipment. Vibration and noise generated during
elevator operation are unpleasant to residents. There is a standard for how to measure elevator noise, but it is
not established separately. ISO 16032 is included as part of construction machinery equipment. In order tocomply with international standards, Korea also enacted the Korean Industrial Standards by citing ISO 16032
as it is. However, the elevator noise measurement method proposed in this standard has a problem in that itis difficult to apply to high-rise residential buildings. The problem is particularly evident in Korea, where
there are many high-rise apartment buildings. Also, elevator noise has different frequency characteristics
from other construction equipment, and since it measures the same frequency band as other construction
equipment, it is difficult to clearly measure the characteristics of elevator noise. This study pointed out the
problems of the elevator noise measurement method suggested by the current international and domestic
industrial standards and tried to suggest alternatives to the operating conditions when measuring the elevator
noise in consideration of the need for a standard for the elevator noise measurement method.
Keywords: High-Rise Residential Building, Elevator Noise, Measurement Method

1. INTRODUCTION
Residential Buildings are becoming higher-rise with the development of construction technology.
Elevator noise in high-rise residential buildings is unpleasant to residents.(1) In particular, in Korea,
where there are many high-rise apartment dwellers, the problem of elevator noise is very serious.
However, there are currently no legal standards or regulations for elevator noise. And there are no
related standards. In previous studies(2, 3), studies were conducted to prepare standards for elevator
noise, but there is currently no standard for elevator noise. Research on elevator noise has been mainly
focused on methods to identify and reduce the cause of elevator noise(4, 5). However, if there is no
accurate measurement method for both legal standards and reduction measures for elevator noise,reliability of it will not be secured. In this study, we tried to study the accurate measurement methodof elevator noise. The problem of the application of high-rise residential buildings of the international
standard ISO 16032[2004 Acoustics-Measurement of Sound Pressure Level from Service Equipment
in Buildings-Engineering Method](6, 7), which mentions the elevator noise measurement method, wasidentified. Among the various items for measurement methods, operating conditions were studied. It
was intended to suggest alternatives for operating conditions that can be effectively applied in high rise residential buildings and to verify them through experiments.

1

drminuby@naver.com

2

oh@mokpo.ac.kr

2. PREVIOUS RESEARCH AND RESEARCH QUESTIONS
2.1 Previous researchPrior to this study, a previous study was performed on the elevator noise measurement method.
First, in the experiment of the measurement and evaluation method study(8) through the correlation
analysis of elevator noise and vibration measurement, the problem of operating conditions whenmeasuring elevator noise was found. The most important content of the operating conditions presented
by ISO 16032 is "Stop the elevator on each floor". Under these operating conditions, occupants cannot
use the elevator during the measurement time. In addition, the measurement time is very long, making
it difficult to measure. Because the measurement is difficult, repeated re-measurements may cause
problems with the elevator machine. In order to clearly understand the problems of these measurement
methods, current standards, measurement methods, and problems arising from measurement methods
were studied(9). In addition, the noise and vibration characteristics of the rope-type elevator usedmost often in high-rise residential buildings in Korea were investigated in more detail(10). Recently,
with respect to the elevator noise measurement method suggested by the current standard, research is
being conducted to identify problems and suggest alternatives for each of the four items: operating
conditions, measurement frequency band, microphone location, and evaluation unit.(11) However,previous studies(11) have limitations in identifying problems and suggesting alternatives. Specificalternatives should be presented for each item through more in -depth research. In this study, theproblem was closely identified by focusing on the operating conditions, and the feasibility of thealternatives suggested in previous studies was analyzed and verified through field experiments.
2.2 Problems of Standard Operating Conditions
We tried to confirm the problem through on-site verification whether the elevator operating
conditions presented in the current standards are appropriate for high-rise residential buildings. The
measurement site is Apartment E located in Busan. Measurements were carried out in 2 buildings, a
total of 9 households. Measurements were made on the uppermost layer, the middle layer, and thelowermost layer, respectively. All are bedrooms, which are the spaces closest to the elevator
passageway. The number of passengers was limited to one person required to operate the elevator. The
location of the microphone in the household is 4 points including the center point (center 1 + corner3).

Figure 1 – Measurement of in Household E Apartment Houses
The measurement results are briefly shown in Table 1. Problems can be summarized into three
categories.
a) It takes a long time to measure (average 800 seconds = about 13 minutes).
b) It is greatly affected by external noise during a long measurement time (various external noise+ especially traffic noise)c) The deviation of the experimental results of the equivalent noise level and the maximum soundpressure level due to external noise is large. (low 7dBA to high 25dBA)
As the measurement time increases, the measurement becomes more inaccurate due t o external
noise, and in particular, the ability to discriminate against elevator noise is greatly reduced.

Table 1 – Field Measurement Results According to ISO 16032
HouseholdOperate

Time

LAeq

LAmax

Different

NumberMethod

(s)

dB(A)

dB(A)

Value

201-2602

818

20.6

35.0

14.4

201-1403

806

22.8

37.9

15.1

201-102

803

20.8

41.3

20.5

201-2605

791

22.1

47.1

25

795

19.3

31.8

12.5

201-205

762

20.5

35.6

15.1

211-2708

785

22.2

29.4

7.2

211-703

857

15.9

26.6

10.7

211-105

823

18.0

28.9

10.9

201-1505

ISO 16032

3. RESEARCH HYPOTHESIS
Three important factors to solve the problem of operating conditions are summarized.
1) The measurement time should be shortened.
2) It should be possible to measure all the noise generated during operation of the eleva tor (start,
operation, stop, door opening and closing sound).
3) In particular, if 1) is satisfied, all b) and c) summarized in the problem can be solved.
An important factor for solving such a problem and the validity of the operating conditions
suggested in the previous study (11) were verified through experiments and correlation analysis.
The operating conditions are as follows.
1- The number of people on the elevator is limited to the minimum number of people required tooperate the elevator.
2- Move 10 floors based on the stop (from the stop until the door is opened) from the measured floor.
3- In the case of the top floor, start from 10 floors below and then go up and stop at the measurement
floor.
4- In the case of the middle floor, depending on the experimental conditions (limited number of floors),
select between moving up and down, and after moving 10 floors, the measurement floor stops.
5- In the case of the lowest floor, depart from the 10th floor, then descend, and stop at the measurement
floor.
In other cases, if it is difficult to secure 10 floors (eg, an apartment with 10 floors or less or a middle
floor of an apartment with 18 floors or less), select the longest operating section based on the measured
floor. Measured on the 1st to 7th floors, if measured on the middle floor (9th floor) of an apartment
on the 18th floor or less, the 1st to 9th floors are measured)

4. MEASUREMENTS AND VALIDATION
4.1 Problem Improvement Verification
In order to solve the three problems (a, b, c) presented as problems in Section 2-2, field experiments
and verification were conducted. The experiment was conducted at the same site where the problem
was identified, and the results are shown in Table 2 below.
The time that was discussed as the most important point was reduced to less than one minute. The
average of the difference between the equivalent noise level and the maximum sound pressure levelof ISO 16032 was 14.6 dB(A), and the average difference between the equivalent noise level and the
maximum sound pressure level of the improvement method was 7.6 dB(A). The error between theequivalent noise level and the maximum sound pressure level was also significantly reduced. It can

be said that it is a verification result of an alternative that can reduce the effect of external noise
generated during the long measurement time of 800 seconds.
Table 2 – Results of Alternative Problem-Solving ExperimentHouseholdOperate

Time

LAeq

LAmax

Different

NumberMethod

(s)

dB(A)

dB(A)

Value

BGN

10

17.0

20.3

ISO 16032

818

20.6

35.0

14.4

16F to 26F

61

19.9

28.0

8.1

ISO 16032

806

22.8

37.9

15.1

4F to 14F

44

21.3

26.3

5

24F to 14F

40

19.9

25.6

5.7

ISO 16032

803

20.8

41.3

20.5

11F to 1F

57

18.6

24.1

5.5

ISO 16032

791

22.1

47.1

25

16F to 26F

54

22.6

41.6

19

ISO 16032

795

19.3

31.8

12.5

5F to 15F

46

18.7

21.5

2.8

25F to 15F

49

20.3

35.2

14.9

ISO 16032

762

20.5

35.6

15.1

12F to 2F

58

17.5

22.8

5.3

ISO 16032

785

22.2

29.4

7.2

17 to 27F

41

22.9

26.2

3.3

ISO 16032

857

15.9

26.6

10.7

17F to 7F

53

16.3

26.8

10.5

ISO 16032

823

18.0

28.9

10.9

11F to 1F

50

17.2

21.4

4.2

201-2602

201-1403

201-102201-2605

201-1505

201-205
211-2708
211-703211-105

4.2 Validation of Alternatives
It was held at E-Apartment in Gyeonggi-do. The experimental method was carried out under thesame conditions as in Chapter 3-2.

Figure 2 – Floor Plan and Measurements in E Apartment Houses
The figure 3 shows the Pearson R 2 values and regression curves of 1-2, 1-3, 1-4, and 1-5. It
shows a high egg-squared value of 0.87 or more. In view of these results, the newly proposed
operating conditions effectively reduced the measurement time. In particular, it has been verified

that the operating conditions are very similar to the measured values of the current standard and at
the same time minimize the influence of external noise.
Table 3 – Alternative Validation Measurements and Correlation Analysis
Measurement
NumberReceive Floor

OperateRunning Time

Correlation

Conditions(s)

Coefficient

Pearson R2

1

25F

ISO 16032

624

2

25F

15F to 25F

31

0.93

0.87

3F to 13F

27

0.98

0.88

23F to 13F

27

0.98

0.80

12F to 2F

28

0.93

0.86

3
4
5

13F
2F

Figure 3 – Pearson R 2 and Regression Curves

5. CONCLUSIONS AND FURTHER RESEARCH
Among the elevator noise measurement methods suggested by the current annex in standard, ISO
16032, the operating conditions are difficult to apply to high-rise residential buildings. To solve theproblem, a new operating condition was proposed. In the first verification experiment, the result of
minimizing the influence from external noise was obtained through time reduction. Through thesecondary verification experiment, the experimental results of the ISO 16032 operating condition andthe proposed operating condition showed a very high correlation coefficient of 0.95 on average as aresult of correlation analysis. As a result of this study, the operating conditions of the elevator noise
measurement methods presented in the current ISO 16032 clearly nee d to be improved for high-rise
residential buildings, and as an alternative, the validity of the new operating conditions was verified
through field experiments and analysis. In the future study, additional research will be conducted toverify the measurement frequency band, microphone position, and 4 improvement measures whenmeasuring elevator noise including operating conditions suggested in the previous study (11). Throughadditional experiments and validation of the four alternatives, the elevator, whi ch is included as one
equipment in ISO 16032, is determined as an important noise source for high -rise residential buildings.

and In order to cope with this, research to propose a new standard of elevator noise measurement
method will be needed.

ACKNOWLEDGEMENTS
1. This research was supported by Basic Science Research Program through the National
Research Foundation of Korea(NRF) funded by the Ministry of Education (NRF2022R1I1A1A01072221)
2. This research was supported by Basic Science Research Program through the National
Research Foundation of Korea(NRF) funded by the Ministry of Education (NRF2020R1A2C1015162)

REFERENCES
1. M. W. Kang and Y. K. Oh, “A survey on the response of apartment house resident on elevator noise” (inKorean), The Regional Association of Architectural Institute of Korea, 19, 181-188 (2017).
2. A. Y. Jung, K. W. Kim, H. K. Shin, and K. S. Yang, “Creteria and characteristics of elevator noise inapartment,” Appl. Mech. Mater. 873, 231-236 (2017).
3. H. K. Shin and K. Y. Kim, “Analysis of subjective responses to elevator noise in apartment houses” (inKorean), Trans. Korean Soc. Noise Vib. Eng. 28, 236- 242 (2018).
4. H. S. Kim, H. G. Kim, M. J. Kim, and Y. I. Oh, “Reduction methods of the elevator-operating noise inapartment housings” (in Korean), Proc. KSNVE. 619-626 (1994).
5. E. S. Jeon and B. H. Cho, “The countermeasure which reduce the noise and vibration of the building
elevator,” Journal of the Korean Digital Architecture Interior Association. 2005, 5, 36-42. ISSN 1738-0790.
6. ISO 16032, 2004 Acoustics—Measurement of Sound Pressure Level from Service Equipment in
Buildings—Engineering Method, 2004. (Note: under version)
7. KS F ISO 16032, 2015 Measurement of Sound Pressure Level from Service Equipment in Buildings—
Engineering Method, 2015.
8. M. W. Kang., M. J. Song, and Y. K. Oh, “Evaluation of elevator noise level of apartment houses throughvibration measurement” (in Korean), JKIAEBS. 12, 641-6483 (2018).
9. M. W. Kang, Y. K. Jang, and Y. K. Oh, “Analysis of noise level and measurement method for elevator inapartment houses” (in Korean), JKIAEBS. 13, 491- 502 (2019).
10. M. W. Kang and Y. K. Oh, “A study on the characteristics and actual conditions of operation noise andvibration of rope elevator in high-rise apartment,” (in Korean), J. Acoust. Soc. Kr. 40, 84-91 (2021).
11. M. W. Kang and Y. K. Oh, “Validity of elevator noise measurement method in international standards onhigh- rise residential buildings,” Sustainability 13, 9806 (2021).

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0327

Relationships between sound pressure level, typicalphysiological parameters and perceptions of the elderly
residents in aged care facilities in northeast China
Jingyi Mu1, Jian Kang2
1

School of Architecture, Key Laboratory of Cold Region Urban and Rural Human Settlement

Environment Science and Technology, Ministry of Industry and Information Technology, Harbin
Institute of Technology
2Institute for Environmental Design and Engineering, The Bartlett, University College London, London
WC1H0NN, UK

ABSTRACT
Residential aged care facilities are places where the elderly conduct their daily activities, anddifferent functional spaces result in various acoustic environments, and the role of sound quality is
being increasingly recognized in the elderly’s well-being. A series of surveys were conducted in 15
residential aged care facilities in northeast China, where the elderly’s perception and physiologicalparameters were measured, to examine the relationships among the sound pressure level (SPL), theobjective physiological indicators and the subjective evaluation of the elderly. The results revealed
the influence of SPL on the elderly with different physical functions and had different degrees ofcorrelation with the elderly’s comfort votes. It is shown that the elderly with visual impairment havea higher demand for the acoustic environment. The elderly have a higher comfort value of theacoustic environment of the activity room. However, the fitting analysis between the comfort value
and the SPL shows that 48dB is the critical value for the elderly to vote the comfort level of the
bedroom acoustic environment, while the critical values of activity room, restaurant andrehabilitation room are 52 dB, 55 dB and 50dB respectively.
Keywords: Residential aged care facilities, Acoustic environment, Acoustic comfort level,
Physiological parameters.

1. Introduction
With the aging of the China’s population, research related to the living environment of
the elderly has attracted much attention. One particular aspect of the living environment, theacoustic environment, is especially relevant, since it influences resident’s experience andplaces such as residential care facilities, nursing homes, or hospitals are often occupied byfragile groups: people with disabilities or the elderly(1). The acoustic environment canseriously affect the health of the elderly (2,3,4). Too much harmful noise may harm theirhealth; in particular, it may prevent elderly people with hearing loss in residential aged carefacilities (RACFs) from functioning properly ( 5 ). Some studies have pointed out that
long-term exposure to sounds above 65 dB (A) can cause serious health problems, such as
sleep disorders, hearing loss, tinnitus, hypertension, and cardiovascular disease ( 6 , 7 ).
According to Du (8) the elderly have a higher tolerance for sound compared to younger people,
but they are also more sensitive to it, since it can interfere with speech communication.
China is one of the countries with the largest aging population and the fastest growing
aging rate in the world. With the increasingly serious aging of society, the number of visual
impairment in the elderly population continues to increase. By 2018, China's visually
impaired and hearing impaired population were 4.1 million and 17 million respectively；andthe number of visually impaired and hearing impaired people will continue to increase . The
research of Alma et al. Shows that the elderly with visual and hearing impairments areaffected by the decline or even loss of their visual and auditory perception, visual and auditory
information recognition abilities, and their physical coordination, movement persistence,
thinking and reaction abilities are also affected (9). Accidents such as slipping and tripping
caused by vision and hearing impairment seriously endanger the life safety of the elderly. At
the level of cognitive impairment, due to the deepening of cognitive aging, the acceptanceability and cognitive ability of the elderly, especially those with visual impairment, havesignificantly decreased. At the level of psychological disorder, the elderly with visual andhearing impairment not only face the obstacles in life, but also bear the psychological andmental pressure caused by the occlusion of the visual and auditory systems, and are more
likely to produce negative psychological emotions such as self-isolation, sensitive anxiety,fear and depression, which seriously endangers the mental health of the elderly. As a social
vulnerable group, a considerable number of the visually impaired and hear ing impaired
elderly have been neglected for a long time.
Due to the differences in physiological characteristics between the visually impaired
elderly，hearing impaired elderly and the ordinary elderly, these three groups of older people
have different perception on their living environment. There is need to explore theRelationships between sound pressure level, typical physiological parameters and perceptionsof the elderly residents in aged care facilities.

2. Method
2.1 Sites
The field surveys were conducted in Three RECFs in Harbin, the capital cities of
Heilongjiang provinces. Harbin has mid-temperate continental monsoon climates. The annual
average temperature in Harbin is 4.5◦C, the average temperature in January in winter isapproximately −19◦C, and the average temperature in July in summer is approximately 23◦C.
The details of these Three RECFs are shown in Table 1.
Table 1- Details of the surveyed residential care facilities.
Name

VolumeNumber of

Year

of

Reconstruction

beds

construction(Y/N)

Ownership

Price range

Number of(RMB/Month)participants

XJ

6250

200

2017

N

Private2000–7000

43

HQFL

8800

260

2004

Y

Public

1999–3199

32

JJS

10000

300

2016

N

Private2500–3200

37

2.2 Participants
The participants in this questionnaire survey were randomly selected from RACFs inseveral areas and comprised 112 people aged 60 and above. These participants were all theelderly in good physical condition who could answer questions independently. Among three
the RACFs surveyed, the number of female participants was almost equal to that of maleparticipants; (54 male and 58 female participants). The age of the participants ranged from 60
to 90. The demographic characteristics of the questionnaire survey participants are presented
in Table 2.
Table 2-Demographics of the participants in the questionnaire survey.
Social characteristics

Classification

Number

Percentage (%)

Gender

Male

54

48.2

Female5851.8

Normal49

43.8

Hearing impairment

34

30.3

Visual impairment

29

25.9

Physical condition

2.3 Hearing and vision level measurement
The hearing thresholds (average of thresholds at 500, 1000, 2000, 4000, and 8000 Hz) of
the participants were first determined by standard pure-tone audiometry with a
Grason-Stadler GSI-61 Clinical Audiometer and Sennheiser HD-600 headphones. The
measurment was performed by an audiologist in a soundproof room and participants were
instructed not to wear hearing aids during the test. The degree of hearing loss was defined as
the hearing threshold in the better ear of the participant. Visual acuity measurement was
conducted according to the group standard of Chinese Geriatrics Society - Specification forassessment of visual function decline for older audit.
2.4 Typical physiological parameters measurements
Heart rate and blood pressure were chosen as typical physiological parameters because
they are significant indicators of cardiovascular disease and have been repeatedly measured toestablish an association between environmental noise and cardiovascular diseases ( 10 )Continuous recordings of the heart rate were obtained with a high accuracy heart rate monitor(Haier YK-80C) placed on the right index finger and expressed as beats per minute. The
systolic and diastolic blood pressure were measured with a certified wrist blood pres suremonitor (AVITA BPM15S) and placed on the left wrist. The measured data were stored byusing the Biopac Physio meter MP100 at 1000 Hz and processed with AcqKnowledge5.1 on acomputer (11).
The participants were exposed to sound sources while simultaneously measuring theirheart rate and blood pressure. Sounds common in RACFs for older adults as described inliterature were selected for this experiment. Generally, music, activity sounds, speech sounds,machine sound and traffic noise have been reported as most common. For the sound source,music, we downloaded a piano song from the Internet (Audioset) named: “Soothing andPeaceful Melody”. The other six sounds were obtained as described below in “soundmaterials”. All the sound sources were calibrated to duration of 4 min to observe the impact
on typical physiological parameters over a longer period of time.
2.5 Questionnaire
The questionnaire focused on perception of different sounds. During the survey,
participants could stay in the survey room for at least 15 min, after which they wereinterviewed through a one-on-one question-and-answer method and the data were collected.
The participants completed the survey within 10 to 15 min (12). The survey used the 7- point
Likert scales (13). After the questionnaire survey, the acoustic environment of the rooms thatwere investigated was measured.

3. Results
3.1 Relationship between sound pressure level and perception
Some researchers have noted that studies on auditory comfort depend on listenerperceptions of the overall acoustic environment. A few suggestions based on these results
have been made for future improvements to RACFs. To achieve these goals, models using
curved fits were adopted to determine the correlation between sound pressure level andperception among three groups of the elderly.
The curve fit results of the perception on acoustic environment have a moderate degree of
fit and better reflected the relationship between the sound pressure level and the perception(Figure 1). The relationship between the SPL and perception of different types of rooms
shows different trends with various elder people groups. The curve relationship between the
SPL in the bedroom’s perception was good, with the R 2 values of the sound pressure level andperception exceeding 0.5 at 0.575, 0.582 and 0.548 respectively. The curve relationshipbetween activity room’s SPL and perception was poor, especially in group of normal older
people (R 2 = 0.364) and the elder with visual impairment (R2 = 0.378). In the restaurant, theelderly with visual impairment and hearing impairment have better degree of fit (R2 = 0.548
and R2 = 0.637, respectively). The elderly with visual impairment have better fitting resultthan the other groups of older people in rehabilitation room, which R2 = 0.612.
It is shown that the elderly with visual impairment have a higher demand for the acoustic
environment. The elderly have a higher comfort evaluation value of the acoustic environmentof the activity room. However, the fitting analysis between the perception and the SPL showsthat 48dB is the critical value for the elderly to vote the comfort level of the bedroom acousti cenvironment, while the critical values of activity room, restaurant and rehabilitation room are
52 dB, 55 dB and 50dB respectively. In bedroom, the highest perception on the soundpressure level of the elderly with hearing impairment is 50 dB, while the critical values for thenormal group of older people is 47dB；It should be noted that the critical values of SPL of theelderly with hearing impairment is generally lower than that of the elderly w ith visual
impairment. In the activity room, the restaurant and the rehabilitation room, the SPL
corresponding to the highest perception of the elderly with hearing impairment is 48dB, 52 dB
and 50 dB respectively

Figure 1-Fitting results for sound pressure level and perception
3.2 Relationship between sound and typical physiological parameters
To evaluate the changes in typical physiological parameters over time, the mean changesof the heart rate and blood pressure were calculated following exposure to different sounds
ranging from 30 s to 500 s. The results in Figure 2-4 show, in general, evident fluctuations in
the physiological parameters. After exposure to each different sound, the heart rate firstdeclines during the initial 90 s. statistically significant differences were found with ANOVA
in all 5 different types of acoustic stimuli across the elderly with different groups of theelderly. The most significant results were seen in music (F=11.240, p<0.01), speech sound(F=13.672, p<0.01). In the group of the elderly with visual impairment, machine sound(mean=89%, SD=3.413) is associated with fewer fluctuations in heart rate and bloodpressure in comparison to music (mean=92%, SD=4.064) and activity noise (mean=93%,
SD=3.857). However, in comparison with the response to music (mean=92%, SD=2.007) inthe hearing impairment group, there was a stronger decrease in heart rate after 350 s of
exposure to traffic sound (mean=96%, SD=1.412) and significant decline in blood pressure
after first initial 50s of exposure to speech sound.

(a). Heart rate(b). Systolic blood pressure

Figure 2-Physiological responses to sounds over time in the group of normal older people.

(a). Heart rate(b). Systolic blood pressure

Figure 3-Physiological responses to sounds over time in the older people with hearing impairment(a). Heart rate(b). Systolic blood pressure

Figure 4- Physiological responses to sounds over time in the older people of visual impairment

4. Conclusions
The residents of three facilities from Harbin in northeast China were invited to participate
in this study. The elderly with different physical conditions (normal group, older people invisual impairment and older people in hearing impairment) have different perception on the
acoustic environment of the RACFs. The present study also measured and analyzed therelationship between different sound and typical physiological parameters (heart rate andblood pressure) and the perception of the elderly with different physical conditions. In general,
exposure to different sound resulted in fluctuations and inconsistent trends in heart rate andblood pressure.
The elderly with visual impairment have a higher demand for the acoustic environment.
The elderly have a higher comfort value of the acoustic environment of the activity room.
However, the fitting analysis between the comfort value and the SPL shows that 48dB is thecritical value for the elderly to vote the comfort level of the bedroom acoustic environment,
while the critical values of activity room, restaurant and rehabilitation room are 52 dB, 55 dB
and 50dB respectively.
These results can provide data-based support as a reference for acoustic environment
research on the elderly with different physical conditions in RACFs. In addition, this study
also explored the correlation between sound pressure level, typical physiological parametersand perceptions of the elderly residents, which helped maintain the accuracy of perception.
The typical physiological parameters have found to be inconsistent and fluctuating, indicating
to a complex interaction between sound source and physiological health.

REFERENCES
1 Aletta, F., Botteldooren, D., Thomas, P., Vander Mynsbrugge, T., De Vriendt, P., Van de Velde,D., & Devos, P. (2017). Monitoring sound levels and soundscape quality in the living rooms ofnursing homes: a case study in Flanders (Belgium). Applied Sciences, 7(9), 874.
2 Peris, E., & Fenech, B. (2020). Associations and effect modification between transportationnoise, self-reported response to noise and the wider determinants of health: A narrativesynthesis of the literature. Science of The Total Environment, 141040.
3 Devos, P., Aletta, F., Thomas, P., Petrovic, M., Vander Mynsbrugge, T., Van de Velde, D., ... &Botteldooren, D. (2019). Designing supportive soundscapes for nursing home residents withdementia. International journal of environmental research and public health, 16(24), 4904.
4 Xie, H., Zhong, B., & Liu, C. (2020). Sound environment quality in nursing units in Chinese
nursing homes: A pilot study. Building Acoustics, 27(4), 283-298.
5 Wang, L., & Kang, J. (2020). Acoustic demands and influencing factors in facilities for theelderly. Applied Acoustics, 170, 107470.
6 Kerns, E., Masterson, E. A., Themann, C. L., & Calvert, G. M. (2018). Cardiovascularconditions, hearing difficulty, and occupational noise exposure within US industries andoccupations. American journal of industrial medicine, 61(6), 477-491.
7 Janus, S. I., Kosters, J., van den Bosch, K. A., Andringa, T. C., Zuidema, S. U., & Luijendijk, H.
J. (2020). Sounds in nursing homes and their effect on health in dementia: a systematic review.
International Psychogeriatrics, 1-18.
8 Du, X. (2020). Investigation of indoor environment comfort in large high-speed railway stationsin Northern China. Indoor and Built Environment, 29(1), 54-66.
9 Alma M A, Van der Mei S F, Feitsma W N, et al. Loneliness and Self-Management Abilities in
The Visually Impaired Elderly[J]. Journal of Aging and Health, 2011, 23(5): 843-861.
10 Van Kempen, E., Casas, M., Pershagen, G., & Foraster, M. (2018). WHO environmental noise
guidelines for the European region: a systematic review on environmental noise andcardiovascular and metabolic effects: a summary. International journal of environmental
research and public health, 15(2), 379.
11 Kraus, U., Schneider, A., Breitner, S., Hampel, R., Rückerl, R., Pitz, M., ... & Peters, A. (2013).
Individual daytime noise exposure during routine activities and heart rate variability in adults:
a repeated measures study. Environmental health perspectives, 121(5), 607-612.
12 Thille, P.; Friedman, M.; Setchell, J. Weight-related stigma and health policy. CMAJ 2017,
189, E223-E224.
13 Dal Palù, D.; Buiatti, E.; Puglisi, G.E.; Houix, O.; Susini, P.; De Giorgi, C.; Astolfi, A. The useof semantic differential scales in listening tests: A comparison between context and laboratory
test conditions for the rolling sounds of office chairs. Applied Acoustics 2017, 127, 270-283.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022, in Gyeongju, Korea
Extended abstractABS-0576

Classification Scheme and Regulation of Rubber Ball Impact Sound in Korea
Jeongho JEONG1
1

Fire Insurers Laboratories of Korea, Korea

ABSTRACTThe Rubber ball was standardized firstly in Japan and Korea to measure the low-frequency floor impact
sound insulation performance of housings. Then, the floor impact sound insulation measurement method wasstandardized in ISO standards after 2010. Recently, the survey method using the rubber ball was standardized
in ISO 10052:2021 and the method to calculate the single number quantity of the rubber ball impact soundwas standardized in ISO 717-2. In addition, ISO/TS 19488 on the classification scheme of dwelling was also
published. However, a classification scheme for the rubber ball impact sound was not included in ISO/TS
19488. In order to propose the classification scheme of the rubber ball impact sound, various previous
subjective experiments of the rubber ball impact sound need to be reviewed and integrated with the rubberball impact sound isolation performance of real apartment buildings. In this study, several previous studies
on the rubber ball impact sound were reviewed and compared with the rubber ball impact sound isolation
measurement results which were conducted in Korea. Also, recently revised building regulation in Korea on
floor impact sound which is based on the in-situ measurement results will be introduced.
Keywords: Floor impact sound, Heavy-weight impact sound, Rubber ball, Classification scheme

1. INTRODUCTION
Floor impact sound is an important factor in the selection of apartment buildings, and the intereston floor impact isolation performance is increasing. The actual impact sound generated in theapartment house has a heavy-weight impact sound characteristic in the low frequency band. Since theearly 2000s, rubber ball impact source had been standardized in Japan and Korea to measure andevaluate the heavy-weight impact sound isolation performance. The rubber ball impact source canmeasure and evaluate the actual heavy-weight impact sound isolation performance by generating an
impact sound similar to that of a real child running and jumping. The Rubber ball was standardized
firstly in Japan and Korea to measure the low-frequency floor impact sound insulation performanceof housings. Then, the floor impact sound insulation measurement method was standardized in ISO
16283 standards after 2010. Recently, the survey method using the rubber ball was standardized in
ISO 10052 and the method to calculate the single number quantity of the rubber ball impact soundwas standardized in ISO 717-2:2020. In addition, ISO/TS 19488 on the classification scheme ofdwelling was also published.
However, a classification scheme for the rubber ball impact sound was not in cluded in ISO/TS
19488. In order to propose the classification scheme of the rubber ball impact sound, various previous
subjective experiments of the rubber ball impact sound need to be reviewed and integrated with therubber ball impact sound isolation performance of real apartment buildings. In this study, several
previous studies [1-6] on the rubber ball impact sound were reviewed and compared with the rubberball impact sound isolation measurement results in field condition which were conducted in Korea.

2. CLASSIFICATION SCHEME OF RUBBER BALL IMPACT SOUND
In order to propose a rubber ball impact sound classification scheme, it is necessary tocomprehensively consider subjective responses to various rubber ball impact sounds and the actual
condition of the apartment floor impact sound isolation performance. As a result of a study on thesubjective response to the impact sound of a rubber ball, Jeon et.al (1) suggested L A,Fmax 52 dB, 53 dB,
and 56 dB as the third class out of 5 class systems according to the subject's noise sensitivity. Jeong1

jhjeong92@gmail.com

(2) performed subjective experiments for classification based on the classification scheme of ISO/TS
19488, and compared the experimental results by varying the background noise level and assigning
the subject a task such as an Internet search. The rubber ball impact sound level corresponding toClass D, which corresponds to the performance of a new apartment building, was 49.6 dB, 52.6 dB,
and 54.5 dB for LiA,Fmax . The level evaluated as Class D increased according to background noise andtask assignment.
As a result of converting satisfaction based on the results of the subjective evaluation for the impact
sound of the rubber ball performed in an environment with low background noise (3,4), the level ofthe impact sound from the rubber ball was satisfied by 50% of the subjects was about 45 dB. In thecase of Japan, the Architectural Institute of Japan suggested the recommended requirement for the
impact sound of a rubber ball, and it was composed of three grades at 5 dB intervals based on thelowest level of 50 dB in LiA,Fmax . As a result of the JND hearing test for rubber ball impact sound ( 5),more than 2/3 of the subjects distinguished 4 dB level difference and suggested that the 4 dB wasappropriate for level difference between classes.
As a result of a survey on the performance of rubber ball impact sound isolation performance for
Korean apartment buildings, it was found that the previously (before 2010) built apartment buildings
were at the level of 54 dB to 66 dB, and those built between 2010 and 2015 were at the level of 52 dB
to 58 dB. The rubber ball impact sound isolation performance of Korean apartment buildings whichwere constructed with a load-bearing wall system is showing a trend of gradually improving. Basedon the previous subjective studies and the results of the apartment building performance survey, therubber ball impact sound evaluation grades were organized. The grades in Table 1 can be impr ovedby reviewing and discussing them based on a survey of member states' actual conditions wheninternational standardization proceeds in the future.
Table 1 Proposition of classification scheme for the rubber impact sound
Class

A

B

C

D

E

F

Rubber ball
impactsound level

LiA,Fmax ≤42

LiA,Fmax ≤46

L iA,Fmax ≤50

LiA,Fmax ≤54

LiA,Fmax ≤58

LiA,Fmax ≤62

In 2022, the Korean government improved the system related to floor impact sound in apartmentbuildings. The main contents are that the existing KS-based measurement and evaluation system ischanged to ISO-based rubber ball impact sound, and after the construction of the apartment house, 2%
is randomly sampled and measured, and then the evaluation result is disclosed. Accordingly, Korean
construction companies are making efforts to improve the floor structure and resilient materials toimprove the low-frequency impact sound isolation performance of apartment buildings. In addition,interest in on-site quality control measures to ensure uniform blocking performance is increasing. For
this purpose, it is expected that the survey method of ISO 10052 :2021 will be usefully utilized in thefield.

REFERENCES
1. J. Y. Jeon, J. Y. Hong, S. M. Kim, P. J. Lee, Classification of heavy-weight floor impact sounds in multidweling houses using an equal-appearing interval scale, Building and Environment, 2015, 94(2), pp. 821828.
2. J. H. Jeong, Background Noise, Noise Sensitivity, and Attitudes towards Neighbours, and a Subjective
Experiment Using a Rubber Ball Impact Sound, IJERPH, 2021, 18 (14), 7569.
3. J. H. Jeong, Y. H. Kim, J. K. Ryu, J. H. Kim, Single number quantity of heavy & soft impact sound, Procof INTER-NOISE 2017; 27-30 August 2017; Hong Kong, China 1996.
4. J. H. Jeong, Y. H. Kim, J. K. Ryu, J. H. Kim, Classification criteria of heavy/soft impact sound, Euronoise
2018; 27-31 May 2018, Crete Greece 2018.
5. J. H. Jeong, Just Noticeable Difference of Rubber Ball Impact Sound, Trans. Korean Soc. Noise Vib. Eng.,
2021, 31 (3), pp. 308-318.
6. J.H. Jeong, Low-frequency impact sound pressure level characteristics with three standard impact sourcesin Korean reinforced concrete structured apartment buildings, J. Phys.:Conf.Ser.1075(2018) 012065.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0660

Towards new acoustic policies in the ‘new normal’ of the Covid-19
pandemic
Ayça ŞENTOP DÜMEN1,2; Konca ŞAHER1,3; Selma KURRA4
1

Turkish Acoustical Society, Turkey
2

Istanbul Bilgi University, Turkey
3

Kadir Has University, Turkey

4dB-Kes Engineering, Turkey

ABSTRACTIn 2020, Turkish Acoustical Society conducted a survey to measure the pandemic’s impact on acoustic
evaluation of residential buildings. 1053 people participated in this survey and answered to the questions on
their noise annoyances before and during the Covid-19. Results indicated an increased acoustical comfort
during the lock-downs due to the decreased environmental noise, but also highlighted the importance ofinterior noises (from neighbouring dwellings and from one’s own dwelling). Other studies from all over theworld reported similar results for the first wave of the pandemics. After two years of experience, thequestion of how user behaviour, acoustical perception and expectance have changed is yet to be answeredin order to develop correct strategies and strengthen the acoustical policies for accomplishing sustainable
cities.
This paper introduces the results of the 2020 study and gives an analysis of the current literature on (1)acoustic perception during the pandemics, (2) working from home and its persistency, and (3) changed user
habits in dwellings and in cities. The acoustical requirements in the era of ‘new normal’ and policy
implications are discussed.
Keywords: Covid-19, New normal, Noise annoyance, Regulation, Neighbour noise

1. INTRODUCTION
Covid-19 pandemic, during its first wave, put a strong emphasize on humans’ dependency on their physicalliving environments. Even before Covid-19, technology developments of 20&21st century and increased
use of indoor environments were associated with dissolved boundaries between residential, educational,
occupational and recreational spaces and with the changes in occupants’ behaviour and expectations. Thesechanges became even more evident after the onset of Covid-19 pandemic, thus emphasizing acousticalrequirements in residential buildings.
Some researchers see Covid-19 as a transition period, which through the sudden changes andmultiple variables pushes the system to change [1]. In order to move towards a better and sustainable
future; we need to learn from the experiences of the pandemic and understand the user preference
and perception in the ‘new normal’ era.

2. METHODSIn 2020, Turkish Acoustical Society conducted a survey to measure the pandemic’s impact on
acoustic evaluation of residential buildings. 1053 people participated in this survey and answered tothe questions on their noise annoyances before and during the Covid-19. The stress and anxiety
1_ayca.sentop@bilgi.edu.tr
3
konca.saher@khas.edu.tr
4
selmakurra@gmail.com
2levels of the participants were also measured using some standardized inventories (further
information is available in [2]. In parallel to this study, Turkish Acoustical Society also made noise
measurements at two residences in İstanbul with different environmental noise characteristics (one iswith 'high environmental noise level’ by a main motorway; the other is with 'moderate environmental
noise level’ and is in a greener area) during the Covid-19. 24-hour environmental noise levelmeasurements both in weekdays and weekends (with curfews) were carried out in these two
residential areas during the first wave of pandemics and the results were compared withpre-pandemic period. The environmental noise surveys at the same locations were done within thescope of another study before the pandemics in 2017. These measurements provided the opportunity
to analyse how environmental noise levels changed during the pandemic and obtain objective data.

3. SUMMARY OF THE SURVEY RESULTS
Weekday measurement results show a decrease of approximately 2 dB in noise levels in bothresidences compared to the pre-pandemic period. The decrease in environmental noise levels is lessthan expected with the increased use of the residences and the balconies. These results indicate thatthe expected decrease due to the decrease in traffic density is not very high due to the increase in
human noise around the residences. This situation is more evident in the results of the weekend
measurements when the curfew is effective. During the weekend measurements, the noise level in the'high-noise' residence decreased by about 8 dB compared to the before the pandemic levels, while thenoise level in the 'moderately noisy' residence increased by 5 dB compared to the pre-pandemic due
to outdoor human activities. In other words, while there is a decrease in transportation noise, there isan increase in noise levels caused by human activities.
In the online survey, participants were asked to evaluate their discomfort due to traffic noise,neighbour noises and noise from other rooms in their own residences, during the one-month period
after the onset of the pandemic and during the pre-pandemic period. The questionnaire also included
a number of questions aimed at measuring dwelling satisfaction, sensitivity to noise, time spent at
home, and the level of stress and anxiety. The results show that 'neighbour noises' were found to be
more disturbing than traffic noise and indoor noises, both before and during the pandemic. However,while there is a significant decrease in the disturbance due to traffic noise, as expected, there is no
significant change in 'neighbour noise' annoyance during the pandemics compared to the previous
period. This indicates that people mostly complained about the 'neighbour noise' during the
pandemic, however, according to the survey results, already high 'neighbour noise' discomfort does
not seem to have increased due to the pandemics. On the other hand, during the pandemic period, it isobserved that the dissatisfaction of people with the noises in their own homes has increased
significantly compared to the before pandemics period.
In the context of this study, people’s conversations, children cry, music, cleaning, and balcony
activities were defined as "disturbing" sounds. Sound of the birds and people’s conversations aredefined as "relaxing" sounds. The participants described people’s conversations as both "disturbing"and "relaxing". When people describe the people’s conversations as "relaxing", they mentioned thatit made them feel less lonely. These dual descriptions are important to show the contextual
perception of the sound. While there is extensive research on the relation between the spectrum andlevel of sound and annoyance, the results of the online survey during the pandemics indicated thatthe psychology of the person and the contextual meaning of the sound is also a very importantparameter when defining annoyance.
This survey study also indirectly presents findings about the transformation in our perception of“home” and our use of the “home”. While 61% of the participants stated that they never left thehouse during the quarantine period, 67% stated that they did work that required high concentration
on a daily basis. As the residences are transformed from the traditional living space into a business,
sports and socializing area; the prolongation of the time spent at home, the presence of many people
in the residences at the same time and the fact that the residences have many different functions at
the same time change the quantity, quality and perception of noise and these changes reshape ouracoustic expectations from these spaces. The results of the survey also showed that people have ahigher awareness of "sound" and "sound insulation".
In order to move towards a better and sustainable future; we need to learn from the experiences ofthe pandemic and understand the user preference and perception in the ‘new normal’ era. Based on
the findings of the survey, the authors predict that in the future, users will make more demands forthe documentation of 'sound insulation' performance in the real estate business, since 'soundinsulation' is not an easily observed parameter among the physical conditions offered by theresidences. The authors also predict that the architects will have to evaluate the performance ofbuilding facades due to the increased noise levels that may occur due to human-activity noise inresidential areas (which were previously synonymous with silence)

4. DWELLING IN THE ‘NEW NORMAL’ AND THE ACOUSTICAL PERCEPTION
An initial review was made for scoping future research in the subject and to highlight potential
implications on acoustical regulations. Three main axis of research was defined as: (1) dwellingsoundscape and its perception during the pandemic, (2) working from home (WFH) and its
persistency after the Covid-19 pandemic, and (3) changed user habits in dwellings and in cities after
the pandemic.
4.1 Dwelling soundscape and its perception during the pandemic:
Lock-downs forced people to spend more time indoors and less time outdoors, thus changed thesoundscapes. Acoustical community throughout the world documented the changes in environmental
noise levels and studied the acoustic perception at dwellings. User perception is analysed in thosepublications through;• Noise complaints made to the governmental organizations• Questionnaires on noise annoyance / comfort / well-being• Attitudes against noise measured with tweets
Figure 1 shows the acoustic perception in relation with the studied parameters in literature.
Official noise complaints increased during the pandemic [3], [4] especially due to neighbourhood
noise [4], [5]. Lee & Jeong made an analysis of tweets from London and reported that noise
complaints and sleep disturbances increased more than twice during the lockdown, meanwhile
talking/shouting, TV/music sounds and DIY were mentioned the most [6]. Yıldırım and Arefi [7]found that the changes in noise complaints were disproportional between urban zones and rural zones.
While noise complaints decreased in the city centre, outskirts of the city (≥8 km) experienced morenoise issues.
Table 1 shows a very brief analysis of survey findings according to the related sound source.

Sound source
Outdoor noises:

Dwelling noises:

Neighbour noise:

Positive sounds:

Table 1 – Acoustical perception of various sound sources
Reported results
There has been a significant decrease (up to 10-15 dB) in environmental noiselevels in large cities around the world during the lock-downs.
Road, air, rail and marine traffic reduction has improved the soundscapeperception [5].
Availability of a quiet side in the dwelling played an important role in perceived
comfort [8].
Annoyance due to noises from separate and shared rooms of the same dwellingsignificantly increased [9]The annoyance and comfort were proportional to the number of residents [8],[10] and the size of the dwelling [8].
Neighbour noise constituted the prevailing noise source that disturbed relaxationand perceived neighbour noise level has increased [6].
Noise from shared spaces of apartments (lifts, corridors etc.) was perceived as
louder and more people were annoyed by this noise source compared to 2019
survey results in Canada [9].
The positive effect of natural sounds that were perceived in the absence of
outdoor noises were mentioned in the current study and also in other research[8], [5] .
Anthropogenic sounds mean also communication and social connectedness forpeople. In the current study, and in a previous study [11] some respondents
stated that the sounds that they heard made them feel like they are not alone.
This was also stated in [12].

Impact on well-being:
Neighbours’ noise during relaxation, and number of people sharing the house was associated withthe comfort and well-being [8]. Mechanical sounds were found to be associated with poorer
self-rated health and lower restorative quality of the home compared to the natural sounds and people
who had garden, quiet room and soundproof windows reported better self-rated health [13].
Comfortable acoustic environments were associated with higher well-being [12]. Diaz et alunderlined the impact of noise on immune system through (1) increased stress, (2) sleep alterations,(3) other health effects such as respiratory rate, blood pressure, heart rate, nervous system; andhighlights its importance for Covid-19 incidences [14]. Koch et al estimated the health impact of
decreased environmental noise levels during Covid-19 lock-down and states that if the lock-down
state was continuous, annual diagnoses of Myocarial infaction, stroke and depression/anxiety would
decrease around 7% - 1% [15].

Figure 1 – Mapping of acoustical perception parameters as documented in the investigated literature
4.2 Working from home and its persistency after the Covid-19 pandemic:
One of the expected permanent effects of the pandemic is on the working environment. In theunusual conditions of the pandemic, it was easier and faster to adapt to the technology and working
from home (WFH). WFH is now an opportunity for many companies either in case of employee’s
urgent needs or scheduled as some days of the week or even permanently. WFH brought someadvantages related with the occupational costs and reduction in travel times. Thus, research has been
conducted throughout the world mainly with following dimensions as measured in surveys:• Productivity• Willingness to WFH• Appropriateness of the house-environment (specifically noise annoyance is addressed inthis review)
Figure 2 shows the mapping of the above dimensions and the effecting parameters as in theinvestigated literature.
Regarding the productivity, some researchers state that productivity during teleworking forms abell shaped curve, which initially increases and later decreases as time passes. However the majorityof employees believe that the productivity was not lost during the pandemic and the share of remote
working is expected to grow in the future [16].
Employees would like to WFH more often in the future and prefer flexible schedule to avoid rush
hours of transport [17]. Willingness to WFH was related with prior WFH experience, technologicalabilities and self-discipline, while need for interaction with colleagues (face-to-face discussions andinformal meetings) was a drawback for WFH [18], [19], [16]. Employees who had children were less

willing to WFH [16]. Meulenbroek et al. indicated that people who worked at open plan offices andwork on individual tasks also prefer WFH in order to avoid office noise [20]. In their study, theposition of the desk in relation to walking routes in an open office, crowdedness and noise were
found to be important aspects on willingness to return to offices [20] .
The appropriateness of the house environment for WFH, depends on several factors such as size,other family members, environmental performance, energy consumption etc. and noise. Leaving
other factors aside, other noise sources that persist at dwellings threaten the productivity andwell-being while working from home. Both indoor and outdoor noise annoyances affect the working
ability [9]. Annoyance due to noises from separate and shared rooms of the same dwelling increased
and constituted the biggest noise issue for WFH during the pandemic (Puglisi, 2021; Torresin, 2022;[9]. People lacking a separate environment for WFH, used bedrooms and living rooms as a working
place [12]. According to a survey in Italy, 43% of the respondents used a shared room for working,resulting in an increased noise annoyance [10]. Other noise issues that most disturbed people while
WFH were related with the traffic noise [8], neighbour noise [8], [9] apartments’ shared spaces [9].
A large number of people had reported using technological equipment (headsets etc.) to mask thenoises [10], [12].
The global work from home survey results indicate that WFH duration is 0.5, 5 days per week
before and during the pandemic and expected to be 2 days per week after the pandemic (GWA, 2020
as cited in [16]). Certainly, the willingness of employees indicates the same trend. However, thecurrent acoustical situation at homes does not support a long-term implementation of WFH [9], [12].
Impact on well-being:
Lack of social interaction and managing work-family balance was found to be a source of
depletion and work exhaustion [21], while sleep quality, decision latitude, work-life balance andexercise played a positive role on well-being while WFH [22].
A research on vocal fatigue symptoms showed that being untrained on how to use their voices
during online meetings, employees suffered from vocal fatigue symptoms [23]. Study also reported
that online communication caused mental fatigue due to simultaneous visual & auditory stimuli andvocal efforts.

Figure 2 – Mapping of working from home parameters as documented in the investigated literature
4.3 Changed user habits in dwellings and in cities after the pandemic:
Changes in user habits after the pandemic is a broad subject that includes many aspects such asenergy consumption, shopping, eating etc. Only the following titles are taken in the scope of thisarticle due to their relation with the urban and dwelling soundscape.
• Transportation,• Use of open-areas and green zones

• Dwelling usage• Relocation towards suburbs
The travellers prefer the transportation modes that decrease the risk of infections [16]. Increased
car ownership was reported in several countries after the on-set of Covid-19 [16]. Studies showedthat in 2020 and 2021 public transportation was less preferred in Turkey and demand for private car
highly increased compared to before pandemic [24], [25]. The interest for walking, biking ande-scooter increased together with renting services [16], [24], [26]. Another impact on transportation
modalities is the increased home-delivery services after pandemic. During the lockdowns, several
restrictions were brought to restaurants, groceries, markets and retails including total closure, limited
hours of service and restriction on number of clients. With these restrictions home-delivery services
strengthened and continue to be a popular option in the new normal [27].
Open areas and green zones gained importance for gathering, exercising, and relieving from stress.
This brought the insufficient capacity and unequal accessibility of green areas in the city into thelight [27]. Offering a safer environment than indoors, outdoor areas also attracted many facilities toexpand their seating areas to occupy streets and greeneries [27]. Recommendations for urban
planning after Covid-19 favour mixed-use (residential, recreational, social and industrial) landplanning and dispersion of services and amenities in order to avoid crowding [27].
Dwelling usage has changed sharply. While time spent at home increased, dwellings replaced e.g.
offices, schools, sports grounds and playgrounds. In order to meet the new functional needs, people
had to reorganize their homes [27] . Khalil and Fatmi developed a machine-learning model onchanges in in-home-activities before, during and after the pandemic to model its impact on energy
consumption [28]. Based on the survey findings they categorized in-home-activities as (1) sleep; (2)leisure and discretionary activities such as relaxing, socializing, watching TV; (3) home and personal
maintenance such as general activities, cleaning; (4) mandatory activities such as remote working
and learning. They predicted the average daily time spent for these activities as approximately 9, 17,
12 hours per day ‘before’, ‘during’ and ‘after’ Covid-19 respectively [28]. The balconies, terraces
and courtyards were occupied more often and the market value of dwellings that offer open spaces
has sharply increased [27]. Recommendations for buildings in the new normal include integration ofopen and semi open spaces, special concern for indoor environmental quality and passive ventilation,
optimization of size, offering work and study zones, avoiding open-plan design, introducing more
lifts and increased size in circulation paths and selection of materials that are more hygienic andvirus-resistant [27].
The demand for less crowded areas, larger living spaces, single-family houses has directed people
towards suburbs while sales in city centres dropped [16]. Nevertheless, historical examples show thatcities survive and continue to populate after the very initial response of evacuation in cases of large
crisis [29], [27].
Impact on well-being:
The house environment played an important role on physical and mental well-being of residents
during the lockdown. People who lived in dwellings with poor indoor environmental quality showed
more depressive symptoms [30]. Satisfaction with the dwelling and home crowding were found to be
associated with the perceived stress [31]. Also residents who were unhappy with the privacy of theirdwelling were more likely to feel helpless (lack of control) [31].

5. REGULATORY IMPLICATIONS
Although in the new normal, time spent outside rather than at home has increased once again, it is
not expected to meet the same levels as before the pandemic primarily because of the changes in user
habits, and secondly because of the mandatory activities such as adoption of remote working andflexible working hours. Thus, changes in dwelling soundscape, its perception and issues related withmulti-functional use of dwellings are expected to become permanent to a certain degree. Therefore, it
is important to build a dialogue with other disciplines and develop effective policies to meet the
acoustical needs. This section builds on the findings of field study conducted by the authors andpublished results in literature and explain policy implementations.
5.1 Urban planningGreen zones are generally observed as a noise control solution [3], [4]. However, in the newnormal, the green zones are more frequently and densely used as a recreation place. This increased
preference of open-air gathering spots bring noise issues caused by people outdoors. For futureactions, this tendency needs to be analysed and noise control solutions need to be developed inside
the green zones to protect surrounding buildings. Special attention needs to be paid to the capacity
and accessibility of the open spaces and the crowd should be distributed in a more balanced way byincreasing the amount and size.
Some researchers favour decentralization in urban design and increased mixed-use to makeservices accessible in larger zones [27]. However mixed-use buildings can introduce noise problems
and acoustical experts needs to be consulted in order to take efficient precautions.
Together with the flexibility of teleworking and preference of less crowded zones andsingle-family houses, a large population has moved from city centres to the suburbs. However
relocation of population together with its demands initiates commercial development in once tranquilzones thereby new noise issues might arise at these locations. On the other hand, the decrease of
population in city centres is expected to be only temporary, thus noise problems in cities cannot be
considered as eased. It was shown that suburban areas experienced more noise problems during the
pandemic [7] possibly in part due to the increased population in these areas. Newly developing
settlements should be planned embracing a soundscape approach to accent positive sound features
while controlling unwanted sounds [32]. Future noise levels should be determined and transportation,entertainment and industrial noises should be evaluated in the light of strategic noise maps andregulated through noise control measures as explained in [33]. New buildings should be constructedwith details and materials that suffice for sound insulation requirements defined in acousticalregulations [34], [35].
The expanded outdoor seating areas, increased use of open and semi-open spaces and open
windows and doors in facilities imply a weaker noise-control. This means that sounds from people’s
talking, shouting, moving furniture, broadcasted or live music can more easily propagate to thesurrounding buildings. The location of such facilities needs to be planned at an urban scale, thecrowd needs to be properly dispersed and open-air noise control solutions (sound level limits,barriers, directed loudspeakers, sound masking etc.) should be planned for facilities. Window frames,
which integrate soundproofed vent, can be an alternative to allow fresh air inside while reducing thenoise that is emitted to the environment. These systems can be automated to respond to the changes
in indoor air quality, and open only when necessary.
5.2 Transportation policies
The drop in public transportation and increased demand for individual cars is concerning withregards to social equality, sustainability, traffic management, and consequently noise. By
implementing correct policies trust should be regained to the public transportation and measures
should be taken such as good sanitization, ventilation and management of crowd during peak times.
The demand for individual and safe transportation should be shifted from individual cars.
Scooters and bicycles can provide a greener and more silent individual travelling option. Provided
the sufficient infrastructure such as safe lanes, proper parking lots, renting options and priority intraffic management, travellers might favour these means of transportation. Pedestrian areas need tobe redesigned to provide safe and joyful travel for walking travellers as well. Some examples of
initiatives are seen in Brussels, Paris and Milan where some roads that were previously occupied bycars, were assigned to the bicycles after the onset of pandemic [16].
Due to increased popularity of home-delivery services, increased use of motorcycles at streetsneeds to be addressed from noise perspective as well. Bicycles and electric motorcycles can be
encouraged by e.g. providing incentives to companies.
5.3 Building design
Building design should allow a quiet façade and access to a garden where it is possible. Greeneryin building lots not only provides a buffer zone against noise but also has psychological benefits [3],[4], [27] one of which is the positive perception of natural sounds [2], [8], [13].
During the lock-downs, one of the most important challenges related with the interior
environments was the crowding. People living in a household should be proportional to the m 2 .
Dwellings with larger room sizes and separate functional areas (instead of an open-plan design) thatoffer privacy are in demand after the experience of a lock-down. Functional zoning should beacoustically optimized in dwellings and sound insulation should be provided both between thedwellings and between the rooms of the same dwelling. Considering the increased teleworking,proper working stations should be considered where people could be isolated both visually andaurally.

Increased demand for open/semi-open areas should be taken into consideration in designing newresidential buildings. The design of balconies needs special attention, as people tend to occupy thesespaces more often in the new normal. The plan layout should separate these features from highly
sensitive rooms in order to avoid noise annoyance during the periods when windows are open. Noisefrom balconies can be controlled through implementation of screens, barriers, absorptive materials,
and soundproof façades.
Due to an increased concern for hygiene in buildings; smooth, closed cell, non-absorbing
materials might appear in designs more often. This implies the necessity of water repelling, easy toclean sound absorbers.
With regards to the building services, designers recommend increasing the number of lifts to
reduce the crowd. Preference of passive ventilation strategies over forced ventilation is also
recommended to decrease the infection risk. Consequently, these strategies are expected to result inhigher noise levels due to lifts, but lower levels due to HVAC ducts. Noise control optimized passive
ventilation solutions should be sought in noisy surroundings.
5.4 Acoustical requirements
Studies indicate that noise disturbance can be critical in a large-scale implementation of WFH andthey highlight the need for reassessing acoustics of dwellings for changed working patterns. Daytime
indoor noise level requirements in residential buildings should be determined considering also the
WFH conditions. Sound insulation requirements between the rooms of the same dwelling should bedetermined considering the noise annoyance, productivity and privacy needs during WFH. Several
studies mention concerns for increasing the interaction while teleworking through infrastructure andsoftware. The impact of increased virtual communication on dwelling soundscape and vocal effort of
employees should also be taken into attention.
Researchers suggest that the daily time spent for in-home-activities has increased compared tobefore pandemic. Noise annoyance in the ‘new normal’ era should be researched and changes inresidential use should be revealed to understand how people are affected by residential noises.
During the lockdown, neighbour noise caused the highest annoyance while annoyance due to noises
from one’s own dwelling showed the largest increase [2]. This shows the necessity of improving
sound insulation performance of partitions. If necessary, stricter requirements should be brought in
the regulations to protect user’s health. Sound insulation of buildings needs to be measured andcertification should be provided in order to inform its users and investors.
In cases of new lockdowns, mediation teams and noise enforcement teams can be beneficial toresolve neighbour disputes.
5.5 Inequalities
Attention should be paid to the disproportional burden of noise among the socio-economic groups
and genders. Studies indicate that low-income residents were associated with more noise complaints
during the pandemic [3], [4]. Teleworking also caused inequalities due to space and technologicalequipment [17], [36]. During the pandemic, it was found that males, people in metropolitan areas,
people with higher income, and older people worked more frequently from home [17] and women
had more difficulties in managing work-life balance while WFH [36].

6. CONCLUSIONS
Covid-19 experience has shaped how people observe their dwellings and what they expect fromtheir physical environment. The experience of being lockdown has put an abnormal emphasize on
indoor environmental quality and specifically, on acoustics. Although we are back to normal, someof the user habits such as transportation choice, in-home-activities, working from home, online
shopping, open space usage continue to be affected from this experience.
This paper introduced the results of an online survey conducted during the first wave of Covid-19
and presented the initial results of a literature review on (1) acoustic perception during Covid-19, (2)working from home and its persistency, and (3) changes in user habits in dwellings and in cities. The
results are discussed from the perspective of acoustical policies. It seems evident that neighbour
noise needs more attention in the new normal, as time spent at home and in-home-activities haveincreased. Current building stock is not well-fit for working from home due to crowding, small m2
and lack of sound insulation and privacy. Resultantly, noise coming from the other rooms of thedwelling is the most important noise threat during WFH, which affect productivity and well-being.

With regards to outdoor sounds, lockdown conditions created an interesting contrast during the
pandemic and draw people’s attention on their soundscape. Many people were more satisfied with
their living environments due to the decrease in the traffic noise. However in the ‘new normal’
people are more prone to use individual transport instead of public transport which can increase thetraffic density, hence the environmental noise. Policies need to be implemented in order to shift thedemand from individual cars to bicycles, e-scooters and walking.

REFERENCES[1] S. Cheval, C. M. Adamescu, T. Georgiadis, M. Herrnegger, A. Piticar, and D. R. Legates, “Observed andpotential impacts of the covid-19 pandemic on the environment,” Int. J. Environ. Res. Public Health, vol. 17,
no. 11, pp. 1–25, 2020, doi: 10.3390/ijerph17114140.
[2] A. Şentop Dümen and K. Şaher, “Noise annoyance during COVID-19 lockdown: A research of public
opinion before and during the pandemic,” J. Acoust. Soc. Am., vol. 148, no. 6, pp. 3489–3496, 2020, doi:
10.1121/10.0002667.
[3] B. Ramphal, J. D. Dworkin, D. Pagliaccio, and A. E. Margolis, “Noise complaint patterns in New York City
from January 2010 through February 2021: Socioeconomic disparities and COVID-19 exacerbations,”
Environ. Res., vol. 206, no. July 2021, p. 112254, 2022, doi: 10.1016/j.envres.2021.112254.
[4] H. Tong, F. Aletta, A. Mitchell, T. Oberman, and J. Kang, “Increases in noise complaints during the
COVID-19 lockdown in Spring 2020: A case study in Greater London, UK,” Sci. Total Environ., vol. 785, no.
January 2020, p. 147213, 2021, doi: 10.1016/j.scitotenv.2021.147213.
[5] C. Bartalucci, R. Bellomini, S. Luzzi, P. Pulella, and G. Torelli, “A survey on the soundscape perception
before and during the COVID-19 pandemic in Italy,” Noise Mapp., vol. 8, no. 1, pp. 65–88, 2021, doi:
10.1515/noise-2021-0005.
[6] P. J. Lee and J. H. Jeong, “Attitudes towards outdoor and neighbour noise during the COVID-19 lockdown:
A case study in London,” Sustain. Cities Soc., vol. 67, no. February, p. 102768, 2021, doi:
10.1016/j.scs.2021.102768.
[7] Y. Yildirim and M. Arefi, “Noise complaints during a pandemic: A longitudinal analysis,” Noise Mapp., vol.
8, no. 1, pp. 108–115, 2021, doi: 10.1515/noise-2021-0008.
[8] S. Torresin et al., “Indoor soundscapes at home during the COVID-19 lockdown in London – Part II: A
structural equation model for comfort, content, and well-being,” Appl. Acoust., vol. 185, p. 108379, 2022,
doi: 10.1016/j.apacoust.2021.108379.
[9] M. S. Andargie, M. Touchie, and W. O’Brien, “Case study: A survey of perceived noise in Canadianmulti-unit residential buildings to study long-term implications for widespread teleworking,” Build. Acoust.,
vol. 28, no. 4, pp. 443–460, 2021, doi: 10.1177/1351010X21993742.
[10] G. E. Puglisi, S. Di Blasio, L. Shtrepi, and A. Astolfi, “Remote Working in the COVID-19 Pandemic:
Results From a Questionnaire on the Perceived Noise Annoyance,” Front. Built Environ., vol. 7, no.
September, pp. 1–19, 2021, doi: 10.3389/fbuil.2021.688484.
[11] A. Şentop Dümen and N. Tamer Bayazıt, “Enforcement of acoustic performance assessment in residentialbuildings and occupant satisfaction,” Build. Res. Inf., vol. 48, no. 8, pp. 866–885, 2020, doi:
10.1080/09613218.2020.1741336.
[12] S. Torresin et al., “Indoor soundscapes at home during the COVID-19 lockdown in London – Part I:
Associations between the perception of the acoustic environment, occupantś activity and well-being,” Appl.
Acoust., vol. 183, no. July, 2021, doi: 10.1016/j.apacoust.2021.108305.
[13] A. M. Dzhambov, P. Lercher, D. Stoyanov, N. Petrova, S. Novakov, and D. D. Dimitrova, “University
students’ self-rated health in relation to perceived acoustic environment during the covid-19 homequarantine,” Int. J. Environ. Res. Public Health, vol. 18, no. 5, pp. 1–21, 2021, doi: 10.3390/ijerph18052538.
[14] J. Díaz, J. Antonio-López-Bueno, D. Culqui, C. Asensio, G. Sánchez-Martínez, and C. Linares, “Doesexposure to noise pollution influence the incidence and severity of COVID-19?,” Environ. Res., vol. 195, no.
January, 2021, doi: 10.1016/j.envres.2021.110766.
[15] S. Koch et al., “Impacts of changes in environmental exposures and health behaviours due to the
COVID-19 pandemic on cardiovascular and mental health: A comparison of Barcelona, Vienna, andStockholm,” Environ. Pollut., vol. 304, no. July 2021, 2022, doi: 10.1016/j.envpol.2022.119124.
[16] A. de Palma, S. Vosough, and F. Liao, “An overview of effects of COVID-19 on mobility and lifestyle:18 months since the outbreak,” Transp. Res. Part A Policy Pract., vol. 159, no. March 2021, pp. 372–397,
2022, doi: 10.1016/j.tra.2022.03.024.
[17] M. J. Beck and D. A. Hensher, “Australia 6 months after COVID-19 restrictions part 2: The impact ofworking from home,” Transp. Policy, no. June, 2021, doi: 10.1016/j.tranpol.2021.06.005.
[18] X. Kong, A. Zhang, X. Xiao, S. Das, and Y. Zhang, “Work from home in the post-COVID world,” Case
Stud. Transp. Policy, vol. 10, no. 2, pp. 1118–1131, 2022, doi: 10.1016/j.cstp.2022.04.002.

[19] A. Al-Habaibeh, M. Watkins, K. Waried, and M. B. Javareshk, “Challenges and opportunities of remotely
working from home during Covid-19 pandemic,” Glob. Transitions, vol. 3, pp. 99–108, 2021, doi:
10.1016/j.glt.2021.11.001.
[20] R. Appel-Meulenbroek, A. Kemperman, A. van de Water, M. Weijs-Perrée, and J. Verhaegh, “How to
attract employees back to the office? A stated choice study on hybrid working preferences,” J. Environ.
Psychol., vol. 81, no. December 2021, 2022, doi: 10.1016/j.jenvp.2022.101784.
[21] X. Hu and M. Subramony, “Understanding the impact of COVID-19 pandemic on teleworkers’
experiences of perceived threat and professional isolation: The moderating role of friendship,” Stress Heal.,
no. March, 2022, doi: 10.1002/smi.3146.
[22] G. Tokdemir, “Software professionals during the COVID-19 pandemic in Turkey: Factors affecting theirmental well-being and work engagement in the home-based work setting,” J. Syst. Softw., vol. 188, 2022,
doi: 10.1016/j.jss.2022.111286.
[23] L. T. D. Siqueira, A. P. dos Santos, R. L. F. Silva, P. A. M. Moreira, J. da S. Vitor, and V. V. Ribeiro,“Vocal Self-Perception of Home Office Workers During the COVID-19 Pandemic,” J. Voice, 2020, doi:
10.1016/j.jvoice.2020.10.016.
[24] M. E. C. Bagdatli and F. Ipek, “Transport mode preferences of university students in post-COVID-19
pandemic,” Transp. Policy, vol. 118, no. December 2021, pp. 20–32, 2022, doi:
10.1016/j.tranpol.2022.01.017.
[25] S. Shakibaei, G. C. de Jong, P. Alpkökin, and T. H. Rashidi, “Impact of the COVID-19 pandemic on
travel behavior in Istanbul: A panel data analysis,” Sustain. Cities Soc., vol. 65, no. November, 2021, doi:
10.1016/j.scs.2020.102619.
[26] L. Li, C. J. Meinrenken, V. Modi, and P. J. Culligan, “Impacts of COVID-19 related stay-at-home
restrictions on residential electricity use and implications for future grid stability,” Energy Build., vol. 251,
2021, doi: 10.1016/j.enbuild.2021.111330.
[27] O. L. Glavan, N. Nikolić, B. Folić, B. Vitošević, A. Mitrović, and S. Kosanović, “COVID‐19 and City
Space: Impact and Perspectives,” Sustain., vol. 14, no. 3, pp. 1–19, 2022, doi: 10.3390/su14031885.
[28] M. A. Khalil and M. R. Fatmi, “How residential energy consumption has changed due to COVID-19
pandemic? An agent-based model,” Sustain. Cities Soc., vol. 81, no. March, 2022, doi:
10.1016/j.scs.2022.103832.
[29] H. Frumkin, “COVID-19, the built environment, and health,” Environ. Health Perspect., vol. 129, no. 7,
pp. 1–14, 2021, doi: 10.1289/EHP8888.
[30] A. Amerio et al., “Covid-19 lockdown: Housing built environment’s effects on mental health,” Int. J.
Environ. Res. Public Health, vol. 17, no. 16, pp. 1–10, 2020, doi: 10.3390/ijerph17165973.
[31] F. Fornara et al., “Space at home and psychological distress during the Covid-19 lockdown in Italy,” J.
Environ. Psychol., vol. 79, no. December 2021, pp. 1–10, 2022, doi: 10.1016/j.jenvp.2021.101747.
[32] BSI The British Standards Institution, “BSI Standards Publication Acoustics — Soundscape Part 1 :Definition and conceptual framework,” BSI Stand. Publ., 2014.
[33] S. Kurra, Environmental Noise and Management. Hoboken, NJ: Wiley, 2021.
[34] B. Rasmussen and M. Machimbarrena, Eds., Building acoustics throughout Europe Volume 1: Towards acommon framework in building acoustics throughout Europe, vol. 1. Di Script Preimpresion, 2014.
[35] B. Rasmussen, “Sound insulation between dwellings - Comparison of national requirements in Europe
and interaction with acoustic classification schemes,” Proc. Int. Congr. Acoust., vol. 2019-September, no.
September, pp. 5102–5109, 2019, doi: 10.18154/RWTH-CONV-239983.
[36] A. Islam, “Work-from/at/for-home: CoVID-19 and the future of work – A critical review,” Geoforum, vol.
128, no. November 2021, pp. 33–36, 2022, doi: 10.1016/j.geoforum.2021.11.018.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0749

A periodic infinity tubes array VS a periodic Helmholtz resonators
array
Rong XUE 1; Cheuk Ming MAK 2; Chenzhi Cai 3; Kuen Wai MA41

Department of Building Environment and Energy Engineering, The Hong Kong Polytechnic University, Hong
Kong, China

2

Department of Building Environment and Energy Engineering, The Hong Kong Polytechnic University, Hong
Kong, China
3

4

School of Civil Engineering, Central South University, China

Department of Building Environment and Energy Engineering, The Hong Kong Polytechnic University, Hong
Kong, China

ABSTRACTThe infinity tube is proved to be an effective duct-borne noise control silencer. In this paper, the infinity tubes
are mounted periodically to achieve wider transmission loss bands. The noise attenuation performance of theperiodic infinity tubes array is analyzed theoretically and numerically and then compared with the periodic
Helmholtz resonators array. Bloch wave theory and the transfer matrix method are used to investigate thesound wave propagation inside these periodic silencers by a one-dimensional approach. The acoustic
impedance of the infinity tube is derived by calculating the transfer matrix between each periodic cell. The
theoretical results are validated with numerical results conducted by commercial software (COMSOLMultiphysics) based on the Finite Element Method (FEM). The transmission loss of the periodic infinity
tubes array is compared with the periodic Helmholtz resonators array. The results show periodic infinity tubes
array would have a potential application in noise control.
Keywords: Helmholtz resonator, infinity tube, Bloch wave theory, transmission loss, transfer matrix method

1. INTRODUCTION

The ductwork system is an important part of modern buildings. As an essential component of theHeating Ventilation and Air Conditioning (HVAC) system, the duct would be used for heat transfer
and air exchange (1). However, the unsteady flow inside the duct always causes duct-borne noise(25). To control the duct noise, the easiest way is to use dissipative mufflers. The principle of dissipative
mufflers is to cover the duct system with sound-absorbing materials(6). These porous materials could
absorb noise by changing sound energy into heat. However, dissipative mufflers are only suitable formedium- and high-frequency noise attenuation. Using reactive mufflers is proved to be an effective
way to control low-frequency duct noise(7). Among all the reactive silencers, the Helmholtz resonator(HR) is most widely used for its affordable and durability (8).
In order to improve the noise attenuation ability in the ductwork system, it is straightforward touse periodically arranged mufflers to attenuate noise(9). Sugimoto et al.(10) investigated the soundwave propagating in a tunnel with a periodic HRs array. They discussed the dispersion relations andBragg reflection on such a system. Wang and Mak (11, 12) applied Bloch wave theory to investigate
acoustic wave propagating inside the main duct with periodic HR mounted on it. They also conductednumerical simulations and experiments to verify the transmission loss (TL) results. To further improverong.xue@connect.polyu.edu.hk
cheuk-ming.mak@polyu.edu.hk
3chenzhi.cai@csu.edu.cn
4kuen-wai.ma@polyu.edu.hk
12the noise attenuation ability of periodic HR, Cai and Mak(13, 14) used a dual HRs array and othermodified HRs array systems to compare the TL results. The TL results showed periodic HRs array is
a useful way to control duct noise.
The infinity tube (IT) is a novel reactive silencer designed by Lato et al.(15), which is modified
from the traditional Herschel-Quincke (HQ) tube(16). The HQ tube needs three parameters to locate
the installation location, which is cumbersome for industry applications. Besides, the HQ tube would
lead to flow repartition (17), which leads to pressure change in the ductwork system. The IT would
overcome these problems and has a simple geometry, making it easy to install and manufacture.
This paper focuses on discussing the noise attenuation ability of periodic reactive mufflers forductwork systems in the low-frequency domain. The Helmholtz resonator is widely used in industry;
the infinity tube is novel and easily manufactured and implemented. For these reasons, these two kindsof silencers are chosen. Bloch wave theory and transfer matrix method are used to calculate theacoustic wave propagating in a periodic ductwork system. Given the beginning and end boundary
conditions, the acoustic wave propagating between each periodic cell is calculated to evaluate thenoise attenuation ability of periodic silencers. The analytical results are evaluated using the Finite
Element Method (FEM) simulation with commercial software COMSOL Multiphysics. At last, theaveraged transmission loss ( TL ) is used to assess the noise attenuation ability of periodic HRs arrayand ITs array.

2. Analytical approach of the periodic infinity tubes array

The sound wave propagation inside a ductwork system is governed by the classical acoustic wave
equation:∂2 P 1 ∂2 P=
∂x 2 c02 ∂t 2

(1)

where P represents the acoustic pressure, t is time, and 𝑐𝑐0 represents the sound speed. Assuming thewave is harmonic in time, the sound pressure and particle velocity could be solved from Eq. (1) as
follows(15):=P( x, t ) PI ei (ωt − kx ) + PR ei (ωt + kx )(2)=u ( x, t )PI i (ωt − kx )P
− R ei (ωt + kx )
e
ρ0 c0
ρ0 c0

(3)

where i= −1 is the imaginary unit, ρ0 represents the air density, PI and PR are complex pressure
amplitudes indicate acoustic waves propagate along with two opposite directions, ω is the angularfrequency, k = ω / c0 is the acoustic wave number.
As shown in Figure 1(a), an infinity tube has a cross-section area S2 and length L2 is mounted on
the main duct with the cross-section area S M. Using the conditions of pressure equilibrium andconservation of volume velocity at the junction position, the relationship between pressure andvelocity can be expressed as follows (15):( L) P=( R) P=( A) P( F )
 P=
(4)

S
U
(
L
)
S
U
(
F
) = S M U ( R) + S N U (A)+N M
Assuming an anechoic termination with no reflected waves from the right side of the duct system,
the acoustic impedance Z IT of a single infinity tube could be solved:

Z IT =i ρ0 c0 sin(kL2 )2S2 [cos(kL2 ) − 1](5)

(a) infinity tube(b) Periodic infinity tubes array

Figure 1: Schematic of an infinity tube and a periodic infinity tubes array
As shown in fig.1 (b), several infinity tubes are mounted periodically on a duct with the periodic
distance D. In the Nth periodic cell which locates between (N-1)D and ND, imagine the sound pressureof positive and negative acoustic waves are PN+ ( x) = PNI e j (ωt − k ( x − ( N −1) D ) and PN− ( x) = PNR e j (ωt + k ( x − ( N −1) D ) ,where PNI and PNR are the pressure amplitudes of the incident and reflected acoustic wave in Nth cell.
According to the principle of sound propagation in periodic structures(9), the relation of acousticpressure amplitudes of Nth and (N+1)th cell are governed by Bloch wave theory:
 PNI +1 
 PNI 
(6)
=
T
 R 
 R
 PN +1  PN 
T is a 2×2 matrix and is called transfer matrix{Sugimoto, 1995 #75}. If Z d means acoustic
impedance of the main duct, T is given by:
Z d − jkD
(1 − 2Z )eIT
T= Z d − jkDe 2Z ITZ d − jkD 
e

2Z IT

Z d − jkD 
(1 +
)e

2Z IT

−

(7)

According to Bradley(19), the acoustic pressure amplitudes between each cell are increased or
decayed exponentially, which means [ PNI +1 PNR+1 ]T = e µ [ PNI PNR ]T . To determine the parameter e µ , theeigenvalue λ = e µ and corresponding eigenvector v =[ v v ] of transfer matrix T need to be solved.
In a finite-length ductwork system, there are both forward and backward traveling acoustic waves
exist, which means T has two eigenvalues λ 1 λ 2 and two eigenvectors v1 =[ v1+ v1− ] v 2 =[ v2+ v2− ] . The
relations between 1 st and the N th periodic cell could be solved:
 PNI PI 
 PI 
v + 
v + 
(8)
a1Tn −1 v1 + b1Tn −1 v 2 =a1λ1n −1  1−  + b1λ1n −1  2− T  NR−1  ==Tn −1  1R  = R =
 P1 
 v1 
 v2 
 PN 
 PN −1 +−

where a1 and b1 are two arbitrary constants related to the incident and reflected acoustic waves in the 1st cell.
To determine these constants, boundary conditions need to be given. At the position x=-Lbegin, where is the
beginning of the duct, the sound pressure is given to be P0. The duct end, where x=ND+Lend, would be ananechoic termination. The two boundary conditions give:λ1−1v1+ e− jk ( D − Lbegin ) + λ1−1v1− e jk ( D − Lbegin )
λ1N −1v1−


λ2−1v2+ e− jk ( D − Lbegin )+ λ2−1v2− e
λ2N −1v2−

jk ( D − Lbegin )  a1   P0   =    b1   0 (9)Combining Eq (5), (7), (8) and (10), the acoustic wave propagating inside a finite duct loaded withperiodically IT tubes is acquired. The averaged transmission loss TL is used to measure the noise attenuation
ability of the periodic infinity tubes array. It can be expressed as:=TLPIa λ −1v + + b λ −1v +2020=
log10 0I
log10 1 N1−1 1+ 1 2N −12 +NPN
Na1λ1 v1 + b1λ2 v2(10)

3. Analytical approach of the periodic Helmholtz resonators array
As shown in Figure.2(a), a Helmholtz resonator is mounted on the main duct with the cross-section area
SM as a side-branch muffler. The length and cross-section area of the neck are LN and SN, while the length andcross-section area of the cavity are LC and SC. The acoustic impedance of an HR is given as (20):

P
1
=
Zr =
Ra + j (ω M a −
)
ω Ca
U

(11)

=
M a ρ0 S N ( LN + ∆L) is sound mass, Ra is sound resistance, and Ca = Vc / ρ0 c02 is sound capacitance.
where
Vc = LC SC is the volume of cavity. According to Ingard(8), at the interface of the neck and cavity, an end
correction is needed to improve the acoustic prediction results. The end correction is given as:r=∆L 0.85rN (1 − 1.25 N ) + 0.85rN
rC

(12)

where rN and rC are the radius of the neck and cavity.
A periodic Helmholtz resonators array is shown in Figure.2(b). There are N HRs installed on the main
duct with distance D. Similar to periodic ITs array, Bloch wave theory is also used to investigate the acoustic
wave propagating between each cell. According to Wang and Mak (12), eq. (7) is used to determine thetransfer matrix T of periodic HRs array, where ZIT is replaced by Zr from eq.(12). Again, eigenvalues λ 1 , λ 2
and the corresponding eigenvectors v1 =[ v1+v1− ] , v 2 =[ v2+v2− ] of periodic HRs array are acquired from T.

At the beginning of the duct, the incident acoustic wave has pressure P0, during the duct end with the anechoic
termination. Eq. (10) is used to solve parameters a1 and b1 and Eq. (11) would be used to calculate averagedtransmission loss TL of periodic HRs array.

(a) Helmholtz resonator

(b) Helmholtz resonators array

Figure 2: Schematic of a Helmholtz resonator and a periodic Helmholtz resonators array

4. Results and discussion
4.1

Validation of the FEM model

As shown in fig.1 (a), the geometries of infinity tubes used in this chapter are: main duct radius rM= 2.5cm,
IT radius rIT=1.25cm, IT length LIT= 31.4cm. Periodic distance D=30cm. A MATLAB script is used to
calculate the transmission loss of the ITs array. A Finite Element Method (FEM) simulation is conducted tovalidate the analytical results. The FEM simulation is performed by the commercial software COMSOLMultiphysics. In FEM simulation, a Background Pressure Field is added with pressure P0=1 Pa to match theboundary condition at the position x=-Lbegin. A Perfectly Matched Layer (PML) is added at the end side toabsorb the reflected wave, which could be regarded as an anechoic termination.
Fig.3 shows the transmission loss results of ITs array with different periodic numbers. The solid lines areanalytical results and the dash lines are FEM simulation results. The analytical results and TEM results
perfectly fit with each other. In fig.3 (a), a single infinity tube has a peak at around 635Hz. As the periodic
number N increasing, the averaged transmission loss TL would have two peaks at the frequency range 11000Hz. At around 400-600Hz, the acoustic pressure would attenuate up to 6dB, which is caused by Braggreflection (21). In the frequency range 600-800Hz, the acoustic wave would attenuate to a higher level—thiskind of noise attenuation results from the resonance of IT. Compare fig.3 (b) and (c), the peak of TL would
become higher when the periodic number N increase.

Figure 3: Comparison of the analytical approach predictions and the FEM simulation of periodic
ITs array for different periodic numbers N.

Figure 4: Comparison of the analytical approach predictions and and the FEM simulation of HRsarray for different periodic numbers N.
The geometries of the Helmholtz resonator used in this chapter are neck length LN=4.55cm, neckradius rN=1.75cm, cavity radius rC=4.7cm, and cavity length rL=4cm. Cross-section area of main duct
S M= 13.2cm2 and periodic distance D=47cm. Fig.4 shows the averaged transmission loss TL of HRsarray with different periodic numbers. In fig. 4(a), the resonance frequency of a single HR is around
391 Hz. The end correction increases the TL results of analytical prediction, which is in good
agreement with FEM simulation results. In fig. 4(b) and (c), the periodic HRs array would have threepeaks in the frequency range 1-1000Hz. In the frequency range 200-400 Hz and 700-900 Hz, noise isattenuated by Bragg reflection. In the 400-600 Hz frequency range, resonance is the main reason fornoise attenuation.
4.2 Transmission loss comparison of periodic HRs array and ITs array
Fig.4 (a) and (b) shows the averaged transmission loss of HRs array and ITs array for different
periodic numbers N. Because of the Bragg reflection, noise attenuation ability at certain frequency
domains can be increased compared to a single silencer. For periodic HRs array, TL between 200400Hz and 700-900 Hz become higher; for periodic ITs array, TL between 400-600Hz is increased.
Therefore, by designing suitable silencer geometries, periodic structures can be used to attenuate noisein certain frequency domains.
Compared with HR, IT has a simple geometry. HR needs a bigger cavity volume to increase abetter noise reduction performance, while IT just needs to change the length LIT to adjust resonancefrequency. For these reasons, IT would be suitable for industrial applications. However, comparing
fig.4 (a) and (b), it can be shown that the bandwidth of IT is smaller than HR. For a given noise
reduction range, the geometry of IT should be carefully designed to meet the demand.

Figure 55: Comparison of the averaged transmission loss of HRs array and ITs array for different
periodic numbers N.

5. Conclusion

This paper conducts a thorough theoretical and numerical investigation of periodic ITs array and
HRs array. Based on the classic wave equation, the conditions of pressure equilibrium andconservation of volume velocity at the junction position are used to solve the acoustic impedance Z IT
of a single infinity tube.The Bloch wave theory and transfer matrix method investigate the acoustic
wave propagating inside a periodic ITs array. The acoustic The averaged transmission loss TL results
are conducted to assess the noise attenuation ability of the periodic ITs array.A Finite Element Method(FEM) simulation is conducted to evaluate the TL results of the periodic HRs array and periodic ITs
array. It shows FEM simulation results fit well with the analytical model, which means Bloch wave
theory is suitable for predicting the acoustic wave propagating inside a periodic silencer array.The

TL results of the periodic HRs array and periodic ITs array are both given. It can be shown these twokinds of mufflers can be used to attenuate noise in the low-frequency domain. IT has simple geometry
and is more suitable for industrial applications.

ACKNOWLEDGEMENTS

The work described in this article was fully supported by a grant from the Research Grants Councilof the Hong Kong Special Administrative Region, China (project 15207820).

REFERENCES

1. Cai C, Mak C. Acoustic performance of different Helmholtz resonator array configurations. Applied
Acoustics. 2018;130:204-209.
2. Mak C, Wang Z. Recent advances in building acoustics: An overview of prediction methods and theirapplications. Building and Environment. 2015;91:118-126.
3. Mak C. A prediction method for aerodynamic sound produced by multiple elements in air ducts. Journalof Sound and Vibration. 2005;287(1-2):395-403.
4. Mak C. A prediction method for aerodynamic sound produced by multiple elements in air ducts. Journalof Sound and Vibration. 2005;287(1-2):395-403.
5. Mak C, Au W. A turbulence-based prediction technique for flow-generated noise produced by in-ductelements in a ventilation system. Applied Acoustics. 2009;70(1):11-20.
6. Shi X, Mak C. Sound attenuation of a periodic array of micro-perforated tube mufflers. Applied Acoustics.
2017;115:15-22.
7. Cai C, Mak C, Shi X. An extended neck versus a spiral neck of the Helmholtz resonator. Applied Acoustics.
2017;115:74-80.
8. Ingard U. On the Theory and Design of Acoustic Resonators. The Journal of the Acoustical Society ofAmerica. 1953;25(6):1037-1061.
9. Bradley C. Time harmonic acoustic Bloch wave propagation in periodic waveguides. Part I. Theory. The
Journal of the Acoustical Society of America. 1994;96(3):1844-1853.
10. Sugimoto N, Horioka T. Dispersion characteristics of sound waves in a tunnel with an array of Helmholtz
resonators. The Journal of the Acoustical Society of America. 1995;97(3):1446-1459.
11 Wang X, Mak C. Wave propagation in a duct with a periodic Helmholtz resonators array. The Journal of
the Acoustical Society of America. 2012;131(2):1172-1182.
12 Wang X, Mak C. Acoustic performance of a duct loaded with identical resonators. The Journal of the
Acoustical Society of America. 2012;131(4):EL316-EL322.
13 Cai C, Mak C. Hybrid noise control in a duct using a periodic dual Helmholtz resonator array. Applied
Acoustics. 2018;134:119-124.
14 Cai C, Mak C, Wang X. Noise attenuation performance improvement by adding Helmholtz resonators on
the periodic ducted Helmholtz resonator system. Applied Acoustics. 2017;122:8-15.
15 Lato T, Mohany A, Hassan M. A passive damping device for suppressing acoustic pressure pulsations:
The infinity tube. The Journal of the Acoustical Society of America. 2019;146(6):4534-4544.
16 Stewart G. The Theory of the Herschel-Quincke Tube. Physical Review. 1928;31(4):696-698.
17 Torregrosa A, Broatch A, Payri R. A study of the influence of mean flow on the acoustic performance ofHerschel–Quincke tubes. The Journal of the Acoustical Society of America. 2000;107(4):1874-1879.
18 Hixson E. Noise Control: An Engineering Discipline. Noise Control Engineering. 1979;12(3):111.
19 Bradley C. Time harmonic acoustic Bloch wave propagation in periodic waveguides. Part II. Experiment.

The Journal of the Acoustical Society of America. 1994;96(3):1854-1862.
20 Cai C, Mak C. Noise attenuation capacity of a Helmholtz resonator. Advances in Engineering Software.
2018;116:60-66.
21 Cai C, Mak C. Noise control zone for a periodic ducted Helmholtz resonator system. The Journal of the
Acoustical Society of America. 2016;140(6):EL471-EL477.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea
ABS-0980

A pilot study on the use of the heavy/soft impact source forbuilding acoustic impact measurements in housing
Birgit RASMUSSEN 1; Rasmus Stahlfest Holck SKOV 2
1

BUILD – Department of the Built Environment, Aalborg University Copenhagen, Denmark
2

Acoustics, Noise and Vibrations, FORCE Technology, Denmark

ABSTRACT
About half of all Danish dwellings in Multi-Storey housing have timber floor constructions with impact
sound insulation performance far below regulations for new housing. Jumping/running children is a major
source of annoyance and complaints in such housing. According to building regulations in Europe and mostcountries worldwide, impact sound is tested using a standardized tapping machine (with steel hammers andtotal weight ~10 kg) defined in building acoustic ISO standards for laboratory and field measurements.
However, in Japan and Korea, they traditionally used a softer impact source like a rubber ball (2.5 kg), whichaccording to research projects and experience provide a better correlation with annoyance fromjumping/running children. Recently, the rubber ball has been implemented in ISO standards as anadditional/alternative impact source and is thus available for use in acoustic regulations and classification. In
a Danish pilot project the rubber ball has been tested as an impact source in laboratory and field measurements
and compared to tapping machine results for traditional Danish timber floor constructions before and aftersound insulation improvement. The results and use in practice will be evaluated and results sent to the ISO
WG having developed the specification ISO/TS 19488 for acoustic classification of dwellings.
Keywords: Building regulations, requirements, sound insulation, airborne, impact, measurement methods

1. INTRODUCTION

Most countries in Europe have building regulations, which include limit values for acoustic qualities
for housing, including airborne and impact sound insulation between dwellings. An overview of suchrequirements in 35 countries in Europe is found in [1], and limits are field values with reference to
ISO 16283 [2] and ISO 717 [3]. For impact sound, the source is the tapping machine. However, the rubberball has recently – initiated by Korea and Japan – been implemented in ISO standards as an additional
impact source, cf. ISO 16283 and ISO 717 as well as the laboratory methods in ISO 10140 [4]. Outside
Europe, the tapping machine is also the most well-known impact source in relation limits for housing.
Several acoustic classification schemes exist in Europe with acoustic quality classes for the same
performance areas and methods, see [1] and [5], and an international classification method for housing
has been defined in ISO/TS 19488:2021 [6], being prepared in ISO/TC 43/SC 2/WG29. The ISO/WG
currently discusses revisions of ISO/TS 19488. Korea and Japan want the impact ball method includedin ISO/TS 19488, since their experiences show better simulation with sounds from jumping children,which is a major source of annoyance worldwide, also in Europe. In Denmark, neighbour noise also
annoys many people, see [7] and [8], and especially in housing with old light-weight timber floors.
This paper deals with sound insulation of floor constructions between dwellings with focus on impact
sound, including results from a pilot study with both the tapping machine and the rubber ball as impact
sources. The pilot study became possible due to interest in cooperation from two BSc students [9] making
a bachelor thesis at DTU about laboratory tests of a typical, old Danish light-weight timber floor and potential
for improvements of sound insulation. Due to constraints in the BSc thesis time period and availabilityof lab facilities, we had limited options for tests, but nevertheless we succeeded to get insight in thechallenges, when trying out the new alternative test with the rubberball as the impact source.
1
2

bira@build.aau.dk
rshs@forcetechnology.com

2. THE MULTI-STOREY HOUSING STOCK IN DENMARKIn Denmark there are in total about 2.7 mio dwellings, of these almost 1.1 mio dwellings in multi-storey(MS) housing. In Figure 1 is shown the number of dwellings in multi-storey housing according toconstruction year. Especially for old housing with timber floors, footsteps and jumping/running children
are major sources of annoyance and complaints. The pilot study is based on such constructions.
Typical timber floor construction
in old Danish MS-housing
constructed ~1850 to ~1950.

The number of such dwellings isabout 500.000 with estimatedacoustic class F, see Table 4 and [10],thus far below the performancerequired for new housing.
Figure from gi.dk,
https://gi.dk/publikationer/2015/nabostoj

Figure 1 – Dwellings in multi-storey housing in Denmark according to construction year. The
diagram is from [5], which includes more information about the Danish multi-storey housing stock.

3. MEASUREMENT METHODS & PROCEDURES: LABORATORY & FIELD
Measurements were carried out according to ISO methods, i.e. for laboratory tests the ISO 10140
standards [4] and for field tests the ISO 16283 standards [2]. For both laboratory and field tests, the rating
methods in ISO 717 [3] were applied. Measurements were made for both airborne sound insulation andimpact sound insulation (tapping machine) as well as impact sound using the rubber ball, being the key
focus of the pilot study, fully implemented in the ISO standards “recently”, inspired by experience from
especially Japan and Korea and already standardized in those countries previously. The latest standards
from Japan and Korea are [11] and [12] with the same impact ball characteristics as in the ISO standards.
The laboratory measurements were carried out in the DTU test facilities (complying with the
ISO 10140 series) in building 355 for test of airborne and impact sound insulation of building
constructions. Test specimen size was 10 m2.
The following test equipment was applied: Sound level meter B&K 2270, tapping machine
B&K 3207, B&K microphones, an old impact ball (Japanese protype, probably from before year 2000)
and a new rubber ball Nor279. The tapping machine and the impact balls are shown in Figure 2.

Figure 2 – Left: Tapping Machine B&K 3207; Middle: Impact Ball Nor279; Right: Impact Ball (Old Ball)
The reason for using two rubber balls was that we started out using FORCE’s old rubber ball, being unawareof the physical characteristics not complying with the new standards, and it was only in the middle of the test
series, when discussing verification checks of equipment, we became suspicious, and rented (later bought) a
new ball to check that the old ball could still be used. However, this turned out to be impossible forstandardized measurements since the results for the two balls were very different. Nevertheless, we continued
to use both impact balls, hoping to see systematic differences and to learn something about these two balls.
Dr. Hiramitsu [13] from Japan explained about the development of the rubber ball (extract mail): “ The actual
impact noise of child jumping and running around had been a problem in apartment buildings around 1970s. Since the noise generated
by the actual impact was lower in frequency range than that of the tapping machine, there was an argument that a different impact source
should be used. Coincidently, the sound generated by car-tire impact (Bang machine) was similar to the sound of child jumping andrunning around. However, the impact force of Bang machine is too excessive (especially for lightweight construction buildings), and thedevelopment of impact ball began in the 1990s. During the development phase, prototypes of various impact balls are being made. Since
these were made from rubber (e.g., natural rubber), the impact force characteristics varied greatly depending on the environmental
temperature. (For example, at higher temperatures, the rubber became softer, thus extending the impact time and reducing the peak impact
force value.) – After that, the impact ball material was reviewed and made from silicone rubber, resulting in an impact source withtemperature-independent impact force characteristics. This background may result in the existence of impact balls (prototypes) that are
not suitable for the impact force exposure levels specified by JIS and ISO.
Calibration is recommended to check the impact force characteristics using a force plate. However, the impact force characteristicsof the impact ball are rarely checked. This is because there is no change over time and no temperature dependence.”

Some physical parameters of the impact balls are shown in Table 1. Compared to the tapping
machine, the ball has approximately ¼ weight and ½ price.
Table 1– Some physical parameters of the impact balls
Weight (kg)
Hardness Shore A*
Old Japanese prototype (assumed to be a Japanese
2,55
76
prototype, probably from before year 2000)
Norsonic (Impact Ball Nor279) – calibrated from factory)
2,45
39* We did not have access to a force plate for check of impact force characteristics and applied a test method
inspired by ISO/TS 11819-3:2021 [14]The measurement procedures applied fulfil the requirements in the ISO test standards. Concerning
the pilot study, the positions of the tapping machine and the impact balls are most important. The
standards specify minimum 4 positions of the impact source for both laboratory and field tests with
instructions concerning positions related to joists/beams and direction for the tapping machine. – The
tests were made with 6 source positions for the laboratory tests and 5 for the field tests. Concerning theimpact ball tests in the laboratory, 6 stationary microphone positions were used for each source position,e.g. in total 36 combinations, and correspondingly 5 for the field tests, e.g. in total 25 combinations.

4. LABORATORY TESTS: CONSTRUCTIONS AND RESULTS

The pilot study was made possible due to cooperation with the BSc students and their flexibility.
After mounting of the basic laboratory timber floor (“original slab”) simulating as far as possible andpractical a timber floor as constructed in the field, se Figure 1, there were in total about three weeks
for all tests, including complicated construction changes between some of the tests. Highest priority
for testing was of course given to the BSc students.
The pilot study included laboratory tests of 6 different floor constructions, see Table 2, four ofthem (P0, P0C, P1, P1C) installed by the BSc students. The results below are however from new tests
made with FORCE Technology equipment, see Section 3. In the end of the test period, two additional
constructions, P5 and P6, were tested. They are similar to P1, but with a new parquet floor of known
type as typically applied by the building association, when a new floor is needed. Two different
interlayers were used under the floor. The intention was to make a field test with a parquet floor likeP5 or P6 for comparison with the laboratory tests, but unfortunately access to relevant apartments could
not be organized within the relevant time period. Thus, comparisons between the “same” constructionsin the laboratory and field are pending and waiting for an opportunity in the future.
An overview of tests for the pilot study is described briefly in Table 2 below and results found in Table 3.
Table 2 – Tested constructions in the pilot study. Sketches based on drawings from [9].

P0 + P0C

Floor heights
P0: 266 mm
P0C: 342mm

P1 + P1C(P5), (P6)
Floor heights
P1: 288 mm
P1C: 364mm
P0
P0C
P1
P1C
P5
P6

The basic laboratory timber floor “original slab” simulates as far as possible and practical a timber floor as constructed in
the field, but with clay replaced with sand.
P0 with added ceiling mounted at P0. The ceiling consists of 2 two gypsum plates mounted on profiles fixed at P0, mineralwool in spacing. Ceiling height 76 mm.
Like P0, but with a parquet floor and a 2 mm foam interlayer on top of the basic floor. The parquet floor was of unknown
origin, but available from previous tests, probably some years ago. Test specimen prepared by the BSc students.
P1 with added ceiling mounted like P0C.
Similar to P1, but with a new parquet floor, same type as applied by the building association, when installing a new floor in
an apartment. Thin interlayer (grey) aiming at reducing impact sound.
The same parquet floor as for P5. Thin foam interlayer (blue).

Table 3 – Laboratory measurements for timber floor with and without additional ceiling:
Airborne sound insulation, Impact sound level and Impact ball.
WITHOUT additional ceiling
WITH additional ceiling
Rw / Rw+C50 Ln,w / Ln,w + C50 Ball (Old / Nor)Rw / Rw + C50 Ln,w / Ln,w + C50 Ball (Old / Nor)
Construction
(dB)
(dB)
LiA,Fmax (dB) Construction
(dB)
(dB)
LiA,Fmax (dB)P0*
53 / 50
63 / 64
73 / 63
P0C
61 / 57
56 / 59
68 / P1
57 / 54
61 / 63
74 / 61P1C
62 / 58
56 / 59
74 / P5
59 / 56
63 / 65
74 / 62P6
59 / 56
63 / 66
75 / 62
Test constructions P0 is the basic construction, P1, P5, P6 has a parquet floor* During all tests, a load 25 kg/m2 was applied, except for P0, which was tested without load.

In Figure 3 are shown laboratory measurement results for timber floor with and without additional
ceiling. Table 3 and results in Figures 3a and 3b show improved results with the ceiling installed. In
Fig. 3c for the rubberball measurement, it is not possible to interpret why the blue dashed line for P0C
is higher (worse) than the others in the upper frequency range.

Figure 3 – Laboratory measurement results for timber floor with and without additional ceiling:(3a) Airborne sound insulation R; (3b) Impact sound level Ln; (3c) Impact ball (Old Ball) Li,Fmax.
Legends: Solid lines for construction without ceiling; Dashed lines with ceiling.
In Figure 4 are shown results for P0 (basic timber floor) and the timber floor with three parquet floor
solutions. Results for P5 and P6 are as expected almost identical, and results for P1 slightly different.
The reason for P5 and P6 was to test very basic floor solutions as typically applied in practice, whenreplacing a worn out floor. Note different dB axes in (4a) and (4b).

Figure 4 – Laboratory measurement results for timber floor with and without additional flooring:(4a) Airborne sound insulation R; (4b) Impact sound level Ln; (4c) Impact ball (Nor279) Li,Fmax.

5. FIELD TESTS: CONSTRUCTIONS AND RESULTS
Field tests were made in a housing block built before 1920, 2200 Copenhagen N, G121, 3rd and 4th floor.
Timber floor as shown in Fig. 1, but with additional ceilings installed in the 3rd floor rooms, height ~ 120 mm,
two gypsum plates mounted on profiles fixed to room walls, i.e. independent from the basic floor
construction (unlike P0C and P1C), mineral wool in spacing. The field measurements consisted of airborne
and impact sound insulation tests being a part of another BUILD project (tests made by Rambøll A/S, project
results to be published ultimo 2022) and rubberball measurements being a part of the pilot study. All measurements were made on 21 April 2022.
The airborne and impact sound insulation results are shown in Fig. 5a and 5b. The results are similar forboth apartments and correspond to acoustic Class C, being the requirements for new dwellings, see Table 4.
The sound insulation before mounting of the new ceilings was Class E for airborne sound and Class F for
impact sound (tapping machine).
The rubberball results are shown in Fig. 5c. Ideally, the two apartments should give similar overall
results, but there are obviously huge differences. The differences between the two upper and two lower
curves are not due to differences in balls. The significant differences must be due to the impact balltest method characteristics and differences in constructions. In fact, for the field situation, we do notknow the actual details of the timber construction or if changes have been made since the construction
about 100 years ago. However, when the ball hits the floor, it is a heavy exposure in one point, andthus it was found worthwhile showing the individual curves for the five ball drops in each room, see Fig. 6.

Figure 5 – Field measurement results for timber floor with additional ceiling, two apartments:(5a) Airborne sound insulation R’; (5b) Impact sound level L’n ; (5c) Impact balls L’ i,Fmax
Table 4 – Occupants expected satisfaction for different sound classes
according to DS 490:2018. Summary based on information in DS 490 [10].

Field test results for the individual rubberball impact positions in the apartments are found in Fig.
6a and 6b for the left and right apartment, respectively. Ideally, the two apartments should give similar
overall results, but there are obviously huge differences between ball impact positions. Other things
being equal, it seems as if much lower levels occur, when the ball hits the joists than when it hits
between the joists. The apartments were occupied, and we did not have access for further measurements in the pilot study. Note different dB axes in (6a) and (6b).

Figure 6 – Field test results L’i,Fmax for the impact ball method in two apartments: Individual impact
positions and average results of the two impact balls, blue (old ball) and green (Nor279) respectively.
(6a): Apartment to the left G121tvSS; (6b) Apartment to the right: G121thSS

6. COMPARISON OF RESULTS FOR THE TWO IMPACT BALLS

Since there is a need to understand better the behaviour of the rubberball impact results, it was
found appropriate to show all results from the laboratory and field in two diagrams, see Fig. 7 withlaboratory results in the left diagram and field results in the diagram to the right.
For the laboratory results, the differences between the old and new ball are similar up to about
250 Hz. However, with an additional floor, there are large differences above 250 Hz. For field results,
the largest differences between the balls are found for the “th” apartment. In summary, the results
show that we cannot convert results from one type of ball to the other one.

Figure 7 – Comparison of the two impact balls in laboratory Li,Fmax (left) and field L’ i,Fmax (right).
The red curves show the differences between the old and new ball.
Note: The two diagrams have different dB-scales (left axes). Differences between the old/new ball are in red (dB scale right axes)

7. DISCUSSION
Due to the unexpected findings during the pilot study – the major one being the awareness of the oldrubberball not complying with the standards – we asked eight building acoustic experts in sevencountries about their application of the rubber ball for laboratory and field measurements according to the
ISO 10140 and ISO 16283 standards and about the ball types and their check of the rubber ball characteristics. The institutes asked were four in Europe, one in Canada, one in Korea and two in Japan. Some of theinstitutes also informed about publications related to previous studies with rubberball measurements.
The rubberball applications in these institutes are quite mixed. Some do not use the rubber ball forstandardized tests, but for other building acoustic research. Some use the rubber ball for laboratory tests
only, some for field tests only, and a few for both. Some institutes use the rubber ball for tests in a mock-up.
In general, the rubber ball tests are mainly used for wooden constructions. – Based on responses fromthe institutes, it seems as if regular checks of the rubber ball characteristics are only used in a few
places, but not yet implemented in most QS systems, which should be changed in the future.
During the pilot study, we discussed the details of the measurement procedures and potential benefitsof using the rubber ball for impact tests. Compared to the tapping machine, the ball has approximately¼ weight, ½ price and much less volume, and the subjective annoyance is reduced for occupants
during field tests. However, considering the total test duration for a measurement, there seems to be
no significant differences between the two impact sources, which is due to restrictions for e.g. number
and positions of sources and microphones as well as other parts of the test procedures.
We would like to understand the reasons for the seemingly random results for some of the impact ballpositions in the field, but further access to the apartments was not possible during the pilot study. A main
problem for field tests in old existing housing is that construction details inside the timber floor areinvisible. A possibility in further studies could be to analyze results for different ball impact positions in
the laboratory tests to observe if a similar spread like in the field occurs or not. Our results indicate thatrubberball impact levels are higher for the rubberball impact on the joists than between the joists.
To evaluate the potential benefits of the rubberball as an impact source, we need more laboratory
and field tests as well as laboratory/field comparisons for similar constructions. Important is also to
get experience for other construction types applied in old and newer/new housing.

8. CONCLUSIONS & RECOMMENDATIONS FOR FURTHER STUDIESThe pilot study included laboratory and field tests using the rubberball as impact source at old
Danish timber floor constructions with and without additional ceiling and/or floor covering. Since only
a limited number of tests was possible within the time frame of the study, and no other construction
types than the old timber floor were tested, several needs for further studies are identified:– Additional field measurements and/or inspections in the two apartments with lack of consistency
between the rubberball results. Analysis of spread in laboratory results for different ball positions.
– More field measurements in other old apartments with rubberball tests both before and after improvementof sound insulation with ceilings and/or new floor constructions. Some of the tests could include theadditional ceiling/floor constructions included in the BSc study, but not tested in the pilot study.
– Laboratory and field measurements for construction types applied in newer and new housing andcomparison between results in the laboratory and field.
– More communication with the institutes having responded to request for information about theirrubberball applications (see above) and study of the publications [15]-[20] from those countries.
– Study on the importance of load on floor constructions, also on light-weight reference floors.
– Check/verification procedures for rubber ball characteristics, including time intervals and ageing.
Results of the pilot study will be presented and discussed in ISO/SC2/TC43/WG29 with acoustic
classes for rubberball tests currently on the agenda and in WG18 having prepared the test methods.

ACKNOWLEDGEMENTS
The authors want to thank the BSc students, Melanie Førsterling Gotfredsen & Julie Bech Liengaard, for their
enthusiasm concerning improvement of the old housing stock and for discussions and cooperation during the BSc
project period. We also want to thank Kurt Larsen and Jan Tobiasen from the Building Association AKB for
discussions about constructions in-situ, for help installing test specimen P5 and P6 in the laboratory and forassistance getting access to the apartments used for the field measurements. Furthermore, thanks to Jens
Oddershede, FORCE Technology, who “jumped in” on a short notice and made the impact ball measurements inthe field and to Lars Sommer Søndergaard, FORCE Technology, who provided comments on the draft paper.

Finally, we want to thank acoustic colleagues from research institutes in Europe (PTB/DE, HFT-Stuttgart/DE,
EMPA/CH, CSTB/FR), in Canada (NRC), Korea (FILK) and Japan (AIST) for responding to our questions about
their use of rubber balls and at last Atsuo Hiramitsu (Kenken/Japan) for explaining the development history of
the rubber ball, including background for the outdated prototype, we had in Denmark.
This article is part of a project funded the Danish National Building Fund (Landsbyggefonden).

REFERENCES[1] Rasmussen, B. (2019). Sound insulation between dwellings – Comparison of national requirements in
Europe and interaction with acoustic classification schemes. Proceedings of ICA 2019 (pp. 5102-5109).
Deutsche Gesellschaft für Akustik (DEGA e.V.). https://doi.org/10.18154/RWTH-CONV-239983[2] ISO 16283, Acoustics – Measurement of sound insulation in buildings and of building elements – Part 1:
Field measurements of airborne sound insulation between rooms, 2014. – Part 2: Field measurements ofimpact sound insulation of building elements, 2020. – Part 3: Field measurements of airborne sound insulationof facade elements and facades, 2016.
[3] ISO 717:2020, Acoustics – Rating of sound insulation in buildings and of buildings elements. – Part 1:
Airborne sound insulation. – Part 2: Impact sound insulation.
[4] ISO 10140:2021 Acoustics - Laboratory measurement of sound insulation of building elements.
– Part 1: Application rules for specific products; – Part 2: Measurement of airborne sound insulation;– Part 3: Measurement of impact sound insulation; – Part 4: Measurement procedures and requirements;– Part 5: Requirements for test facilities and equipment.
[5] Rasmussen, B. (2020). Encouraging acoustic renovation of housing in Denmark by extending acoustic
classification with two lower classes E and F for old housing. In J. Yong Jeon (Ed.), Proceedings of 2020
International Congress on Noise Control Engineering: INTER-NOISE 2020 The Korean Society of Noiseand Vibration Engineering, Seoul, Korea.
[6] ISO/TS 19488:2021. Acoustics — Acoustic classification of dwellings.
[7] Rasmussen, B., & Ekholm, O. (2021). Neighbour noise in multi-storey housing - Annoyance and potential
health effects. Proceedings of INTER-NOISE 2021 (Vol. 263(4), pp. 2783-2792). [#2228] Institute of NoiseControl Engineering. Noise-Con Proceedings Vol. 21 (Print) https://doi.org/10.3397/IN-2021-2228.
[8] Jensen, H. AR., Rasmussen, B., & Ekholm, O. (2019). Neighbour noise annoyance is associated with various
mental and physical health symptoms: Results from a nationwide study among individuals living in multistorey housing. BMC Public Health, 19, 1-10. [1508]. https://doi.org/10.1186/s12889-019-7893-8[9] Melanie Førsterling Gotfredsen and Julie Bech Liengaard (2022). Sound insulation of wooden slabs inexisting buildings. Department of Electrical and Photonics Engineering, Technical University of Denmark.
[10] DS 490:2018. Lydklassifikation af boliger. (Sound classification of dwellings). Danish Standards, Denmark.
[11] A 1418-2:2019. 建築物の床衝撃音遮断性能の測定方法− 第 2 部：標準重量衝撃源による方法. Acoustics - Measurementof floor impact sound insulation of buildings – Part 2: Method using standard heavy impact sources. Japan.
[12] KS F 2810-2:2012. 건축물의 바닥충격음 차단성능 현장 측정방법 – 제 2 부: 표준 중량 충격원에 의한 방법. Field measurementsof floor impact sound insulation of buildings – Part 2: Method using standard heavy impact sources. Korea.
[13] Personal communication, e-mail 2022-07-15 with Dr. Hiramitsu, Building Research Institute, Ibaraki, Japan.
[14] ISO/TS 11819-3:2021 Acoustics – Measurement of the influence of road surfaces on traffic noise – Part 3:
Reference tyres.
[15] Heinrich Bietz, Volker Wittstock (2015). Vibroakustische Eigenschaften von technischen Ersatzschallquellen
im Vergleich zu Gehern. Proceedings of DAGA2015, p.1237-1240.
[16] Atsuo HIRAMITSU; Ryuta TOMITA; Susumu HIRAKAWA; Masayoshi SATO (2019). Floor impact
sound insulation of the six-story wood-frame model building. Proceedings of ICA2019, p.5007-5012.
http://pub.dega-akustik.de/ICA2019/data/articles/001442.pdf.
[17] Zeitler, B.; Nightingale, T. R. T.; King, F (2008). Methods to control low frequency impact noise in wood
frame construction. Proceedings of Acoustics '08, pp. 5589-5594. Paris, France.
[18] Zeitler, Berndt; Sabourin, Ivan; Schoenwald, Stefan; Wenzke, Erik (2012). On reducing low frequency
impact sound transmission in wood framed construction. Proceedings of InterNoise2012, pp. 6653-6662.
New York, USA.
[19] Hiroshi SATO; Junichi YOSHIMURA (2014). Classification scheme of floor impact sounds with thestandard rubber ball in dwellings. Proceedings of Inter-Noise 2014, Melbourne, Australia.
[20] J. H. Jeong (2021). Background Noise, Noise Sensitivity, and Attitudes towards Neighbours, and a
Subjective Experiment Using a Rubber Ball Impact Sound. IJERPH, 2021, 18 (14).
Int. J. Environ. Res. Public Health 2021, 18(14), 7569; https://doi.org/10.3390/ijerph18147569

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0981

Acoustic classification of dwellings – A growing diversityof sound insulation descriptors in national schemes in Europe
Birgit Rasmussen 1
1

BUILD – Department of the Built Environment, Aalborg University Copenhagen, Denmark

ABSTRACT
Acoustic classification schemes for dwellings exist in several countries in Europe, typically prepared andpublished as national standards. The schemes define quality classes intended to reflect different levels of
acoustic comfort. The main criteria concern airborne and impact sound insulation between dwellings, facadesound insulation and service equipment noise. The schemes have been implemented and revised gradually
since the early 1990s. However, due to lack of coordination, there are significant discrepancies, and new
standards and revisions continue to increase the diversity in Europe. Descriptors, number of quality classes,
denotations, class intervals, total range of classes and class levels vary – as well as the status in relation toregulations. The diversity in Europe is an obstacle for exchange of experience about constructions fulfilling
different classes and thus for design and trade. The paper presents an updated overview of acoustic
classification schemes in Europe and detailed information about the variety of descriptors applied for soundinsulation between dwellings. The implications of interaction – or lack of interaction – between acoustic
classification schemes and national acoustic regulations will be indicated and discussed. Finally, the mainfeatures of ISO/TS 19488 about acoustic classification of dwellings will be included in the comparative studyof national schemes.
Keywords: Sound insulation, descriptors, acoustic classification, building regulations, housing

1. INTRODUCTIONIn Europe, acoustic regulations for dwellings are included in building regulations in more than 30
countries, cf. [1]. In some countries, requirements have existed since the 1950s or even before, whilein other countries, acoustic regulations came later or do not yet exist. However, complying withregulatory requirements does not guarantee satisfactory conditions for the occupants in dwellings, andsince the early 1990s, several countries have developed and introduced acoustic classification schemes(abbreviated ACS in this paper) with classes intended to reflect different levels of acoustic protection
and comfort, see illustration in Table 1. The ACS in Europe are national schemes, the majority being
published by national standardization organizations. The schemes are very different due to lack of
coordination between countries.
Table 1 – Illustration of acoustic quality classes using various, partly FICTIVE ranges and denotations.
Acoustic quality classes☺☺☺

High acoustic
protection andcomfort

A

B

C

III

II

I

A

D

E

F

a

b

c

d

I

II

III

IV

B

C

D



Low acoustic
protection andcomfort

In both acoustic regulations and ACS, limits relate to airborne and impact sound insulation, noiselevels from traffic and service equipment as well as other acoustic and noise aspects, and limit values
must be complied with in the completed building. This paper deals with airborne and impact sound1

bira@build.aau.dk

insulation between dwellings in multi-storey housing. Test and rating methods are described in ISO
16283 [2] and ISO 717 [3], and estimation methods for acoustic performance of buildings in
ISO 12354 [4], which are all so-called harmonized standards and thus implemented also as EN
standards and as national standards in CEN countries.
In the following Sections are found overviews for Europe of acoustic classification schemes, airborne
and impact sound insulation descriptors applied in ACS, sound insulation requirements in selected
countries and use of low-frequency descriptors in regulations and ACS. Discussion, conclusions andrecommendations are found in the last part of the paper.

2. ACOUSTIC CLASSIFICATION SCHEMES (ACS) IN EUROPE – HOUSING
Acoustic classification schemes (ACS) for dwellings exist in at least 14 countries in Europe. In Germany,
there are two schemes, one published by VDI, the other by DEGA. Thus, there are in total 15 schemes[5]-[19] in Europe (and maybe more not known by the author of this paper). An overview of theschemes is found in Table 2. The schemes considered are those having minimum three acoustic classes.
For each scheme listed, the class denotations, number of classes and relation to the national buildingcode are indicated. The ISO Technical Specification ISO/TS 19488 [20] is added for comparison. For
more information about the development of ISO/TS 19488, see [21]. Table 2 also includes numbers of
acoustic classes below and above the national regulations. – A similar table was presented in [1], but
Table 2 below has been extended with the new Spanish scheme UNE 74201 [16] and updated due torevisions of NS 8175 [8] and ÔNORM B 8115-5 [15] – and publishing of ISO/TS 19488 [20].
Table 2 – European schemes for acoustic classification of dwellings, [5]-[19], relation to building
regulations and class information. ISO/TS 19488 (2021), [20], included for comparison.

From Table 2 it is seen that four of the five Nordic countries (FI, IS, NO, SE) and IT have one
quality class below regulations, LT and ES have two classes + npd, AT and NL two classes, and DE(DEGA 103) 1+npd. DK and TR have three classes below regulations, implying a much higher chanceof classifying older housing. DE (VDI 4100) and PL have none, thus following the original idea of
acoustic classes to be only/mainly for specifying better acoustic conditions than regulations. To sum up
briefly, the existing acoustic classification schemes do in general not include acoustic classes fitting all
major parts of the existing housing stock, although an extension with lower classes for old housing could
pave the road for a future acoustic labelling in a similar way as for the mandatory energy labelling.

3. SOUND INSULATION BETWEEN DWELLINGS: DESCRIPTORS IN ACS
Airborne and impact sound insulation descriptors applied in the national acoustic classification
schemes listed in Table 2 are found in Tables 3 and 4. Limit values have not been inserted, but shouldbe part of future studies. For airborne sound insulation, higher values mean better performance, for
impact sound insulation, it is opposite, so lower values mean better performance.
Thus, for airborne sound insulation, limit values are in general minimum values to be complied
with, and for impact sound insulation, limit values are in general max values. Exceptions are thelowest classes in Austria and Spain, where no limits must be complied with, see Tables 3 and 4.
Comparing the data from the classification schemes in Europe, see Table 2, detailed class criteria
in [5]-[19] and overview of descriptors in Tables 3 and 4, significant differences are found, e.g. the following:– Number of quality classes (3 to 6) and denotations. Note: “npd” not counted as a class.
– Descriptors used for sound insulation criteria.
– Use of low-frequency spectrum adaptation terms according to ISO 717:2020.
– Intervals between classes.
– Range of quality classes ( 8 to 23 dB for airborne,  14 to 30 dB for impact) and position.
– Relation to regulatory requirements.
– Procedure/rules for class assignment based on sample measurements.
– Verification of class, which could be by field measurements only or a combination of calculations,visual inspections, and field measurements.
– Subjective descriptions of acoustic conditions for various types of sounds and neighbour noises.
Other relevant comparisons between the national acoustic classification schemes could be e.g. about:Sound insulation internally in dwellings; Sound absorption in stairwells; Outdoor noise levels;
Classification certificates.
Table 3 – Airborne sound insulation between dwellings. Descriptors in acoustic classification schemesin Europe. References [5]-[19]. ISO/TS 19488 (2021), [20], has been included for comparison.

Table 4 – Impact sound insulation between dwellings. Descriptors in acoustic classification schemesin Europe. References [5]-[19]. ISO/TS 19488 (2021), [20], has been included for comparison.

While Tables 3-4 do not present limit values, such limits have been included in some of theprevious studies, e.g. in 2020 for the Nordic countries, cf. [22], and in 2012, see [23], for 10 of the 15
schemes included in Tables 2-4. Tables with descriptors for 2018 are found in [24]. Comparing thechanges over time shows a growing diversity, not only for descriptors.
Focus in most of the acoustic classification schemes have been to provide quantitative descriptions
about limits and methods. Few of them, e.g. [13], [14] and [15], provide qualitative descriptions of
acoustic conditions, although such information would be useful for all groups of users. In the below
Table 5 is found a quite simple description of classes in DS 490 related to occupants' expected satisfaction.
Table 5 – Occupants' expected satisfaction for different acoustic classes
according to DS 490:2018 [5]. Summary based on information in DS 490.

4. SOUND INSULATION BETWEEN DWELLINGS: EXAMPLES REQUIREMENTS
A comparative study of airborne and impact sound insulation descriptors and requirements for
multi-storey housing in 35 countries in Europe was carried out in 2019 and findings presented in [1],which includes both limit values ([1], Tables 2-3) and graphical presentations ([1], Figures 1-2). Note:
There is at least one typo and a mistake in Table 3 in [1], since Finland applies a descriptor based on L’nT,w(not L’ n,w) and Ireland had/has a requirement L’ nT,w ≤ 58 dB (not 62 dB).
The results clearly indicate significant discrepancies in descriptors and requirements for dwellings. An
overview of number of countries with various sound insulation descriptors is found in Table 6 below (copiedfrom [1]) for 31 countries in Europe (since 4 of the 35 countries do not have such regulations),. The
dominant descriptors are clearly R'w and L’n,w, although there has been a trend during the last decade
towards descriptors based on D nT,w and L’nT,w as e.g. in Sweden and Finland, see [22].
Table 6 – Sound insulation between dwellings: Number of countries applying
various descriptors for regulations in Europe. The table is a copy from [1].
Sound insulation descriptors applied for regulatory requirements
between dwellings in 31 countries in Europe. Status April 2019.
Airborne soundNo. ofcountries
15
7
3
3
1
1
1
?
?
?

Descriptor
R' w
D nT,w
R‘ w + C
D nT,w + C
D nT,w + C 50-3150
D nT,A (≈ D nT,w + C 100-5000 )D nT,w + C tr
Variants
Recommendations
Special rules

Impact soundNo. ofcountries
17
9
2
2
1
?
?
?

Descriptor
L’ n,w
L’ nT,w
L’ nT,w + C I
L’ nT,w + C I,50-2500
L’ w
Variants
Recommendations
Special rules

To the author’s best knowledge, there have not been changes in regulations between April 2019and May 2022. Nevertheless, it is found relevant to show a table with selected countries, see Table 7-8.
Included are primarily those countries having quite strict requirements and (except for Belgium) ACS,
implying potential learning about construction details f ulfilling high requirements and classes with
LF-terms. References to building regulations for the 8 countries are [25-29] for the Nordic countries
and [30-32] for Austria, Belgium and Germany. Of special interest are how the current LF-recommendations,cf. Tables 7-9, and the challenges related to wooden buildings will be dealt with in the future.
Table 7 – Airborne sound insulation between dwellings.
Main requirements in 8 selected countries (1)Table 8 – Impact sound insulation between dwellings.
Main requirements in 8 selected countries (1)5. ISO 717 LF SOUND INSULATION DESCRIPTORS IN REGULATIONS AND ACS
The history of ISO 717 sound insulation descriptors is described in [24] and [3 3-34], and nochanges in spectrum adaptation terms were made in the latest version from 2020. In many European
countries, the need for including low frequencies appropriately in rating of construction performancehas been increasingly acknowledged by the building industry due to experience and surveys pointing
in that direction, see e.g. [35] and [36]. Impact sound is clearly the most disturbing/annoying neighbour noise,not least in light-weight buildings. Thus, there is a high need for good prediction models, particularly forwooden buildings. However, due to high data uncertainties for wooden materials and products, the ISO 12354
methods for calculation of airborne and impact sound insulation between rooms have shortcomings, butdevelopment efforts are done in an ISO WG to improve applicability for CLT timber constructions.
A summary of low-frequency findings in the comparative studies of descriptors in regulations,recommendations and classification schemes in Europe is found in Table 9. It is seen that 8 of 14
countries listed in Table 2 have included LF-descriptors in the upper classes in acoustic classification schemes(for details, see Tables 3-4). Two countries have applied LF descriptors in mandatory airborne and/or impact
sound insulation requirements, and further four countries have made recommendations, for one of thesecountries (DK) related to light-weight constructions only, see Tables 7-8.

Table 9 – Number of countries in Europe using ISO 717 low-frequency sound insulation descriptors.
LF descriptors in acoustic regulations, recommendations
and acoustic quality classes in Europe. Status May 2022.
Acoustic regulations
NumberAcoustic
of countries
LF mandatory
LF recommended quality classes
Airborne
Impact1 (SE)
2 (SE & FI)

3 (IS, NO. LT) + 1 (1)

8 (2)

(1)

8 (2)

3 (IS, NO. LT) + 1(1) In DK, it is recommended using LF-descriptors in case of light-weight constructions (walls< 100 kg/m2, floors < 250 kg/m2), [21].
(2) Classes A and B in DK, FI, IS, NO, SE, LT, LV, AT: LF-descriptors included.

In general, there is an increasing attention to the LF-performance. In Germany, LF performance is notincluded in requirements [32] or in VDI 4100 [13], but due to strong customer requests, a German
book [37] about sound insulation of wooden buildings have LF data included. In [36], describing research
results from Swedish case studies about sound insulation of wooden housing, it is recommended to make the
Swedish impact requirements L’nT,w,50 stricter and for lightweight/wooden housing to go further down to
25 Hz, i.e. design for L’nT,w,25.

6. SUMMARY & RECOMMENDATIONSThe national acoustic classification schemes (ACS) in Europe differ significantly concerning soundinsulation descriptors, numbers/levels of classes and relation to building regulations etc., see Sections 2-3. The
diversity of descriptors is high and growing, and the former direct relations to regulations have disappearedin some countries. For example, regulations in four (DK, IS, NO, SE) of the five Nordic countries in 2012 [23]referred to class C in the national ACS, and FI did not have such reference, but the limit values were the same.
In 2020, ACS descriptors had changed in three of the five countries, and relation to regulations reduced [22].
Building regulations typically specify only minimum requirements for acoustic conditions for new
dwellings, cf. [1]. It seems obvious that acoustic classes are relevant both for higher comfort andprotection in new housing as well as for existing housing before renovation by having classes suitable forolder housing with a performance far below current regulations, thus making the gap to regulations visible.
Recommendations for further activities/initiatives/studies– In each national ACS: Make a clear relation/interaction between BR and ACS, see [1] and this paper.
– ISO/TS 19488 [20] was developed based on experiences from many countries. The ISO/TS could be
developed further, see topics in [21], and some countries could get useful input to national BR and ACS.
– Number of quality classes in ACS should be adapted to enable labelling of the whole national housing stock.
– Spectrum adaptation terms in ISO 717 [3]: For impact sound, prepare for potential new (LF) descriptors
suitable for lightweight constructions (ISO 717-2). For airborne sound (ISO 717-1), suggest removing terms
up to 5 kHz, thus reducing number of terms to the half.
– Add information about subjective perception/audibility for various sound sources like in DE [13-14](VDI & DEGA103) and AT [15]. Examples of neighbour noise sources are also found in [38].
Harmonization is still good ☺, see [20, 21, 39]. In the end, acoustic classification and regulations shall serve
the needs of people, who need privacy, comfort and protection in their homes during various activities.

ACKNOWLEDGEMENTS
The author is grateful to the acoustic colleagues, who assisted by answering questions about thenational acoustic regulations, classification schemes or guidelines in their country. However, theauthor is solely responsible for errors in the paper, and any comments, corrections and updated
information will be appreciated.

REFERENCES[1] Rasmussen B. (2019) Sound insulation between dwellings – Comparison of national requirements in Europe
and interaction with acoustic classification schemes. Proceedings of ICA 2019, 23rd International Congresson Acoustics, Sept. 2019, Aachen, Germany. Deutsche Gesellschaft für Akustik (DEGA e.V.).
https://doi.org/10.18154/RWTH-CONV-239983[2] EN ISO 16283, Acoustics – Measurement of sound insulation in buildings and of building elements – Part 1:
Field measurements of airborne sound insulation between rooms, 2014. – Part 2: Field measurements ofairborne sound insulation of facade elements and facades, 2020. – Part 3: Field measurements of impact soundinsulation of building elements, 2016.
[3] EN ISO 717:2020, Acoustics – Rating of sound insulation in buildings and of buildings elements. – Part 1:
Airborne sound insulation. – Part 2: Impact sound insulation.
[4] EN ISO 12354:2017 Building acoustics – Estimation of acoustic performance of buildings from theperformance of elements – Part 1: Airborne sound insulation between rooms – Part 2: Impact sound insulation
between rooms. – Part 3: Airborne sound insulation against outdoor sound.
[5] DS 490:2018, Lydklassifikation af boliger (Sound classification of dwellings). Danish Standards, Denmark.
[6] SFS 5907:2004, Rakennusten Akustinen Luokitus, Finland. (English version 2005: Acoustic classification of
spaces in buildings).
[7] IST 45:2016, Hljóðvist - Flokkun íbúðar- og atvinnuhúsnæðis (Acoustic conditions in buildings - Sound
classification of various types of buildings), Icelandic Standards, Iceland. Note: For more information, seeGuðmundsson, S (2016). Acoustic Classification and Building Regulations. Nordic/Baltic Harmonization?
Proceedings of BNAM2016.
[8] NS 8175:2019, Lydforhold i bygninger - Lydklasser for ulike bygningstyper (Acoustic conditions in buildings Sound classification of various types of buildings), Standards Norway. English version published March 2020.
[9] SS 25267:2015, Byggakustik – Ljudklassning av utrymmen i byggnader – Bostäder (Acoustics – Sound
classification of spaces in buildings – Dwellings). Swedish Standards Institute, Stockholm, Sweden.
[10] STR 2.01.07:2003, Dél Statybos Techninio Reglamento Str 2.01.07:2003, Pastatu Vidaus Ir Isores Aplinkos
Apsauga Nuo Triuksmo (Lithuanian building regulations. Protection against noise in buildings). Patvirtinimo,
Lithuania.
[11] Noteikumi par Latvijas būvnormatīvu LBN 016-15 "Būvakustika” (Regulations Regarding Latvian
Construction Standard LBN 016-15 “Building Acoustics”).
[12] UNI 11367:2010 Acustica in edilizia – Classificazione acustica delle unità immobiliari – Procedura di valutazionee verifica in opera (Building Acoustics - Acoustic classification of building units - Evaluation procedure and insitu measurements).
[13] VDI 4100:2012, Schallschutz im Hochbau - Wohnungen - Beurteilung und Vorschläge für erhöhten
Schallschutz (Sound insulation between rooms in buildings - Dwellings - Assessment and proposals for enhanced
sound insulation between rooms". VDI-Handbuch Lärmminderung. Beuth, Germany.
[14] DEGA-Empfehlung 103 (2018), Schallschutz im Wohnungsbau – Schallschutzausweis, DEGA, January 2018.
https://www.dega-akustik.de/fileadmin/dega-akustik.de/publikationen/DEGA_Empfehlung_103.pdf[15] ÖNORM B 8115-5:2021, Schallschutz und Raumakustik im Hochbau - Teil 5: Klassifizierung. (Sound insulation
and room acoustics in building construction – Part 5: Classification). ÖNORM, Austria.
[16] UNE 74201: 2021. Acústica. Esquema de clasificación acústica de edificios (Acoustics. Building acoustic
classification scheme). AENOR.
[17] NEN 1070:1999, Geluidwering in gebouwen – Specificatie en beoordeling van de kwaliteit (Noise control inbuildings – Specification and rating of quality), Netherlands.
[18] PN-B-02151-5:2017, Akustyka budowlana -- Ochrona przed hałasem w budynkach -- Część 5: Wymagania
dotyczące budynków mieszkalnych o podwyższonym standardzie akustycznym oraz zasady ich klasyfikacji(Building acoustics - Protection against noise in buildings - Part 5: Requirements for residential buildings witha higher acoustic standard and the rules for their classification), Poland.
[19] Turkish Ministry of Environment and Urbanization (2017). Binalarin Gürültüye Karşi Korunmasi Hakkinda
Yönetmelik (Regulation on Protection of Buildings against Noise). Republic of Turkey Official Gazette,
31 May 2017. www.resmigazete.gov.tr/eskiler/2017/05/20170531-7.htm. Note: For more information, see
Bayazit, NT, Kurra, S, Ozbilen, BS, & Sentop, A (2016). Proposed methodology for new regulation on noiseprotection for buildings and sound insulation in Turkey. Proceedings of 45th international Congress andExposition on Noise Control Engineering (pp. 923–934), Hamburg. 2016.
[20] ISO/TS 19488 (2021), Acoustics - Acoustic classification of dwellings.
[21] Rasmussen, B, Machimbarrena, M (2019). Developing an international acoustic classification scheme fordwellings – From chaos & challenges to compromises & consensus? Proceedings of InterNoise2019.
[22] Rasmussen, B. (2020). Encouraging acoustic renovation of housing in Denmark by extending acoustic
classification with two lower classes E and F for old housing. In J. Yong Jeon (Ed.), Proceedings of2020 International Congress on Noise Control Engineering: INTER-NOISE 2020 The Korean Societyof Noise and Vibration Engineering.
[23] B. Rasmussen (2012), Sound classification of dwellings: Quality class ranges and intervals in national
schemes in Europe. EuroNoise 2012 proceedings, pp. 1178–1183.
[24] Rasmussen, B. (2018). Building acoustic regulations in Europe – Brief history and actual situation. BalticNordic Acoustics Meeting 2018, Reykjavik. Nordic Acoustics Association, Proceedings, Vol. 2018.
[25] Bygningsreglement 2018 (Building regulations 2018). Danish Transport, Construction and Housing
Authority, 2017. Copenhagen, Denmark. http://bygningsreglementet.dk (with link to all previous building
regulations found at the same page). Note: BR2018 refers to BR2018 Vejledning om lydforhold (BR2018
Guideline for acoustic conditions). http://bygningsreglementet.dk/Tekniske-bestemmelser/17/Vejledninger.
[26] Miljöministeriets förordning om ljudmiljön i byggnader, 796/2017 (in Swedish). Miljöministeriet,
Helsingfors, 2017. https://www.finlex.fi/sv/laki/alkup/2017/20170796)[27] Byggingarreglugerd 2012 - nr. 112/2012 med breytingum (Building regulations 2012 - No. 112/2012
with amendments, latest version 1278/2018). Reglugerðasafn, Reykjavík.
https://www.reglugerd.is/reglugerdir/allar/nr/112-2012[28] Byggteknisk Forskrift (TEK17). Veiledning om tekniske krav til byggverk. (Regulations on technicalrequirements for building works). Direktoratet for byggkvalitet (Norwegian Building Authority), Oslo.
https://dibk.no/byggereglene/byggteknisk-forskrift-tek17/ Note: The latest version (June2020) refers to Class
C in NS 8175:2012 concerning acoustic requirements. (https://dibk.no/globalassets/byggeregler/regulation-ontechnical-requirements-for-construction-works--technical-regulations.pdf)[29] Boverkets byggregler, BFS 2011:6 (Building regulations, latest version with amendments BFS 2020:4– BBR 29). Boverket (Swedish National Board of Housing, Building and Planning), Karlskrona,
Sweden. http://www.boverket.se/sv/lag--ratt/forfattningssamling/gallande/bbr---bfs-20116/[30] OIB (2019). OIB-Richtlinie 5 Schallschutz 330.5-002/19. Österreichisches Institut für Bautechnik, Wien,
Austria. https://www.oib.or.at/de/oib-richtlinien/richtlinien/2019/oib-richtlinie-5[31] NBN (2008). NBN S 01-400-1:2008, Akoestische criteria voor woongebouwen (Acoustic criteria forresidential buildings). Note: From January 2023 to be replaced by NBN (2022). NBN S 01-400-1:2022
with the same title as in 2008.
[32] DIN (2018). DIN 4109-1:2018, Schallschutz im Hochbau - Teil 1: Mindestanforderungen (Sound
insulation in buildings - Part 1: Minimum requirements). DIN, Berlin, Germany.
[33] Rasmussen, B (2010). Sound insulation between dwellings - Requirements in building regulations in Europe.
Applied Acoustics. 71(4):373-385. DOI 10.1016/j.apacoust.2009.08.011[34] Rasmussen, B, Rindel JH (2010). Sound insulation between dwellings - Descriptors applied in building
regulations in Europe. Applied Acoustics. 71(3), 171-180. Available from: 10.1016/j.apacoust.2009.08.011[35] A Løvstad, JH Rindel, CO Høsøien, I Milford (2016). Sound quality in dwellings in Norway – a socioacoustic investigation. Proceedings of BNAM 2016, Stockholm, Sweden.
[36] Fredrik Ljunggren (2022). “Sound insulation, residents’ satisfaction, and design of wooden
residential buildings”. Proceedings of EuroRegio-BNAM2022, 9-11 May 2022.
https://www.conforg.fr/erbnam2022/output_directory/data/articles/000086.pdf[37] A Blödt & A Rabold (2019), Schallschutz im Holzbau – Grundlagen und Vorbemessung. Holzbau
Deutschland.
[38] Rasmussen, B., & Ekholm, O. (2021). Neighbour noise in multi-storey housing - Annoyance and potential
health effects. Paper #2228. Proceedings of INTER-NOISE 2021 (Vol. 263(4), pp. 2783-2792). Institute of
Noise Control Engineering, Washington DC, USA. https://doi.org/10.3397/IN-2021-2228[39] COST Action TU0901: Integrating and Harmonizing Sound Insulation Aspects in Sustainable Urban
Housing Constructions, http://www.costtu0901.eu/ (with access to e-books, vol. 1 and 2). Alternatively, vol 1
can be found here: COST Action TU0901(2014). COST Action TU0901 – Building acoustics throughout
Europe. Vol. 1: Towards a common framework in building acoustics throughout Europe.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0994

Application of building acoustics standards to Indoor
Environmental Quality (IEQ) Standards
Hiroshi SATO1
1

National Institute of Advanced Industrial Science and Technology
1-1-1 Umezono, Tsukuba, Ibaraki 305-8566, Japan

ABSTRACTThe standard “ISO/TS 19488:2021 Acoustics — Acoustic classification of dwellings” presents detailed
acoustical parameters to classify performance of dwellings with consideration to residences in them. In toher
field, ISO/TC 163 and ISO TC 205 form the joint working group to establish IEQ to design an energyefficient and comfortable indoor environment. ISO 17772-1 addresses only noise criteria to rate IEQ in the
acoustical part. This paper discusses the role of building acoustics standards for IEQ and the potential usageof ISO/TS 19488 to develop acoustics related IEQ for dwellings.
Keywords: IEQ, Sustainable Development, Human-Centered, Standard, Wellbeing

1. INTRODUCTION
The term “sustainable development” has long been of interest to citizens, developers as wel l as
government agencies. One of the things we engineers can do is to build an environment which has
better performance for functions and comforts, less uses resources and accommodates longer withhuman beings. Governmental agencies and standard bodies are working to create efficient andmeaningful role for engineers. Researchers and engineers are also providing efforts to crateinternational standards to guide such development in the world.
This paper pay attention to IEQ standard how to balance performance of building and sustainability
in terms of acoustics to expand role of acoustics to sustainable development.

2. GREEN BUILDING INITIATIVES
Regarding activities to promote green building, the World Green Building Council was officiallyestablished to gather all the GBCs (Green Building Council) under one umbrella in the world in
2002[1]. GBCs published building certification models such as BREEAM (Building Research
Establishment Environmental Assessment Method) in United Kingdom[2], LEED (Leadership in Energy and Environmental Design) in United States of America [3],Miljöbyggnad in Sweden [4], DBGN System in Germany [5] and CASBEE (Comprehensive
Assessment System for Built Environment Efficiency) in Japan [6]. Most of these certification systems
have grading systems, those have typically 4 to 6 categories to evaluate building performance in termsof sustainability. They also have evaluation elements both for sustainability and human -centeredelements such as comfort and wellbeing.

3. STANDERDIZATION FOR SUSTAINABLE BUILT ENVIRONMENTIn the big picture, there are also developments related to sustainable built environment in thestandardization. “ISO/TC 43 Acoustics/SC 2 Building Acoustics/WG 29 Acoustic classification
scheme for buildings” developed “ISO/TS 19488:2021 Acoustics — Acoustic classification of
dwellings” to classify acoustical performance of dwellings [7]. “ISO/TC 59 Buildings and civilengineering works/SC 14 Design life” developed “ISO 15686-5:2017 Buildings and constructed assets— Service life planning — Part 5: Life-cycle costing [8].” “ISO/TC 159 Ergonomics/SC 5 Ergonomicsof the physical environment/WG 4 Integrated environments” developed “ISO 10551:2019 Ergonomicsof the physical environment — Subjective judgement scales for assessing physical environments” to1sato.hiro@aist.go.jp

evaluate comfort in an environment [9]. “Joint ISO/TC 163 - ISO/TC 205 WG: Energy performanceof buildings using holistic approach” developed “ISO 17772-1:2017 Energy performance of buildings— Indoor environmental quality — Part 1: Indoor environmental input parameters for the design andassessment of energy performance of buildings[10]” and “ISO/TR 17772-2:2018 Energy performanceof buildings — Overall energy performance assessment procedures — Part 2: Guideline for using
indoor environmental input parameters for the design and assessment of energy performance ofbuildings[11]” to balance energy performance and all aspect of comfort of indoor environment.
“ISO/TC 314 Ageing societies/WG 1 Workforce” developed “ISO 25550:2022 Ageing societies —General requirements and guidelines for an age-inclusive workforce [12]” to assess not only IEQ
factors in a workplace but also social factors such as economic factors and regulations in workforce.
In addition, “ISO/TC 314 Ageing societies/WG 4 Wellbeing” is developing wellbeing promotion
framework [13] to maintain wellbeing of community members as well as the community itself.
Human Factors
ISO/TC 159/
SC 5
ISO/TC 314
SocialFactors

ISO/TC 43/
SC 2
IndoorEnvironment
ISO/TC 163& TC 205

Life Cycle
Cost
ISO/TC 59/
SC 14

EnergyPerformance

Figure 1 Standardization for sustainable built environment

4. IEQ RELATED STANDERD
4.1 ISO 17772 Series
ISO 17772-1 and ISO/TR 17772-2 were developed in the context of EPB (Energy Performance of
Buildings) with consideration of comfort.
The scope of ISO 17772-1 states that “This document specifies requirements for indoor
environmental parameters for thermal environment, indoor air quality, lighting and acoustics andspecifies how to establish these parameters for building system design and energy performance
calculations.” We can find the term “acoustics” in the scope, but it means only for ventilati on noise.
We should find that this standard is for “building system design and energy performance calculations .”This suggests that we acoustics engineer should expand field of acoustics in terms of EBP to cratelarger role in building systems and/or functions. Unfortunately, this standard doesn’t give the design
parameters to the design of acoustics.
The scope of ISO 17772-1 states also that “It also specifies occupancy schedules to be used instandard energy calculations and how different categories of criteria for the indoor environment canbe used.” This means that IEQ depends on activity of occupancy and energy calculations would bedone with activities. This aspect is not often considered in acoustics.
4.2 IEQ categories in ISO 17772 Series
ISO 17772-1 presents IEQ categories from IEQ I : High, IEQ II : Medium, IEQ III: Moderate, IEQ IV:
Low. The levels described with “High” to “Low” are related to the level of expectations the occupants
may have. In the standard, a normal level is intended to be “Medium” and higher level may be selected
for occupants with special needs (children, elderly, handicapped, etc.). A lower level will not provide
any health-related risk but may decrease comfort. ISO/TR 17772-2 noted that the intention to provide
these categories is not that a building should be operated strictly in one class the whole year round.
There is a room for each national body to manage design regulations and/or guidelines their way tooptimize their natural environment as well as economic and cultural context based on internationallyshared knowledge. Actually, each GBC manages their certification system suits its national regulations
and guidelines each country has.
The most important consensus for IEQ is that higher level of IEQ always requir e more energy andresources. Most dominant factors to maintain IEQ is protection from outdoor climate and reductionof indoor pollutant. These two factors always use energy resources if mechanical system would beequipped.
4.3 Classification classes in ISO/TS 19488
In ISO/TS 19488, six classes (A to F) are used to specify different levels of acoustic conditions indwellings. Table 1 presents classes and categories used in standards and certification systems forcomparison. Most of classes/categories are defined with numerical criterion. ISO/TS 19488 describesthat class A is the highest class, class F is the lowest class. Annex B of ISO/TS 19488 describes
explanation of intention of each class. class D seems to be the minimum requirement in most of
countries and recognized as the minimal category. The concept of differentiate of each class is basedon protection from noise from neighbors (and noise to neighbors as concept of speech privacy
suggests).
The difficulty to justify the acoustics class is that noise from neighbors is unstable because it
greatly depends on behaviors of neighbors and their timing. In contrast, outdoor climate is usually
predictable for longer term and indoor pollutants, those numerical models are provided in ISO/TR
17772-2, are also predictable.
Table 1 Classes and categories used in standards and certification systems
Standard/
GBC(Better)Class/
Category(Worse)Note

ISO/TS 19488

ISO
17772-1

BREEAM

LEED

Miljöbyggn
ad

DGNB

CASBEE

A
High
B
Good
C
NormalD
Minimal

IEQI
High
IEQII
MediumIEQIII
Moderate
IEQIV
Low

Outstanding ≥85%
Excellent≥70%
Very Good
≥55%
Good
≥45%

Platinum
80+ pGold
60–79 p
Silver50–59 pCertified
40–49 pGold

Platinum
≥80%
Gold
≥65%
Silver≥50%
Bronze*
≥35%

S

E*
Low

Pass
≥30%

F*
Very low
NPD(No
performance
determined)canbedeclared*Only
forbuildings
beforerenovation

Unclassified <30%

SilverBronzep: points
earnedExcellentA
Very Good
B+
Good
BFairy PoorC
Poor

* Only forexistingbuildings

Another difficulty is to find clear relationship between a class and cost to achieve the class. Thisdifficulty is also created by outdoor climate. For example, high performance insulation of outer wall
requires materials more than expected in mild climate but nothing in colder climate because of higher
thermal insulation allows higher sound insulation. This discussion breaks tradeoff relations between
IEQ and energy consumption, which is a clue to the relationship between running costs and initialcosts.

5. HOW TO GIVE A PRIORITY TO ACOUSTICS IN IEQ?
Elements of IEQ are directly related to energy cost, are monitored every second with easy -to-

understand numbers which can give imagine of comfort and give clear relationship between initialcost and running cost. Most of elements are perceived comfort/discomfort passively.
Standards in building acoustics are useful to do measurement in physical domain for building
elements. This information can give design tools to optimize acoustical performance with possibl ecost but may not give a method to reduce running cost because acoustic elements are basicallycontributed to reduce initial cost.
There are also evaluation method standards for performance of rooms, which can tell the room canfunction as designed purpose or not in terms of acoustics. This kind of standard is useful to evaluate
and manage performance of built environment. If we could have solid tool to estimate acoustical
performance while designing considering unstable neighbors’ behavior, clams as well as cost for
fixing problems would be reduced.
Both acoustics and lighting are functioning element of rooms especially for specific activities. We
know when a room works or not for specific purpose in terms of acoustics. If we can create next
generation IEQ, which is activity based indoor environmental quality, we can provide anotherdimension to decide quality of an environment with relationship between human behavior and physicalenvironment. This would be a message that function of a room is as important as reducing energy for
comfort. This idea might be fit to design an indoor environment for remote working at home toaccommodate pandemic era. We can refer standardization activities for Activity-Based-Working in“ISO/TC 159 Ergonomics/SC 4 Ergonomics of human-system interaction/WG 3 Controls, workplaceand environmental requirements” to create more human-centered standard. Regarding ageing
population growth in the world, consideration to older occupants is quite important for their wellbeing.
Accessible design of acoustical cues [14] are also taken into account as a function of rooms.

ACKNOWLEDGEMENTS
The author thanks to members of ISO/TC43/SC 2/WG 29 for their productive discussion for
meetings.

REFERENCES[1] https://www.worldgbc.org/[2] https://bregroup.com/products/breeam/[3] https://www.usgbc.org/leed[4] https://www.sgbc.se/certifiering/miljobyggnad/vad-ar-miljobyggnad/[5] https://www.dgnb.de/en/council/certification/[6] https://www.ibec.or.jp/CASBEE/english/index.htm[7] ISO/TS 19488:2021 Acoustics — Acoustic classification of dwellings, (International Organizationfor Standardization) Geneva, Switzerland (2021).
[8] ISO 15686-5:2017 Buildings and constructed assets — Service life planning — Part 5: Life-cycle
costing, (International Organization for Standardization) Geneva, Switzerland (2017).
[9] ISO 10551:2019 Ergonomics of the physical environment — Subjective judgement scales forassessing physical environments” to evaluate comfort in an environment, (International
Organization for Standardization) Geneva, Switzerland (2019).
[10] ISO 17772-1:2017 Energy performance of buildings — Indoor environmental quality — Part 1:
Indoor environmental input parameters for the design and assessment of energy performance ofbuildings, (International Organization for Standardization) Geneva, Switzerland (2017).
[11] ISO/TR 17772-2:2018 Energy performance of buildings — Overall energy performanceassessment procedures — Part 2: Guideline for using indoor environmental input parameters forthe design and assessment of energy performance of buildings, (International Organization forStandardization) Geneva, Switzerland (2018).
[12] ISO 25550:2022 Ageing societies — General requirements and guidelines for an age-inclusive
workforce, (International Organization for Standardization) Geneva, Switzerland (2022).
[13] ISO 25554(Working Draft) — Ageing Societies-- Guidelines for Promoting Wellbeing in Local
Communities and Organizations, (International Organization for Standardization) Geneva,
Switzerland (2022).
[14] ISO/TR 22411:2021 Ergonomics data for use in the application of ISO/IEC Guide 71:2014,(International Organization for Standardization) Geneva, Switzerland (2021).

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022, in Gyeongju, Korea
Extended abstractABS-0578

Sound Pressure Level Generation of Emergency Broadcasting
Speakers in A Fire Situation
Jeongho JEONG1; Kyewon PARK; Yichul SHIN
1 Fire Insurers Laboratories of Korea, Korea

ABSTRACTIn this study, the sound generation of 13 types of emergency broadcasting speakers was tested under the test
set-up of UL 2043 and compared. Before the UL test of emergency loudspeakers, generated sound pressurelevels were compared with the same amplifier set-up. The SPL of the 15 W speakers was approximately 20
dB higher in some frequency bands. After the SPL measurements, fire tests were conducted with the set-up
in which fire situation that the speaker installed on the ceiling, was directly exposed to flame and hightemperature. During the fire test, the amplifier keeps supplying the sound signal to the speakers. The sounds
generated from the speaker were recorded using an Omni-directional microphone at two positions near the
speakers. Most of the speakers stopped the generation within 30 s after the fire test started. This result meansthat when the fire starts and the flame expanded to touch the indoor ceiling, the emergency broadcastingsound will net continue within 30 s.
Keywords: Emergency broadcasting speaker, Sound pressure level, Fire Situation

1. INTRODUCTION
In order to minimize the loss of life in the event of a fire, it is necessary to promptly and clearlycommunicate the situation of the fire to the occupants of the building so that they can evacuate to asafe space at an early stage. For this, the alarm system and emergency broadcasting system must be installed
and operated so that the fire situation can be effectively communicated to all occupants in the building
through voice language or standardized acoustic alarm signal. In the case of alarm facilities, only thesound pressure level generated in the alarm is defined as 90 dB or more at a distanc e of 1 m in Korean fire
safety code (1). It was proposed to apply the method considering the noise characteristics of the provincial
workplace and to use the NFPA standard ( 2), which sets the fire alarm sound to be 15 dB(A) higher thanthe background noise when the workplace noise is 85 dB(A) or higher (3,4,5). In this study, the soundgeneration of 13 types of emergency broadcasting speakers was tested under the test set-up of UL 2043
(6) and compared. Before the UL test of emergenc y loudspeakers, generated sound pressure levels
were compared with the same amplifier set-up. The SPL of the 15 W speakers was approximately 20
dB higher in some frequency bands (7). After the SPL measurements, fire tests were conducted with the
set-up in which fire situation that the speaker installed on the ceiling, was directly exposed to flame andhigh temperature. During the fire test, the amplifier keeps supplying the sound signal to the speakers.
The sounds generated from the speaker were recorded using an Omni-directional microphone at two
positions near the speakers.

2. MEASUREMENT OF SOUND GENERATION TIME IN FIRE SITUATION
For emergency broadcast speakers, sound power. materials and size were considered to selec t emergency
broadcast speakers on the market. As shown in Table 1, 13 types of the emergenc y broadcasting speakers
targeted. The emergency broadcasting speakers have 3 types of 1 W, 2 types of 3 W and 5 W, 4 types of
10 W, and an output of 15 W or more. The acoustic characteristics and sound generation time in firesituation of each of the 13 emergency broadcast speakers were measured based on the test conditions of
UL 2043. The emergency broadcast speaker was connected to a power amplifier, and pink noise withthe same output was driven as a sound source. The broadband noise reproduced through the speaker wastransmitted to the omni-directional microphone (Type 4942,
1

jhjeong92@gmail.com

B&K) at a distance of about 1 m from the speaker (see Figure 1). Table 1 shows the A-weighted soundpressure levels generated when the same signal input is delivered to the emergency broadcast speaker
during a UL-based fire test. Also, sound generation time which is the time between the start of the generationof sound and when the generation of sound was significantly diminished by flame damage, was tabulated
in Table 1. The sound generation time showed a large difference from 17 s to 78 s. Among the 13 speakers,
7 speakers had a sound generation time shorter than 30 s, and 1 speaker produced a sound for more than
1 minute. The average value of the sound generation time was about 33.6 s, and the standard deviationof the sound generation time of 13 speakers was 17.3 s.

Figure 1. Experimental set-up for acoustics
characteristics of emergency broadcasting speakers
based on UL 2043 test

Figure 2 Characteristics of sound generation during fire test of
Speaker 04 (A-weighted Overall level and sound pressure levelof 1/1 octave band)

Table 1 – Physical parameters of liquids
Speaker
S01 S02 S03 S04 S05 S06 S07 S08 S09 S10 S11 S12 S13
Power
15 W
10 W
5W
3W
1W
LA [dB]
73.1 78.8 74.7 75.1 74.0 74.9 72.9 71.5 68.4 68.4 61.7 61.6 64.7
Sound Generation time
17
17
37
40
51
27
22
21
23
40
21
43
78
in Fire condition[s]3. SUMMARY AND CONCLUSIONS
The result of this experiment means that, in case of a fire, if the flame directly touches the emergency
broadcast speaker, the emergency broadcast sound is interrupted within an average of 33.6 seconds. Most
emergency broadcast speakers are connected in parallel by region. If a generation of sound from theemergency broadcasting speaker is stopped by a flame from one speaker, the broadcast signal is nottransmitted to the next connected speaker, so emergency broadcast delivery may not be possible. In orderto minimize casualties in the event of a fire, it is important to continuously generate an emergency
broadcast sound at the beginning of a fire. For this, future studies on materials for emergency broadcasting
speakers and wiring systems are needed.

REFERENCES
1. National Fire Safety Code of Korea 202, Fire Safety Code for Emergency Broadcasting System.
2. NFPA 72, National fire alarm code. Quincy, MA, USA, National Fire Protection Association, 2002.
3. Y. S. Lee, D. H. Lee, A study on sound level of the fire alarm system in the factory, Journal of KOSHAM,
2012, Vol. 12, No. 6, pp.179~184.
4. Y. S. Lee, D. H. Lee, A study on awareness rate of the fire alarm sound in the factory, Journalof KOSHAM,
2012, Vol. 13, No. 2, pp.163~173.
5. Y. S. Lee, A study on noise generation and awareness of the fire alarm sound in the factory. J. Korea Saf.
Manag. Sci., 2015, Vol. 17, No. 4, pp.97~103.
6. UL 2043 Standard for fire test for heat and visible smoke release for discrete products and their accessories
installed in air-handling spaces, 2013.
7. J.H. Jeong, B.Y. Seo, K.W. Park, S.Y. Shin, W.H. Hong, Acoustic Characteristic of Emergency
Broadcasting Speakers, Fire Sci. Eng., 2019, Vol.33, no.1, pp.130-137.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0668

The listening difficulty of the announcement in the subway platform
through acoustical simulation for young and elderly persons

Eunsung Song1; Suhong Kim1; Jongkwan Ryu2
1

Architectural & Civil Engineering, Chonnam National University, Korea
2

School of Architecture, Chonnam National University, Korea

ABSTRACTThe subway platforms typically have long reverberation time of 2.0 s or more. This characteristic affects thelistening of announcement in the platform, and the effect is greater especially for the elderly with severe
hearing loss. Therefore, this study evaluated the listening difficulty of announcement for young and elderly
persons by using the sound source of the subway platform created through acoustical simulation (Odeon).
The reverberation times of 0.5 s, 1.5 s, and 2.5 s were obtained by adjusting the finishing material in theplatform. In the listening test, subjects with normal hearing rated the listening difficulty for the original (foryoung person) and the revised announcement (for applying elderly person’s hearing loss), which was filteredout the hearing loss values of the elderly. As a result, there were significant variations due to S/N ratio, RT,
and noise type for both announcement sources of the young and the elderly. It was also found that listening
difficulty of revised announcement for elderly person’s hearing was higher up to 30 % than for young persons
under the condition of an S/N ratio of 20 dBA and a reverberation time of 0.5 s.
Keywords: Underground subway platform, Announcement, Listening difficulty, Hearing loss

1. INTRODUCTION
The underground subway platform not only occupies a higher proportion than the above platform[1], but also shows high sound pressure level of noise [2]. The sound reflection from boundary of theunderground platform resulted in a long reverberation time of more than 2.0 s on average [3], and the
S/N ratio was found to be lower than 10 dBA [4] in the platform of Korean underground subway. Thisis a poor environment for listening to the announcement from the subway platform. In the previous
study [5], the degree of listening difficulty for young people with normal hearing was 55 % at the S/Nratio of 10 dBA and RT (500 Hz) of 2.2 s. Since the elderly with hearing loss show higher listening
difficulties than young people at the equal acoustical condition, it is judged that the elderly will show
higher listening difficulties even at the appropriate S/N ratio to young people. From a barrier-freeperspective, acoustics for platform and announcement design standards for PA system are needed as
the elderly can listen clear announcement on the subway platform, which is a public space.
Therefore, this study compared the listening difficulties of young people and the elderly about theannouncement from subway platforms where various noise sources are occurred.

2. Method
2.1 The listening difficulty evaluation
The listening difficulty evaluation was conducted by evaluating the announcement in theconditions with the noise sources that may occur in the platform and an artificial noise source. The
1
2218272@jnu.ac.kr
jkryu@jnu.ac.kr

subjects were a total of 28 young people with normal hearing, and the experiment was conducted
while wearing headphones. The listening difficulty evaluation was conducted on a 4-point scale: 'Notdifficult, 'A little difficult', 'Fairy difficult', and 'Extremely difficult'. Listening difficulty rating score
was calculated as the ratio of the number of responses from 2 (A little difficult) to 4 (Extremely
difficult) excluding 1 (Not difficult). In order to reduce the dependence on words, a total of 212 words
were selected as test words with a consonant among subway station name in metropolitan cities, Korea.
2.2 Sound Sources
Noise sources are common noise sources in subway platforms as shown in Table 1. There are atotal of three noise sources: hoth noise as background noise, crowd noise, and a train brake noise. The
noise sources were edited to acoustic characteristics similar to those of subway platforms measured
in the field by adjusting the sound absorption coefficient through acoustic simulation (Odeon ver.10.1)
as shown in Figure 1. Therefore, the acoustic characteristics of the subway platform model with RT(500 Hz) of 0.5 s, 1.5 s, and 2.5 s were synthesized with the selected test words.
2.3 Revised sound sources for considering elderly people’s hearing loss
For the listening difficulty evaluation of the elderly with severe hearing loss, the hearing loss value
suggested in ISO 7029 was filtered out from the sound source and provided to the subjects. As shownin Table 1, the announcement level of original sound source for young people was 70 dBA, but it waspresented as 52 dBA due to the hearing loss value in the case of the revised sound source for theelderly.
Table 1 – Experimental design of listening difficulty evaluation
Evaluation type

Noise type

S/N ratio

RT (500Hz)

Announcement

[dBA]

[s]

level [dBA]

0 / 10 / 20

0.5/1.5/2.5

Train brake sound (TA2)
The difficulty oflistening

Crowd sound (A+C)

70 (Young)
52 (Elderly)

Ambient sound (A)(1) 3D modeling of subway platform(2) The RT of the each sound field

Figure 1 – RT for each frequency band of sound fields by computer simulation

3. RESULTS
3.1 The listening difficulty rating according to reverberation time by noise type
As shown in Figure 2, when the reverberation time increases from 0.5 s to 1.5 s, the listening
difficulty rating increases in all experimental conditions with original for the young and revised soundsources for the elderly. However, at the reverberation time of 1.5 s to 2.5 s, the increase in listening
difficulty rating was found to be insignificant. In the case of original sound sources, train break (TA)sound among noise sources showed the largest variation of 43.8 % of listening difficulty rating at the
S/N ratio of 10 dBA. In the case of the revised sound source for the elderly, the ambient sound source
was found to be in the listening difficulty rating variation of 33.5 % in an S/N ratio of 20 dBA. In
addition, it was found that there is no clear tendency of variation in listening difficulty rating
according to noise type, but the variation increased with increasing RT. The difference in listening
difficulty rating between original and revised sound source decreased with increasing RT and waslargest at 29.4 % in the RT of 0.5 s.

(a) S/N Ratio : 0 dBA(b) S/N Ratio : 10 dBA(c) S/N Ratio : 20 dBA

Figure 2 – The listening difficulty rating according to RT by noise type for each S/N ratio (red: original forthe young, blue: revised for the elderly)
3.2 The listening difficulty rating according to S/N ratio by noise type
As shown in Figure3, as the S/N ratio increased, the listening difficulty rating significantly decreased
for all experimental conditions. In the case of original sound source for the young, the largest variationin listening difficulty rating according to S/N ratio was 77.6 % in the RT of 0.5 s for ambient soundsource (A). In the case of the revised sound source for the elderly, the A+C sound source showed thelargest variation according to the S/N ratio at 60.6 % in the RT of 1.5 s. The difference in listening
difficulty rating between original and revised sound source increased as the S/N ratio increased, and
30 % difference was shown at the S/N ratio of 20 dBA.

(a) RT : 0.5 s(b) RT : 1.5 s(c) RT : 2.5 s

Figure 3 – The listening difficulty rating according to S/N Ratio by noise type for each RT (red: original forthe young, blue: revised for the elderly)4. SUMMARY
This study evaluated the listening difficulty of announcement in the acoustic environment that may
occur in the underground subway platform by considering hearing loss of elderly person. The listening
difficulty rating test for the announcement sounds with the three S/N ratios and three noise sources,
including the three reverberation times produced through sound simulation was conducted in alaboratory. Original sound source for the young was edited to the revised sound source for the elderly
and both sound sources were used in the test. As a result, there were significant variations due to S/Nratio, RT, and noise types for both announcement sources of the young and the elderly. The differencein listening difficulty rating between the young and the elderly sound source increased as the S/N ratio
increased, and RT decreased and was found to be up to 30 %.

ACKNOWLEDGEMENTS
This research was supported by Research Program through the National Research Foundation of
Korea (NRF) (No.2019R1A2B5 B01070413).

REFERENCES
1. World metro figures, 2018, Advancing public transport, statistics brief, pp. 2 ~ 6
2. Shimokura, R., & Soeta, Y., 2011, Characteristics of train noise in above-ground and undergroundstations with side and island platforms. Journal of Sound and Vibration, 330(8), 1621 -1633.
3. Gomez-Agustina, L., 2012, Design and Optimisation of Voice Alarm Systems for Underground
Station, London south bank University, PhD dissertation
4. Song, E. S., Kim, S. H., Kim, J. H., Lee, S. M., & Ryu, J. K., 2022, The Distribution Characteristicof Noise and Signal Guide Sound in Subway Platform, Transactions of the Korean Society for
Noise and Vibration Engineering, 32(1), 11-21
5. Song, E. S., Kim, S. H., Kim, J. H., Lee, S. M., & Ryu, J. K., 2022, Listening difficulty of publicannouncement at subway platform with long reverberation time, Proceeding of Inter noise 2022

ABS-0298

Speech intelligibility in classroom when the speaker is dysphonic
Pasquale BOTTALICO(1) , Silvia MURGIA(2)(1) University of Illinois at Urbana-Champaign, United States, pb81@illinois.edu(2) University of Illinois at Urbana-Champaign, United States, smurgia2@illinois.edu

ABSTRACT
School children need clear auditory signals and low background noise to learn. When classroom acoustics arepoor, teachers often compensate by raising their voices, usually with limited effect against background noise,
and, long-term, this makes vocal overuse the primary cause (60%) of the high prevalence of voice problems
in teachers. Speech intelligibility tests were performed in primary schools with normal hearing students using
words produced by an actor with normal voice quality and simulating a dysphonic voice. The speech was played
by a Head and Torso Simulator. Artificial classroom noise and classrooms with different reverberation times
were used to obtain a range of Speech Transmission Index from 0.2 to 0.7 (from bad to good). Results showeda statistically significant decrease in intelligibility when the speaker was dysphonic with a maximum of 15%
intelligibility loss. This study extends an important pairing of problems related to student learning: classroom
acoustics and teachers with voice disorders. It provides important insights into the enormous variability inspeech intelligibility in classrooms by characterizing students’ intelligibility when students receive degradedauditory input. The degraded auditory input results from the intersection of classroom acoustics and poor teacher
voice quality.

Keywords: Speech intelligibility, Classroom acoustics, Voice quality

1

INTRODUCTION

Clear speech signal and good acoustic quality are essential for children in order to understand what is beingtaught in the classroom and have the best learning experience. Speech intelligibility, defined as the percentage
of a message understood correctly (1), provides a measure of communication effectiveness. Speech intelligibility accounts for the influence of (1) the communication channel between the speaker and the listener, (2) the
quality of the verbal signal, and (3) the hearing status of the receiver (2).
The communication channel between the speaker and the listener can be influenced by background noise andreverberation time. High background noise and reverberation time have the potential to impact speech intelligibility since background noise can mask target sounds in the speech signal, and high reverberation reduces thequality of the signal (3).
Bradley and Sato (4) sought to identify children’s speech intelligibility in real classrooms as a function of
A-weighted signal-to-noise ratios (S/N(A)), varied room acoustics, and the age of the children. Speech intelligibility with different S/N(A) was tested in 41 Canadian classrooms in 12 different schools with 840 students
in grades 1, 3, and 6 using the WIPI test. The results of these tests indicated that children in the younger
grades required a significantly higher S/N(A) value to obtain the same intelligibility score as older children.
The trends in this study indicated that grade 1 students require a 7 dB quieter classroom environment in orderto achieve the same intelligibility scores as grade 6 students. For 80% of the students to experience ideal conditions, S/N(A) values of +20 dB is needed for grade 2, +18 dB for grade 3, and +15 dB for grade 6 students.
The result of this study revealed that only 19.5% of grade 1, 33.9% of grade 3 students, and 49.3% of grade 6
students experienced near-ideal conditions.
These studies give insight into how background noise affects intelligibility, but the presence of long reverberation times has been proven to negatively impact students’ understanding. Astolfi et al. (5) looked at speechintelligibility in 3 elementary school classrooms where they administered a diagnostic rhyme test to 983 children aged 7-11. Different types of noise such as traffic noise, classroom babble, fan-coil, and impulse noise
were presented randomly to each class at different noise levels while the intelligibility tests were administered.
Classroom babble and traffic noise were shown to interfere the most with IS. The lowering of RT from 1.6 s to
0.4 s showed a 10% constant increase in IS over the S/N(A) range of -15 to +6 dB in the case of traffic noise.
STI values were obtained from an impulse response measurement at the beginning of testing. Results show thatin order to achieve intelligibility of 75% (or “good” intelligibility according to ISO 9921), an STI of 0.40 was
required for younger elementary school children and an STI of 0.25 for older elementary school children. An
STI of 0.9 achieved an IS of about 97% for all grades, which would indicate the level of “excellent” intelligibility.
The quality of the speech signal, together with the acoustic of the classroom, can impact children’s speech
understating. The acoustic complexity of a classroom is often compensated for by increased vocal effort byteachers (6, 7, 8). Teachers represent the largest group of professionals who use their voice as a elementary
tool of the trade, with 3.3 million elementary and secondary school teachers in the United States (9). The
teaching profession is a common place for dysphonia to occur because of the strain put on teachers’ voices
every day as they compete with background noise and classroom acoustics (10). Roy et al. (9) found that theprevalence of reporting a voice disorder during a teacher’s lifetime is 57.7% verse 28.8% for nonteachers. It is
well documented that professionals who use their voice every day are at risk for dysphonia, but recent interest
is on the impact of dysphonia on speech intelligibility.
If adults have reduced intelligibility with a dysphonic speaker, children will likely experience a similar or worse
reduction in intelligibility. Oliveira et al. (11) analyzed the intelligibility of 39 students with an average age of
10. Students performed a transcription task when the speaker was normal, mild, moderate, and severely dysphonic. Results found no difference between the normal vocal quality and mildly dysphonic voice, but a significant
difference was found between the intelligibility of moderate and severely dysphonic voices compared to thenormal voice quality. The chances of making a transcription mistake were 2.55 times greater with a moderately
dysphonic speaker and 3.06 times greater with a severely dysphonic speaker. Chui and Ma (10) looked at the
impact of normal, mildly dysphonic, and severely dysphonic voices on spoken language comprehension for 134
students in Chinese elementary schools. The students listened to 7 spoken passages, one in Cantonese that contained directions and 3 in Cantonese, and 3 in English, and afterward answered six multiple-choice questions tocheck for comprehension. Results showed that mean scores of listening comprehension were reduced for both
the Cantonese and English spoken passages as vocal quality went from normal, mild, to severely dysphonic. It
is questionable whether Cantonese being a tonal language impacted the results of this study. However, it canstill be considered a useful study because the students were tested in English too. These studies reveal thatstudents listening to a dysphonic speaker risk reduced listening comprehension and intelligibility.
Recent literature has shown that dysphonic speech not only affects spoken language understanding but it worsens with the addition of background noise (12). Schiller et al. (13) investigated the effects of speech-shaped
noise (SSN) and a speaker’s impaired vocal quality on spoken language processing in 53 first-grade children.
This study tested language using a speech discrimination task rather than an intelligibility task but gives insight
into the effects of a dysphonic vocal quality on primary school children’s language processing. Speech discrimination was assessed with a phoneme discrimination task and listening comprehension with a sentence-picture
matching task. Stimuli were randomly presented in a 2x2 factorial design with factors of no noise vs. 0 dB
SNR of SSN and normal vocal quality versus impaired vocal quality. The impaired voice was a speech-language
pathologist imitating dysphonia. Outcome measures showed that SSN and impaired vocal quality significantly
lowered children’s speech discrimination (p<0.001). SSN significantly affected listening comprehension when
the speaker’s voice was impaired (p=0.23) but not when it was normal. These results suggest that impaired
vocal quality causes signal degradation, creating more processing errors in young children. Schiller at el. (14)published a follow-up study looking at children’s processing of dysphonic speech with the addition of background noise in real primary school classrooms in Belgium. A total sample of 77 typically developing children
with an average age of 6 years were given a speech perception and listening comprehension task using speechwith normal vocal quality and dysphonic vocal quality. SNR values ranged from +2 to +9 dB depending on
where students were seated in the classroom, and speech was presented at 70 dBA. Classroom noise, recorded

in a 4th-grade primary classroom, was played at 65dBA during the experiment. Acoustic measurements of the
8 classrooms showed RT ranging from 0.4 s to 0.8 s and STI values ranging from 0.69 to 0.89. Results ofthis study indicated that vocal quality had a significant effect on the speech discrimination task, as children
discriminated pseudowords with 8% less accuracy when the speaker had a dysphonic vocal quality (p=0.001).
No effect was found on vocal quality and listening comprehension, but there was an effect of vocal quality
on task demands (p=0.004) where if the task was easier, the listening comprehension was actually higher forthe dysphonic voice. This was possibly due to students paying more attention knowing that the voice would
be impaired. This study revealed that listening to a dysphonic speaker in a noisy classroom can sometimes
impede children’s speech perception, but in the case of task demands, it could actually increase comprehension.
Overall, the literature shows that listening to dysphonic speech in the presence of background noise can impede
children’s speech intelligibility.
This study aims quantify the acoustical conditions in which an optimal intelligibility and low listening effort canbe achieved in real classrooms from young students, even if the teacher reports a voice disorder, in the presenceof typical classroom noise in real classrooms. It is hypothesized that (1) IS will increase as STI increases, (2)LD will decrease as STI increases, (3) dysphonic voice quality will be less intelligible and more difficult tolisten to on equal condition of STI. The knowledge acquired with this experiment will provide insights into theenormous variability in speech intelligibility in classrooms by characterizing students’ abilities in terms of spoken word recognition when students receive degraded auditory input. The degraded auditory input results fromthe intersection of classroom acoustics and poor teacher voice quality. This study will contribute to provide
a better understanding of the communication conditions needed by students, particularly young children in theearly grades, to understand their teacher even with a degraded voice quality.

2

METHOD

2.1 Case study
Tests were conducted in four classrooms at two schools across the United States. The first school is locatedin the University of Illinois Urbana Champaign campus area. Both classrooms selected for measurements arelocated on the ground floor. The first classroom has an area of about 39 m2 , an average height of 2.7 m, and a
volume of 106 m3 . Sound absorbing panels are present in the ceiling, and windows are located in the upper partof the back wall. The second classroom has an area of 61 m2 , an average height of 3.15 m, and a volume of
191 m3 . Again, the windows are located in the upper part of the back wall of the classroom. The reverberation
times in the unoccupied condition are 0.34 s and 0.71 s for the first and second classrooms, respectively.
The second school is located in a residential area. The third classroom, located on the second floor, has anarea of 58 m2 , an average height of 2.7 m, and a volume of 156 m3 . Sound absorbing panels are located in
the ceiling and two windows in the sidewall. The fourth classroom, located on the ground floor, has an area of
72.4 m2 , an average height of 3.0 m, and a volume of about 216 m3 . The ceiling is made of sound-absorbing
panels, and two windows are on one side wall. The reverberation times for the third and fourth classrooms, inthe unoccupied condition, are 0.29 s and 0.39 s, respectively.
The four classrooms accommodated 55 students from second to fifth grade and ages ranging from 7 to 11
years old and were equally distributed between genders. All children received a hearing assessment from anaudiologist, and all showed a normal hearing status.
2.2 Speech material
The speech material of the experiment consisted of words from the Word Identification Picture Identification(WIPI) test. The WIPI is a 25-item word list with vocabulary appropriate for children between 5-to 11 years
old and assesses the ability to identify speech (15). The speech material was recorded in a single-wall soundproof booth with a Class 1 microphone with a sampling rate of 44.1 kHz and a resolution of 32 bits connected
to a computer through a soundboard UH7000 (TASCAM, Montebello, CA). A female American English native
speaker who is a professional voice user was asked to read all the words from the WIPI lists. The first time
she was asked to read the words with normal voice quality, and the second time she was trained by a speechlanguage pathologist to simulate a dysohonic breathy voice. The words were played in the sound-proof boothwith a Head and Torso Simulator with Mouth Simulator (HATS, 45BC KEMAR, GRAS, Holte, Denmark) andthe volume was adjusted at 66 dBA at 1 meter. The words were then combined in 8 tests, each containing
eight words. Four tests were composed using the normal voice quality, while the remaining four were madeof words pronounced with the dysphonic voice quality. Each word was presented by the carrier phrase “Please
pay attention and mark the ...” A children babble noise was played along with the speech stimuli during theperformance of the experiment in the classroom in order to simulate a real classroom environment.
2.3 Procedure
The experiment was conducted where students typically attend classes and lasted less than 60 minutes. The
speech material was played in the classroom using the HATS with a signal level of 66 dBA at one meter of
distance. The HATS was placed on the desk in the front of the classroom in the typical position of the teacher.
The children babble noise was played at three different volumes through four directional loudspeakers (JBL Flip
5) placed on children’s desks in different spots of the classroom to obtain a uniform environment. The experiment consisted of eight tests comprising a combination of two voice qualities (normal and dysphonic voice
quality) and four noise conditions (quiet, low, mid, and high noise level). After a practice test which was notincluded in the analysis, the children were asked to select the word they heard among six pictures. Immediately
after hearing a word, a six second break allowed the children to rate the difficulty in listening to the word on
a visual analogue scale from 0 (not at all difficult) to 4 (extremely difficult). The tests were delivered to thestudents randomly to reduce systematic effects of confounding factors, such as tiredness or decreased concentration that may be due to order effects.
Six Tascam DR 40 X recorders, each with a Behringer ECM 8000 microphone, were located around the classroom to record the acoustic measures. The microphones were placed to represent a group of children in order
to correlate the subjective measures (i.e., intelligibility scores and listening difficulty rate) obtained from the test
and the objective acoustic measures from the nearest microphone. After the test, the children were asked tostay quiet to perform the acoustic measurements of the room. The SNR and STI were calculated at each pointby measuring (1) the noise level, (2) the speech level, and (3) the impulse response of the room. The noiselevel was assessed by simulating the four noise conditions. The continuous speech level was measured using a
special sentence consisting of one carrier phrase and a sequence of the words linked together without pauses.
Finally, the impulse responses for each path of HATS to the microphone were measured using a sinusoidal
sweep signal.
2.4 Statistical analysis
Generalized linear mixed models (GLMM) fit by maximum likelihood (Laplace approximation) were applied
for the statistical analysis of both IS and LD using the software R3.6.0 and the lme4 (version 1.1–10) package.
The IS response variable in the model was coded with a binary score (0/1 corresponding to a wrong/correct
response), while the LD response variable was rated on a 5-point scale from 0 to 4. The LD values wererecoded to restrain the range between 0 and 1. A secondary factor of interest was the normal vocal quality anddysphonic vocal quality. The GLMM outputs include the estimates of the fixed effects of the coefficients, thestandard error associated with the estimate, the test statistic, z, and the p-value.

3

RESULTSA total of 55 elementary school children participated in this study selecting the word that they heard and rating
the subjective difficulty in listening to the speech produced with two voice qualities (heathy and dysphonic),
and four noise conditions (quiet, low, mid, and high noise levels). For each condition, the SNR and STI havebeen measured in six points of each classroom and the range values are shown in Table 1.
Two models has been built to analyze the effect of vocal status on IS and LD. The following predictors
were considered: (1) vocal status (normal vs dysphonic), and (2) STI. The listener ID was considered as arandom factor. Model results of the intelligibility and listening difficulty are reported in Table 2.
The relationship between IS and STI, grouped by voice quality, are shown in Figure1. The model showed astatistically significant difference between IS and STI with the intelligibility score that increases when the STI

Table 1. SNR and STI range values for each test conditions
Speech level

Vocal status

Noise

SNR range (dB)

STI range

66 dB(A) at 1m

NormalQuiet

5.6 / 22.6

0.43 / 0.73

66 dB(A) at 1m

NormalLow

1.4 / 16.0

0.25 / 0.68

66 dB(A) at 1m

NormalMid-5.8 / 10.4

0.19 / 0.55

66 dB(A) at 1m

NormalHigh-12.9 / -7.4

0.07 / 0.45

66 dB(A) at 1m

Dysphonic

Quiet

5.6 / 22.6

0.52 / 0.73

66 dB(A) at 1m

Dysphonic

Low

1.4 / 16.0

0.25 / 0.68

66 dB(A) at 1m

Dysphonic

Mid-5.8 / 10.4

0.19 / 0.55

66 dB(A) at 1m

DysphonicHigh-12.9 / -7.4

0.07 / 0.45

Table 2. Generalized linear mixed effect model (binomial family) for response variables speech intelligibility
and listening difficulty. The interaction between STI and vocal status (dysphonic vs normal voice quality) was
considered as fixed factor. Listener was used as a random factor. Significance codes for the p-values: ***<0.001, ** <0.01, * <0.05.
Intelligibility (%)

Estimate

Std. Error

z-valuep-value(Intercept)

-2.64

0.27

-9.94

<0.001***

STI:DxDysphonic

6.51

0.54

11.98

<0.001***

STI:DxNormal

7.50

0.54

13.95

<0.001***

Difficulty (%)

Estimate

Std. Error

z-valuep-value(Intercept)

3.84

0.33

11.68

<0.001***

STI:DxDysphonic-10.020.68-14.65<0.001***

STI:DxNormal-11.52

0.69-16.62<0.001***increases. The two regression curves have different slopes for the normal (slope= 7.50, p<0.001) and dysphonic(slope=6.51, p<0.001) voice qualities. There is a statistically significant difference between the regression curves
until value of STI of about 0.43 meaning that on equal STI conditions, the normal voice quality was more
intelligible compare to the dysphonic voice quality. For lower values of STI the confidence intervals of the tworegression curves overlap suggesting that there is no statistically significant difference between the two voice
qualities. The relationship between listening difficulty and STI, grouped by voice quality, are shown in Figure2.
The model showed a statistically significant difference between listening difficulty and STI with the listening
difficulty that decreases when the STI increase. The Y axis is reversed with “100” at the bottom representing“extremely difficult” and “0” at the top representing “not at all difficult”. The two regression curves have a
different slope for the normal (slope= -10.02, p<0.001) and dysphonic (slope=-11.52, p<0.001) voice qualities.
There is a statistically significant difference between the regression curves until value of STI of about 0.42
meaning that on equal STI conditions, the normal voice quality was less difficult to understand compare to thedysphonic voice quality. For lower values of STI the confidence intervals of the two regression curves overlap
suggesting that there is no statistically significant difference between the two voice qualities.

Figure 1. Regression curves from the model between STI and Speech Intelligibility in %. The results aregrouped by normal voice quality and dysphonic voice quality, where the shaded regions indicate ± confidence
interval.

Figure 2. Regression curves from the model between STI and Listening Difficulty in %. The results aregrouped by normal voice quality and dysphonic voice quality, where the shaded regions indicate ± confidence
interval. The y axis is reversed with “100” at the bottom representing “extremely difficult” and “0” at the top
representing “not at all difficult”.

4

CONCLUSIONS

The results from this study support previous literature that poor classroom acoustics leads to decreased speech
intelligibility and increased listening difficulty for elementary school aged children. Additionally, this experimentshowed that the presence of dysphonia further decrease intelligibility and increase listening difficulty especiallywhen the quality of the acoustic environment is decreasing. Given the high risk of developing dysphonia among
teachers, speech disorders should be taken into account alongside classroom acoustics in order to ensure optimalcommunication in school. These results highlight the importance of ensuring the acoustics of a classroom areappropriate for the transmission of speech even in presence of a dysphonic voice.

ACKNOWLEDGEMENTS
This work was funded by the Campus Research Board Awards (RB20006) from the University of Illinois
Urbana-Champaign, and by the 2019 New Century Scholars Research Grant from ASHFoundation.

REFERENCES[1] ISO, International Organization for Standardization ISO 9921 Ergonomics- assessment of speech communication, Geneva, 2003.
[2] Mattys SL., Davis MH., Bradlow AR., Scott SK. Speech recognition in adverse conditions: A review. Lang
Cogn Process. 2012;27(7-8):953-978.
[3] Bradley JS., Reich RD., Norcross, SG. On the combined effects of signal-to-noise ratio and room acoustics
on speech intelligibility. J Acoust Soc Am. 1999;106(4):1820-1828.
[4] Bradley JS., Sato H. The intelligibility of speech in elementary school classrooms. J Acoust Soc Am.
1999;123(4):2078-2086.
[5] Astolfi A., Bottalico P., Barbato G. Subjective and objective speech intelligibility investigations in primaryschool classrooms. J Acoust Soc Am. 2012;131(1):247-257.
[6] Bottalico P., Astolfi A. Investigations into vocal doses and parameters pertaining to primary school teachers
in classrooms. J Acoust Soc Am. 2012;131(4):2817-2827.
[7] Bottalico P., Graetzer S., Hunter EJ. Effect of training and level of external auditory feedback on the singing
voice: volume and quality. J Voice. 2016;30(4):434-442.
[8] Bottalico P., Astolfi A., Hunter EJ. (2017). Teachers’ voicing and silence periods during continuous speech
in classrooms with different reverberation times. J Acoust Soc Am. 2017;141 (1):EL26-EL31.
[9] Roy N., Merrill RM., Thibeault S., Parsa RA., Gray SD., Smith EM. Prevalence of voice disorders inteachers and the general population. J Speech Lang Hear Res. 2004;47(2):281–293.
[10] Chui J.C., Ma EP. (2019). The impact of dysphonic voices on children’s comprehension of spoken language. J Voice. 2019;33(5):801.e7-801.e16[11] Oliveira GM., de Melo DC., Serra LS., Granjeiro RC., Sampaio AL. Dysphonia interference inschoolteachers’ speech intelligibility in the classroom. J Voice. 2021
[12] Ishikawa K., Boyce S., Kelchner L., Powell MG., Schieve H., de Alarcon A., Khosla S. (2017). The effectof background noise on intelligibility of dysphonic speech. J Speech Lang Hear Res. 2017; 60(7):1919-1929.
[13] Schiller IS., Morsomme D., Kob M., Remacle A. Noise and a speaker’s impaired voice quality disrupt spoken language processing in school-aged children: Evidence from performance and Response Time Measures.
J Speech Lang Hear Res. 2020; 63(7): 2115–2131.

[14] Schiller IS., Morsomme D., Kob M., Remacle A. (2021). Listening to a dysphonic speaker in noise may
impede children’s spoken language processing in a realistic classroom setting. Lang Speech Hear Serv Sch.
2021;52(1):396–408.
[15] Cienkowski KM., Ross M., Lerman J. The word intelligibility by picture identification (WIPI) test Revisited. J Educ Audiol. 2009;15:39-43.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0414

Investigation of the Subjective Speech Perception Performance
Depending on the Classroom Sizes
Chan Jae PARK1; Min Hyeok KIM2; Chan Hoon HAAN3
1

Korea Institute for Local Educational Finance, Korea
2

3

Daesin Civil Engineering & Construction Co., Ltd

Dept. of Architectural Engineering, Chungbuk National University, Korea

ABSTRACTThe classroom is the special space that transmits the speech of speakers to students. For this reason, soundtransmission characteristics are the most important in the classroom. In general, the sound transmission
characteristics are changed by the volume and the sound absorption of the classroom. Thus, in this paper,compare the experimental results of the acoustical performance and scores of the speech intelligibility test
which was undertaken in the different size of classrooms. In addition, changes were investigated which werecaused by changes in some of experimental conditions such as the directivity patterns of the sound sources.
Keywords: Classroom, Speech Perception, Room Size, Speech Intelligibility Test

1. INTRODUCTION
As the size of the space increases, the acoustical performance increase or decrease proportionally.
On the other hand, subjective speech perception performance is affected by acoustical performance.
In a classroom where learning information is transmitted through teacher’s voice, this is a very
important issue. For this reason, recently, interest in subjective speech perception performance rather
than physical acoustic performance in the classroom is increasing. Internationally, research on therelationship with the physical acoustic performance according to the listen er's speech intelligibility
test method (PBW, CVC, etc.) is in progress.
This study was conducted as a pilot study to study the effect of classroom size on speech perceptionof Korean. To analyze this, the results of the acoustical performance measurement and the Korean
speech intelligibility test results are compared which conduct in 3 different classrooms.

2. RESEARCH METHOD
2.1 Classrooms sizes
In order to compare the acoustical performance and subjective speech perception performanceaccording to the size of the space, 3 sizes of classrooms are selected. The subject classroom is aclassroom in C University in Cheongju, South Korea. The architectural dimensions and volume ofeach classroom are described in Table 1. The architectural finishing materials for each part ofclassrooms are listed in Table 2. Table 3 shows the floor plan of each classroom, the interior, and thelocation of the sound source and sound receiving point.
cjpark024@gmail.com
elshnut@naver.com
3chhaan@chungbuk.ac.kr
1
2

Table 1 – Architectural dimension of each classroom.
Classroom

Size

Seating capacity

Width(m)Length(m)Height(m)Volume(㎥)

A

small

32

8.0

6.4

2.8

143.4

B

medium

54

7.5

10.4

3.3

257.4

C

large

72

8.3

12.8

3.5

371.8

Table 2 – Architectural finishing material of each classroom.
Area

A

B

C

Floor

vinyl tile

vinyl tile

vinyl tileWallwood fiber board covered
with fabricpainted concrete

perforated panel(front),
wood fiber board covered
with fabricCeiling

acoustic fiber board

acoustic fiber board

painted concrete

Door

metal

metal

glass

Window

glass

glass

glass

Desk

PB board

PB board

MDF boardChairpolypropylene

polypropylene

polypropylene

back painted glass

back painted glass

back painted glass

Blackboard

Table 3 – Floor plan and view inside of each classroom.
Classroom

A

B

C

Floor plan*

Photo (inside)*Speakers and listeners are marked on the floor plan.

[ ●: speaker, ●: receiver (listener) ]2.2 Measurement of acoustical performances
In this experiment, the acoustic performance of each classroom is measured according to KS F
2864. This standard corresponds to ISO 3382:1997 and defines a method for measuring thereverberation time and other acoustic performance of a space. However, instead of the using omnidirectional speaker, the directional speaker used which directivity character similar to human voice.
The speaker was installed in front of the blackboard of the classroom where the actual lecture washeld. The masturbation points were set evenly in the classroom. The location and other details of thesound source and receiver are described in Table 4. The following figure 1 shows the installation
diagram of the equipment used in the experiment.

Table 4 - Experiment details of the sound source and receiver.
Classroom
Speaker
Receive point

quantity
output level
quantity

A

B

C

1

1

1

60.1 ~ 62.1

61.9 ~ 63.9

61.6 ~ 62.1

12

24

30

Figure 1 - Experimental equipment installation diagram.
2.3 Speech intelligibility test
The output level of the sound source for the speech intelligibility test was set to be the same as
when measuring the acoustical performance, and this is descried in Table 4. The test method for the
speech intelligibility test uses the PBW method(word) and the CVC method(syllable). During theexperiment, the subject listens 1 word and writes it down in 3 seconds as shown in figure 2. All test
consists of 50 questions per 1 set. In all classrooms, listen to 1 set of each PBW and CVC soundsource and proceed with the test. In all classrooms, one set of PBW and CVC method tests are
conducted. The speech perception of the classroom is evaluated through the speech intelligibility testscore. At this time, the sound source uses an anechoic sound source recorded in an anechoic chamber.
The number of subjects was 24, all of whom were adults in their twenties with normal hearing. The
following figure 2 shows the progress of speech intelligibility test.

Figure 2 - Speech intelligibility test.

3. RESULTS
Table 5 shows the average of the acoustic performance measured in each classroom. To analyze
the effect of classroom size on speech perception, the energy parameter, time-based parameter andspatial parameter are measured.
As a result of the measurement, the larger the space, the larger the reverberation time(T 30). Signalto-noise ratio (SNR), D 50 , and RASTI are inversely proportional to the size of the space. On the other
hand, in classroom B, SPL is the largest and the interaural level difference(ILD) is the smallest. Thisis expected because the left and right width of the classroom is narrow and the walls are all made ofreflective materials.

Table 5 - Results of acoustic performance measurement for each classroom
ClassroomSize

SPL (dBA)

ILD

T30 (s)SNR (dBA]

D50

RASTI

IACC

A

small

61.2

1.98

0.36

24.3

0.87

0.85

0.67

B

medium

69.2

0.30

0.79

22.3

0.69

0.72

0.61

C

large

61.8

0.54

1.22

18.5

0.47

0.53

0.56

Figure 3 displays the average of the speech intelligibility test scores conducted in each classroom.
In all cases, the larger the space size, the lower the speech intelligibility score. Overall, the scores of
the PBW test higher than the CVC test.

Figure 3 - Comparison of average scores of speech intelligibility test for each classroom( ■ CVC test, ▨ PBW test )● A classroom (CVC)○ A classroom (PBW)● B classroom (CVC)○ B classroom (PBW)● C classroom (CVC)○ C classroom (PBW)

Figure 4 – Comparison of acoustical performance and speech intelligibility test results

Figure 4 shows the significant results among the graphs comparing the speech intelligibility test
and acoustic performance measurement results for each classroom.
Table 5 shows the results of the speech intelligibility test and the correlation analysis results ofeach acoustic parameter. For the parameter most affected by the size of classroom, T 30 shows thegreatest correlation. In addition, SNR, D 50 , RASTI show significant results.
Table 5 - Comparison of correlation between acoustic parameter and speech intelligibility test results
Speech intelligibility test

Leq

ILD

T30

SNR

D50

RASTI

IACC

CVC test-0.0040.662-0.835*0.781*

0.804*

0.826*

0.727

PBWtest

0.296

0.494

-0.853*0.828*

0.840*

0.853*

0.668* The correlation coefficient is significant at the 0.05 level (both sides).

4. CONCLUSIONSThe conclusions of this study can be summarized as follows.
1)
2)
3)
4)

The classroom size affects the physical and acoustic performance.
The classroom size affects the speech intelligibility test score.
If the classroom size is too large, it may negatively affect students' speech perception.
Acoustic factors affecting speech recognition performance were T 30, RASTI, D 50, SNR, and
IACC in order.

In this paper, an error may occur by performing a correlation analysis between the speech
intelligibility evaluation result and the acoustic performance using the average value. In addition, it
is difficult to generalize to three test subjects. Therefore, the study to compare the change in speech
recognition performance according to the size of more various spaces will be conducted.

ACKNOWLEDGEMENTS
This research was supported by Basic Science Research Program through the National Research
Foundation of Korea(NRF) funded by the Ministry of Education, Science and Technology (NRF 2016R1D1A1B03933011)

REFERENCES
1. ISO 3382:1997, "Acoustics - Measurement of the reverberation time of rooms with reference to otheracoustical parameters", International Standardization Organization, 1997.
2. KS F 2864, "Measurement of the reverberation time of rooms with reference to the other acousticalparameters", Korean Standard, 2022.
3. ISO 9921 "Ergonomics: Assessment of speech communication", International Standardization
Organization, 2003.
4. ANSI/ASA S3.2 "Method for Measuring the Intelligibility of Speech over Communication Systems",
American National Standard, 2009.
5. Park, C.J., Haan, C.H., Effect of the Interaural Level Differences on the Speech Intelligibility Dependingon the Room Ab-sorption in Classrooms, The journal of the acoustical society of Korea, 2013, v.32 (4),pp.335-345.
6. Park CJ. Establishment of the acoustical performance criteria for middle and high school classrooms (inKorean), (Ph.D. thesis, Chungbuk National University, 2014).

ABS-0038

Development of microperforated panel sound barriers
Masahiro TOYODA
Kansai University, Japan, toyoda@kansai-u.ac.jp

ABSTRACT
High-rise sound barriers are often required to control road trafﬁc noise. Such sound barriers interfere with thelandscape, sunlight, and safety, and are also undesirable in terms of cost. To solve these problems, various
edge-modiﬁed sound barriers have been developed. Among them, an edge-effect suppression barrier, which focuses on controlling air particle velocities at the top of the barrier, shows higher sound insulation performance.
However, the edge-effect suppression barrier using ﬁbrous materials requires a cover for durability and weather
resistance. This cover can deteriorate the performance. Herein, an edge-effect suppression barrier using microperforated panels, which does not require a cover, is proposed. Based on numerical analyses, appropriate
physical parameters of the microperforated panels are searched and the results of sound insulation performanceobtained by the edge-effect suppression barrier using the microperforated panels are shown.

Keywords: Sound barrier, Edge effect, Microperforated panel

1

INTRODUCTION

To control the propagation of noise from roads and rails to neighboring residential units, sound barriers areoften installed along their propagation paths. Charts proposed by Maekawa [1] and Koyasu et al. [2] are widelyused to predict the insertion loss of such barriers. Although such barriers can be installed at relatively low costand have high sound reduction performance, very tall ones are sometimes required to achieve environmental
standards. Such high-rise sound barriers interfere with landscape, daylight, and drive safety. They are also
undesirable in terms of cost. To solve this problem, various edge-modiﬁed sound barriers have been proposed[3]. Some of them use porous materials to suppress the sound pressure at the top of the sound barrier andothers intend to reduce the sound pressure to zero at a speciﬁc frequency with sound wave interference.
On the other hand, Kawai et al. [4] proposed an edge-effect suppression barrier as one of the edge-modiﬁed
sound barriers. The edge effect means a phenomenon where air particle velocities at the top of a thin barrier
becomes very large due to a drastic difference in sound pressure between the front and back sides. The purposeof the edge-effect suppression barrier is not to suppress the sound pressure at the top of the barrier, as is thecase with the existing edge-modiﬁed sound barriers, but to suppress the particle velocity caused by the edge
effect. The theoretical analysis described below shows that the diffraction ﬁeld is dominated by the particle
velocity at the top of the sound barrier. Therefore, the edge-effect suppression makes it possible to efﬁciently
reduce the diffraction sound. To suppress the particle velocity, it is sufﬁcient to install a thin porous material
such as cloth which is advantageous from a cost and environmental point of view. Furthermore, it has beenreported that the sound reduction performance can be further improved by gradually reducing the ﬂow resistanceand surface density from the bottom to the top of the thin porous material. Here, such a change in physicalproperties is referred to as gradation.
Edge-effect suppression barriers are already commercially available [5]. In the product, the porous material
is covered with perforated metal for practical durability and weather resistance. This cover is expected to be
acoustically transparent, but probably has some adverse effects. In addition, the porous material inside the coveris supposedly designed to be thin at the top in order to achieve gradation. Herein, an edge-effect suppression
barrier that does not require any special treatments to achieve gradation and does not have any adverse effects
caused by a cover is proposed.

F
Ω1

Ω2
Φ1 Φ2
n

PS
S
Semi-infinite
barrier
Figure 1. Diffraction model with a semi-inﬁnite sound barrier.
Microperforated panel (MPP) is a perforated panel with submillimeter holes, about 1% perforation ratio,
and submillimeter thickness [6]. Basically, it is one of the next-generation sound-absorbing materials that forma Helmholtz-type resonance absorption mechanism with a rigid back wall. Its resistance and reactance aredesigned to be appropriate for sound absorption. However, herein, it is used as a kind of sound insulationmaterial to suppress an edge effect. MPPs can be made from a wide range of materials, including metal, plastic,
and glass. Therefore, they can be used without a cover to solve durability and weather resistance problems. In
addition, by gradually changing the perforation ratio or hole diameter, gradation can be easily realized.
Section 2 describes the theoretical background, Section 3 introduces some numerical examples, and Section
4 summarizes the present paper.

2

THEORY

2.1 Semi-inﬁnite sound barrier
As shown in Fig. 1, consider a three-dimensional sound ﬁeld Ω1,2 divided by a sound barrier S and a virtual
boundary surface F extended above S. A point source Ps is located in Ω1 . Let Φ1,2 be velocity potentials inΩ1,2 , respectively. As shown in Fig. 2, to represent the velocity potential Φ1 at the sound receiving point P in
Ω1 , the basic solution considering the mirror image Pi of the sound receiving point with respect to S and F isintroduced as
eikri
eikr
G(P, Q) =+,(1)
4π r 4π ri
where Q is a point on the boundary, r is the distance between PQ distance, and ri is the distance between Pi Q.
Using this, Φ1 can be expressed with an unknown ∂∂Φn1 on the boundary F. Note that the time factor e−iω t is
assumed and omitted, where e is the base of the natural logarithm, i is the imaginary unit, ω is the angularfrequency, and t is the time.
As shown in Fig. 2, σ and σs are microspheres centered at the sound receiving point and the sound source,
respectively, and their radius is ε . Let Σ be a sphere of inﬁnite radius centered at P. Applying Green’s formulaor partial integration to the domain Ω1 − σ − σs and considering the limit of ε → 0, Φ1 can be expressed as∫∫∂ Φ1 (Q)
G(P, Q)dS∂n
F∫∫1∂ Φ1 (Q) eikr
= ΦD (P) + ΦD (Pi ) −dS
2π F ∂ nr

Φ1 (P) = ΦD (P) + ΦD (Pi ) −(P ∈ Ω1 , S, F),(2)where ∂∂n is the inward normal derivative and ΦD is the direct sound component. Note that Eq. (2) also holds
for the case where P exists on the boundaries S and F. The integral with respect to Σ can be omitted byassuming Sommerfeld’s radiation condition. For the other region Ω2 , one can derive the same equation by

Σ

F

Ω1
n

P

Pi

r

ri
Q

PS σ
σS

n
S

Figure 2. Boundary integral region in region Ω1 .
considering the absence of a source and the outward normal asΦ2 (P) ==∫∫∂ Φ2 (Q)
G(P, Q)dS∂n
F∫∫
1∂ Φ2 (Q) eikrdS
2π F ∂ nr(P ∈ Ω2 , S, F).

(3)

On F, Φ1 = Φ2 (= Φ ) and ∂∂Φn1 = ∂∂Φn2 (= ∂∂Φn ) due to the continuity condition. Therefore, if P is on F,
considering that P and Pi coincide, subtracting Eq. (3) from Eq. (2) yields
1π∫∫∂ Φ (Q) eikr
dS = 2ΦD (P)∂nrF(P ∈ F).

(4)

By solving Eq. (4), the unknown ∂∂Φn on F can be obtained. Furthermore, substituting it into Eq. (3), thevelocity potential of the diffraction ﬁeld can be calculated. It should be noted that the diffraction ﬁeld expressedby Eq. (3) is governed by ∂∂Φn on F, i.e., the particle velocity perpendicular to the boundary. Therefore, theedge-effect suppression barrier is designed to control particle velocity instead of sound pressure.
A numerical example of the particle velocity distribution on F under the conditions of Fig. 3 is shown in
Fig. 4. The ﬁgure also includes approximate values obtained by the Kirchhoff’s diffraction theory. Note that
although F is semi-inﬁnitely extended, only a sufﬁciently wide range (0 ≤ x ≤ 10λ , 0 ≤ y ≤ 10λ ) was consideredin the numerical analysis, where λ is the wavelength. In addition, the discretized element length was set to beless than λ /5. The solution was conﬁrmed to sufﬁciently converge under these conditions. The source was set
so that the velocity potential amplitude at a point 1 m away from the source was 1 m2 /s.
The phenomenon where the particle velocity becomes extremely large is called the edge effect. Since thesound pressure changes drastically between the front and back sides of a thin barrier, such a large particle velocity is generated near the top of the barrier. Figure 5 shows the distribution of particle velocity perpendicular
to the sound barrier. It can be seen that there is a point where the particle velocity becomes very large near the
top of the barrier. The edge effect suppression barrier attempts to reduce the velocity potential of the diffraction
ﬁeld by suppressing this effect.
2.2 Edge-effect suppression barrier
As shown in Fig. 6, consider three-dimensional sound ﬁelds Ω1,2 where an MPP A is located above a soundbarrier S and a virtual boundary F is assumed above it. Other conditions are same as those in the previous
section. Due to the continuity condition, Φ1 = Φ2 (= Φ ) on F and ∂∂Φn1 = ∂∂Φn2 (= ∂∂Φn ) on F and A. Similarly toyxz
Semi-infinite
Point source
barrier(0, −3, 3) [m]Relative amplitude of particle velocity [m/s]

Figure 3. Positional relationship between the semi-inﬁnite sound barrier and the sound source.

3
Exact boundary value
Kirchhoff’s boundary value

2

1

0
0

2
4
6
Distance from the edge upward [m]Figure 4. Particle velocity distribution in the z-direction just above the sound barrier.

1

0.5

0

-0.5

-1
-1

-0.5

0

0.5

1 [m]

0
1
2
Relative amplitude of particle velocity [m/s]
Figure 5. Particle velocity distribution in the z-direction around the sound barrier.
the previous section, the equations can be given by∫∫1∂ Φ (Q) eikrdS
π F+A ∂ nr∫∫1
∂ Φ (Q) eikr
Φ1 (P) − Φ2 (P) +dS
π F+A ∂ nr

= 2ΦD (P)(P ∈ F),(5)∫∫z ∂ Φ (Q) 1+iωρ ∂ nπ
= 2ΦD (P) (P ∈ A),= −∂ Φ (Q) eikr
dS
∂n
r
F+A
(6)

where z is the transfer impedance of the MPP. By solving Eqs. (5) and (6) as simultaneous equations, theunknowns ∂∂Φn on F and A can be obtained. Using this, the velocity potential of the diffraction ﬁeld is calculatedby∫∫1∂ Φ2 (Q) eikr
Φ2 (P) =dS (P ∈ Ω2 , S, F, A).
(7)
2π F+A ∂ nr
2.3 Transfer impedance of a microperforated panel
According to Maa’s approximation, the transfer impedance zp of the hole of the MPP is expressed aszp=zresist=zreact=X=

zresist + zreact ,
(√
)
√
2dp X
8η0 h
X2
1+
+
,
(dp /2)2328h()
0.85dp1+−iρ0 ω h 1 + √,h
9 + (X 2 /2)√
dp ρ0 ω
,
2
η0

(8)
(9)
(10)
(11)

MPP

F
Ω1

Ω2
A
Φ1 Φ2
n

PS
S
Semi-infinite
barrier
Figure 6. Diffraction model with an edge-effect suppression barrier.
where zresist is the resistance component of the hole impedance, zreact is the reactance component of the hole
impedance, dp is the hole diameter, h is the thickness of the MPP, and η0 is the viscosity of air. Figure 7 showsa schematic diagram near the MPP, where p1 and p2 are the sound pressures on the incident and transmittedsides of the MPP, vb is the vibration velocity of the MPP, va is the relative particle velocity of air passing
through the holes of the MPP relative to vb , and vx is the average particle velocity of air near the MPP. If σ isthe perforation ratio of the MPP, the volume velocity continuity is expressed asvx = σ va + vb .

(12)

On the other hand, the equation of motion of the MPP can be written asm∂ vb= p1 − p2 ,
∂t

(13)

where m is the surface density of the MPP. Since the particle velocity of air in the hole va can be expressed asva =p1 − p2,
zp

from Eqs. (12)–(14), the total transfer impedance z of the MPP can be obtained as()
p1 − p2
1
σ −1
z=
+
= −
.
vx
iω m zp

3

(14)

(15)

NUMERICAL EXAMPLES

Based on the formulation introduced in the previous section, some numerical examples are shown in this section.
The conﬁguration of the calculation is shown in Fig. 8. The point A is a sound receiving point. The assumed
range of physical properties of an MPP were from 0.01 to 100 mm in hole diameter, from 0.01 to 100 mm
in thickness, from 0.0001 to 30% in perforation ratio, and from 0.01 to 500 kg/m2 in surface density. First,
parametric studies were conducted by varying only the hole diameter, thickness, and so on. However, no simple
trend could be found. Therefore, a number of calculations were repeated with giving values within the above
range. About 200 combinations of physical properties were considered and the best reduction performance wasobtained with a hole diameter of 0.06 mm, a thickness of 0.5 mm, a surface density of 0.6 kg/m2 , a perforation
ratio of 1.4% at the lower end, and a perforation ratio of 8% at the upper end. The numerical results of insertion
loss with these properties are shown in Fig. 9. The ﬁgure includes the results of the rigid conﬁguration, where
the MPP is replaced with a rigid and non-perforated plate. Note that the two conﬁgurations have the same totalheight. By replacing the top part of the barrier with the MPP, 5–20 dB improvements in insertion loss can beachieved above 500 Hz.

p1 p2

vx

vx

h
va
vb

dp
MPP
Figure 7. Schematic diagram of a microperforated panel.

0.2 m

Rigid / MPP

0.7 m
A
45°
0.7 m

0.7 m

Figure 8. Conﬁguration of an edge-effect sound barrier.

50
Rigid
MPP

Insertion loss [dB]

40

30

20

10

0
31

63

125 250 500 1k

2k

4k

8k

16k

Frequency [Hz]Figure 9. Sound insertion loss of example 1.

50
Rigid
MPP

Insertion loss [dB]

40

30

20

10

0
31

63

125 250 500 1k

2k

4k

8k

16k

Frequency [Hz]Figure 10. Sound insertion loss of example 2.
However, we were informed that perforation with a hole diameter of 0.06 mm is not easy to manufacture andthat a hole diameter of 0.1 mm is the minimum with a typical processing scheme. Additionally, the stiffness of
0.5-mm thickness with 0.6-kg/m2 surface density would be too weak to stand alone. Therefore, the considered
range of hole diameter and thickness were reset to at least 0.1 mm and 1 mm, respectively. The density of
the MPP is also ﬁxed to be 7890 kg/m3 , which is assumed to be a steel. Only relatively simple values for the
perforation ratio were used in the search. The best results obtained after some calculations are shown in Fig. 10
for a hole diameter of 0.1 mm, a thickness of 1 mm, a surface density of 7.89 kg/m2 , a perforation ratio of
1% at the lower end, and a perforation ratio of 10% at the upper end. Although the performance above 8 kHz
is lower than Fig. 9, higher performance below 1 kHz can be achieved.

4

CONCLUSIONS

Herein, an edge-effect suppression sound barrier with an MPP is proposed. Since MPPs can be made froma wide range of materials and can be used without a cover to solve durability and weather resistance problems. From the numerical examples, it is shown that the higher reduction performance can be achieved byreplacing the top part of the sound barrier with an MPP. However, it has not been conﬁrmed that the Maa’s
approximations are valid for physical properties considered here. It is necessary to verify the improvements by
experiments.

REFERENCES[1] Maekawa Z. Noise reduction by screeens. Appl Acoust 1968;1(3):157–173.
[2] Koyasu M, Yamashita M. Scale model experiments on noise reduction by acoustic barrier of a straight line
source. Appl Acoust 1973;6(3):233–242.
[3] Fujiwara K, Okubo T. Reduction of road trafﬁc noise using edge-modiﬁed barriers. Noise Control
2010;34(5):347–352.
[4] Kawai Y, Toyoda M. Development of edge-effect suppression barriers. Acoust Sci & Tech 2014;35(1):28–34.
[5] Nihon Environmental Amenity Co, Ltd. https://www.nea-ltd.com/sangyo/pickup_efx.html.
[6] Maa DY. Microperforated-panel wideband absorbers. Noise Control Eng J 1987;29(3):77–84.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0330

Sound absorption through micro-capillary plates:modelling and experimental studies2
Teresa BRAVO1; Cedric MAURY2
1

Instituto de Tecnologías Físicas y de la Información, Consejo Superior de Investigaciones Científicas, Spain
2

Aix Marseille Univ, CNRS, Centrale Marseille, Laboratory of Mechanics and Acoustics, France

ABSTRACTMicro-perforated resonance absorbers have proved to be efficient wall acoustic treatments in the
mid-frequency range with applications in building acoustics and in severe environments such as duct flows
and turbo-engines. In order to broaden their half-bandwidth absorption while keeping high acoustical
performance, a strategy is to decrease the holes diameter while increasing the perforation ratio, thereby
achieving impedance matching over the whole bandwidth. In practice, this is difficult to achieve withstandard micro-perforated panels due to manufacturing constraints. The current study examines theabsorption properties of micro-capillary plates (MCP) characterized by a dense distribution of micro-holes
with diameter between 1 and 60 microns and with a typical open area ratio greater than 60%. Impedancemodelling and Kundt tube measurements show that MCPs have almost zero reactance and constant resistancethat can be tailored to achieve a target absorption value over a broad frequency band. Unbacked MCPs
provide wideband absorption greater than 0.85 at low frequencies whereas the half-bandwidth of MCPs
backed by a shallow cavity may span more than 3 octaves with an absorption staying above 0.8. The
influence of the acoustical load behind unbacked MCPs is examined as it greatly affects their acoustical
performance.
Keywords: Micro-Capillary Plates, Absorption, Broadband Performance

1. INTRODUCTION
The study of improved absorbers for the control of the noise in the low frequency band constitutes
a continuous area of research. Typical solutions involving classical materials are too bulky and heavy
for most of the noise sources with significant low-frequency content (1). Sound absorbers need
generally to be protected from the surrounding environment, by covering them with an impervious
membrane, such as a plastic sheet or a layer of paint, that significantly decreases the absorption at highfrequencies, which is usually highly undesirable. A common solution is to use a perforated facing as acovering for the classical porous materials, which also changes the absorption characteristics. They arecharacterized by their flow resistivity which is a function on their perforation rate or porosity, theirhole size and their thickness.
Demanding environments claimed for more effective non-fibrous absorptive materials. These
included especial hygienic and cleaning conditions, high temperature, high-speed flow and humidity.
Micro-Perforated Panels (MPPs), with perforations of sub-millimetric diameter, or width for slits,
have been proposed (2, 3) as an alternative in architectural acoustics and noise control engineering
design. Unlike fibrous materials, they do not release airborne fine particles in the atmosphere and arerobust to severe surroundings. Applications include auditoriums or swimming pools using glass
structures (4) to allow natural lighting (5), acrylics for desktop use (6), acoustic liners in combustion
chambers such as gas turbines or jet engines (7), and any place where non-fibrous sound absorptive
materials are expected such as in air-flow duct (8, 9).
Although these acoustic absorbers provide good absorption values for low-frequency noisecontents, they are based on the principle of Helmholtz resonances, being limited in frequency
bandwidth of control (10). MPPs are characterized by sub-millimetric holes diameters greater than 0.2
12

teresa.bravo@csic.es
cedric.maury@ centrale-marseille.fr

mm and a perforation ratio typically lower than 1%, When rigidly-backed, they are mid-frequency
resonant absorbers with half-bandwidth that extends over 1 or 2 octaves. Their absorption bandwidth
can be extended through serial or parallel distributions of MPPs with different cavity depths (11, 12)
but at the cost of increasing the partitions size. Their performance can also be improved in the
low-frequency range using architectured cavities extended the effective acoustical path in the cavity
beneath the MPP (13). The increase of the effective path length allows downshifting theHelmholtz-type resonances.
To get rid of limitations concerning the backing cavity, the use of free-standing, unbacked
micro-perforated panels has also been proposed for the damping of acoustic spinning modes in an
air-conditioning system (14). Other studies (15) have shown that the improvement of the bandwidth
efficiency for this configuration can be achieved provided that the MPP holes diameters fall in therange 100 – 200 µm and the perforation constant is strongly increased. The photolithographic process,well-suited to produce MEMS (Micro-Electro Mechanical Sensors), has been used inbio-microfluidics to fabricate freestanding micro-perforated membranes made of solid polymer withholes diameter down to 10 µm. This technology has been applied to fabricate silicon MPPs withminute holes diameters down to 27 µm and a perforation ratio up to 19%, thereby providing a
bandwidth between 3 – 4 octaves with maximum absorption exceeding 0.85 (16).
In the current study, we analyze this strategy to design broadband micro-perforated absorbers
efficient at low frequencies. The goal is to have purely resistive MPPs with almost zero reactance overa broad frequency band so that wideband impedance matching condition could be achieved, and soconstant high absorption values over this bandwidth. This would require having a high density of
micrometric holes together with a high perforation ratio, the so-called Micro-Capillary Plates (MCP)
described in Section 2. Although they are currently used as image intensifiers or as detectors of cosmic
rays, they have been considered in the field of acoustics as anechoic terminations in test benches forthe characterization of the performance of absorbing materials (17).
In this work we are going to analyze the acoustic performance in terms of the absorption, thetransmission and the dissipation of both unbacked and rigidly-backed MCPs. Section 3 develops ananalytical model comprising different regimes of interest for the MCPs. Using the slip-flow regime,
some parameters studies are carried out to show the potential importance of MCPs in the field of
acoustics due to their dissipative properties. The simulated results are compared in the next section
with measurements carried out in a small Kundt tube for different configurations. They have been
performed considering both the free-standing, unbacked configuration, and the rigidly-backed
configuration. Finally, we conclude with a summary of the main results and some ideas for futurework.

2. FROM MPP TO MCP ABSORBERS
2.1 MCP morphology
The physical characteristic parameters constituting a cavity-backed MCP are outlined in Figure 1.

 

The optimal selection includes the holes diameter, d , the perforation ratio    d 2 42 , the holes
pitch  and the panel thickness t . The thickness of the backing cavity is denoted by D .

Figure 1 – Rigidly-backed MCP constituting parameters.
MCPs have micro-holes with diameter typically lower than 50 µm and a perforation ratio greaterthan 50 %. In Figure 2 we can see a Glass Capillary Array with 12.5 µm holes diameter and aperforation ratio of 50% with one hundred thousand holes per square centimeter. This can be comparedon the same scale with a classical MPP with 0.5 mm holes diameter and 1 % perforation ratio.

Figure 2 – Comparison between a classical MPP and a MCP at the same scale.
Using X-ray tomography (Figure 3), we can zoom on the MCP surface over an area of 0.7 square
millimeters to observe a high density of channels of micrometric diameter as well as straight channels
within the half millimeter depth of the MCP.

Figure 3 – MCP X-ray laminography obtained on a front surface (left) and on the MCP thickness dimension(right).
2.2 MCP slip-flow modelling
The well-established continuous laws that have been used to study the propagation of soundthrough MPPs do not hold when addressing the problem with MCPs with holes diameters typically ofthe order of the microns. The accurate modeling of microflows must take into account several
characteristic lengths to ensure that the sampling volume is in thermodynamic equilibrium. Thisimplies that the mean free path  must be small compared with the characteristic length L of the
micro-pores. The ratio between both quantities is called the Knudsen number,
Kn 


L

.

(1)

The condition Kn  1 constitutes the requirement for thermodynamic equilibrium. Based on thisparameter, a classification has been stated for different flow regimes (18). For Kn  10 -3 the flow isin continuum regime, and it is accurately modeled by the compressible Navier-Stokes equations withclassical boundary condition that express the continuity of temperature and velocity between the fluid
and the wall. For 10 -3  Kn  10 -1 the flow is in slip flow regime with a velocity slip and a temperature
jump taken into account at the walls. For 10 -1  Kn  10 the flow is transitional regime and thecontinuum approach of the Navier-Stokes equations is no longer valid. Finally, for Kn  10 the flow
is in free molecular regime, with collisions predominant between the gas molecules and the walls. The
limits between the different regimes could vary depending on the selection of the characteristic length
L . For flows in channels, L is generally taken as the radius or the depth of the channel.
Typically, most of the microsystems that use gases work in the slip flow regime, or in the earlytransition regime. For instance, when considering variation of the holes radius r0 such as

0.64 m  r0  64 m , we obtain a Knudsen number such that 10 -3  Kn  10 -1 . In the slip-flow
regime, continuum laws stay valid within the channels, but not near the walls of the MCP holes. The
axial particle velocity decreases down to a slip velocity (Figure 4) that can be expressed as a function

of the derivative of the axial velocity with respect to the normal exiting the wall, v / n  , and a
proportionality constant B v called the coefficient of slip. This coefficient can be calculated from thekinetic theory of gases in terms of the fraction of molecules  v absorbed by the surface (19). The
velocity jump can be expressed asv  Bv

2 v
v
v

Kn
.
n 
v
n 

(2)

Figure 4 – Knudsen layer and slip-flow velocity.
Assuming straight cylindrical channels in harmonic regime ( e j t ), and applying linearized
momentum and energy conservation to solve the momentum boundary-value problem, the viscoustransfer impedance of the channel, given per unit length can be expressed as
J 1 k v r0 2
Z v  j 0 t 1 
 k v r0 J 0 k v r0   Bv k v r0 J 1 k v r0 
where k v 

1

(3)

 j 0  is the viscous diffusion wavenumber,  the air dynamic viscosity and 0 the

air density, and J 0 and J 1 are the Bessel functions of the first kind of orders 0 and 1 respectively. As
MCPs have narrow channel behavior, k v r0  1 , over a broad frequency range, we can perform Taylor
series expansion of Equation (3) with respect to the Shear number Sh  k v r0 leading to1  8t4(4)
 2  j  0 t 1  6 Bv .
1  4 Bv  r03
Considering plane wave normal incidence, the amplitude reflection and transmission coefficients aredefined as r  Z1  Z 0  Z1  Z 0  and   2 Z 0 Z1  Z 0  with Z1  Z v   Z 0 , the input impedance
Zv of the absorber backed by an anechoic termination, and Z 0   0 c 0 . On can then calculate the dissipation,22

  1  r   , as the fraction of incident energy not reflected, nor transmitted.
2.3

The MPP and MCP acoustical performance
The previous expressions have been used to calculate the acoustic performance of two different
samples composed of one MCP and one MPP in the unbacked configuration with constituting
parameters defined in Table 1.

Plate type
MPP
MCP

Table 1 – Physical parameters for the two samples.
KnudsenChannelPerforation
numberradius (µm)
ratio (%)
Kn
250
0.79
1.3  10 4
3
12.5
50
5.1  10

Thickness
(µm)
500
500

The real and imaginary parts of the specific input impedance, presented in Figure 5, can help tounderstand the acoustic performance of the samples. It can be seen that the imaginary part for the MCP
is zero-valued over a broad frequency range due to its high perforation ratio. In this frequency range,
the MCP transfer impedance behaves as a pure resistance that equals the optimal input impedancevalue. The MPP presents this behavior in the very low frequency range, but progressively deviatesfrom the optimal value as frequency increases.

Figure 5 – Comparison between the specific transfer resistance (top) and reactance (bottom) for a
MCP (solid) and a MPP (dashed).
The corresponding absorption, reflection and dissipative coefficients calculated from these transfer
impedances are presented in Figure 6. The MCP pure resistive values provides a flat absorption,transmission and dissipation spectra of respectively 0.75, 0.25 and 0.5, the latter being the maximum
value that can be reached for the dissipation in unbacked configuration. The MPP exhibits poor
performance with significant transmission at low frequency and significant back-reflections at higher
frequencies.

Figure 6 – Comparison between the absorption (top), transmission (middle) and dissipation(bottom) coefficients for a MCP (solid) and a MPP (dashed).

3. EXPERIMENTAL STUDY OF MCPs ACOUSTIC PERFORMANCE
3.1 Unbacked MCPs
The predictions presented in previous section have been verified experimentally using a small
Kundt tube situated in a semi-anechoic chamber. A photograph and a schema to locate the main
component are presented in Figure 7. The Kundt tube is situated vertically and connected on thebottom side to a loudspeaker that generates a random noise in the frequency range between 80 Hz and
7 kHz. The cut-off frequency of the Kundt tube that provides confidence in the measurement is slightly
less than 6700 Hz for an inner radius equal to R  1.5 cm . As this dimension is smaller than the MCP
radius, equal to 1.275 cm, an annular adaptor has been printed in PVC and has been situated in theupper side of the tube to facilitate the placement of the sample test (Figure 7). The adaptor introduces
a constriction of radius r = 1 cm and thickness l = 1 cm. Applying continuity of the pressure andacoustic flow rate at the holder position, it is possible to obtain an estimate of the MCP specific input
impedance (20).
The two microphones method (21) has been used using 1/4" condenser microphones. The
separation distance between them, d  5 cm , provides a lower cut-on frequency of analysis which isequal to 200 Hz for this configuration. The pressure and the microphone positions has been acquired
using the OROS (type OR38) multi-channel system over a bandwidth 80 Hz – 6.7 kHz, at a sampling
rate of 12.8 kHz and with a spectral resolution of 1.56 Hz, triggered on the generation of the white
noise drive signal.

Figure 7 – Photograph and schema of the experimental set-up with a small tube Kundt that holds anannular adaptor where the MCP sample is situated horizontally.
The estimated absorption coefficient for the unbacked MCP sample is presented in Figure 8. As it
can be appreciated, it presents a broadband value that remains constant and equal to 0.86 up to 1 kHz.
Then it steady decreases down to a value of 0.7 until reaching the duct cut-on frequency. Thismeasurement is compared to different analytical predictions. The black curve represents the calculated
absorption assuming plane wave radiation load. It achieves a constant value of 0.72 that
underestimates by 20% the measured value. To improve this comparison, the radiation of an unflanged
cylinder has been included in the prediction by considering the model of Silva et al. (22). Near-fieldpressure and air particle normal velocity have been determined using a miniature pressure-velocity
probe and the radiation impedance has been calculated with a pressure-velocity ratio surface-averaged
at close proximity of the sample side.

.
Figure 8 – Normal incidence absorption coefficient for the unbacked MCP measured values (redwith circles) and estimated assuming anechoic radiation loads (black) and unflanged radiation loads(green). The measure of the open adaptor termination is presented in yellow with squares.

When including the radiation of the cylinder into the load impedance, the predicted results,
represented in green in Figure 8, closely follow the measured values. It should be outlined that,
unplugging the MCP, we obtain a significant drop in absorption due to very small radiation leakage
that slowly increases with frequency.
3.2 Rigidly-backed MCPs
Previous section has shown that free-standing MCPs are able to provide broadband absorption
performance in the low frequency range. It is of interest to quantify the differences when consideringa rigidly-backed partition. A measurement has been carried out with the same sample rigidly-backed
by a 24 mm-depth cavity. The results (red with circles) are presented in Figure 9 and compared with theprediction.

Figure 9 – Normal incidence absorption coefficient for the rigidly-backed MCP measured values(red with circles) and predicted analytically (green).
It can be seen that the performance has changed considerably. The partition is still able to provide
a broadband absorption almost flat between 1500 and 5500 Hz, that spans almost 12 octave bands witha maximum value of 0.86. However, at very low frequencies, the absorption coefficient drops due tothe air cavity that prevents dissipation energy within the channels. It should be noted that the holes
radius have been selected when considering the free-standing configuration, and the current results
could be further improved by a better selection considering the backed characteristics in the costfunction optimization. Despite this drawback, the MCP efficiency clearly overcomes the resultscorresponding to a MPP partition, with a performance extending over two octave bands for the samebacking dimensions. We can also appreciate a good agreement between the simulation and themeasurement, except an over-estimated predicted absorption performance below 700 Hz.

4. CONCLUSIONS AND PERSPECTIVESIn this work we have studied the possibilities of MCP to work as absorbers able to overcome thedifficulties associated to classical materials in the low frequency range, or to MPP partitions
presenting a narrowband performance. These devices are slabs constructed from a highly resistive
material with a regular array of slots or microchannels densely distributed over the whole surface.
They are characterized by holes diameters between 0.6 μm and 50 μm and a large perforation ratio,
typically between 50 and 65%. As classical continuous laws do not hold in this case, we have presented
a model considering the working conditions in the slip-flow regime. An analytical solution is provided
for the viscous transfer impedance of the channels that have been used to predict the acoustic
performance in absorption and transmission.
Experimental measurements carried out in laboratory conditions have shown that, when thephysical parameters have been properly selected, free-standing MCPs behave as broadband absorbers.
They are able to achieve absorption values greater than 0.7 up to 4 kHz with a flat absorption plateau
above 0.85 up to 7 kHz under normal incidence. They present then great potential to use in engineering
noise control problems as an alternative to classical materials.
For comparison purposes, the behavior of rigidly-backed MCP partitions has also been tested using
the same set-up with a backing cavity of 2.5 cm depth. The measured results present a behavior that has
considerably changed, with a narrow-band absorption range, narrower than considering the unbacked
configuration, but clearly overtaking the results obtained for a MPP partition of the same dimensions.
To overwhelm the low-frequency limitation, a solution can be proposed that uses openly-backed MCPs.

In this case, high absorption is retrieved at very low-frequency, at the expense of drops that occur at ¼
wavelength cavity resonances that provoke zero velocity at the MCP surface and no dissipation. A
hybrid configuration should then be sought for.

ACKNOWLEDGEMENTS
This study was funded in Spain by the Ministerio de Economía y Competitividad project
TRA2017-87978-R, AEI/FEDER, UE, and the mobility program ILINK+2022. It was supported in
France by the ANR VIRTECH (ANR-17-CE10-0012-01).

REFERENCES
1. Zwikker C., Kosten C.W. Sound Absorbing Materials, New York, USA : Elsevier Pub. Co.; 1949.
2. Maa D.Y. Potential of microperforated panel absorbers. Journal of the Acoustical Society of America
1998; 104: 2861–2866.
3. Maa D.Y. Microperforated-panel wideband absorbers. Noise Control Engineering Journal 1987; 29:
77–84.
4. Fuchs H.V., Zha X. Acrylic-glass Sound Absorbers in the Plenum of the Deutscher Bundestag, Applied
Acoustics 1997; 51: 211–217.
5. Kang J., Brocklesby M.W. Feasibility of applying micro-perforated absorbers in acoustic window
systems. Applied Acoustics 2005; 66: 669–689.
6. Sakagami K.,Kusaka M.,Okuzono T., Kido S.,Yamaguchi D. Application of transparent microperforated
panels to acrylic partitions for desktop use: A case study by prototyping. UCL Open Environment 2021;
3 (1): 1-10.
7. Bielak G. W., Gallman J., Kunze R., Murray P., Premo J., Kosanchick M., Hersh A.S., Celano J., Walker
B., Yu J., Kwan H.W., Chiou S., Kelly J., Betts J., Follet J., Thomas R. Advanced Nacelle Acoustic
Lining Concepts. Report NASA/CR-2002-211672 2002; 3: 8-18.
8. Guo Y., Allam S., Åbom M. Micro-perforated Plates for Vehicle Application. Proc. of Internoise 2008,
Shanghai, China, 2008. p. 1918–1936.
9. Allam S., Åbom M. A New Type of Muffler Based on Microperforated Tubes. ASME Journal of
Vibration and Acoustics 2011; 133: 1–8.
10.Ingard U. Noise Reduction Analysis. Sudbury, Massachusetts, USA: Jones and Bartlett Publishers, 2010.
11.Sakagami K., Morimoto M., Koike W. A numerical study of double- leaf microperforated panel
absorbers. Applied Acoustics 2006; 676: 609–619.
12.Sakagami K., Nagayama Y., Morimoto M., Yairi M. Pilot study on wideband sound absorber obtainedby combination of two different microperforated panel (MPP) absorbers. Acoust. Sci. & Tech. 2009; 30:
154–156.
13.Simon F. Long Elastic Open Neck Acoustic Resonator for low frequency absorption, J. Sound Vib.
2018; 421: 1–16.
14.Sack S., Åbom M., Modal filters for mitigation of in-duct sound, Proc. Mtgs. Acoust. 2016; 29: 040004.
15.Maury C., Bravo T., Mazzoni D. The use of micro-perforations to attenuate the cavity pressure
fluctuations induced by a low-speed flow. J. Sound Vib. 2019; 439: 1–16.
16.Qian Y. J., Kong D. Y., Liu S. M., Sun, Zhao Z. Investigation on micro-perforated panel absorber withultra-microperforations. Appl. Acoust. 2013; 74: 931–935.
17.Dalmont J.-P., Kergomard J., Meynial X. Realization of an anechoic termination for sound ducts at low
frequencies, C. R. Acad. Sci. Paris 309 II;1989: 453–458
18.Kandlikar S., Garimella S., Li D., Colin S., King M.R. Heat Transfer and Fluid Flow in Minichannels
and Microchannels, 2nd Edition, Oxford, United Kingdom: Elsevier Ltd.; 2014.
19.Maxwell J. C. On Stresses in Rarefied Gases Arising from Inequalities of Temperature, Phil. Trans. Roy.
Soc. Part I 1879; 170, 231–256.
20.Maury C., Bravo T. Wideband sound absorption and transmission through micro-capillary plates:modeling and experimental validation, Journal of Sound and Vibration 2020; 478: 115356.
21. ASTM E1050-12, Standard Test Method for Impedance and Absorption of Acoustical Materials Using aTube, Two Microphones and a Digital Frequency Analysis System, ASTM International, WestConshohocken, U.S.A., 2012.
22.Silva F., Guillemain Ph., Kergomard J., Mallaroni B., Norris A. Approximation formulae for the acoustic
radiation impedance of a cylindrical pipe, Journal of Sound and Vibration 2009; 322: 255–263.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022, in Gyeongju, Korea
Extended abstractABS-0375

Designable heterogeneous MPPs and their applications
Kimihiro SAKAGAMI1; Midori KUSAKA1; Takeshi OKUZONO1
1

Environmental Acoustics Lab., Grad. Sch. of Engineering, Kobe University,
Rokko, Nada, Kobe 657-8501 Japan

ABSTRACTIn general, microperforated panels (MPPs) are homogeneous materials, but heterogeneous MPPs have also
been proposed in recent years to improve sound absorption properties and to meet design requirements.
Recently, MPPs with design pattern made by holes using dotted-art technique have been proposed. However,the prediction of their sound absorption characteristics has not been sufficiently investigated, and this may
cause problems in predicting sound absorption characteristics in the design stage. In this study, the synthetic
impedance method, which is a method for predicting the sound absorption characteristics of heterogeneous
MPPs and was proposed in a previous paper, was used to investigate the possibility of predicting various
types of heterogeneous MPPs, and two conditions were shown for the applicability of this method: (1) theholes are distributed over the entire surface, and (2) the hole spacing is constant. As a design for dotted-art
heterogeneous MPP that satisfies the above two points, this study proposed a method using two types of holes,
one large and one small, where the larger hole (diameter of 0.8 to 1.0 mm) is used to draw a design pattern
and the smaller hole (diameter of 0.2 mm) is used for the background, and conducted a prototype experiment.
Nine different specimens were examined and it was found that the measured and predicted values for all
specimens were in good agreement.
Keywords: Sound Absorption, Microperforated Panel (MPP), Heterogeneous MPP, Dotted-Art MPP

1. INTRODUCTION
Since its proposal by Maa (1), MPPs have attracted attention as a next-generation sound-absorbing
material and have been widely studied (2). MPPs are inherently homogeneous sound-absorbing
material, with parameters assumed to be uniformly distributed across the plate surface, andhomogeneity is also assumed in conventional prediction theories.
In recent years, along with the pursuit of a wider range of design possibilities, heterogeneous MPPs,
i.e., those where the parameters are not uniformly distributed on the plate surface, have also beenstudied (3). The authors have also proposed a method for predicting the sound absorption propertiesof heterogeneous MPPs, which we call the synthetic impedance method (SIM), in a previous paper(4).
Most recently, MPPs with artistic features have been proposed using the dotted-art technique (5),and have attracted much attention. However, the same paper (5) does not show clearly the method topredict their sound absorption characteristics. It is needed a prediction method for their soundabsorption characteristics, because it is important to know them in the design stage.
In this study, the scope of application of the SIM is first examined to search for conditions underwhich the sound absorption characteristics of heterogeneous MPPs can be predicted. Based on this, aprototype MPP with an attempted design using the dotted-art technique is prepared. With these
prototypes, the possibility of predicting their sound absorption characteristics are investigated in detail.
Then, a design concept for an artistic MPP using dotted-art is proposed.

1

saka@kobe-u.ac.jp (KS)

2. SCOPE OF APPLICATION OF THE SYNTHETIC IMPEDANCE METHOD
2.1 Synthetic impedance method [4]The synthetic impedance method (SIM) considers a heterogeneous MPP as a combination ofhomogeneous MPPs and determines the overall impedance by synthesising them. In the previous paper(4), we made a case study with four specimens to show that the SIM gives reasonably good prediction.
The impedance of a heterogeneous MPP is denoted as ZMPP. The impedance of a hypothetical MPP
with only one type of hole diameter in a surface area S is considered for n types of holes with diametersfrom d 1 to d n . The impedance of a hypothetical MPP with holes of diameter d1 is defined as ZMPP,1 , theimpedance of a hypothetical MPP with holes of diameter d 2 as ZMPP,2 , up to ZMPP,n, respectively. A
conceptual diagram is shown in Fig. 1. The ZMPP is considered as a composite of Z MPP,1, ZMPP,2, ...,Z MPP,n. The ZMPP is then the following equation:
𝑍MPP =

1
∑𝑛𝑖=1

(1)

1
𝑍MPP,𝑖Fig. 1. Diagrams of the hypothetical MPPs. The upper MPP is the original MPP, and the lower
MPPs are the hypothetical MPPs, which have holes of different diameters only in surface area S.
The impedance Z MPP,i of a hypothetical MPP with a hole of diameter d i is obtained by combining
the impedances of the part with holes and the part without them (Z rigid , i,e, infinity). Let S i be the areaof the part with holes of diameter d i, and Z i be the impedance of the part with holes. Z i can be calculatedusing existing prediction theory because the perforated area is homogeneous. Thus, Z MPP,i is calculated
by:𝑍MPP,𝑖 =11

1 𝑆𝑖
𝑆 − 𝑆𝑖𝑍𝑖 𝑆 + 𝑍rigid 𝑆

=

𝑆
𝑍
𝑆𝑖 𝑖

(2)

Calculate ZMPP,1 , ZMPP,2 , ..., ZMPP,n , respectively, according to Eq. (2), and substitute them into Eq.
(1) to obtain ZMPP as follows.
𝑍MPP =

1𝑆∑𝑛𝑖=1 𝑖
𝑆𝑍𝑖=

𝑆
𝑆
∑𝑛𝑖=1 𝑖𝑍𝑖

(3)

2.2 ExperimentTwelve heterogeneous MPP specimens 1-12, shown in Fig. 2, were prepared and the normal
incidence sound absorption coefficient was measured at 1.25 Hz intervals up to the upper limit of

1

2

3

4

5

6

7

8

9

10

11

12

Fig. 2. Photographs of the specimens 1 to 12.
1700 Hz according to JIS A 1405-2 (ISO 10534-2 compatible). For each specimen, measurement was
performed under the four conditions of the air-back cavity depth: i.e., 25, 50, 75 and 100 mm. The
measurement results were compared with the calculated results by the SIM and the prediction errors
were evaluated using the error indices described below.

2.3 Error indices of the predicted value
In this study, the following three error indices were defined to examine the prediction error of the
SIM and to determine its predictability.
- Relative error of the peak frequency, ferror (%):
𝑓error (%) =𝑓pre − 𝑓mea
× 100
𝑓mea

(4)

where fpre is the peak frequency of the predicted sound absorption coefficient and fmea is the peakfrequency of the measured sound absorption coefficient.
- Relative error of the main resonant peak absorption coefficient, error (%):
𝛼error (%) =𝛼max,pre − 𝛼max,mea
× 100
𝛼max,mea(5)

where α max,pre is the peak value of the predicted sound absorption coefficient and α max,mea is that of themeasured sound absorption coefficient.
- RMS error of the overall sound absorption characteristics, RMS error:𝑛

𝑅𝑀𝑆 𝑒𝑟𝑟𝑜𝑟 = √12∑ (𝛼pre,1.25𝑖 − 𝛼mea,1,25𝑖 )
𝑛

(6)

𝑖=100

where pre,1.25i is the predicted value of absorption coefficient at 1.25i Hz and  mea,1.25i is the measured
value of absorption coefficient at 1.25i Hz.
Depending on the magnitude of the error indices, specimens 1 to 12 are classified into groups (1)to (3). The magnitude of the error indices is determined by the average of the absolute values for eachof the four air-back cavity depth conditions.
- Group (1): ferror and error both below 5% and RMS error below 0.05.
- Group (3): ferror or error is larger than 10% or RMS error is larger than 0.1.
- The specimens that are neither classified as group (1) nor group (3) are classified as group (2).
2.4 Results and discussion
The results of classification of the specimens into groups (1) to (3) are given below. From thecharacteristics of the specimens in each group, the conditions for heterogeneous MPPs to which the
SIM can be applied are found.
Specimens 1 and 2 fell into group (1). The common features of these specimens are as follows:
Holes are distributed over the entire surface;
The hole spacing is constant.
As an example, Fig. 3 shows the comparison results between the measured values and predictedvalues by the SIM for specimen 1, which falls into group (1). The both two specimens are in good
agreement for all four air-back cavity conditions.
Group (2) corresponded to specimens 3 to 7. The common features of these specimens are as
follows:
Holes are distributed over the entire surface;
The hole spacing is not always constant.
The other specimens, i.e., specimens 8 to 12, fell into group (3). The common features of these
specimens are as follows:
Holes are distributed only on a part of the surface;
The hole spacing is not always constant.
Based on the above results, the characteristics of group (1), which are:A) Holes are distributed over the entire surface;B) The hole spacing is constant;should be the conditions in which the sound absorption characteristics of heterogeneous MPPs can bepredicted by the SIM.
In this study, both f error and α error were set to less than 10% and RMS error to less than 0.1 asacceptable error values. These were obtained from the error when the homogeneous MPP waspredicted by Guo theory (6). The errors for group (2) fulfill these conditions.
In group (2), where the error is acceptable, some of the hole spacings are not constant. Condition
B above is therefore not essential, but can be considered desirable as a condition that enables reliablepredictions to be made by the SIM. On the other hand, heterogeneous MPPs with holes distributed
only on a part of the surface, which is common to all specimens in group (3), are likely to be outside
the scope of the SIM.
Air-back cavity depth 25 ㎜

Air-back cavity depth 50 ㎜

Air-back cavity depth 75 ㎜

Air-back cavity depth 100 ㎜

Fig. 3. Comparison of measured and predicted vertical incident sound absorption
coefficient for test specimen 1. Solid orange line: measured value; dotted blue line: predictedvalue.

3. EXPERIMENTAL EXAMINATION OF THE PREDICTABILITY OF DOTTED-ART
MPPs BY PROTOTYPINGThe design of dotted-art heterogeneous MPPs should satisfy the two aforementioned conditions A)
and B), so that its absorption characteristics can be predicted using the SIM in the design process.
Therefore, we conceived a design in which holes are placed at regular intervals over the entire
surface, with large holes in the patterned areas and small holes in the background areas: We consider
that by using holes with a diameter so small that they are almost invisible for the background areas,
only the large holes in the patterned area would be visible.
In this study, nine specimens of different designs, A to I, were produced. In all of them, 0.2 mm
diameter holes were used for the background and 0.8 or 1.0 mm holes for the designed pattern. As
examples, photographs of specimens A, F and H are shown in Fig. 4. In these three specimens, thebackground and patterns were made using 0.2 mm diameter holes and 0.8 mm holes, respectively.
Measurements and predicting calculations by the SIM were carried out in the same way as in theprevious section. As an example, a comparison of the results for specimen A is shown in Fig. 5.

A

F

H

Fig. 4. Photographs of the specimens of dotted-art MPP designed by the proposed concept.
Specimens A (star pattern), F (bear face) and H (outline of letters ‘KOBE’) are shown as examples.
By calculating error indices from both measured and predicted results, the prediction error of eachspecimen was examined and found to be within the predictable range for all specimens. From this, it
can be concluded that the sound absorption characteristics of the dotted-art heterogeneous MPPs using
the method proposed in this study can be predicted by using the synthetic impedance method (SIM).
To look closer, the specimen surface was divided into small areas, and the standard deviation of
the number of larger holes were calculated by counting their number in each area. The results showedthat the prediction accuracy is higher when the larger holes are unbiasedly distributed.
For detailed discussion, one can consult Reference (7).

REFERENCES
1. Maa, D-Y., Theory and design of microperforated panel sound-absorbing constructions. Sci. Sinica, 17,
55-71 (1975)
2. Herring, D., A guide to the applications of microperforated panel absorbers. Sound Vib., 51, 12-18 (2017)
3. Carbajo, J., Ramis, I., Godinho, L., Amado-Mendes, P., Assessment of the methods to study the acoustic
properties of heterogeneous perforated panel absorbers. Appl. Acoust., 133, 1-7 (2018)
4. Kusaka, M., Sakagami, K., Okuzono, T., A basic study on the absorption properties and their predictionof heterogeneous micro-perforated panels: A case study of micro-perforated panels with heterogeneoushole size and perforation ratio. Acoustics, 3, 473-484 (2021)
5. Lee, H. P., Kumar, S., Aow, J. W., Proof-of-concept design for MPP acoustic absorbers with element ofart. Designs, 5, 72 (2021)
6. Guo, Y., Allam, S., Abon, M., Micro-perforated plates for vehicle applications. Proc. Internoise, Shanghai,
China, 26-29 October, 2008.
7. Sakagami, K., Kusaka, M., Okuzono, T., A basic study on the design of dotted-art heterogeneous MPP
sound absorbers. Acoustics, 4, 588-608 (2022)
Air-back cavity depth 25 ㎜

Air-back cavity depth 100 ㎜

Fig. 5. Comparison of measured and predicted vertical incident sound absorption coefficientfor specimen A. Solid orange line: measured value; dotted blue line: predicted value.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0653

Optimization of sound insulation performance of a layered structurewith perforated honeycomb panel
Kyungsoo KONG1; Naohisa INOUE2; Tetsuya SAKUMA3
1

Graduate School of Frontier Sciences, The University of Tokyo, Japan
2
3

Maebashi Institute of Technology, Japan

Graduate School of Engineering, The University of Tokyo, Japan

ABSTRACT
A honeycomb panel is often used as resonator-type sound absorbing material by perforating an array of holeson the surface. By layering the perforated honeycomb panel (PHP) with a flexible sheet out of contact on theperforated surface, the layered structure acts as double panel, thus improving sound insulation performancein a high frequency range but causing low-frequency resonance transmission. In this paper, the resonancetransmission phenomenon of the layered structure is theoretically modeled, and a parametric study isconducted for optimization of sound insulation performance. The results clarify the effects of the porosity of
PHP, the thicknesses of PHP and air layer, and the areal density of sheet. In addition, the overall performanceis evaluated by single-number quantity based on ISO-717-1, and several charts are presented for optimal
design of the structure.
Keywords: Insulation, Honeycomb panel, Resonance transmission

1. INTRODUCTION
Recently, a variety of acoustic materials have been actively developed to overcome the limitationsof existing acoustics materials and to obtain high performance in a low frequency range although it
has thin thickness and light weight. One of such materials is a honeycomb plate (sandwich panel
having a honeycomb core) that has lightweight and high rigidity. It can be used for exterior materials
in various fields such as transport vehicle, construction and so on. Moreover, it is also proposed as anacoustic material by perforating on the surface to compose a Helmholtz resonator [1] [2]. A study on
the sound absorption characteristics of a back-perforated honeycomb panels (BPHP) with an air layer
was carried out, and it was confirmed that BPHP has a specific acoustical mechanism due to coupling
the resonator arrays and the panel vibration [3]. Furthermore, it has been confirmed that highinsulation performance can be obtained by layering a flexible sheet on PHP although it is thin andlightweight [4]. However, performance degradation due to resonance transmission occurs in a low
frequency range. In this paper, a simple theoretical model is used to figure out the insulation
mechanism of the layered structure in detail. In addition, a parametric study is conducted to devise amethod for optimizing sound insulation performance in consideration of resonance transmission, anda validity has been confirmed by measurements in the reverberation chamber.

2. THEORETICAL ANALYSIS
2.1 Formulation
Figure 1-(a), (b) defines the theoretical model-related variables of layered structure with PHP andflexible sound insulation sheet. We construct a simple theoretical model that sound waves pass the
PHP by incidence angle 𝜃 as shown in Figure 1-(c). At this time, equations of motion of the flexible
sheet, the PHP structure and the neck mass are given by the following equations (1) to (3), respectively.
1
2
3

4709384469@edu.u-tokyo.ac.jp
inoue@maebashi-it.ac.jp

sakuma@arch1.t-u-tokyo.ac.jp

(1)
(2)
(3)
Where P i, P r and Pt are the incident, reflected and transmitted wave amplitude. ms, mp are the areal
density of flexible sheet and PHP. mn is the effective areal density of the neck. Sn is a hole area, andS is the area of the single honeycomb core. and c pn is the viscous damping coefficient of the neck,which is given as follows based on the Allard-Ingard model [5].

The spring coefficient k sp, k ps, k sn, k ns, k pn, k psn is exspressed as follows.

Where , 0, c 0 are the viscosity coefficient, density of air and the speed of sound, respectively. And
with respect to the incident and transmitted surface, the continuity condition of the particle velocity
in the normal direction of the sound wave and the vibration velocity of the flexible sheet and PHP
structure are given by the following equations (4) and (5).
(4)(5)
Calculate the transmittance (P t/P i) at each angle of incidence with equations (1) to (5), and random
incidence is solved by statistical average with Paris’ law. Previous proceeding has covered the detailresults of parametric studies based on these theories, so it was omitted in this paper [3].

2.2 Resonance mechanism and frequencies
A free vibration of the system is considered and given as the matrix form as follows.

(6)

Three resonance frequencies of the system are obtained from a solution in which the matrix expressionof the left side matrix becomes 0. One of the solutions is a rigid body mode (0 Hz) in which the wholemodel vibrates integrally. Another is a resonance frequency using an air layer between the panel andthe sheet as a spring, and since the interval is very small in this paper, resonance is not seen in thefrequency range to be observed. The other is the resonance frequency of the system, where resonancetransmission, the effect of the double wall, occurs, which is referred to as f sys. Figure 2 shows thetransmission loss and the resonance frequency f sys in terms of perforation ratio changing perforation
diameter. In addition, the eigen-frequencies asymptotic to f sys curve was also shown in Figure 2. These
are the resonance frequency of the resonator of PHP (f res ) and the resonance frequency of the air springof total thickness (Lp+Ls) (f rmd ) and given as follows.

(7)(8)
As shown In Figure 2, if the perforation ratio is small, diameter is smaller than 0.25 mm, the effectof the double wall and resonance transmission do not occur, and it has insulation characteristics likesingle wall. In contrast, if the perforation ratio is big enough, a dip occurs clearly at f sys, and in thehigh frequency range, a peak occurs at f res, which is the Helmholtz resonance frequency. From theseresults, the sound insulation characteristics of the layered structure with PHP has changed according
to perforation ratio. In addition, the dip is blunt near a certain perforation ratio (ϕc) as given as follows
that f res and f rmd crossed.
(9)

In this range, the loss of insulation performance due to the dip is reduced, and it is possible toobtain a performance improvement due to peak in the high frequency range. Higher performance
improvement can be obtained by increasing the perforation ratio, but the dip due to resonancetransmission is fatal in insulation performance and should be avoided. This range seems to have aratio of f res/f rmd approximately between 1 to 2, and if it is lower than 1, it gradually has thecharacteristics as a single wall. In the following section, a parametric study is conducted for the
optimal design of the layered structure with PHP in consideration of these characteristics.

3. PARAMETRIC STUDY
In Section 2.2, it was confirmed that resonance transmission occurred at the resonance frequency
f sys of the theoretical model system. And the loss of the resonance transmission can be improved bychanging the perforation ratio properly. In this section, a parametric study is performed whilechanging the two variables of the layered structure. First, the frequency and transmission loss at f sys
were calculated by focusing on the resonance transmission phenomenon. Second, a single number
quantity based on ISO-717-1 was calculated to index the sound insulation performance of the entire
frequency range.

3.1 Discussion on resonance transmission
Assuming d = 1 mm, p = 10 mm, ms = 3.83 kg/m 2, mp = 3.05 kg/m 2, Lp = 28.5 mm, Ls = 0 mm (noncontact) and l n = 1 mm as basic conditions, the frequency and transmission loss at f sys are calculated
while changing two variables. And resonance frequency ratio (f res/f rmd ) is also calculated.
Figure 3 shows the results when changing (a) PHP thickness L p and perforation diameter d, (b)flexible sheet areal density ms and interval thickness between PHP and flexible sheet L a, (c) flexible
sheet areal density ms and perforation diameter d. (a) changes the design variables related to PHP, and(b) changes the variables that can be changed during layering existing PHP. At the (c), the variables
that are relatively easy to change in (a) and (b) were selected.
As shown in Figure 3-(a), The f sys increases as the diameter d increases and PHP thickness Lp
decreases. As the perforation ratio increases, f sys approaches the plate resonance frequency of thespring coefficient of the air layer of the total thickness (Lp +Ls), so it has the characteristic of asymptote
to a constant value. And as the PHP thickness Lp becomes thinner, the rigidity k p of the air layer inside
the honeycomb becomes stronger, and the f sys becomes higher. The transmission loss in f sys does notchange considerably when PHP thickness Lp changes. In contrast, when the diameter d is small, thetransmission loss improves, and when d is large, the dip is generated, such as the double wall effect.
As shown in Figure 3-(b), f sys decreases as the sheet areal density ms increases and the interval
thickness L a increases. Because the mass of system increases and the rigidity decreases, respectively.
The transmission loss is not significantly changed as compared with Figure 3-(a). And there is a rangethat the dip deepens, where the m s is equal to PHP areal density mp about 3 kg/m 2. Figures 3-(c) shows
the sound insulation characteristics while changing the ms and d shown in Figure3-(a), (b). If ms has
the same weight as mp, the dip deepens, and depending on the diameter d, the dip disappears like asingle wall, or the resonance transmission occurs by double wall effect. In addition, where the ratioof the resonance frequency (f res/f rmd) is 1 to 2, the transmission loss increases as shown in Section 2.2.
From these results, it is possible to know in detail the resonance transmission phenomenon according
to the change of each variable, so it is expected to improve the sound insulation performance by
avoiding f sys. However, the improvement of sound insulation performance in the high frequency range,
which is one of the characteristics of the layered structure with PHP, is unknown. Thus, theperformance evaluation over the whole frequencies is conducted based on ISO in Section 3.2.
3.2 Discussion on single-number quantity based on ISO-717-1
ISO-717-1 covers indexes for evaluating the sound insulation performance in buildings [6].
Generally, the results of experiments according to the ISO standard are evaluated, but in this paper,
the indexes are calculated using the theoretical analysis results for reference. As a result of thetheoretical analysis, since the transmission loss in resonance transmission is very low compared toother frequency bands, it is difficult for the Rr value evaluated as the lowest value to represent theinsulation performance of the entire frequency. Therefore, a parametric study is performed to calculate
the Rw value that evenly reflects the insulation performance of the entire frequency rather than the Rrvalue. The basic conditions of the parametric study are same as Section 3.1. As shown in Figure 4, theRw value was calculated while changing two variables among the PHP design variables or the
installation variables in the layering step.
As shown in Figure 4-(a), it is seen that as perforation diameter d increases, the Rw value decreases
due to the influence of resonance transmission. And as the PHP thickness Lp increases, the resonancetransmission frequency shifts to a low frequency and the Rw value increases. Figure 4-(b) shows thatthe interval thickness of the layered structure Ls does not significantly affect the Rw value, and that
the Rw value increases as the areal density of the sheet ms becomes heavier. If d is very small, thesmaller d is, the higher the Rw value tends to be inverted once as shown in Figure 4-(c).
To verify the validity of the theoretical analysis, a measurement was conducted using a small
reverberation chamber (sound receiving chamber: 23.2 m 3, sound source chamber: 24.8 m 3) and asmall specimen (1.24 m 2). Measurement is performed by changing the flexible sheets which are
different areal density ms and using PHP of p = 10 mm, mp = 3.05 kg/m 2, Lp = 28.5 mm, l n = 1 mm, d= 0.8 mm and La = 0 mm (non-contact). Each areal density of the sheets used in the measurement is
2.18, 3.83, 4.79 kg/m 2. Each condition is shown as A, B and C in Figure 4-(c), and as the results oftheoretical analysis, Rw value is 23, 25 and 26 dB, respectively. As the same condition, Rw value of
measurement is 31, 33 and 35 dB, respectively, and the insulation performance is improved by theweight of the areal density of the sheet. It is confirmed that the theoretical results correspond toexperimental results in terms of the difference in Rw values. Therefore, these results of the theoreticalanalysis can be used for improving the performance of PHP layered structure.

4. CONCLUSIONSIn this paper, we constructed a simple theoretical model with lumped constant system to calculate
the transmission loss for the layered structure with PHP and flexible sheet. As a result of transmission
loss according to the perforation ratio, the sound insulation mechanism was confirmed in detail. The
PHP layered structure can obtain an improvement in the insulation performance in high frequency
range due to the double wall effect, but resonance transmission also occurs. Parametric studies wereconducted to minimize the insulation performance degradation due to the resonance transmission andto index the performance of the whole frequency range by using ISO 717-1. As a result, it was obtained
a contour map to know the characteristics of resonance transmission according to the parameters of
the PHP layered structure and a contour map to know the insulation performance tendency according
to parameters approximatively. It can be used for optimizing the PHP layered structure.

REFERENCES
1. M. Toyoda, M. Tanaka and D. Takahashi, Reduction of acoustic radiation by perforated board andhoneycomb layer system. Appl. Acoust., 68, 71-85 (2007)
2. M. Toyoda and D. Takahashi, Sound transmission through a microperforated-panel structure withsubdivided air cavities, J. Acoust. Soc. Am, 124, 3594-3603 (2008)

3. K. Kong, T. Sakuma, N. Inoue: Sound absorption characteristics of a back-perforated honeycomb panel
with an air-layer, Proc. 23rd Int'l Cong. Acoust., No. 507, 8p (2019)
4. K. Kong, N. Inoue, T. Sakuma: Sound insulation characteristics of a layered structure using perforated
honeycomb panel, Proc. Inter-Noise 2020 (Seoul), No.1_5_466, 8p., 2020.
5. J.F. Allard and N. Atalla, Propagation of sound in porous media, 2nd ed., Wiley (2009)
6. ISO 717-1:2013 Acoustics — Rating of sound insulation in buildings and of building elements — Part 1:
Airborne sound insulation

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022, in Gyeongju, Korea
Extended abstractABS-0759

Study on acoustic coupling by micro-perforated panel inasymmetric Helmholtz resonator
Jonghoon JEON1; Byeongwoong JANG2; Junhong PARK3
1

Department of Mechanical Engineering, Hanyang University, Republic of Korea

2

Department of Mechanical Engineering, Hanyang University, Republic of Korea

3

Department of Mechanical Engineering, Hanyang University, Republic of Korea

ABSTRACTIn this study, the acoustic properties due to the acoustic coupling effect of the sound-absorbing structurecomposed of two Helmholtz resonators with different characteristics and a microporous panel wereconfirmed. The two resonators are designed with intrinsic acoustic characteristics distinctly distinguished infrequency domain even if when measured together, and the porous panel is inserted between the structures.
The sound absorption coefficient, reflection coefficient, and acoustic impedance results of the proposed
structure were obtained through eigenvalues of the transfer matrix that was calculated from the frequency
response function measured using the impedance tube and the 4-microphone method. Through a case study,
the contribution to effective factors such as the impedance of the resonator, the size and number of holes on
the boundary surface was identified. The performance in the target frequency band was verified through thetheoretical model of the sound absorption structure to which the above parameters were applied. An active
control system that can control the sound-absorbing structure composed of an actuator and a perforated plate
was established, and noise reduction effects were produced according to various noise environments.
Keywords: Acoustic coupling, microporous panel, Helmholtz resonator

1. INTRODUCTION
Since the Helmholtz resonance structure is a system of one degree of freedom, it has a single
sound-absorbing peak with a very narrow width in the frequency domain. Various sound absorption
structures have been proposed from the past to reduce a wider frequency band using a resonator. In
previous studies, a two-freedom system was implemented by applying a flexible panel between
Helmholtz resonance structures, thereby expanding the sound absorption band. [1] In addition, anotherstudy attempted to implement sound absorption performance ranging from a low frequency band to ahigh frequency band by combining a perforated panel with a neck. [2] In this study, when one wall ofa resonant structure with different resonant frequencies was composed of a perforated plate, thecoupling effect according to the variables related to the hole of the perforated plate was confirmed.

2. MATERIALS AND MEHTODS
2.1 Double-Helmholtz resonator coupled with porous panel
Two types of Helmholtz resonators with non-identical sound absorption peaks in frequency domain
is designed. The resonators share one perforated wall. To confirm the dependency of acoustic
properties to direction of sound transmission, the necks of resonator are placed in parallel to opposite
directions so that propagating sound from one neck to the other.

1

Jhjeon01@hanyang.ac.kr
raphaeljj@naver.com
3
parkj@hanyang.ac.kr
2

Figure 1. Schematics of double-Helmholtz resonator with perforated panel
2.2 4-Microphone method using impedance tube
To measure acoustic properties; Acoustic impedance, absorption coefficient and transmission loss,
4-microphone or 2-microphone methods using impedance tubes are available. The two-microphonemethod requires a rigid wall boundary condition with infinite impedance, so only the sound energy
dissipated in the absorber can be considered, excluding other effects. The 4-microphone method canmeasure transmission properties as well as reflection components. Two microphones are placed on thefront and back of the absorber, respectively. Transmission loss can be measured through the response
calculated by the pressure of transmitted sound and reflected sound.

3. RESULTS FOR SCATTERFING COEFFICIENTSThe sound absorption coefficient of the resonators measured using the impedance tube was shownin figure 2. When each resonator is completely decoupled, absorption peak components are clearly
divided, and the bandwidths of peak are narrow. It can be seen that by opening the shared wall, theresonators behave like one resonator. When coupled through the perforated panel presented in thisstudy, sound absorbing performance could be obtained broadening effect in the band between the two
peaks.
1.0

Absorption coefficent

0.8

0.6

0.4

0.2

0.0
100

150

200

250

300

350

400

450

500

550

600

650

700

750

800

Frequency [Hz]Figure 2. Measured absorption coefficients for Helmholtz resonators; dashed line: decoupled
Helmholtz resonator; red, green line: coupled with perforated panel; blue line: coupled withcompletely open conditions.

4. DISCUSSION
The results showed that it was possible to control the degree of coupling according to the variable
control of the perforated panel. It is practical to control the acoustic interference effect by changing

the number of holes rather than controlling the size of the holes in micro units. From this result, it canbe confirmed that the transmission loss in the negative direction tends to be the same as in the positive
direction, but the tendency was not consistent in the reflection coefficient. It was clarified that the
acoustic properties depended on the sound direction when the coupling effect was expressed. From
the difference between the theoretical calculated value and the experimental result, it was possible toderive the dispersion effect by Willis coupling in the frequency band.

REFERENCES
1. SANADA, Akira; TANAKA, Nobuo. Extension of the frequency range of resonant sound absorbers using
two-degree-of-freedom Helmholtz-based resonators with a flexible panel. Applied Acoustics, 2013, 74.4:
509-516.
2. PARK, Soon-Hong. Acoustic properties of micro-perforated panel absorbers backed by Helmholtz
resonators for the improvement of low-frequency sound absorption. Journal of Sound and Vibration, 2013,332.20: 4895-4911.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0879

Trial measurement of sound absorption characteristics of
microperforated panel absorbers by in-situ measurement method
using ensemble averaging technique
Noriko OKAMOTRO1; Reiji TOMIKU1; Toru OTSURU1; Arisa TABARU2; Kana IKEDA2
1

Department of Innovative Engineering, Oita University, 700 Dannoharu, Oita, Japan
2

Graduate School of Engineering, Oita University, 700 Dannoharu, Oita, Japan

ABSTRACTThe authors have recently proposed the in-situ measurement method using ensemble averaging technique,i.e., EA method, as a simple and highly reproducible sound absorption measurement method of materials. In
this paper, EA method is applied to evaluate sound absorption characteristics of microperforated panel
absorbers which satisfy requirements for both sound absorptivity and designability. First, the soundabsorption characteristics of polycarbonate panel with and without perforation are measured by the EA
method, and a difference in the sound absorption coefficient is observed depending on the presence orabsence of perforations. Next, MPPs with different thicknesses of air space or glass wool are measured
respectively, and systematic differences of sound absorption coefficients for the thickness can be captured by
the EA method. Finally, in comparison with theoretical values and measurements by the impedance tube
methods, sound absorption coefficients obtained by the EA method are good agreement with those by theory
and the impedance tube methods, and the applicability of EA method to sound absorption measurement of
MPP absorbers is clarified.
Keywords: MPP, Sound absorption characteristics, in- situ measurement

1. INTRODUCTION
Sound absorbers are necessary to control the sound in the room, and various materials have beendeveloped in recent years. Among them, microperforated panel (MPP) sound absorbers are expected
to be applied as an attractive material from the viewpoint of environmental friendliness anddesignability, and various studies have been actively conducted by theory, experiment and numericalanalysis1-5).
When measuring the sound absorption characteristics of building materials, the impedance tube
method or the reverberation room method, which are standardized by JIS and ISO6-9)., are generally
used. However, these methods are known to show large deviations of measured absorption
coefficients due to the installation condition of materials to the tube or the diffuseness of sound fields,
respectively. In the impedance tube method, it is necessary to cut out the material according to themeasurement frequency, and, in the reverberation room method, it is necessary to prepare a large areasample of 10m2 to 12 m2 . Therefore, both methods are considered unsuitable for trial and error formaterial development.
On the other hands, the authors have recently proposed the in-situ measurement method using
ensemble averaging technique, i.e., EA method, as a simple and highly reproducible sound absorption
measurement method of materials10,11).
In this paper, EA method is applied to measure sound absorption characteristics of microperforated
panel absorbers. First, the sound absorption characteristics of polycarbonate panel with and without
perforations are measured to confirm whether there is a clear difference between them. Next, MPPs
1n-okamoto@oita-u.ac.jp

with different thicknesses of air space or glass wool are measured respectively, and it is investigatedwhether systematic differences can be captured by the EA method. Finally, in comparison withtheoretical values and measurements by tube methods, the applicability of EA method to soundabsorption measurement of MPP absorbers is clarified.

2. METHODOLOGY
2.1 The outline of EA method
Figure 1 illustrates the basic setup of EA method 10,11). The EA method is a simple and efficient insitu measurement method of the surface normal impedance of materials in a sound field assuming
random incidence. The basic repeatability and applicability of the method in several practicalenvironments have been presented in Refs12,13). This method can reduce the interference effect caused
mainly by the sample edge by using random incidence sound source and allow measurements on
samples of relatively small size. The impedance measured by the method can be regarded as a kind of
ensemble-averaged quantity for multiple sound incidences at/around a point. In the practicalmeasurement, the random incidence condition is achieved by using the ambient noise exists around amaterial or by moving some portable speakers radiating noise.
As shown in Fig. 1, there is the method using two microphones (EApp method) and the method
using a pressure-velocity sensor (EApu method). In this study, the EApu method is employed. It isdifficult to install the pu-sensor which has 1/2-inch diameter at a material surface because of its
physical size. Therefore, the authors locate the pu-sensor at the position where d, which is distancefrom the material surface, equals 10 mm. When the pu-sensor is used in EA method, normalized
surface impedance of a material: Zn,EA , is simply defined as:
𝑍!,#$ = 〈𝑍〉 = 〈𝑝/𝑢! 〉(1)

Where <->, Z, p and un denote the ensemble average, surface impedance, sound pressure andparticle velocity with respect to the normal direction at the material surface, respectively. Assumingthat the system has ergodicity, Zn,EA is expressed in the following equation.
𝑍!,#$ = 〈𝑍〉 = 〈𝑝〉/〈𝑢! 〉(2)To check and evaluate the results, the "corresponding sound absorption coefficientas follows:%

𝛼!,#$ = 〈𝛼〉 = 1 − +,𝑍!,#$ − 𝜌𝑐//,𝑍!,#$ + 𝜌𝑐/+

10,11)" is defined(3)

Microphone
mic. al mic. bdRandom Incidence(i) Using pp sensor

Material

Sensor2ch FFT
Spectrum
Analyzerpu sensord(ii) Using pu sensor(a) Block diagram of measurement(b) Actual condition of measurement

Figure 1 – The outline of the EA method.
2.2 Absorbers to be measured
In this study, the MPP absorber shown in Fig. 2 is measured by the EA method. The polycarbonate
MPP (size: 600 mm × 500 mm, panel thickness: 0.5 mm, hole diameter: 0.5 mm, perforation ratio:
0.785 %, surface density: 0.6 kg/m2 ) is backed by an air space with a rigid back wall. In order to create
an air space, an acrylic frame with different heights is installed behind the MPP. The depth of backair spaces is set to 25 mm, 50 mm and 100 mm, respectively. The measurements are carried out under
the following conditions.

1010

460

Air space

20
600

600

unit: mm(a) Specification of an MPP absorber

500

RP1
RP2
RP3

20

250

MPP

250

• Polycarbonate panels behind an air space with and without perforations• MPP behind an air space or a glasswool (density: 32 kg/m3 )(b) Actual MPP absorber(c) Receiving points

Figure 2 – The MPP absorber to be measured.
2.3 Measurement setup
Measurements are conducted in an irregularly-shaped reverberation room with diffusers (roomvolume: 168 m3 , surface area: 180 m2 ). The absorber is located at around the center of the room floor.
To create the random incidence condition, six portable loudspeakers (Micro Wireless, JBL) radiating
incoherent pink noises are moved manually. A pu-sensor (PU-Regular, Microflown Technologies) is
located at the upside of the center of a material, and three receiving points are placed near the centerof the material as shown in Fig. 2 (c). The pressure sensor and particle velocity sensor are plugged
into 2ch FFT analyzer, and the transfer function is calculated. The frequency resolution of FFT is set
to 3.125 Hz and linear averaging was performed 150 times using Hanning window. The pu-sensor wascalibrated using a standing-wave-tube with 55 mm × 55 mm × 250 mm. The mean value formeasurements at three receiving points is used in the following investigations.

3. RESULTS AND DISCUSSION
3.1 The effect of perforations
Figure 3 shows comparisons of sound absorption coefficients of panel with and without
perforations. In the case where there is an air space behind the panel, sound absorption coefficientsfluctuate greatly with frequency. On the other hand, in the case where there is a glasswool behind thepanel, they change smoothly with frequency. Regardless of the presence or absence of a backing
material, the panel with perforations, i.e. MPP, has high sound absorption coefficients in a wide
frequency range, and a difference in the sound absorption coefficient was observed depending on thepresence or absence of perforations.

(a) Panel with an air space(b) Panel with a glasswool
Figure 3 – Comparison of absorption coefficients between polycarbonates with and without perforations.
3.2 The effect of thicknesses of a backing layer
Figure 4 shows comparisons of absorption coefficients of MPPs which have different thicknessesof a backing layer. In the case of the MPP with an air space, sound absorption coefficient becomes
higher and larger as the air space becomes thicker. In the case of the MPP with a glasswool, as the air
space becomes thicker, sound absorption coefficient becomes higher, however, the peak of soundabsorption coefficient became almost same regardless of the thickness. From these results, thedifference in thickness of the backing layer can be captured by the EA method.

(a) MPP with an air space(b) MPP with a glasswool

Figure 4 – Comparison of absorption coefficients among MPPs that have different thickness of abacking layer.
3.3 Comparison with theoretical values
Comparisons of sound absorption coefficients obtained by the EA method and theoritical values ofnormal incidence sound absorption coefficient, which are caluclated with reference to literature, foreach MPP with a glasswool are shown in Fig. 5. Although the peak frequency is different between EA
method and theory, the correspondence between values measured by the EA method and the theoreticalvalues is good. The thicker the material, the better the agreement between EA method and theory.

(a) 25 mm thick(c) 100 mm thick(b) 50 mm thickFigure 5 – Comparison between values obtained by the EA method and theoretical values.
3.4 Comparison with values to be measured by the impedance tube method
Finally, sound absorption coefficients obtained by the EA method are compared with those of the
impedance tube method.
The normal surface impedance at normal-incidence was measured by the two-microphone method,in accordance with JIS 1405-2:2007. The cylindrical impedance tube having an inner diameter of 100
mm was used. The measurements are conducted for MPPs with glasswool of 25 mm thick and 50 mm
thick. In the measurement, two 1/4-inch microphones as a sensor were used. The sound pressures at(a) 25 mm thick(b) 50 mm thickFigure 6 – Comparison of absorption coefficients for MPP with a glass wool between the EA
method and the impedance tube method.

each microphone position were measured, and the transfer function between two positions were
calculated. The setting of FFT was same as that of the EA method. The normal surface impedance andabsorption coefficient at normal-incidence were calculated using the transfer function. Twomeasurements per sample were carried out, and the average of these values is used for comparison.
Figure 6 shows comparisons of sound absorption coefficients obtained by the EA method and thoseobtained by the impedance tube method for the MPP with a glass wool. Regardlss of the thickness ofglasswool, sound absorption coefficients measured by the EA method are lower than those of theacoustic tube method at around the peak frequency. However, good agreements are observed between
the results of both methods at frequency range except for around the peak frequency. Especially, thepeak frequency of both method is almost same.

4. CONCLUSIONS
To extend the range of application of the EA method, the absorption characteristics measurementof MPPs were carried out by the method. The difference of absorption characteristics of materials
with different backing structure can be discriminated by the EA method, and the effectiveness of themethod is confirmed. In addition, sound absorption coefficients by the EA method are good agreementwith the impedance tube method and theoretical values. However, since slight discrepancies between
EA method and theory/the impedance tube method were observed at around the peak frequency,
further investigations are required.

ACKNOWLEDGEMENTS
The authors would like to thank Prof. K. Sakagami and Asst. Prof. T. Okuzono (Kobe University)
for their advice on material selection. The authors also would like to thank A. Yoshida, A. Kanazawa
and S. Suzuki (Graduate School of Engineering, Oita University) for their cooperation in theexperiments.

REFERENCES
1. Maa D-Y. Theory and design of microperforated panel sound-absorbing constructions. Scientia Sinica
1975;18:55-71.
2. Maa, D-Y. Potential of microperforated panel absorber, J Acoust Soc Am, 1998; 104: 2861-2866.
3. Sakagami K, Yamashita I, Yairi M, Morimoto M. Sound absorption characteristics of a honeycombbacked microperforated panel absorber: Revised theory and experimental validation. Noise Control Eng
J 2010; 58 (2):157–162.
4. Okuzono T, Sakagami K. A finite-element formulation for room acoustics simulation withmicroperforated panel sound absorbing structures: Verification with electro-acoustical equivalent circuit
theory and wave theory. Appl Acoust, 2015; 95: 20–6.
5. Hoshi K, Hanyu T, Okuzono T, Sakagami K, Yairi M, Harada S, Takahashi S, Ueda Y. Implementation
experiment of a honeycomb-backed MPP sound absorber in a meeting room. Appl Acoust, 2020; 157:
20–6.
6. ISO 10534-2:2007, Acoustics–determination of sound absorption coefficient and impedance in
impedance tubes. Part 2: transfer function method.
7. JIS 1405-2:2007. Determination of sound absorption coefficient and impedance in impedance tubes–Part
2: Transfer-function method.
8. ISO354:2003, Acoustics–measurement of sound absorption in a reverberation room.
9. JIS A 1409:1998. Method for measurement of sound absorption coefficients in a reverberation room.
10. Takahashi Y, et al. In situ measurements of surface impedance and absorption coefficients of porous
materials using two microphones and ambient noise. Appl Acoust, 2005; 66(7): 845-865.
11. Otsuru T, et al. Ensemble averaged surface normal impedance of material using an in-situ technique:
Preliminary study using boundary element method. J Acoust Soc Am, 2009; 125(6): 3784-3791.
12.Din N. B. C., et al. Reproducibility and applicability of ensemble averaged surface normal impedance ofmaterials using an in-situ technique. Acoustics Australia; 2013; 41 (3): 207–212.
13.Okamoto N, Development of construction condition management system by absorption characteristics
measurement of building materials. AIJ J Technol Des. 2017; 23(54):517-520.
14. Miki Y, Acoustical properties of porous materials –Modifications of Delany-Bazley methods-． J Acoust
Soc Jpn.(E), 1990;11(1); 19- 24.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-0896

MPP sound absorbers investigation to optimize a lecture hallspeech intelligibility

Matteo CINGOLANI 1; Gioia FUSARO 2; Massimo GARAI 3; Giulia FRATONI4; Dario D’ORAZIO5;
Luca BARBARESI6
ABSTRACTThe recent pandemic has drawn attention to the built environment’s hygiene, sustainability, and durability.
Furthermore, studies on micro-perforated panels (MPPs) have recently highlighted their potential for soundabsorption in such a context. On the other hand, metal additive manufacturing has become a very popularand convenient method to test acoustic metamaterials (AMMs) performance; however, their deployability
in several civil indoor environments and functions still lacks assessment. So, the present work assesses thesuitability of metal 3D printed MPP systems to fulfil speech requirements in lecture rooms. Firstly, ananalytical optimization process defined two MPP steel specimens in terms of sound absorption performance.
Secondly, these models were physically manufactured through 3D additive metal printing, and theiracoustic performance was measured experimentally on a double-layer configuration. Finally, experimental
results were used as input data for characterizing finite-difference time-domain (FDTD) simulations,highlighting the potential enhancement of oral communication through double-layer MPPs on the ceiling ofa historical university lecture hall. An FDTD code with a full-spectrum wave-based method was chosen tobetter handle time-dependent signals, like verbal communication. The outcomes of the process show theinfluence of the acoustic treatment in terms of reverberation time (T30).
Keywords: Sound absorption, MPP, FDTD.

1. INTRODUCTION

In the last decades, Micro-Perforated Panels (MPP) have been investigated as a resourcefulsolution to acoustic problems instead of classical porous and fibrous sound absorbers (1,2,3). For
example, in room acoustic and environmental noise control, MPP have been used to address new
requirements such as durability, recyclability, hygienic problems, environmental sustainability andoptical transparency (4,5,6). A variety of methods served the development of more accurate MPP
configuration. Maa (7,8) assessed the first analytical model which combined two different
mechanisms of absorption: i) the cavity induced Helmholtz-type resonance, and ii) the viscosity
effect resulted by the proximity of the sub-millimeters perforations. Furthermore, Equivalent Fluid(EF) model was theorized by Atalla and Sgard (9) as an alternative to Maa’s model introducing theeffective density and the flow resistivity to describe the viscous and inertial local MPP effects. Even
though MPP applicability in terms of sound absorption is acknowledged, their impact on the humanbuilt environment has not been extensively assessed in terms of quality of verbal communication.
Specific application within the built environment, such as historical lecture halls could provide a
new field of application of MPP systems.
matteo.cingolani6@unibo.it, Department of Industrial Engineering, University of Bologna, Viale Risorgimento
2, Bologna, 40136, Italy
2
gioia.fusaro@unibo.it, Department of Industrial Engineering, University of Bologna, Viale Risorgimento 2,
Bologna, 40136, Italy3
massimo.garai@unibo.it, Department of Industrial Engineering, University of Bologna, Viale Risorgimento 2,
Bologna, 40136, Italy
4
giulia.fratoni2@unibo.it, Department of Industrial Engineering, University of Bologna, Viale Risorgimento 2,
Bologna, 40136, Italy5
dario.dorazio@unibo.it, Department of Industrial Engineering, University of Bologna, Viale Risorgimento 2,
Bologna, 40136, Italy6luca.barbaresi@unibo.it, Department of Industrial Engineering, University of Bologna, Viale Risorgimento 2,
Bologna, 40136, Italy
1

For these reasons, this study aims at optimizing a double-layer MPP configuration in order toreduce the reverberation time within an historical lecture hall, according to the standard
requirements for such environments. Firstly, following the EF analytical model, a double-layer MPP
configuration has been developed targeting the human voice frequency range sound absorption (2502000 Hz). In second instance, 3D additive printing has been used to manufacture double-layer MPP
metal specimens, which have been experimentally measured in the impedance tube according toISO-10532-2 (10). At the same time, simulations based on finite-difference time-domain (FDTD)(11,12,13) were carried out to handle time-dependent signals as verbal communication and were
calibrated over experimental measurement of a historical university hall. After the calibration, theresulting MPP specimens’ surface impedance values were embedded into the FDTD model byplacing them as false ceiling (14). A comparison between the reverberation time related to thehistorical lecture hall configurations with and without the double-layer MPP system has been
investigated to assess the influence of such structure on the verbal communication optimization.

2. METHOD
2.1 Analytical Model
Micro Perforated Panel (MPP) is a specific kind of tunable absorber and consists of a thin
perforated panel with sub-millimeter perforations backed by an air cavity and a rigid wall. Itsabsorption properties depend only on the combination of its constitutive geometrical parameters: d,the holes diameter, t, the thickness of the front panel, φ, the perforation ratio, and D, the cavity
length. The perfect sound absorption is provided if the surface impedance 𝑍𝑍1 of the MPP system
matches with the air impedance. According to Maa’s definition, the surface impedance is a complex
quantity defined as the sum of three different contribution:(1)

𝑍𝑍𝑀𝑀𝑀𝑀𝑀𝑀,𝑆𝑆𝑆𝑆 = 𝑍𝑍ℎ𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜 + 𝑍𝑍𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 + 𝑍𝑍𝑐𝑐

Where 𝑍𝑍ℎ𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜 represents the viscous dissipation within the holes, 𝑍𝑍𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 defines the distortion of
the flow within the holes’ edge and 𝑍𝑍𝑐𝑐 defines the impedance of the air cavity (Figure 1). In
practical applications, a double-layer MPP system can be implemented to enhance the absorption
bandwidth: the absorption depends globally on eight constitutive geometrical parameters: 𝑑𝑑1 , 𝑑𝑑2 , thediameter of the first and second layer, respectively, 𝑡𝑡1 , 𝜙𝜙1 , 𝑡𝑡2 , 𝜙𝜙2 the thickness and perforation ratioof the first and second front panel, 𝐷𝐷1 , 𝐷𝐷2 , the first and second air cavity, respectively.

Equivalent circuit

Equivalent circuit

Figure 1. Single layer (SL) and Double Layer (DL) configurations and equivalent circuits of Micro-Perforated panels.

An alternative approach to study single-layer and double-layer MPP system has been introduced
by Atalla and Sgard: they defined the so-called Equivalent Fluid (EF) model, following the JohnsonChampoux-Allard approach with the introduction of an equivalent tortuosity and effective density
for the viscous and inertial effects inside the perforations to define the distortion of the flow and theviscous dissipation of the holes, respectively (9). The surface impedance of a double-layer MPP
system is:
𝑍𝑍𝑀𝑀𝑃𝑃𝑃𝑃,𝐷𝐷𝐷𝐷 = 𝑍𝑍𝑀𝑀𝑀𝑀𝑀𝑀1 + 𝑍𝑍0𝑍𝑍𝑀𝑀𝑀𝑀𝑀𝑀2 𝑐𝑐𝑐𝑐 𝑠𝑠(𝑘𝑘𝑘𝑘2 ) + 𝑖𝑖𝑍𝑍0 sin (𝑘𝑘𝐷𝐷1 )𝑍𝑍0 𝑐𝑐𝑐𝑐 𝑠𝑠(𝑘𝑘𝑘𝑘2 ) + 𝑖𝑖𝑍𝑍𝑀𝑀𝑀𝑀𝑀𝑀2 sin (𝑘𝑘𝐷𝐷1 )(2)

where 𝑍𝑍𝑀𝑀𝑀𝑀𝑀𝑀1 is the impedance related to the first layer and 𝑍𝑍𝑀𝑀𝑀𝑀𝑀𝑀2 is the complex impedance
resulting by the second layer and 𝑍𝑍0 is the characteristic impedance of the air.

The sound absorption coefficient of a double-layer MPP system is:
𝑍𝑍𝑀𝑀𝑀𝑀𝑀𝑀,𝐷𝐷𝐷𝐷 − 𝜌𝜌𝜌𝜌
𝛼𝛼 = 1 − ��
𝑍𝑍𝑀𝑀𝑀𝑀𝑀𝑀,𝐷𝐷𝐷𝐷 + 𝜌𝜌𝜌𝜌2

(3)

3. SAMPLES MANIFACTURING

The Equivalent Fluid model has been used as a reference to develop different geometricalconfigurations of micro-perforated panels. In particular, the aim of this study was to find the best
configuration of double-layer MPP to match the characteristic curve of the speech, in view of theapplication to a university lecture hall.
The best setting of geometrical parameters for the aim of this study is summarized in Table 1.

First Layer
Second Layer

Thickness(mm)
1
1

Perforation
Ratio (%)
0.5
0.5

Holes diameter
(mm)
0.5
0.5

Air cavity
thickness (mm)4030Table 1. The constitutive parameter of the Double-Layer configurations chosen for the application.

Considering the constraint of durability, endurance, hygiene and manufacturing precision needed
for the present work, stainless steel has been chosen as material. Two samples of MPP, with circularcross-section and a diameter of ~40 mm, were manufactured through 3D additive printing technique.
A 316L grade stainless steel powder has been used with the following printing processparameters: powder grains diameter equal to 30-40 µm, powder layer height equal to 60 µm, laser
rated power equal to 360 W and laser rated diameter equal to 50 µm. The material specific weightwas 7.98 g/cm3 . The manufacturing process allowed to respect the planned geometrical dimensions
with a tolerance of ≈ ±0.3 − 0.6 mm. The perforations showed irregular cross-section and adiameter slightly different from the expected, as shown in Figure 2.

Figure 2. The MPP specimen (left) and the effective visualization of the perforations seen at the microscope (right).

As already demonstrated by Ning et al. (15), irregular cross-sections may increase the sound energy
dissipation and, consequently, enhance the sound absorption and the bandwidth.
3.1 Experimental measurements
The experimental campaign was carried out in the impedance tube. The double-layer
configuration has been measured in terms of sound absorption coefficient and acoustical surface

Figure 3. Data flow: excitation signal generation, processing, comparison with models, output of results.

impedance for normal sound incidence, according to the standard ISO 10534-2. Considering theaccuracy of the used signal processing equipment and the physical dimension of the tube, theworking frequency range of the tube is 300-4400 Hz. The schematic of the digital measurement flow
is shown in Figure 3. The results of the measurements in the impedance tube in terms of soundabsorption coefficient and surface impedance of the DL MPP are shown in Figure 4.

Figure 4. Sound absorption coefficient (left) and surface impedance of the double-layer MPP considered in this study.

4. FINITE-DIFFERENCE TIME-DOMAIN SIMULATION

The finite-difference time-domain (FDTD) method is among the oldest numerical methods tosolve time-dependent partial differential equations, like the wave equation. In this type of numericalmethod, a discretization with regular Cartesian grids is applied to space and time continuous
domains. The acoustic pressure 𝑝𝑝(𝑥𝑥, 𝑡𝑡) and the particle velocity 𝑢𝑢(𝑥𝑥, 𝑡𝑡) are calculated in the nodal
points through updating recursions. The solution 𝑝𝑝(𝑥𝑥, 𝑡𝑡) of the wave equation, where x ∈ ℜ3 , is𝑛𝑛approximated by a grid function 𝑝𝑝𝑙𝑙,𝑚𝑚,𝑝𝑝
at spatial points 𝑥𝑥 = 𝑙𝑙ℎ, 𝑦𝑦 = 𝑚𝑚ℎ, 𝑧𝑧 = 𝑝𝑝ℎ , and at temporaltime 𝑡𝑡 = 𝑛𝑛𝑛𝑛 , where l, m, n represent integer numbers, h is the grid spacing and k is the time step.

4.1 Application of MPP as a ceiling acoustic treatment
Three-dimensional numerical acoustic analysis is a solid tool for preliminary performanceassessment of indoor spaces (16). Therefore, such method was used to assess double-layer MPPs
implemented ceiling of a large historical lecture hall in the University of Bologna (Figure 5). The
acoustical characterization of the room and the intelligibility indexes have been collected through aprevious measurements’ campaign. The setting of sound source and receiver locations chosen for themeasurements campaign is also provided in Figure 5.

Figure 5. Interior view (left) and 2D plan (right) of the lecture hall under study. Sound sources (S1, S2) and thespatial grid of microphone receivers (R1, R2,..,RN) used in the measurements campaign are reported.

The commercial software Sketchup was used to model in 3D the 900 m3 lecture hall. The mostcharacterizing materials were included for a simplified but reliable representation with reduced
material-related uncertainties. The energy-based parameters’ characterization generally used for
simulating large lecture hall through geometrical acoustic (GA) techniques (sound absorption
coefficients) are not suitable for MPPs. So, FDTD models (using a wave-based algorithm) can beused instead, taking into account diffraction effects of the object’s edges. A numerical model
calibration has been performed through the experimentally measured reverberation time (T 30 ) before
introducing MPPs into the 3D geometry. For this purpose, the sound source in location S1 and theaveraged values of all the receiver points (Figure 5) have been considered. The geometricalcharacterization consisted in applying the DL-MPP configuration reported in Table 1 instead ofexisting false-ceiling, as shown in Figure 6.

Figure 6. Exterior (left) and interior (right) view of the acoustic treatment virtually introduced into the CAD model. The
ceiling mounted MPPs are highlighted in red.

In this case, it has been possible to avoid some of those typical uncertainties in the workflow bydirectly starting with complex acoustic impedances values as input boundary conditions.
The outcomes of a compensation model considering the locally reactive absorption properties of
MPPs have been implemented to fit complex impedances to a boundary impedance model, which
comprise a parallel network of second-order RLC circuits (12,13).
Specifically, the values of the complex admittance of the MPPs shown in Figure 7 has been used
as input of the FDTD model. The selected FDTD method simulated up to 8000 Hz with 6.75 points
per wavelength (Cartesian grid spacing h=6.35 mm and time step k=18.5µs), which required
approximately 2h per sound source using four Nvidia Titan X (Maxwell) GPUs.

Figure 7. Real (left) and imaginary (right) parts of the specific admittance from MPP measured data.

𝑇𝑇30 results related to the experimental and numerical configuration without MPPs and thenumerical configuration with MPPs are compared in Table 2.

T 30 (s)Without MPP (Meas.)
Without MPP (FDTD)
With MPP (FDTD)

125 Hz
1.48
1.44
1.32

250 Hz
1.36
1.25
0.92

500 Hz
1.60
1.54
0.88

1000 Hz
1.84
1.73
1.22

2000 Hz
1.83
1.70
1.52

4000 Hz
1.51
1.45
1.44

Table 2. T mean values corresponding to the measurements (Meas.), the equivalent values derived from the calibrated FDTD
model and the variations due to the introduction of MPPs.

The DL-MPP configuration performs an overall significant sound absorption in the frequency
range 250-2000 Hz and a maximum sound absorption in the frequency range 500-1000 Hz.
Therefore, the use of such material instead of common porous and fibrous materials has theadvantage of reducing excessive reverberation time of historical lecture halls within the entire
human voice frequency range, especially at 250-500 Hz.

5. CONCLUSIONS

Micro-Perforated Panels have been implemented in order to optimize the oral communication
within a historical teaching class. A double-layer customization of an MPP system allowed abroadband absorption effect over the frequency range from 125 Hz to 4000 Hz. This, in turn,resulted in a significant reverberation time reduction (with a minimum of 0.33 s and a maximum of
0.66 s in the range 250-2000 Hz), and consequently enhanced the speech intelligibility in the humanvoice frequency range. MPP can be considered a solid alternative to standard fibrous and porous
absorbers due to their advantages in terms of low-middle frequencies sound absorption, durability,
maintenance, hygiene, fire resistance, and customizable design.

ACKNOWLEDGEMENTS

This research was funded by Ministero dell’Istruzione dell’Università della Ricerca (Italy), in theframe of the project PRIN 2017, grant number 2017T8SBH9: “Theoretical modelling andexperimental characterization329 of sustainable porous materials and acoustic metamaterials fornoise control.”

REFERENCES

1. Johnson, D. L.; Koplik J.; Dashen, R. Theory of dynamic permeability and tortuosity in fluid-saturated
porous media. J. Fluid., Mech. 1987, 176, 379–402.
2. Allard, J.F.; Champoux, Y. New empirical equations for sound propagation in rigid frame fibrousmaterials. J. Acoust. Soc. Am., 1992, 91, 3346–3353.
3. Cucharero, J.; Hänninen, T.; Lokki, T. Angle-Dependent Absorption of Sound on Porous Materials.
Acoustics 2020, 2, 753–765.
4. Pan, L.; Martellotta F., A Parametric Study of the Acoustic Performance of Resonant Absorbers Made ofMicro-perforated, Membranes and Perforated Panels. Appl. Sci. 2020, 10, 1581.
5. Asdrubali, F.; Pispola G., Properties of transparent sound-absorbing panels for use in noise barriers. J.
Acoust. Soc. Am. 2007, 121, 214–221.
6. Sakagami, K.; Okuzono, T. Space sound absorbers with next-generation materials: Additional soundabsorption for post-pandemic challenges in indoor acoustic environments. UCL Open Environ. Prepr.
2020.
7. Maa, D. Theory and design of microperforated panel sound-absorbing constructions. Sci. Sin. 1975, 18,
55–71.
8. Maa, D. Potential of microperforated panel absorber. J. Acoust. Soc. Am. 1998 104, 2861–2866.
9. Atalla, N.; Sgard, F. Modeling of perforated plates and screens using rigid frame porous models. J. Sound
Vib. 2007, 303, 195–208.
10. EN ISO 10534–2:2001. Acoustics-Determination of Sound Absorption Coefficient and Impedance in
Impedance Tubes-Part.2: Transfer-Function Method; International Organization for Standardization:
Geneva, Switzerland, 2001.
11. Kowalczyk, K.; Van Walstijn, M. Room acoustics simulation using 3-D compact explicit FDTD
schemes. IEEE Trans. Audio Speech Lang. Process. 2011, 19, 34–46.12.
12. Bilbao, S.; Hamilton, B.; Botts, J.; Savioja, L. Finite volume time domain room acoustics simulation
under general impedance boundary conditions. In IEEE-ACM Transactions on Audio, Speech, andLanguage Processing; IEEE: Piscataway, NJ, USA, 2016; Volume 24, pp. 161–173.
13. Fratoni, G., Hamilton, B., D'Orazio, D., Feasibility of a finite-difference time-domain model in largescale acoustic simulations, J. Acoust. Soc. Am., 2022, 152, 330.
14. Cingolani, Matteo, et al. "A trial acoustic improvement in a lecture hall with MPP sound absorbers and
FDTD acoustic simulations." Applied Sciences 11.6 (2021): 2445
15. Ning, J.F.; Ren, S.W.; Zhao, G.P. Acoustic properties of micro-perforated panel absorber having
arbitrary cross-sectional perforations., Appl. Acoust. 2016, 111, 135–142.
16. D’Orazio, D.; Fratoni, G.; Rovigatti, A.; Hamilton, B. Numerical simulations of Italian opera houses
using geometrical and wave-based acoustics methods. In Proceedings of the 23rd International Congresson Acoustics, Aachen, Germany, 9–13 September 2019.

PROCEEDINGS of the24th International Congress on Acoustics
October 24 to 28, 2022 in Gyeongju, Korea

ABS-1020

The acoustic performance of natural ventilation with thin MPP
absorbers
Indra Sihar1; Iwan Prasetiyo2; Anugrah S. Sudarsono3; Joko Sarwono4
1,2,3,4Engineering Physics, Faculty of Industrial Technology, Institut Teknologi Bandung, Ganesa 10, Bandung,
40132, Indonesia.

ABSTRACT
Natural ventilations are beneficial to improve the indoor air quality and energy demand of a building.
However, it allows outdoor noise to enter the building and reduces its acoustic comfort. In this study, thin
MPP absorbers with coiled backing cavities were introduced into an opening window to reduce soundtransmission of natural ventilation. Numerical calculations are performed to assess the absorption andtransmission loss of this opening over the frequency range of 125-2000 Hz. It is found that the resulting
attenuation is related to the number of MPP unit cells used in the opening. The sound attenuation
characteristics are dictated by the absorption characteristics of the MPP and can be configured to span overa broadband frequency range. Moreover, the MPP introduced in the opening can attain 10 dB attenuation
while space for the backing cavity length is minimized by the coiling structure. This approach can be adopted
by a green building designer who wants to utilize natural ventilation while concerned about acoustical
comfort.
Keywords: natural ventilation, sound attenuation, thin micro-perforated panel

1. INTRODUCTION
The natural ventilation system is a critical component for buildings, particularly green buildings ,in which such a system is designed to allow fresh air and daylight into the building and to realize
energy efficiency and sustainability. However, the use of such a system usually conflicts with noise
pollution when it is installed on the façade. Hence, it is important to have a ventilation system thatconsiders natural air circulation and noise shielding.
Noise control efforts in building ventilation have been introduced since the 1990s, as reviewed in(1). However, these strategies lead to a bulky system due to the components used in the system, e.g.,
the use of a quarter-wavelength resonator around the ventilation where more space is required. To
date, active and passive systems have been introduced to tackle the problems(2, 3). Passive
components are used by applying porous material (4) and perforated panels (5, 6). Recently, advancesin acoustic metamaterials have also offered the possibility of embedding sub-wavelength structures inthe ventilation. This structure, or so-called ventilated material, can meet ergonomic requirements
without deteriorating the performance (7-10).
With a relatively simple configuration and ease of tuning, micro-perforated panels (MPP) can be abasis for developing soundproof ventilation. The feasibility of MPP for such a purpose was studied
by Kang and Brocklesby (5). It was found that attenuation performance can be maintained whileallowing the airflow up to 2 m/s. However, the configuration for broadband attenuation has not yet
been demonstrated in the previous studies. MPP can be an alternative solution since MPP can attenuate
low-frequency noise with sub-wavelength structure configurations (11) and even broadband
absorption (12). Moreover, MPP can be utilized to form a metamaterial unit cell in a periodic
arrangement that is applicable for noise reduction in duct systems (13). Hence, it is promising todevelop soundproof ventilation using MPP units that have thin and broadband attenuation
1

i.prasetiyo@fti.itb.ac.idcharacteristics while providing practical ventilation in terms of flow rate and ergonomics.
In this paper, we report on the development of natural ventilation using MPP units to attenuatenoise passing through the ventilation system. The frequency range of interest is between 125 Hz up
to 2 kHz, which coincides with the frequency range of traffic noise as a major source of environmental
noise. It is expected that the thin and broadband MPP system developed in the previous study (12) can
obtain sufficient attenuation while the practical dimensions of the ventilation are still acceptable byadopting coiled structures to save space. Numerical models are developed, and an optimization
approach is applied to balance the performance, acceptable dimensions, and the number of MPP units.
Meanwhile, CFD analysis of air pressure and the flow rate has not yet been carried out and will be a
subject for future study.

2. METHODOLOGY
2.1 Natural ventilation configuration
In this section, the configuration of the ventilation system as well as the MPP attenuator are given.
The ventilation system is an opening with an area dimension of 6 cm × 6 cm. The ventilation is madeof varying depths depending on the expected sound attenuation. The MPP attenuators are installedaround its perimeter using four sub-MPP parallel systems on each side. The MPP panels have the same
panel thickness, 𝑡𝑝 = 1 𝑚𝑚 , pore diameter, 𝑑 = 0.3 𝑚𝑚 , and distance between pores, 𝑏 = 2 𝑚𝑚 .
However, each sub-MPP has a different backing cavity length 𝐷1 , 𝐷2 , 𝐷3 , and 𝐷4 . The same MPP
attenuator on each side of the ventilation is provided, as shown in Figures 1(a) and 1(b).

(a)(b)
Figure 1– (a) Illustration of natural ventilation with MPP attenuators on four sides, (b) One MPP
attenuator with four parallel sub-MPPs. This attenuator is installed at each ventilation side.
To investigate the acoustic performance of the MPP attenuator, numerical simulation is applied
using the finite element method (FEM), as discussed in Section 2.2. The depths of each sub-MPP arechosen by maximizing the absorption of the MPP attenuator on each side of the vent ilation system.
This absorption was obtained through Maa's formulation for the absorption of the system MPP in thenormal incident plane wave (14). These cavity depths are selected using the optimization method asshown in Section 2.3. It is assumed that increasing the absorption of the MPP attenuator will increase
the transmission loss of the ventilation system. It should be noted that the MPP attenuators are built
using coiled backing cavities to save space and a parallel system to achieve broadband attenuation.
2.2 Numerical simulations
Several numerical simulations utilizing FEM by the COMSOL Multiphysics 5.6 software areconducted to determine absorption coefficient (𝛼), and the transmission loss (TL) of the proposed
natural ventilation. The frequency range of interest is between 125 Hz and 2000 Hz. The soundpropagation in the frequency-domain is modeled using the Helmholtz equation: 1
 2 p   − p  − 2 = 0,
 
 c

(1)

with 𝑝 is the sound pressure, 𝜌 is the air density, and 𝑐 is the speed of sound in air. The problem
domain is illustrated in Figure 2. There are four sub-domains, i.e., perfectly matched layer (PML),
front and rear waveguides, and the ventilation system. The waveguides are intended to initiate thebackground pressure field and transmit plane waves for the natural ventilation consisting of MPP
attenuators, as shown in Figure 2. The PML region is given to allow anechoic termination of the
waveguides. The PML, front and rear waveguides domains have a cross-section of 6 cm × 6 cm withdepths of 6 cm, 30 cm, respectively. The ventilation system is shown in detail in Figure 1 , and thedepth for one cell attenuator is 6 cm, and for two cells attenuators is 12.5 cm where the distance
between cell is 0.5 cm (see Figure 2(b)).
The waveguides and ventilation system domains are discretized by tetrahedral elements.
Meanwhile, structured prismatic elements are employed for the PML domains. All elements havedimensions well below 𝜆𝑚𝑖𝑛 ⁄6, with 𝜆𝑚𝑖𝑛 is the minimum wavelength of the incoming wave, andquadratic basis functions are used in each element.

(a)

(b)
Figure 2 –The numerical domain of the natural ventilation. (a) Illustration of the ventilation systemcross-section, (b) Simulated configurations with one and two cells MPP attenuators at the ventilation
perimeter.

To model the MPP panel, the structural vibration of the MPP is omitted. Therefore, the MPP can be
implemented as interior impedance BC (red line) as:

Z MPP − n = rn + jxn ,(2)where 𝑟𝑛 and 𝑥𝑛 are the resistance and reactance of the n th -MPP unit. Following Maa's
formulation (14), the resistance and the reactance are defined as:

32 t   k 2 
rn =
1 +

 cd 2   32 

12



+

2 d 
k,
32 t p (3)t   k 2 xn =1+ 1+  c  2

−1 2

+ 0.85



d 
.
tp 

(4)



The 𝑘 = 𝑑√𝜔𝜌⁄4𝜂 is the perforation constant, 𝜔 = 2𝜋𝑓 is the angular frequency, 𝜂 is the
dynamic viscosity of air, 𝑡𝑝 is the panel thickness, and 𝜎 is the perforation ratio. The thickness of
the MPP panel is assumed to be negligible since it is accounted for by the interior impedance.
The power reflection coefficients (𝑅) are obtained by the ratio between the scattered and incoming
sound power evaluated at the inlet of the ventilation unit. The power transmission coefficients (𝑇)are obtained by the ratio of the transmitted and incoming sound power evaluated at the outlet border(see Figure 2(a)). Meanwhile, the sound absorption coefficient (𝛼) is defined by 𝛼 = 1 − 𝑅 − 𝑇 as
the consequence of the energy conservation principle. Finally, the sound transmission loss 𝑇𝐿 [𝑑𝐵] isgiven by:
𝑇𝐿 = 10 log10 (1⁄𝑇).
(5)

2.3 Optimization procedure
To obtain the depths for each sub-MPP, an optimization procedure based on a genetic algorithm isconducted in MATLAB. The objective function is developed by minimizing the sum of the powerreflection coefficients (𝑅(𝑓)) over frequency of the parallel MPP system at a normal incidence angle.
The objective function and constraints are given as follows: Z ( f ) −1 minR( f ) =  eq
 Z ( f ) + 1 
D1 , D2 , D3 , D4
f =125Hz eq

2.2kHz Nwhere Z eq ( f ) =   an Z n ( f )  n =1

2s.t 10  Dn  200 mm ,

(6)

−1

is the normalized equivalent impedance, with 𝑎𝑛 is the area ratioof each 𝑛 sub-MPP. In this study, the range of cavity depth is between 10 mm - 200 mm, and eacharea of the sub-MPP is equal in size to ease the coiling of the backing cavities. However, in Section
3.3, further consideration is given to including four area ratios in the optimization procedure utilizingstraight backing cavities.

3. RESULTS AND DISCUSSION
3.1 Optimized MPP attenuator
In this section, the optimization results of the four sub-MPP are given. The properties of the MPP
panel are the same for each sub-MPP except for the cavity depth as shown in Table 1.
Table 1 – Depth of each backing cavity for the MPP attenuator
ID

Cavity depth before coiling

Sub-MPP 1

99

Sub-MPP 2174

Sub-MPP 3

13

Sub-MPP 433(𝐷𝑛 ) [mm]Please note that the cavity depths given in Table 1 are for MPP absorbers with straight backing
cavities. While to coil the backing cavities, the effective cavity depths are calculated according to themethod shown in Reference (12). The sound absorption coefficients for the normal incident angle ofthis parallel MPP absorber are shown in Figure 3. It can be seen that the absorption coefficients covera broadband frequency range of more than four one-octave bands. These bands are important,especially for traffic noise, and could be beneficial for building applications.

Figure 3 –The broadband absorption coefficients for the parallel MPP system.
3.2

Absorption and Transmission loss of the ventilation system

The MPP units placement in the air passage is instructive for investigating their performance innoise attenuation. It is obvious that the attenuation capacity increases as the number of MPP units on
the sides of ventilation increases, as shown in Figure 4(a). It can be enhanced further by repeating the
MPP unit along the air passage, as demonstrated by the one and two cells attenuators in Figure 4(b).

(a)

(b)

Figure 4-Transmission loss comparisons for a different number of MPP units along the air passage.
(a) The MPP units are installed between 1 to 4 sides in one cell attenuator; (b) The MPP units arefurther expanded by two cells attenuator.
It is shown that about 2-5 dB improvement in TL is observed at low frequencies (<800 Hz), while
about 7 dB improvement is observed at high frequencies (>1000 Hz). It is also shown that the TL canachieve more than 10 dB for most of the frequency range in the case of two cells attenuators. It should
be noted that the use of MPP unit cells should be limited along the air passage to ensure the ventilation
dimensions are still acceptable for building applications.
Further results can be seen in Figures 5 (a)-(b) for one and two cells of MPP attenuators. The
reflection coefficients for one or two cells of attenuators give approximately the same performance.
However, the sound absorption coefficients increased significantly with the number of cells, causing
the transmission coefficients to decrease significantly at above 200 Hz. Hence, the transmission lossof the ventilation increases as expected.

(a)

(b)

Figure 5 –The sound power absorption, reflection, and transmission coefficients of the natural ventilation
system for (a) one cell and (b) two cells MPP configurations.

3.3

Effect of sub-MPP area ratio on the absorption and transmission loss

This section presents the optimization results in terms of cavity depths and area ratio. It is clearthat the area ratio can also affect the absorption characteristics of the MPP unit. The optimi zation
procedure is the same as in Section 2.2, with the variables 𝐷1 − 𝐷4 and 𝑎1 − 𝑎4 are included, which
results in sub-MPPs with unequal area ratios. The results of this optimization are shown in Table 2,
and the acoustic properties of this MPP unit for the two cells attenuators are shown in Figures 6(a)(b).
Table 2 – Depth and area ratio of each backing cavity for the MPP attenuator
ID

Cavity depth (𝐷𝑛 ) [mm]Area ratio (𝑎𝑛 ) [%]Sub-MPP 1

110

40

Sub-MPP 227

10

Sub-MPP 3

37

18

Sub-MPP 4

16

32

(a)

(b)

Figure 6- (a) Sound absorption coefficients and (b) TL of the ventilation system with two cells MPP
attenuator

Sound absorption comparison can be seen in Figure 6 (a), where the area ratio is varied. Comparedto the equal area ratio configuration, the use of different area ratios, as shown by the non-equal area ratio
configuration, can improve the absorption between 800 Hz and 1800 Hz. However, sound absorption
deteriorates at lower frequencies (<800 Hz). Therefore, such an approach is useful to meet certain absorption
characteristics.
The different sound absorption properties are also correlated with the transmission loss, as shown in
Figure 6 (b). It is clear that the transmission loss is higher between 800 Hz and 1900 Hz, as shown for the
Non-equal ratio, while the equal area ratio configuration performs better at lower frequencies. Hence,
obtaining a proper enhancement in the MPP unit's absorption can directly affect the resulting transmission
loss.

4. CONCLUSIONS
The implementation of MPP as a noise attenuator for natural ventilation has been discussed. It isfound that specifying the MPP absorption characteristics is of importance to satisfy the transmission
loss design target. Optimization approaches are helpful in finding optimal parameters to attain abroadband attenuation as well as avoid deficiency in transmission loss indicated by the presence ofdips in the transmission loss curve. The further evaluation also shows that the transmission loss canbe increased by adding more MPP cells to the ventilation system. Meanwhile, adjusting area ratio toparticular configuration can improve sound absorption and transmission loss at certain frequency
range so that this offers flexibility in design phase. This study is beneficial for the further developmentof natural ventilation, which can effectively reduce noise while allowing fresh air and daylight into abuilding.

ACKNOWLEDGEMENTS
The authors would like to express their sincere appreciation to KEMDIKBUKRISTEK Indonesia
for financing through the Excellent Basic University Research Program 202 2.

REFERENCES
1. De Salis MHF, Oldham DJ, Sharples S. Noise control strategies for naturally ventilated buildings.
Building and Environment. 2002;37(5):471-84.
2. Lam B, Shi C, Shi D, Gan W-S. Active control of sound through full-sized open windows. Building andEnvironment. 2018;141:16-27.
3. Lam B, Shi D, Gan WS, Elliott SJ, Nishimura M. Active control of broadband sound through the open
aperture of a full-sized domestic window. Sci Rep. 2020;10(1):10021.
4. Tsukamoto Y, Tomikawa Y, Sakagami K, Okuzono T, Maikawa H, Komoto Y. Experimental assessmentof sound insulation performance of a double window with porous absorbent materials its cavity perimeter.
Applied Acoustics. 2020;165:107317.
5. Kang J, Brocklesby MW. Feasibility of applying micro-perforated absorbers in acoustic window systems.
Applied Acoustics. 2005;66(6):669-89.
6. Carbajo J, Ghaffari Mosanenzadeh S, Kim S, Fang NX. Sound absorption of acoustic resonators withoblique perforations. Applied Physics Letters. 2020;116(5):054101.
7. Fusaro G, Yu X, Kang J, Cui F. Development of metacage for noise control and natural ventilation in awindow system. Applied Acoustics. 2020;170.
8. Kim S-H, Lee S-H. Air transparent soundproof window. AIP Advances. 2014;4(11).
9. Xiang X, Wu X, Li X, Wu P, He H, Mu Q, et al. Ultra-open ventilated metamaterial absorbers for soundsilencing applications in environment with free air flows. Extreme Mechanics Letters. 2020;39.

10. Kumar S, Xiang TB, Lee HP. Ventilated acoustic metamaterial window panels for simultaneous noise
shielding and air circulation. Applied Acoustics. 2020;159.
11. Wu F, Xiao Y, Yu D, Zhao H, Wang Y, Wen J. Low-frequency sound absorption of hybrid absorber basedon micro-perforated panel and coiled-up channels. Applied Physics Letters. 2019;114(15).
12. Prasetiyo I, Sihar I, Sudarsono AS. Realization of a thin and broadband microperforated panel (MPP)sound absorber. Applied Acoustics. 2021;183.
13. Kim D-Y, Ih J-G. Wideband reduction of in-duct noise using acoustic metamaterial with seriallyconnected resonators made with MPP and cavities. Applied Physics Letters. 2020;116(25).
14. Maa D-Y. Potential of microperforated panel absorber. The Journal of the Acoustical Society of America.
1998;104(5):2861-6.