4.1 This classification provides a family of single-number ratings for describing high-frequency impact sound insulation. "High-frequency" in this context refers to the third-octave bands from 400 to 3150 Hz, which is approximately the upper half of the frequency range of interest in building acoustics measurements. Common sources of high-frequency impact sound include the impact of hard-heeled shoes, dragging furniture, dog toenails, and dropping objects on hard-surfaced flooring.

4.2 The high-frequency impact sound insulation of an assembly is primarily determined by the characteristics of the floor topping, largely independent of the other details of the assembly.3 For many assemblies, the existing ratings (such as IIC) become controlled by frequency bands below 400 Hz. For these assemblies, the existing ratings are not representative of the impact insulation at high frequencies. The high-frequency ratings defined here have been shown to accurately represent the behavior of assemblies at high frequencies.4^,5 These ratings are intended to aid the acoustical professional in evaluating the high-frequency insulation of an assembly, and in evaluating, rank-ordering, and specifying floor topping products that will affect the level of high-frequency impact sound.

4.3 The ratings in this classification have similar numerical range and behavior as the existing ratings of Classification E989. Further, the ratings in this classification can be calculated from existing test reports without additional testing. This was done to take advantage of the existing test results and body of knowledge.

4.4 This classification describes only the high-frequency range of impact sound and no other aspects of impact noise. It does not address impact sound below 400 Hz, such as thudding from footfalls, and additional ratings are required to describe impact sound in these frequency ranges. This classification does not replace Classification E989 (Impact Insulation Class) and is not interchangeable with it. For example, the HIIC rating of an assembly does not determine its IIC rating and cannot be used to show compliance with an IIC requirement. The expectation is that the high-frequency ratings would be reported alongside the existing ratings.

4.5 The family of ratings described use the same calculation method and differ only in the origin of the third-octave data used in the calculation. There is a high-frequency version of each existing impact rating, in which this classification is used instead of Classification E989 to calculate the single-number rating.