Impact insulation class (or IIC) is an
integer
An integer is the number zero (), a positive natural number (, , , etc.) or a negative integer with a minus sign ( −1, −2, −3, etc.). The negative numbers are the additive inverses of the corresponding positive numbers. In the language ...
-number rating of how well a building floor attenuates impact sounds, such as footsteps. A larger number means more attenuation. The scale, like the
decibel scale for sound, is
logarithm
In mathematics, the logarithm is the inverse function to exponentiation. That means the logarithm of a number to the base is the exponent to which must be raised, to produce . For example, since , the ''logarithm base'' 10 of ...
ic. The IIC is derived from
ASTM
ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, a ...
method E989, which in turn uses a
tapping machine A tapping machine is a device used to test the impact sound insulation of floors, for measurements of impact noise (noise of footsteps) in the field of building acoustics.
The standard tapping machineISO 16283-2:2015(E) Acoustics — Field measure ...
specified in ASTM method E492.
The IIC number is derived from sound attenuation values tested at sixteen standard frequencies from 100 to 3150
Hz. "Real world" footstep noise is also generated at frequencies below 100 Hz, so the IIC value may not accurately describe the complete noise attenuation profile of a floor.
[Described in California Building Code, Section 1207.9, ''Sound Transmission: Tested Assemblies''.]
References
{{reflist, 1
Sound measurements