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Acoustic Underlay and Sound Transmission Classes
Floating floors tend to sound different. A little louder and sometimes more hollow sounding, especially when you walk on them with hard sole shoes. An acoustic underlay can make the sound more like a glued or nailed floor, while providing additional benefits.
There are two widely accepted tests for sound that travels: Impact Insulation Class (IIC) and Sound Transmission Class (STC).
STC is a measurement that indicates how much noise is absorbed, and therefore stopped, by the wall or floor. This generally applies to airborne noise within a room. IIC is a measurement that indicates how much impact noise is stopped in the floor or ceiling, reducing the noise traveling from one level to another.
If you live in a condo, the IIC rating is important because many associations have minimum IIC ratings for floors. The minimum rating for IIC is usually 50. The higher the rating, the better the sound absorption.
Acoustic underlayment with a high STC and IIC rating can make a dramatic difference in the sounds that your floor makes. Additionally, most premium/acoustic underlayments help smooth out minor imperfections in the subfloor better than the entry level varieties.
