NRC, CAC and STC and the ABC's of wall and ceiling sound isolation and acoustics

What's the difference between NRC, CAC and STC and what are the ABC's of acoustics? Armstrong Building Products' Acoustics Expert, Dr. Ken Roy, explains...

You have read it in all the books and seen it on all the sound related forums. Let the good doctor say it out loud so it makes sense.

STC rating is the much ballyhooed acronym for sound transmission class that sticks to you like jelly for the first 6 or 9 months. Then it becomes to you what it was to the experts all along. Another piece of the puzzle. It is used as reference for walls, but each of us has used this as a measurement for any panel, wall, ceiling and floors. It works, so we use it.

NRC or noise reduction coefficient is a tad different. This is the measure that a material has to absorb sound. How good it does is rated with a NRC rating. 1.0 is about as good as an NRC can get.

CAC, or ceiling attenuation class, is the measurement for the performance of a ceiling. Obviously, if you were paying attention, the higher a CAC rating, the better.

That leaves us with the ABC's. Right. Well, it may not be a direct requirement for recording studio construction diy'ers but it never hurts to be able to pop it into conversation at the grand opening of the local Piggly-Wiggly. Never know who is paying attention these days.

A=absorb
B=blocking
C=covering sound

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