PROCEEDINGS of the23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Ratings and classiﬁcations for high-frequency impact noiseisolation
John LOVDERDE1; Wayland DONG2; Jochen Scheck3
1,23

Veneklasen Associates, USA

University of Applied Sciences, Stuttgart, Germany

ABSTRACT
A two-rating method of evaluating impact noise isolation has been proposed by two of the authors (1), inwhich low and high-frequency components are evaluated independently. Numerous other researchers haveinvestigated the issue, and although the details diơer, there has been some convergence of ratings andclassiﬁcations for low-frequency impact noise. For the high frequencies, most have assumed that the existing
IIC/Ln,w ratings are appropriate, while the authors have proposed high-frequency ratings which are based on
the existing ratings but with a limited frequency range of 400–3150 Hz. Analysis of impact data from ﬂoor
assemblies common to North America shows that the proposed ratings evaluate high-frequency impact
sources and mitigation measures better than the existing ratings. The analysis is extended to include datafrom German ﬂoor systems and heavyweight and lightweight stairs. The ratings are compared and possibleclassiﬁcations are suggested.
Keywords: High-frequency, Impact, Insulation,

1. INTRODUCTION
Most current classifications for impact noise insulation in multifamily housing is based aroundImpact Insulation Class (IIC) per ASTM E989 (2) or Ln,w per ISO 717-2 (3). These ratings are both
based on the impact noise level in third-octave bands from 100–3150 Hz. There is agreement by otherresearchers that frequencies below 100 Hz are important for evaluating human reaction (4), but theexisting IIC or Ln,w rating is often assumed to be suitable to evaluate the remaining frequencies. Otherresearchers are attempting to create new reference curves that include both low and high frequencies(5,6).
Two of us have proposed that impact noise occurs independently in two frequency domains (1).
While we arrived at this conclusion empirically based on our experience in field testing, theoreticalmodels of impact noise lead to the same conclusion that a separate high-frequency impact rating is
the best way to design for high-frequency impact noise sources and evaluate floor coverings.
The work has to date been based on test data collected in North America and therefore based on
assembly types that are common there. Other countries have different construction methods andtraditions. Here we extend the analysis to examine some common German floor-ceiling assemblies.

2. HIGH-FREQUENCY IMPACT NOISE
2.1 Theoretical Behavior of Floor Coverings
Impact noise has long been modeled by a simple impedance model (7,8). The low frequency
behavior is defined by the momentum transfer between the hammer and the assembly ; this isdetermined by the mobility of the structure, and the floor covering is unimportant . The high frequency
1

jloverde@veneklasen.com
wdong@veneklasen.com
3jochen.scheck@hft-stuttgart.de25057

response is determined by the local compliance of the floor at the hammer location. As Wattersemphasizes, resilient floor coverings do not, strictly speaking, isolate the system from forces, but
reduce the generation of high-frequency vibration (8).
Following this model, the reduction in impact noise due to floor covering (i.e., compared to thebare structure) can be shown to follow a simple power law with respect to frequency; that is,ȟ‫ܮ‬௡ ൌ ‫ ܭ‬݂݂଴(1)where ȟ‫ܮ‬௡ is the reduction in impact sound level at frequency f, and ݂଴ is the resonance frequencyof the floor covering. Below ݂଴ , ȟ‫ܮ‬௡ is negligible. The constant K (i.e., the slope of the line) depends
on the details of the product and how it couples with the subfloor. Vér derives a value of 40 for locallyreacting resilient flooring and 30 for point-supported floors (9). ISO 12354-2 (10) Annex C
recommends 30 for floating floors with screeds of sand/cement or calcium-sulphate and 40 for asphalt
or dry floating floors.
These derivations generally assume that the floor coverings are installed on a rigid, heavy structuresuch as a poured concrete slab, that is, where the mobility of the structure is much lower than themobility of the floor covering. How does the theory extend to lightweight floors that are framed withwood or light gauge steel joists? Unlike monolithic slabs, no analytical solutions are available ; onetechnique is to develop numerical models (11). For our purposes, we do not need to be able to calculate
the mobility of the joist-framed structure; we can empirically determine if a similar behavior applies.
In Figure 1 we compare the improvement in impact insulation provided by three common floor
coverings on a 200 mm (8 in.) concrete slab and two lightweight wood-framed assemblies, one framedwith 457 mm (18 in.) open-web wood trussed and one with 300 mm (12 in.) wood I-joists. Both havea thin (about 19 mm) gypsum concrete pour and a gypsum board ceiling attached with resilient channel.
Note that the fall-off at high frequencies is due to the noise floor in the laboratory. The curves are notidentical, and the performance is in general better with the heavyweight floor as opposed to the wood
joist floors. However, we can conclude that the structural properties do not change the essential
behavior of floor coverings, and that Eq. (1) is approximately correct for all structural types.
40

8" Concrete Slab35

18" OWT

30

12" I-Joist

2520
15
10
550
80
125200
315
500
800
1250
2000
3150
5000

5080
125200
315
500
800
1250
2000
3150
5000

5080
1252003155008001250
20003150
5000

0Figure 1–Improvement in impact insulation (reduction in impact sound level) on three structural systems
for carpet tile (left), luxury vinyl plank over foam mat (middle), luxury vinyl plank without sound mat(right).
2.2 Proposed single number ratings
The authors have demonstrated (1) that changes in impact sound level due to floor covering can be
described by considering only the third-octave bands from 400 Hz and above. Although floor
coverings with resonance frequencies below 400 Hz are readily available, due to the shape of therating curve, the IIC ratings for assemblies with such floor coverings are controlled by the bands
below 400 Hz. Therefore, while lower resonance frequencies results in better IIC or L n,w ratings ingeneral, this relationship breaks down for floor coverings with low resonance frequencies, and the5058

rating tends to stop changing even as the resonance frequency continues to decre ase. That is, theIIC/Ln,w ratings are not representative of the effectiveness of the floor covering.
The authors therefore proposed a family of new high-frequency ratings to better evaluate theacoustical performance of floor coverings and high -frequency noise sources in general (Table 1). The
laboratory version is called High-frequency Impact Insulation Class (HIIC). The reference spectrum
and calculation method is the same as the existing ratings except that the lowest frequency band is
400 Hz. The maximum deficiencies remain at 2 per band (20 total); the 8 dB rule is not implemented.
Note that this rating can be easily calculated from existing test data, and can th erefore be evaluatedfor previously tested assemblies.
Table 1– Proposed family of high-frequency impact noise single-number ratings and their correspondencewith existing ratings.
Existing Ratings
RatingName
Normalization
ASTM
ISO
High-frequency
HIR
None
ISRL′w
Impact Rating
Field
NHIR
Normalized HIR
T0 = 0.5 s
NISR
L′nT,w
AHIR
Absorption-normalized HIR
A0 = 10 m2
AIIC
L′n,w
High-frequency
HIIC
A0 = 10 m2
IIC
Ln,w
Impact Insulation ClassLab
ΔHIIC
Improvement in HIIC
A0 = 10 m2
ΔIIC
ΔLw
2.3 Behavior of Single Number Ratings
Here we proceed with the assumption that Eq. (1) is accurate. Knowing the impact sound level ofa structural system without a floor covering (measured in a laboratory), we can calculate the single
number ratings for the assembly with a theoretical floor coverings of arbitrary resonance frequency.
Figure 2 shows the IIC and HIIC rating of a floor as a function of floor covering resonance frequency
for the same three structural systems referenced above .
The LIIC rating (Low-frequency Impact Insulation Class) is also shown. This rating evaluates
impact sound below 100 Hz; higher ratings are better. We do not discuss it further except to note that
low-frequency impact sound is not affected by floor covering and is therefore constant in the figure.
A very high resonance frequency indicates a floor covering with surface resilience similar to thebare structure. Therefore, the floor covering has no effect, and the ratings are the same as for the bareslab (the far right hand side of the curves are constant). Both IIC and HIIC ratings indicate steadily
improving isolation as the resonance frequency of the floor covering decreases, but at some point theIIC (and equivalently, L n,w) curves flatten. This is an illustration of the issue described above that led
to the development of HIIC. As can be seen, the limited frequency range of the HIIC rating allows it
to continue to accurately describe the improvement of floor coverings with low resonance frequencies.
It is apparent from Figure 2 that the “branching point” between the IIC and HIIC depends on thestructural assembly. The existing IIC rating performs worse with the lightweight assemblies, whilewith the concrete slab, the branching point is at a lower frequency and there is a smaller difference
between the ratings.

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8" Concrete SlabSingle number rating'80
7060
IIC50HIIC40LIIC

302050500

5000

Resonance frequency of floor covering

Single number rating'

12" TJI

18" OWT

80
7060
50
40
30
2050500

5000

50

Resonance frequency of floor covering

500

5000

Resonance frequency of floor covering

Figure 2 – Single number ratings as a function of resonance frequency of theoretical floor covering
behaving as Eq. (1) for three structural systems: 200 mm concrete slab (top), 457 mm open web woodtrusses (bottom left), and 300 mm wood I-joists (bottom right).

3. GERMAN FLOOR-CEILING ASSEMBLIESThe above analysis was based on assemblies common in North America. Typical German
residential projects have concrete slab structure with an approximately 5 cm screed over various
resilient mattings. The resonance frequencies of the floating floor can be as low as 50 Hz. In theshower pans, thinner resilient matting is used to accommodate the waterproofing and drainage systems.
There are also lateral impact issues with both concrete and wood or steel stairs mounted to theseparating wall between units. Single number ratings for these assemblies is shown in Table 2 and thespectra are graphed in Figure 3.

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Normalized impact sound pressure level(dB)

Table 2– Single number ratings for some common German floor assemblies.
Condition
Ln,wIICHIIC
Typical living space
4462
73
Shower system 149
5671
Shower system 23971
72
Lightweight stair
4066
81
Heavyweight stair, isolated
38
72
70
Heavyweight stair, unisolated
6938
39
70.0
60.0

typical living

50.0

shower 1

40.0

shower 230.0

lightweight stair

20.0
10.0

heavyweight stair,isolatedheavyweight stair

0.0

Figure 3 – Impact spectra of the German floor-ceiling assemblies shown in Table 2.
Although these assemblies have wildly different levels at the lower frequencies, they are consistentin the high-frequency side of the spectrum. Except for the stairs, the HIIC ratings are within a few
points of each other. In addition, the high-frequency performance is very good. The authors had
previously suggested (13) that an HIIC rating of 65 would be considered Preferred or Class A in theNorth American market; all of these floors exceed this rating (excluding the un-isolated concrete stair).
For these assembly types, the high-frequency isolation is good enough (meets a Preferred standard)that only the low-frequency issue remains to be solved; in practice, the problem is reduced to a single
dimension. The exception is the un-isolated concrete stair, which has, as expected, poor high frequency performance. Thin resilient mats are placed below the finish flooring on top of the unisolated concrete stair may be a situation one might observe the benefits of the high-frequency ratings
as seen in North American assemblies. This condition is relatively uncommon. Additionally, Figure 2
suggests that the benefit of using HIIC instead of IIC is smaller for concrete slab structures comparedto lightweight assemblies.
Considering these factors, therefore, it may not be surprising that researchers used to these typesof assemblies do not experience the same motivation to improve the evaluation of high frequency
impact noise as researchers in North America. However, this does not mean that the high frequency
ratings should not be analyzed or reviewed, if only to ensure that the situation reduces to a single
frequency domain. As described previously, there are strong theoretical reasons to consider impact
isolation in two frequency domains. Design practices can change, and high frequency insulation may
become more important in the future.

4. CONCLUSIONSThe theoretical behavior of floor coverings is well documented in both theory and experiment, thatthe benefit increases directly with the reduction in the resonance frequency of the floor covering. As
the resonance frequency is lowered, IIC and HIIC are initially similar, but at some resonancefrequency the IIC ratings levels off while HIIC continues to accurately track the floor covering. The5061

frequency at which the ratings diverge and the magnitude of the difference between IIC and HIIC
depends on the structural system.
Analytical expressions exist for the improvement due to floor coverings for monolithic slabs; whilelightweight assemblies are more difficult to analyze, experiments indicate that the performance offloor coverings is approximately the same on lightweight assemblies as on heavyweight ones. The
benefit of HIIC over IIC is greatest on lightweight systems.
In the North American market, lightweight separating floor-ceiling assemblies are common, andthe benefit of HIIC over IIC is clear. In German residences, the standard assemblies already have very
good high frequency impact insulation due to the topside isolation common to the construction ofthese assemblies. In this condition where one frequency domain is already at the preferred state, theproblem is reduced to a single dimension. This may reduce the motivation for improving the highfrequency insulation metric in these markets, but it should not be ignored. Both frequency domains
are present and should be evaluated, even if it turns out that only one will be significant, asconstruction methods change and that may not always be the case. A dual-rating method is suggested
to better evaluate impact noise insulation over all types of building construction.

ACKNOWLEDGEMENTS
Funding was provided in part by the Paul S. Veneklasen Research Foundation. The authors thank
Veneklasen Associates and the Acoustics Workgroup at the Hochschule für Technik Stuttgart for theirsupport.

REFERENCES
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