Impact Insulation Class (IIC), the single-number rating for evaluating the impact noise insulation of a floor-ceiling assembly, and the associated field testing ratings, are unsatisfactory because they do not have strong correlation with subjective reaction nor provide suitable detailed information for evaluation or design of floor-ceiling assemblies. Various proposals have been made for improving the method, but the data presented indicate that no single-number rating can adequately characterize the impact noise isolation of an assembly. For realistic impact noise sources and floor-ceiling assembly types, there are two frequency domains for impact noise, and the impact noise levels in the two domains can vary independently. Therefore, two ratings are required in order to satisfactorily evaluate the impact isolation provided by a floor-ceiling assembly. Two different ratings are introduced for measuring field impact isolation in the two frequency domains, using the existing impact source and measurement method. They are named low-frequency impact rating (LIR) and high-frequency impact rating (HIR). LIR and HIR are proposed to improve the current method for design and evaluation of floor-ceiling assemblies and also provide a better method for predicting subjective reaction.

The experimentally determined normal incident mass-air-mass resonance frequency for a double leaf cavity stud building element is significantly greater than the theoretically predicted frequency for wood studs and steel studs manufactured from thicker sheet steel. This paper gives a method for calculating the effective mass-air-mass resonance frequency as the root mean square sum of the mass-air-mass resonance frequency and the resonance frequency of the first bending wave mode of the leaves between the studs. This calculation should use the isothermal mass-air-mass resonance frequency if the building element cavity contains porous sound absorbing material. If the cavity does not contain porous sound absorbing material, the usual adiabatic mass-air-mass resonance frequency should be used in the calculation. Because the exact boundary conditions of the building element leaves at the studs and the effective in situ damping are unknown, the paper gives empirical correction factors to determine the actual resonance frequency and the depth of the dip in the predicted sound insulation. This paper also gives empirically derived formulae for the line and point equivalent translational compliances of steel studs manufactured from different sheet steel gauges and compares them with formulae derived by other authors for the case of 25 gauge steel studs.

Field impact sound insulation in the United States is typically quantified in terms of field impact insulation class, which is defined in ASTM E1007. This standard requires averaging the receiving room impact sound pressure levels (ISPL) generated by the tapping machine in four defined positions. In a previous paper [LoVerde and Dong, J. Acoust. Soc. Am. 121, 3113 (2007)] the authors analyzed several hundred field tests to determine effects of reducing the number of tapping machine positions on the FIIC rating. In this paper the analysis is extended to look at the detailed effects on the third-octave band ISPL, which may impact design decisions more than the overall FIIC rating. The effect of reducing the number of positions as a function of assembly construction is also examined.

Impact insulation is currently described with a single number metric impact insulation class (IIC), which correlates poorly with subjective reaction and does not often properly rank order acoustical performance of assembly components. Modifications to IIC have been proposed, but the methods are limited to changing the source or the metric. Experience indicates that impact noise can be divided into two broad classes: Low frequency thudding (e.g., footfalls) and mid/high frequency noise (e.g., heel clicks, dragging furniture, etc.). Low-frequency impact sound pressure level (ISPL) is generally influenced by different variables than the mid/high-frequency ISPL; the authors propose that the two are largely independent. Therefore, two domains are required to adequately characterize the impact noise insulation of an assembly [LoVerde and Dong, 33rd Inter-Noise Proceedings Paper 296, 167 (2004)]. A variety of candidate two-domain systems have been reviewed, where one domain describes the low-frequency performance and the second domain the mid/high-frequency performance [LoVerde and Dong, 14th International Congress Sound and Vibration Paper 476 (2007)]. The two domains are calculated using third-octave ISPL data obtained from recent field impact noise tests. The results suggest that a two-domain system offers considerable improvement over current single-number metrics for evaluating and designing assemblies.

Impact insulation class testing per ASTM E 492 requires measurement of the sound field at exactly four tapping machine positions. Previous research by the authors [J. Acoust. Soc. Am. 121, 3113 (2007), J. Acoust. Soc. Am. 122, 2955 (2007)] indicated that for field tests, the variation between tapping machine positions was small. To our knowledge, a systematic investigation has not been performed for tapping machine positions in the laboratory, and some recent results indicate that the variation may be larger than expected. Large variation in sound level may be inherent to the method, or may point to problems in construction or installation of flooring materials. The variations with tapping machine position are analyzed for a set of laboratory tests, and the previous field test studies are updated with additional data. The authors investigate possible changes to the standards to mandate a maximum allowable variation between tapping machine positions, and to require additional positions as necessary.