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 The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a po ...

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 o ...

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, an ...

method E989, which in turn uses a tapping machine 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