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Soundproofing Floors

Acoustic Reference Guide

Sound is classified into two basic types:

Airborne Noise – talking, music, TV

Structure-Borne Noise – impact floor noise commonly referred to as footfall noise, dragging furniture, dog walking, etc

acoustics-guideSTC (Sound Transmission Class)

A value for evaluating the performance of interior walls and the floor/ceiling assembly to stop or insulate airborne

The higher the STC number the better the ability of the assembly to block airborne noise

Weight & mass play a major factor in the overall STC rating, the heavier the structure the higher the STC ratings will be.




IIC (Impact Isolation Class)

A value for evaluating the performance of the floor/ceiling assembly from structure borne noise

Floor underlayments in general are lightweight and designed specifically for impact isolation (IIC)

The higher the number the better the performance

Weight & mass helps with low frequency performance and will help the IIC performance of an underlayment

Note: The Δ IIC is a new ASTM test that measures the improvement in decibels.Example a Δ IIC 21 would mean a 21 point improvement . The IIC tests is only tested on a 6″ concrete slab with no ceiling below.


Typical STC & IIC Ratings of untreated floor / ceiling assemblies

Underlayment Product Selector


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