PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

How ISO 3382-3 acoustic parameter values are affected by furniture,barriers and sound absorption in a typical open plan office
Remy WENMAEKERS; Nicole VAN HOUT 1
1

Level Acoustics & Vibration, The Netherlands

ABSTRACTISO 3382-3 offers a set of acoustic parameters to describe acoustic conditions in open plan offices such as
speech transmission index, spatial decay rate of speech and background noise level. In this research, theseparameter values were measured in a typical open plan office while varying furniture, barriers and soundabsorption. In many open plan offices a high acoustic quality may be desirable, requiring significant amountsof barriers and (additional) sound absorption. Acoustic designs of open plan offices can be tested using
modelling or measurements. In practice one may get very similar design questions such as: ‘Do we needscreens and how high do they need to be?’. Measured results from offices are available in international
literature, but direct comparison is difficult because of different building dimensions, floor plans and furnitureelements. This research presents results from measurements in a single open plan office that is representative
for many Dutch offices. Furniture, barriers and sound absorption were varied to study the feasibility ofachieving certain parameter values. The results from this study give insight in the acoustic design that isnecessary to achieve a certain acoustic quality in the open plan office.
Keywords: Open plan office, ISO 3382-3

1. INTRODUCTION

The acoustics in open plan offices is influenced by the building and its furniture elements. A
generally good starting point is a sound absorbing ceiling and carpet on the floor. And, possibly, thefloor plan and furniture arrangement can be optimized to avoid acoustically unfavorable combinationsof functions. As a third step, table dividers and free standing barriers might be used to reduce transfer
of sound between workstations or areas. Sound absorption can also be integrated into the screens orapplied to walls. In this study, a large set of measurements have been obtained in a typical open plan
office while varying screens and absorption. Examples are shown in figure 1 with table dividers andside panels (left) and additionally with free standing barriers between groups of tables (right).

Figure 1 – examples of measured variations of screens in an open plan office
12437

2. LITERATURE
2.1 Studies on office acoustics
Some research papers have studied acoustic solutions in a number of different offices by means ofmeasurements based on ISO 3382-3 methods, such as Virjonen et al. (1), Keränen and Hongisto (2),
Yadav et al. (3), Selzer and Schelle (4) and Haapakangas et al. (5). Most papers present room
properties and the acoustic solutions in the measured offices in tables, including room size and height,
ceiling absorption, barrier height, etc. Still, without knowing the actual office layouts it is hard tocomprehend why some offices perform better than others. Specifically, the Finnish Institute ofOccupational Health (1,2,5) has measured rather extreme values for acoustic quality descriptors. Just
one example is available in figures 1 and 2 in Virjonen et al. (1), where ‘office 11’ seems to have rowsof bookcases and single workstations between them. Even though this office might have a very highspatial decay rate of speech, one can question whether such an office can be considered as ‘open plan’.
On the other hand, it is well understood that open plan offices without any acoustic barriers have a
low spatial decay rate of speech resulting in irrelevant speech being too intelligible and rooms being
too noisy.
Some researchers have systematically investigated the changes in acoustic conditions whilevarying room absorption and furniture elements. Two studies by Bradley and Wang (6) and Schmich
et al. (7) show results from such investigations under laboratory conditions with only two adjacentworkstations. In the test rooms, reflections from walls were suppressed heavily by sound absorption
and only ceiling and floor reflections influenced the measurements. Even though these studies give
great insight on which elements contribute most to the reduction of the sound level on the other sideof a set of workstations, the absolute measured values cannot be used for practical situations becauseof the lack of room reflections. A study by Keränen (8) did take into account the effect of reflections
from walls in a 9 x 9 m2 room with 4 groups of 3 workstations, while using the ISO 3382-3 descriptors
to study the effect of screens and wall absorption. However, still these measurements were notrepresentative for a typical open plan office where multiple groups of workstations continue along aline. There is a lack of systematic research on acoustic solutions in real offices.
2.2 Acoustic descriptors and guidelines
Four single number ratings are proposed in ISO3382-3: the decay rate of speech (level reduction
when doubling the distance), D 2,S, the A-weighted sound pressure level of speech at a distance of 4m, Lp,A,S,4m, the distraction distance, rD (above which the Speech Transmission Index, STI, falls below0.50), and the average A-weighted background noise level, Lp,A,B. Detailed explanation of theseparameters is given in Virjonen et al. (1) and in the ISO standard. The relation between theseparameters has been discussed by Wenmaekers and Hak (9).
Specifically, the Speech Transmission Index is not only influenced by the acoustics of space by thesmearing of sound but also by the ratio of speech level and background noise level, see Wenmaekers
and Hak (10). In current paper, three levels of background noise have been considered that cover the
typical range of levels in offices. The spectrum is based on the NR = 30 dB curve for the relevant
frequency range 125 to 8000 Hz to simulate typical noise from HVAC systems, see table 1. Note that
active noise masking might be necessary to achieve the higher noise levels 40 and 45 dB(A), while aquiet office may have a 35 dB(A) background noise level.
Table 1: background noise levels based on NR curve 30 dB
125
250
500
1000
2000
4000
NR27 = 35 dB(A)
45
37
31
27
24
22
NR32 = 40 dB(A)
50
42
36
32
29
27
NR37 = 45 dB(A)
55
47
41
37
34
32

2438

8000
20
25
30

Currently, guidelines exist in Finland (11), Germany VDI 2569, see (12) and France NF S 31, see(13) for (some) of the acoustic parameters. Figure 2 shows the distribution of measured data for the
speech level related parameters D 2,S and Lp,A,S,4m for Finnish and German guidelines. The French
guidelines use D 2,S ≥ 7 or 9 dB and speech level reduction at the opposite desk D n ≤ 4 dB or D n ≥ 6
dB. It is clear that a large part of the data falls into the lower categories and only few offices meet thehighest requirements. Also, only the offices measured by the Finnish Institute of Occupational Healthseem to reach D2,S values above 9 dB. It is striking that the German guidelines have chosen lower
values. Perhaps because these are more realistic? Nevertheless, also very few measured offices reachthe highest category of the German guidelines.

Figure 2: measured data from (1,2,3,4,5) compared to guidelines from Finland (left) and Germany (right)
Even though D2,S and Lp,A,S,4m are useful parameters for describing the acoustics of the open plan
offices, research by Haapakangas (5) indicates that these parameters do not correlate with thepercentage of people that are highly disturbed by (speech) noise. The parameters that relate to speech
intelligibility, STI and distraction distance rD , did show a correlation with highly disturbed people.
The Finnish guidelines describe 5 different classes for rD . Figure 3 shows the distribution of measured
data for the speech intelligibility related parameters rD and Lp,A,B and the r D classes. Again, very few
offices achieve the highest class and most offices are in the lower categories. Also, it is shown that ingeneral a higher background noise level results in a lower distraction distance but with large variations.

Figure 3: measured data from (1,2,3,4,5) compared to guidelines from Finland
We can conclude that the different guidelines allow the possibility of achieving an office designthat can meet the different quality levels (A-E and 1-3). Offices in the highest categories A-B and 1
seem to be rare, while offices in the middle classes (C and 2-3) are found in all available literaturesources. Also, it is clear that most offices fall into the lower categories (D-E or <3).

2439

2.3 Research goal
Few guidelines exist how to actually achieve a certain quality level or category using ISO 3382-3
parameters. What solutions can the user expect when he asks for a certain quality level? Are thenecessary acoustic measures realistic or even desired from other viewpoints than acoustics? Surely,high screens will improve acoustic quality but does it match the expectation of the user within the
open plan office concept?
To get more insight, an experiment was conducted in a single office while gradually increasing theamount of acoustic measures such as screens and absorption. The office and the acoustic measures
were chosen to be representative for modern offices and office furniture in The Netherlands. Results
show what measures are needed for the given office to achieve the different quality levels. They canserve as examples for other office designs or as benchmarks for simulations of other office layouts.
Also, it is shown that some of the higher quality levels are not (easily) reached with realistic measures.

3. METHOD
3.1 Measurement procedure and equipment
Measurements have been performed following ISO 3382-3 over two measurement lines, one along
the wall and one along the aisle with the sound source in front of the wall. An omnidirectional soundsource (B&K 4292) and an omnidirectional microphone were connected to a laptop with measurement
software Dirac 6 (B&K 7841) via a triton usb device (AE) and amplifier (B&K 2734). The soundsource was calibrated in a reverberation room using the ‘system calibration’ function in Dirac. The
microphone was calibrated in Dirac using a reference tone (B&K 4231). Source and receiver typically
had a 1.2 m height, except for experiments with a workstation for standing where the source had 1.5
m height. The source-receiver distance was derived from the impulse response measurements of theroom with only tables using the Dirac software.
3.2 Room and furniture
A vacant office was selected that was available for two weeks to perform the measurements. Floor
plan and dimensions are shown in figure 4 on the next page. The room is typical for many Dutch open
plan offices as it has a long and narrow floor plan to provide daylight and with closed rooms to
subdivide the long space. The space between table groups is approximately 2 x 0,9 m which is the
typical space required to reach the workstations. When the barrier between workstation groups isapplied, the same distance is preserved, even though it is common to provide more space (1.2 m
between workstation and barrier), such that measurements with and without barrier can be directlycompared.
Within the group of four workstations, table dividing panels can be placed and side panels on theside of the wall and aisle and in the middle, see figure 4. The distance between workstations and theside wall is 0.5 m and extensions for the table dividing panel and free standing barrier are available
to close the gap.
3.3 Room materials and furniture elements
The room has a sound absorbing ceiling with 20 mm Rockfon panels on a > 500 mm cavity. The
floor is covered by carpet and the walls are acoustically reflective (glass and gypsum board). Except
for the 20 workstations (5 groups of 4 workstations) the room was completely empty. As a result, it
might be more reverberant and reflective than a fully furnished office, which makes the results fromthe experiment pessimistic.
Table dividing panels and free standing barriers were constructed from 25 mm chipboard, whichis relatively heavy for office screens but guarantees that sound transmission through the screen is
negligible. In most cases, the table dividing screens run to the floor and have a 1.2 m or 1.5 m height
which is typical for a solution that allows seeing each other while being seated or standing respectively.
The free standing barriers between groups of workstations are 2 m high.
Sound absorption could be applied separately to the screens on each side of the chipboard. Assound absorption, 30 mm melamine foam was applied only to the upper 1.3 m height of the screens
were it is most effective. Thicker sound absorption on either side of a core was not considered to becommon in standard office screens. In one case, 60 mm melamine foam was used as a screen without
the core. In another case, sound absorption was also applied to the back wall behind the sound source.
The sound absorption coefficients of the materials are shown in the graph in figure 4.

2440

Figure 4: floorplan and section with dimensions
graph with sound absorption coefficients2441

4. RESULTS

27 iterations of changes in the screens setup were tested to understand the relevance ofcombinations of solutions while taking over 500 impulse response measurements. Figure 5 shows themeasurement results for four variations of the setup that made a considerable improvement comparedto the empty tables and each other. The variations are as follows:v1: only the tables in the roomv2: tables with 1.2 m high table dividers made of 60 mm thick sound absorption without a corev3: tables with 1.5 m high table dividers made of 30 mm thick sound absorption of each side of acore together with reflective side panels
v4: as v3 combined with a 2 m high free standing barrier between groups of tables, the upper 1.3 mof the barrier is covered with 30 mm of absorption on each side of the core. On the same height,
sound absorption is applied to the back wall behind the sound source.
Figure 5 shows the A-weighted speech level (Lp,A,S ) as a function of distance, the speech transmission
index (STI) as a function of distance with a 40 dBA background noise level, reverberation time T30
per frequency and the distraction distance for each variation for three background noise levels 35, 40
and 45 dBA . In the legend of the graphs, results for single number ratings are presented.

Speech Level in dBA

60
55
45

STI [-]

Lp,A,S [dB]

50
40
35
30
25

1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0

0

5

10

15

20

STI, 40 dBA BGN

0

5

10

15

Distance [m]Lp,A,S,4m = 54.1 | D2,S = 4.3 | Dn = 0.7
Lp,A,S,4m = 51 | D2,S = 4.9 | Dn = 3.8
Lp,A,S,4m = 48.3 | D2,S = 6.2 | Dn = 5.9
Lp,A,S,4m = 45.2 | D2,S = 6.8 | Dn = 6.8

rd = 13 | rp = 26.4 | 40 dBA BGN
rd = 9.1 | rp = 21.4 | 40 dBA BGN
rd = 5.4 | rp = 14.7 | 40 dBA BGN
rd = 2.1 | rp = 10.9 | 40 dBA BGN

T30Distraction distance

35
30
25
20
15
10

18

14

13
9

5
0
125

250

500

1000 2000 4000 8000

Distance [m]Tmid = 0.72 s
Tmid = 0.54 s
Tmid = 0.54 s
Tmid = 0.53 s

35 dBA

6

9

5

8
2

40 dBA

4

1

45 dBA

Masking noise level (NR based)

v1: only tables
v2: Table dividers 1.2 m of absorption no corev3. Table dividers 1.5 m abs. with core + side panels refl.
v4: Solution 3 + Barrier 2 m abs. with core + Abs back wall

Figure 5: measurement results for four different variations of furniture setups

2442

20

Distance [m]rd [m]

T30 [s]

20

1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0

4.1 V1: Only tables
The results with empty tables confirm that without any screens the acoustic parameters related tospeech levels are in the worst categories as described in section 2.2 (Class E or Step <3). The
distraction distance is too long when background noise is low. Nevertheless, with a 45 dBA
background noise level (which requires active sound masking), it seems possible to achieve ‘Class B’from the Finnish guidelines (rD > 8 dB).
4.2 V2: Table dividers
A first step of improvement is made by applying the table dividing panels. Measurements show
little difference in screen height 1.2 m or 1.5 meter. Neither does a standing table with source height
1.5 m result in significant change in parameter values compared to a sitting table with source height
1.2 m. However, if the 1.5 m high dividing panel is only above table level, the opening under the table
has a large impact and this type of screen is therefore not recommended. The setup with reflective
table dividing panels was found to ‘sound’ very unpleasant and is therefore not considered as an
appropriate solution.
Because the measurement results for various heights and finishes of the table dividing panels arecomparable, the most suitable solution is a 1.2 m screen with 60 mm of absorption without a soundinsulating core. With this solution, ‘Step 3’ from the German guidelines is met, while in the Finnish
Class system still the poor class ‘E’ is reached for speech level parameters. However, a ‘Class C’
distraction distance is achieved with 40 dBA background noise level or even ‘Class A’ with 45 dBA.
4.3 V3 Table dividers and side panels
The next step of improvement is made by applying side panels, see figure 1 left. These panels
block sound that is travelling around the screen in the horizontal plane. Near a wall, the side panels
block the reflection of sound via this wall, which can also be solved by extending the table dividing
panel to the wall. Experiments with applying sound absorption to the wall on the side of the aisle did
not show considerable improvement. Also, applying sound absorption to the side panels on the sideof the table did not give considerable improvements. This means that the side panels can be reflective
on both sides. Listening experiments confirmed that the absorption on the table dividing panel issufficient to provide a pleasant ‘sound’ even when speaker with one’s head between the panels.
Looking at the acoustic parameter results, this setup can fulfill ‘Step 2’ from the German guidelines
but still only ‘Class D’ from the Finnish guidelines regarding speech levels. Class C, B and A
distraction distance is achieved with 35, 40 and 45 dBA background noise level respectively. With a
D2,S of 6.2 dB, the lowest requirement of the French guidelines of D2,S ≥ 7 dB is still not met, whilewith a D n of 5.9 dB the French guideline of D n ≥ 6 dB is almost met which corresponds with resultsin figure 1 from reference 13.
4.4

V4 Adding a free standing barrier
Looking at the speech level and STI as a function of distance, a clear zig-zag shape can beobserved in variation v3. It is clear that the position directly behind a screen benefit most from it.
Therefore, the next logical step is to introduce free standing barriers between groups of workstations,see figure 1 right (note that the absorption shown on the side panels is not necessary). However, thefirst experiment with a reflective barrier showed a worsening of acoustic conditions. Sound is beingreflected back to the source, arriving at work stations in front of the barrier. It is clear that the barrier
has to be sound absorbing to take away this effect, as well as the back wall behind the loudspeaker.
A significant speech level reduction was achieved by adding the barriers. However, the rate ofspeech level decay over distance hardly changed. As a result D2,S increased slightly from 6.2 dB to
6.8 dB. It was found that sound travelling via the horizontal path along the side panels and barriers islimiting the decay rate. When the barriers are extended to the internal wall, a D2,S of 8.2 dB is achieved
from the measurement line next to this wall.
With the measured results close to the wall, including the barrier to wall extension, the German‘Step 1’ is achieved. A next quality level is reached for the Finnish guidelines with ‘Class C’ forspeech level parameters and the French requirement for D 2,S > 7 dB is met. For the distraction distance,
the highest Finnish quality level ‘Class A’ is achieved for nearly all background noise levels.
No attempts were made to further improve the setup because this was not considered being realistic.
It should be noted that it is common to have 30 cm more space between the barrier and the work
station, which might have a (small) negative effect on the measurement results.

2443

5. DISCUSSION AND CONCLUSION

The results from this research show that it is possible to design acoustic solutions that can fulfill
the German guidelines regarding speech level and the Finnish guidelines regarding distraction
distance. In an office with the German ‘Step 1’ quality, it seems that the distraction distance is low
enough to nearly meet rD ≤ 5 m (‘Class A’ Finnish guidelines) under all background noise conditions
35-45 dBA. With a ‘Step 2’ or ‘Step 3’ quality, this ‘Class A’ distraction distance is only achieved
with a higher background level up to 45 dBA.
The highest Finnish and French guidelines for the speech level parameter D 2,S have not beenreached (≥ 9 dB). It is questionable whether this is possible in realistic scenarios that fit the typicalarchitecture of (Dutch) open plan offices. Besides, such high D2,S has proven to be unnecessary
because a low distraction distance can already be achieved with D2,S ≤ 8 dB even in a quiet office.
Looking at the pictures in figure 1, it is clear that the acoustic solutions have a big impact on thedesign and cost of the open plan office. Depending on the type of work and the type of office, carefulselection of criteria is needed to match users’ needs and expectations.

ACKNOWLEDGEMENTS

This research was done in cooperation with Royal Ahrend who have generously provided all necessary
materials and the measurement location. Special thanks to Marianne Wind and Jurriaan van Heese
from Royal Ahrend for their input in designing the measurement setup and executing the experiment.
Also, thanks to Ioanna Christia and Kevin de Beer for their contribution to this research paper.

REFERENCES

1. Virjonen P, Keränen J, Hongisto V. Determination of acoustical conditions in open-plan offices: proposal
for new measurement method and target values. Acta Acust. u/w Acustica. 2009 Mar 1;95(2):279-90.
2. Keränen J, Hongisto V. Prediction of the spatial decay of speech in open-plan offices. Applied Acoustics.
2013 Dec 1;74(12):1315-25.
3. Yadav M, Cabrera D, Love J, Kim J, Holmes J, Caldwell H, de Dear R. Reliability and repeatability of
ISO 3382-3 metrics based on repeated acoustic measurements in open-plan offices. Applied Acoustics.
2019 Jul 1;150:138-46.
4. Selzer J, Schelle F. Practical aspects of measuring acoustics in German open plan offices. In11th European
Congress and Exposition on Noise Control Engineering (Euronoise) 2018
5. Haapakangas A, Hongisto V, Eerola M, Kuusisto T. Distraction distance and perceived disturbance bynoise—An analysis of 21 open-plan offices. JASA 2017 Jan 12;141(1):127-36.
6. Bradley JS, Wang C. Measurements of sound propagation between mock-up workstations. Institute for
Research in Construction, National Research Council Canada; 2004.
7. Schmich I, Rougier C, Jean P, Chevret P. Efficiency of an acoustic table screen between two work stationsin open plan offices. InAcoustics 2012 2012 Apr 23.
8. Keränen J, Hongisto V, Oliva D, Hakala J. The effect of different room acoustic elements on spatial decayof speech–a laboratory experiment. In Proceedings of Euronoise 2012 Jun 10 (p. 624e629).
9. Wenmaekers RHC, Hak CCJM. Spatial decay rate of speech in open plan offices: the use of D2,S and
Lp,A,S,4m as building requirements. In Euronoise 2015, May 31-June 3, 2015, Maastricht.
10. Wenmaekers RHC, van Hout N, Hak CCJM, van Luxemburg L. The effect of room acoustics on themeasured speech privacy in two typical European open plan offices. In INTER-NOISE 2009 Aug 23 (Vol.
2009, No. 5, pp. 2040-2045).
11. Hongisto V, Keränen J. Open-plan offices-New Finnish room acoustic regulations. Proceedings ofEuroNoise2018. 2018.
12. Nocke C. Open plan offices-classification scheme based on ISO 3382-3 parameters. InINTER-NOISE
Proceedings 2014 Oct 14 (Vol. 249, No. 3, pp. 4345-4349). Institute of Noise Control Engineering.
13. Le Muet Y, Chevret P. Acoustics of Open Spaces–Towards a New French Standard. Euronoise 2015.
2015:1192-6.

2444