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

Development of a modified impact testing method for
simultaneously evaluating multiple floor toppings
Wayland DONG1; John LOVERDE2
1,2

Veneklasen Associates, USA

ABSTRACT
Materials such as floor coverings, screeds, and resilient matting are commonly applied on top of a floorceiling (structural) assembly to improve the impact noise insulation. Theory and experience show that thebenefit of such materials increases with frequency, with minimal eơect below the natural frequency of theresilient materials and the largest eơect at high frequencies. This improvement in impact insulation is added
to the base performance of the structural assembly. Floor design can involve multiple parameters (finish floor,
screed thickness, resilient mat thickness) even from the same manufacturer or product line, and the numberof permutations rises quickly. These permutations must also be tested on multiple structural assemblies. The
authors investigated a modified testing method where multiple top-side assemblies could be installed on thesame structural assembly, allowing for a more eƥcient testing process allowing direct comparison ofmaterials. The expectation is that airborne and low-frequency impact insulation would be consistent since
the base assembly is unchanged, but high-frequency impact insulation would provide the same, consistent
result as a full-scale test. Data from the investigation is presented and analyzed to validate the model anddocument the uncertainties.
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 systems, 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 is
1
2

5112

wdong@veneklasen.com
jloverde@veneklasen.com

determined by the base assembly, but the impact insulation is determined largely by the properties ofthe floor covering.
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) andis calculated by(1)‫ ܴܫܮ‬ൌ ͳͻͲ െ ʹ‫ܮ‬ହ଴ି଼଴
where ‫ܮ‬ହ଴ି଼଴ 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, this rating is well correlated with‫ܮ‬ᇱ௡்ǡ௪ ൅ ‫ܥ‬ூǡହ଴ିଶହ଴଴ , which is the recommended metric in the COST Action (6), and the recommended
classification schemes for the LIR are also consistent with the COST Action guidelines (7).
Although originally intended for field testing, the same rating can be applied to any measurementof impact sound pressure levels at the appropriate frequency bands, including laboratory testing. Whencalculated using normalized levels measured in the laboratory per ASTM E492 (8), the rating is named
Low-frequency Impact Insulation Class (LIIC) and is calculated in the same manner:(2)‫ ܥܫܫܮ‬ൌ ͳͻͲ െ ʹ‫ܮ‬ହ଴ି଼଴
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 be tween
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 (ȟ‫ܮ‬௡ ) due to floor coverings isȟ‫ܮ‬௡ ൌ ‫ ܭ‬

݂
݂଴

(3)

where ݂ is the frequency, ݂଴ 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 ‫ܮ‬௡ǡ௪ become
controlled by lower frequency bands, and therefore do not accurately describe the amount of highfrequency isolation that the assembly provides.
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; the laboratory rating
is High-frequency Impact Insulation Class (HIIC).
For most floors with ratings below IIC 55 (‫ܮ‬௡ǡ௪ above about 55), the HIIC and the IIC are usually
the same. For high-performing floors with high-performing floor coverings (i.e., with low resonancefrequencies), however, the HIIC can greatly exceed the IIC. Consider the numerous case studies inwhich floors with insufficient high-frequency impact insulation were successfully mitigated withchanges to the assembly (7,11). In these assemblies, the HIIC ratings increase dramatically (15-20
points) along with subjective reaction, while IIC ratings remain nearly unchanged.

5113

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. T he 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 locations will in general be different withmultiple floor coverings as oppose to a single one. Since the result is averaged over tapping machine
positions, however, the low frequency rating on average should be the same whether measured oversingle 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 (12) 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 (13) 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 impact 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 of
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 (8), except oriented based on the center of each zone
rather than the center of the entire floor area. The receiving room microphone positons andmeasurement procedure is the same as for an 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.

5114

4. Evaluation
The Floor Zone concept has been tested on a wide variety of base structural assemblies, including
concrete slabs, wood and steel trusses, timber joists, wood I-joists, and cross-laminated timber. Here
we present the data for tests using wood open web trusses, 457 mm (18 in.) deep, with fiberglass
insulation, 19 mm (3/4 in.) oriented strand board subfloor, an d one layer of 16 mm type C gypsum
board ceiling on resilient channel. All of the assemblies tested included a gypsum concrete screed(various thicknesses), with a variety of sound mats both above and below the screed. Finish floors
included none (bare gypsum concrete), several luxury vinyl plank floors, engineered wood, ceramictile, and carpet. Over 30 full floor installations were measured and over 20 Floor Zone installations
with four floor coverings each.
4.1 Airborne
Histograms of the STC ratings for full installation versus Floor Zone (FZ) is shown in Figure 2.
Almost all of the full floor installations used 25 mm (1 in.) gypsum concrete screeds. The Floor Zone
toppings sometimes varied the gypsum concrete thickness from 19 mm (3/4 in.) to 38 mm (1.5 in.),but the average over the floor was a similar total weight. Therefore it is not surprising that the airborne
isolation tests do not show any difference between full installation and Floor Zone.
16
14
12
10
8

FULL

6

FZ

4
2
0
55

56

57

58

59

60

61

62

63

64

STC rating

Figure 2 – Histogram of STC ratings for full installation vs. Floor Zone
4.2 Low-frequency impact
The statistics of LIIC ratings is shown in Table 1 and Figure 3. There was no apparent differencein the low frequency rating of this assembly with changes in floor topping. That is, selecting subsetsof the tests with specific flooring or matting types or gypsum concrete thickness did not affect the
average or the width of the distribution. This confirms the previous study (9).
Table 1 – LIIC statistics for open web truss assemblies
Full floor
Floor Zone
Count
23
83
Mean
56.5
55.4
Standard deviation
3.2
4.6

5115

6
5
4
3

Full
FZ

2
1
0
48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

LIIC

Figure 3– Histograms of LIIC ratings for full installation vs. Floor Zone
The spread of the data is wider with the Floor Zone compared to full floor installations. Some ofthe variation may be attributed to tapping machine position, which are closer to one corner for the
Floor Zone testing. However, there is no apparent bias in the average LIIC of each quadrant and theoverall average. Therefore, the LIIC ratings for the zones can be averaged to obtain a measurement of
the LIIC of the structural system, irrespective of finish floor.
4.3 High-frequency impact
Confirmation that the high frequency impact ratings were similar between full floor and Floor
Zone installation proved to be more difficult than expected. The issue was that even though all of thetesting was performed in the same lab, the repeatability between different tests of the same assembly
was poor. For example, the two tests shown in Figure 4 and Table 2 have identical descriptions andwere tested in the same lab less than one year apart. Both assemblies are full floor installations withno finish floor.
Table 2 – Single number impact ratings for nominally identical assemblies
Test A
Test B(blue)
(red)
IIC
53
55
LIIC
62
56
HIIC
52
56
Impact sound pressure level (dB)

70
65
60
55
50
45
40
35
30
25

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

20

Figure 4 – Impact spectra for nominally identical assemblies

5116

The authors have measured the variation in “rebuild repeatability” before (14,15). Uncertainties ofthis magnitude require averaging a large number of tests to evaluate the difference between full floor
and Floor Zone testing. Without a very large number of tests, it is difficult to separate the differences
between floor coverings from the uncertainty in the overall test method. As an indication, Table 3 andFigure 5 are a subset of the open web truss data; the tests on the left have no finish floor while thetests on the right have an engineered wood finish floor. The Floor Zone tests shown are not fromdifferent quadrants of the same test; they are of single quadrants of different tests that had the same
floor topping.
From this data, the variation between Floor Zone tests of the same assemblies is not any larger andmay be smaller than the variation between full floor tests of the same assemblies. There remains
variation between the Floor Zone tests and the full floor tests. However, this variation does not appear
to be any larger than the variation between full floor tests, i.e., between the uncertainty in themeasurement method.
Table 3 – Single number ratings for nominally identical assemblies
Floor
Floor
Floor
Floor
Floor
Full
Full
Full
Zone
Zone
Zone
Zone
Zone
(blue
(blue
(blue)
(red
(red
(red
(red
(red dotsolid)dash)solid)
dash)solid)
dash)
dash)
IIC
53
55
57
58
57
54
57
55
LIIC
62
56
60
63
53
49
53
49
HIIC
52
56
57
58
63
59
58
58

Impact sound pressure level (dB)

70
65
60
55
50
45
40
35
30
25
20

Figure 5 – Impact spectra of tests shown in Table 3. Full floor tests are blue and Floor Zone are red.

5. SUMMARY
A method (Floor Zone) has been developed to measure multiple floor coverings on the sameassembly. As expected, the division of the floor covering does not affect the airborne noise isolationor the low frequency impact noise isolation of the assembly. The exact relationship between the fullfloor and Floor Zone tests for the broadband and high-frequency impact noise ratings is currently
undetermined due to the large uncertainty and poor repeatability of the measurement method , which
was anticipated. This investigation shows that the Floor Zone method is viable and does not show asignificant reduction in accuracy from the Full Floor method. The adoption of the method does notappear to negatively affect the measurement limitations.
Although not the purpose of the modified method, this testing also provides confirmatory evidence
to the theoretical expectations that low frequency impact noise is determined by the structure, while
the high frequency noise is largely determined by the reduction in impact noise pr ovided by the floor
covering. That is, evaluation, prediction, and design of impact noise isolation should occur in two
independent frequency domains, which has been proposed as a means to evaluate impact noise (4).

5117

ACKNOWLEDGEMENTS
The authors wish to acknowledge the assistance of USG Corporation in the gathering of this dataand include Mr. Brett Fleury, Mr. Alex MacDonald, Mr. Randy Mullett, Mr. Ray Kaligian and Mr. Phil
Ciesulka as being instrumental in this work. The authors also wish to thank the continued support of
the Paul S. Veneklasen Research Foundation and Veneklasen Associates, Inc.

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. 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. 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.
7. LoVerde J, Dong W. Developing classifications using a dual-rating method of evaluating impact noise.
In: Proc INTER-NOISE 2018. Chicago, IL; 2018.
8. ASTM Standard E492, “Standard Test Method for Laboratory Measurement of Impact Sound
Transmission Through Floor-Ceiling Assemblies Using the Tapping Machine.” ASTM International;
2009.
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. LoVerde J, Dong DW. Optimizing floor-ceiling assemblies in wood-framed multifamily buildings using
a two-rating method of evaluating impact isolation. In: Proc ICA2016. Buenos Aires, Argentina; 2016.
12. ISO 10140-1 (2016), Acoustics - Laboratory measurement of sound insulation of building elements Part
1: Application rules for specific products. International Standards Organization; 2016.
13. ISO 10140-5, Acoustics - Laboratory measurement of sound insulation of building elements Part 5:
Requirements for tests facilities and equipment. International Standards Organization; 2010.
14. LoVerde J, Dong DW. Addressing the lack of statistical control in acoustical testing laboratories. J Acoust
Soc Am. 2017 May 1;141(5):3929–3929.
15. Dong W, LoVerde J, Holmgreen E, Bergquist S. Investigation of Extended Repeatability Conditions inLaboratories. In: Proc ICSV25. Hiroshima; 2018.

5118