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
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