Sound control effectiveness is measured by Sound Transmission Class. Sound Transmission Class (STC) is a measurement used to reat the resistance of a wall, ceiling, or floor to the passage of sound. The higher the STC number, the more sound is deadened. Each STC reduces sound energy by one decible. The table below gives examples of STC ratings that have been measured in a laboratory with perfect installation. Every increase of 10 STC reduces the sound intensity by 1/2.
Cellulose insulation is much higher in laboratory tests than standard insulation is (shown chart above). More importantly, cellulose holds its STC rating infield useage and testing. In comparision, fiberglass' rating is destroyed by the same imperfections that cut its R-value by as much as 1/2. This is the result of installation imperfections inherent in fiberglass compression, gaps and voids, inset stapling, air movement, etc. Fiberglass only performs about 1/2 as well as cellulose, if that much.
Because of this short-circuiting of fiberglass, Happy Home Insulation is called out to about 5 to 10 buildings a year that have noise problems- you guessed it, they had fiberglass in the walls.
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