New ASTM ratings for impact noise insulation John LoVerde 1 Wayland Dong 2 Samantha Rawlings 3 Veneklasen Associates, Inc. 1711 16 th Street, Santa Monica, CA 90404 USA

ABSTRACT New ratings to evaluate impact noise insulation have recently been published as ASTM standards, which are commonly used to evaluate building acoustics measurements in North America. ASTM E3207 defines new ratings for low-frequency impact insulation, defined by the 50-80 Hz third-octave bands. ASTM E3222 defines new ratings for high-frequency impact insulation, defined by the 400- 3150 Hz bands. These ratings are based on the two-rating method of evaluating impact noise isolation proposed by the authors [1]. By evaluating the low and high-frequency components of impact noise independently, the proposed ratings perform better than existing ratings in terms of correlating with subjective reaction, designing assemblies, and evaluating products and mitigation measures. Motivations, development, and examples illustrating the use of the new ratings are presented, and suggested classification schemes are discussed.

1. INTRODUCTION

Most current classifications for impact noise insulation in multifamily housing are based around Impact Insulation Class (IIC) per ASTM E989 [2] or L n,w per ISO 717-2 [3]. These ratings are nearly equivalent and are based on the impact noise level generated by the standard tapping machine in third- octave bands from 100–3150 Hz. The existing ratings are insufficient to describe impact insulation and do not adequately correlate with subjective reaction [4], [5]. On the one hand, impact noise below 100 Hz is clearly important for evaluating human reaction [6], [7], which has led to various methods to include these frequencies in the rating, most notably the spectrum adaptation terms in ISO 717-2. On the other hand, while it is often assumed that the existing ratings are suitable for high-frequency isolation, the existing ratings are often controlled by frequency bands that do not describe the high- frequency performance of the assembly.

To address these concerns, the authors have proposed that impact noise occurs independently in two frequency domains [1]. The measurement, evaluation, and design of floor-ceiling assemblies is greatly improved with this change in perspective. This can be concisely illustrated by Figure 1, which shows the impact spectra of three typical floor-ceiling assemblies using construction systems and products common in the North American market. These floors have the same IIC/L n,w rating, but vary widely in their acceptability and character. Both the low-frequency and high-frequency performance of these floors ranges from very good to poor. Improvements to the low and high-frequency

1 jloverde@veneklasen.com 2 wdong@veneklasen.com 3 srawlings@veneklasen.com

performance of these systems are generally addressed using different methods and are changed independently. Further, these assemblies are perceived very differently.

It should be emphasized that the spectra in Figure 1 are not unusual or contrived. These spectra are not only typical of tested floor assemblies but are expected on theoretical grounds, as will be demonstrated in the follow sections.

8050801252003155008001250200031505000

70

Impact sound pressure level

60

50

40

30

20

10

0

Figure 1: Example impact sound spectra for three floor-ceiling assemblies. All three curves have the same IIC/Ln,w rating but differ drastically in both low- and high-frequency impact isolation.

2. NEW IMPACT INSULATION RATINGS

Both sets of new ratings are based on the existing laboratory and field measurement methods without modification (except for frequency range).

2.1. Low-frequency Ratings

The new low-frequency ratings are defined in ASTM standard E3207-21 [8]. For field measurements, the rating is called Low-frequency Impact Rating (LIR) and is calculated by

𝐿𝐼𝑅= 190 −2𝐿 50−80 (1)

where 𝐿 50−80 refers to the energetic sum of the impact sound pressure levels in the 50, 63, and 80 Hz third-octave bands. The same calculation can be applied to the normalized sound pressure levels generated by laboratory impact insulation testing, in which case the rating is named Low-frequency Impact Insulation Class (LIIC).

The low-frequency impact rating is based on impact sound levels that are not normalized to a standard reverberation time or amount of absorption. The low-frequency rating can be calculated from existing tests as long as the sound levels down to 50 Hz are reported.

2.2. High-frequency Ratings

The new high-frequency ratings are defined in ASTM standard E3222-20 [9]. By intent, the high- frequency ratings are the same as the existing ratings except for the frequency range. The rating is calculated using third-octave impact sound pressure level data and a reference curve in the same manner as the existing IIC and L n,w ratings. The reference curve (see Table 1) is the same as the existing contour, except that it includes only the bands from 400 to 3150 Hz. The method of calculating the rating is also the same, with the maximum total deficiencies remaining at 2 per band (20 total). The 8 dB rule is not implemented.

Table 1. Ref erence contour for the high-frequency im pact ratings.

Band center frequency, Hz

Reference contour value, dB 400 1 500 0 630 -1 800 -2 1000 -3 1250 -6 1600 -9 2000 -12 2500 -15 3150 -18 Note that the high-frequency ratings can be easily calculated from existing test data. The ratings can therefore be calculated for previously tested assemblies and can utilize the large amount of impact test data that has been gathered over the decades.

Just as with the existing ratings, the calculation method describes a family of ratings depending on whether the third-octave data was acquired in the laboratory or the field, or what normalization was used. See Table 2. For each existing rating, there is a corresponding high-frequency version.

Table 2: New family of high-frequency impact ratings per ASTM E3222, showing normalization and c orrespondence with existing ratings

Rating Name Field or Lab; Normalization

Corresponding Existing Rating

HIR High-frequency impact

Field Non-norm

ISR

rating

L′ w

NHIR Normalized HIR Field T 0 = 0.5 s

NISR L′ nT,w

AHIR Absorption-normalized

Field A 0 = 10 m 2

AIIC

HIR

L′ n,w

HIIC High-frequency impact

Lab A 0 = 10 m 2

IIC L n,w

insulation class

ΔHIIC Improvement in HIIC Lab A 0 = 10 m 2

ΔIIC ΔL n,w

3. THEORETICAL CONSIDERATIONS

Simple models for impact noise that have been developed long ago [10], [11] have proved useful for understanding impact noise transmission. The low-frequency behavior is defined by the momentum transfer between the hammer and the assembly; this is determined by the mobility of the structure, and the floor covering is unimportant. The high-frequency response is determined by the local compliance of the floor at the hammer location. As Watters emphasizes, resilient floor coverings do not, strictly speaking, isolate the system from forces, but reduce the generation of high-frequency vibration [11].

Following this model, the reduction in impact noise due to floor covering (i.e., compared to the bare structure) can be shown to follow a simple power law with respect to frequency; that is,

Δ𝐿 𝑛 = { 𝐾lg 𝑓

, 𝑓> 𝑓 0

(2)

𝑓 0

0, 𝑓< 𝑓 0

where Δ𝐿 𝑛 is the reduction in impact sound level at frequency f , and 𝑓 0 is the resonance frequency of the floor covering. Below 𝑓 0 , Δ𝐿 𝑛 is expected to be 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 but is typically taken to be 30 or 40 (that is, 9 or 12 dB/octave) [12], [13]. Field testing results (see Fig. 6 in [1]) confirm that this simple equation is a good description of the behavior of most common floor coverings.

The derivation of this behavior and the field testing mentioned above are both for a massive homogenous structure such as a concrete slab. However, we have shown that lightweight joist-framed structures show the same behavior [14], and that Eqn. (2) can describe the improvement in impact insulation due to floor coverings for all structural systems.

Assuming the Eqn. (2) is correct with K = 40, and knowing the impact sound level of a 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. The resultant single number ratings are shown in Figure 2 for two floor assemblies: a 200 mm concrete slab and 457 mm open web wood trusses with gypsum concrete screed and resiliently suspended ceiling. The existing IIC rating is plotted along with the new LIIC and HIIC ratings.

8" Concrete Slab

18" OWT

100

100

IIC

90

90

HIIC

80

80

LIIC

Single number rating'

70

70

60

60

50

50

40

40

30

30

20

20

20 200 2000

20 200 2000 Resonance frequency of floor covering

Resonance frequency of floor covering

Figure 2: Single number ratings as a function of resonance frequency of the theoretical floor covering for 200 mm concrete slab (left) and 457 mm open web wood trusses (right)

Figure 2 contains many interesting features. Consider the low-frequency rating (green curves). • The LIIC rating is primarily determined by the impedance (i.e., the mass and stiffness) of the structure. The concrete assembly has much higher LIIC ratings compared to the wood joist assembly. Footfalls on the concrete assembly will be acceptable, while the wood joist assembly will have audible low frequency noise that will be objectionable to some percentage of the population. • The LIIC rating is not affected by floor covering and is therefore constant in the figure, except for very soft coverings such as carpet. Now consider the existing IIC rating (blue) and high-frequency rating (red), starting from the right- hand side of the plots and evaluating as the resonant frequency of the flooring goes down.

• The far right-hand side of the curves are constant. In this region, a very high resonance frequency indicates a hard floor covering with surface resilience similar to the bare structure. Therefore, the floor covering has no effect, and the ratings are the same as for the bare slab.

• As the resonance frequency of the floor covering decreases, both IIC and HIIC ratings indicate steadily improving isolation. For floors in this range, the rating is controlled by the high frequency bands, and therefore the IIC and HIIC ratings are very similar. • As the floors continue to improve, the existing ratings such as IIC become more and more influenced by the sound level below 400 Hz. At some point the IIC (and equivalently, Ln,w) curves flatten, and the IIC rating barely changes even as resonance frequency of the flooring decreases significantly. The spectra in Figure 1 have the same IIC rating because they are in the flat portion of these curves. • The HIIC rating, in contrast, continues to accurately describe the improvement of floor coverings down to arbitrarily low resonance frequencies.

4. SUBJECTIVE EVALUATION

4.1. Low frequency Impact Sources

As described in [1], the numerical constants in Eq. (1) were chosen so that LIR of 50, 60, and 70 corresponded to Minimum, Acceptable, and Preferred classes of performance. (These classification names were taken from the ICC G2-2010 Guideline for Acoustics [15].) This was based on our experience with occupant reactions.

We have shown that for floor-ceiling assemblies that are controlled by low frequency sound (i.e., thudding), the LIR is highly correlated with the ISO rating 𝐿 𝑛𝑇,𝑤

′ + 𝐶 𝐼,50−2500 [16]. The ISO rating was in turn used to describe recommended harmonized European classifications in COST TU0901 [7]. Considering just low-frequency performance (i.e., for assemblies with good high-frequency performance), the Minimum, Acceptable, and Preferred classes line up with COST Classes D, B or C, and A, respectively. That is, the classification schemes have independently converged to a consistent recommendation.

A detailed review of a large set of residential projects for a single developer was performed [17]. These projects involved a continuous and iterative optimization of the assembly. The low-frequency rating for this assembly remained mediocre, with an average of approximately LIR 50, while the high-frequency rating steadily improved High-frequency isolation appears to be more important to this client and their tenants than low-frequency performance. Therefore, LIR of 50 or less may be tolerated in many project types, so the label of “minimum” may not be appropriate.

4.2. High frequency Impact Sources

Common high-frequency impact sources in residences include heel clicks from footfall with hard- soled shoes, dropping objects, dragging furniture, and dog toenails. While much attention has been paid to low-frequency “thudding” from footfalls, high-frequency impact sources also cause complaints in multifamily projects.

There is much evidence that occupants are sensitive to high-frequency impact noise even with significant low-frequency footfall noise. We mentioned above the optimization program of the floor- ceiling assembly for a large developer of high-rent multifamily homes [17]. The resulting assembly has mediocre low-frequency isolation but good performance at high frequencies, and the isolation is considered good by most tenants.

We have also reported [16] on recent field testing experience in a number of projects where mitigation was successfully implemented (as judged by occupant complaints) that significantly increased the high-frequency rating while the broadband rating remained unchanged. The high frequency rating predicted the subjective reaction, while the broadband rating did not correlate with either the measured spectra or the subjective reaction.

While there is no doubt that low-frequency footfall noise causes complaints, isolation against high- frequency sources is also important to occupant reaction. Further, the existing ratings do not adequately represent the level of high-frequency performance of an assembly or floor covering.

4.3. Classification

Based on the above findings, we have tentatively suggested the classification scheme shown in for field testing in multifamily homes. The classes A–D are intended to correspond to the performance of the classifications of Ref. [7] and ISO Draft Technical Specification 19488 [18]. These classifications are suggested as a starting point for discussion and have not been adopted by any regulatory agency.

Table 3: Su ggested classifications with the new ratings

LIR NHIR Class A 70 65 Class B 60 58 Class C 50 52 Class D None 45

5. IMPLEMENTATION

5.1. Comparing Structural Systems

The low-frequency ratings can be used to evaluate the performance of floor assemblies, and to predict the likelihood of complaints from thudding.

The primary factor affecting LIR is the structural system. Much work remains in order to be able to predict, for example, the LIR of a system based on structural design or laboratory testing. However, current work has shown that LIIC is a useful design tool for comparing the effect of changes to the design within a given laboratory. For example, we have determined that an 8-inch (200 mm) concrete slab is 5 LIIC points better on average than a 6-inch (150 mm) slab. In contrast, adding a ceiling to a concrete slab, while it greatly improves the impact insulation at most frequencies, has no measurable effect on the LIIC [19]. Different brands of resilient channel can account for 7 LIIC points difference between wood truss assemblies [20].

5.2. Specifying Flooring

It has long been a problem in the flooring and resilient underlayment industry to differentiate between high-performing floor coverings. The IIC rating of a floor rarely exceeds 60 (c.f. Figure 2). The customer, not having technical knowledge of impact ratings, assumes that products can be compared by their IIC ratings, but products with the same IIC rating (even on the same base structural assembly) can vary at the high frequencies by over 10 points. Using the HIIC and ΔHIIC ratings instead of IIC and ΔIIC will greatly clarify the situation. Products can be accurately rank-ordered and cost-benefit decisions can be made more accurate. Several manufacturers have already started calculating and publishing the high-frequency ratings for their tested assemblies.

5.3. Flooring Changes

One class of projects where the high-frequency ratings are particularly useful is buildings where the finish flooring is regularly altered (e.g., condominiums, hotels, schools) and the performance of the flooring needs to be evaluated and regulated. Many condominiums are older wood joist buildings with poor performance at low frequencies, but still wish to require flooring products that achieve a level of performance regarding high-frequency sources.

For many buildings, it is impossible to achieve this goal using the existing ratings. As an example, in one building discussed in Ref. [1], the floors with resilient matting were clearly preferred to floors without. This is obvious from examination of the impact spectra (Figure 3), but the ISR ratings of these spectra are almost identical. The existing ratings did not accurately describe the floors and did not provide a method of evaluating other flooring products. The HIR ratings of these floors varied by 10 points, which much more accurately characterizes the performance of the floor.

Figure 3: Impact spectra from the building discussed in the text. Same as Fig. 8a from Ref. [1]

Now that the high-frequency ratings have been published as an ASTM standard, we encourage and expect regulatory bodies such as condominium associations to adopt the high-frequency ratings instead of the existing ratings to evaluate and regulate permissible flooring.

6. CONCLUSIONS

The traditional broadband impact ratings (IIC/L n,w ) are a poor choice for representing the impact insulation performance of assemblies. They do not accurately evaluate assemblies, either in terms of the physical behavior or subjective reaction. To address this, two new ratings have been introduced. The low-frequency rating, recently published as ASTM E3207, is based on the sound levels in to 50– 80 Hz bands and correlates well with subjective reaction.

The new high-frequency impact rating method has been developed with a frequency range that is limited to the range of interest and therefore more accurately correlates with the behavior of floor coverings. This new family of high-frequency impact ratings, each corresponding to an existing rating, has been defined and recently published as ASTM E3222. The new ratings do not require any change in measurement procedure.

The new ratings can be used to evaluate the performance of assemblies. Use of the new ratings in flooring specifications and requirements will improve the comparison and rank-ordering of products and systems, and provide additional information to designers of floor-ceiling systems.

7. ACKNOWLEDGEMENTS

Portions of this work were funded by the Paul S. Veneklasen Research Foundation.

8. REFERENCES

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[3] “ISO 717-2 (2013), Acoustics - Rating of sound insulation in buildings and of building elements Part 2: Impact Sound Insulation,” International Standards Organization, 2013. [4] W. E. Blazier and R. DuPree, “Investigation of low-frequency footfall noise in wood-frame, multifamily building construction,” J Acoust Soc Am , vol. 96, no. 3, p. 1521, 1994, doi: 10.1121/1.410230. [5] T. Mariner and H. W. Hehmann, “Impact-Noise Rating of Various Floors,” J Acoust Soc Am , vol. 41, no. 1, p. 206, 1967, doi: 10.1121/1.1910319. [6] V. Belmondo, T. Heebink, and F. Brittain, “Ranking the Impact Sound Transmission of Wood-Framed Floor-Ceiling Assemblies,” J Acoust Soc Am , 1974. [7] B. Rasmussen and M. Machimbarrena, “COST Action TU0901 - Building acoustics throughout Europe. Volume 1: Towards a common framework in building acoustics throughout Europe,” COST Office Action TU0901, 2014. [8] “ASTM E3207-21, Standard Classification for Determination of Low-frequency Impact Noise Ratings,” ASTM International, 2021. doi: 10.1520/E3207-21. [9] “ASTM E3222-20, Standard Classification for Determination of High-frequency Impact Sound Ratings,” ASTM International, 2020. doi: 10.1520/E3222-20. [10] L. Cremer, M. Heckl, and B. A. T. Petersson, Structure-Borne Sound: Structural Vibrations and Sound Radiation at Audio Frequencies , 3rd ed. Berlin Heidelberg: Springer-Verlag, 2005. Accessed: Apr. 10, 2018. [Online]. Available: //www.springer.com/gp/book/9783540226963 [11] B. G. Watters, “Impact-Noise Characteristics of Female Hard-Heeled Foot Traffic,” J Acoust Soc Am , vol. 37, no. 4, pp. 619–630, 1965. [12] I. L. Vér, “Impact Noise Isolation of Composite Floors,” J. Acoust. Soc. Am. , vol. 50, no. 4A, pp. 1043–1050, Oct. 1971, doi: 10.1121/1.1912726. [13] “ISO 12354-2. Building acoustics - Estimation of acoustic performance of buildings from the performance of elements Part 2: Impact sound insulation between rooms.” [14] J. LoVerde, W. Dong, and J. Scheck, “Ratings and classifications for high-frequency impact noise isolation,” presented at the 23rd International Congress on Acoustics, 2019. [15] “ICC G2-2010 Guideline for Acoustics,” International Code Council, 2010. Accessed: Dec. 09, 2015. [Online]. Available: http://shop.iccsafe.org/icc-g2-2010-guideline-for-acoustics-1.html [16] J. LoVerde and W. Dong, “Developing classifications using a dual-rating method of evaluating impact noise,” Chicago, IL, 2018. [17] J. LoVerde and D. W. Dong, “Optimizing floor-ceiling assemblies in wood-framed multifamily buildings using a two-rating method of evaluating impact isolation,” presented at the 22nd International Congress on Acoustics, Buenos Aires, Argentina, Sep. 2016. [18] “ISO/DTS 19488 - Acoustics -- Acoustic classification of dwellings,” International Standards Organization, 2020. [19] J. LoVerde and W. Dong, “Laboratory measurement of low-frequency impact sound,” Hiroshima, 2018. [20] W. Dong and J. LoVerde, “Quantitative comparisons of resilient channel designs in walls and ceilings,” Lexington, KY, 2022.