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Sound transmission ratings are closely aligned with fire
endurance ratings for assemblies. This is because flame
penetration and sound penetration follow similar paths of
least resistance.
Sound striking a wall or ceiling surface is transmitted
through the air in the wall or ceiling cavity. It then strikes the
opposite wall surface, causing it to vibrate and transmit the
sound into the adjoining room. Sound also is transmitted
through any openings going into the room, such as air ducts,
electrical outlets, window openings, and doors. This is
airborne sound transmission.
The Sound Transmission Class (STC) method of rating
airborne sounds evaluates the comfortability of a particular
living space. The higher the STC, the better the airborne
noise control performance of the structure. An STC of 50 or
above is generally considered a good airborne noise control
rating. The following table describes the privacy from each
STC rating:
| STC Rating |
Privacy Afforded |
|
25
30
35
40
45
50
55
|
Normal speech easily understood
Normal speech audible but not intelligible
Loud speech audible and fairly understandable
Loud speech barely audible but not intelligible
Loud speech barely audible
Shouting barely audible
Shouting not audible
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