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    Michelle NCARB


    I think you're referring to STC, not SAC.  Assuming that's the case: no, they're not the same thing.

    NRC (noise reduction coefficient) is a measure of how well something absorbs sound.  STC (sound transmission class) is a measure of how well something blocks sounds from going through.  NRC is about making a room quieter, while STC is about keeping sound from going into other rooms.

    Lots of good resources for this online.  You might also check out Plumbing, Electricity, Acoustics by Norbert Lechner.  Hope this helps!

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    Katherine Long

    The SAC is different from the STC. SAC stands for Sound Absorption Coefficient. My understanding is that the NRC is based on an average of SACs on a surface.

    See link:

    "The Noise Reduction Coefficient (NRC) is a scalar representation of the amount of sound energy absorbed upon striking a particular surface. An NRC of 0 indicates perfect reflection; an NRC of 1 indicates perfect absorption. In particular, it is the average of four sound absorption coefficients of the particular surface at frequencies of 250 Hz, 500 Hz, 1000 Hz, and 2000 Hz. These frequencies encompass the fundamental frequencies and first few overtones of typical human speech, and, therefore, the NRC provides a decent and simple quantification of how well the particular surface will absorb the human voice. A more broad frequency range should be considered for applications such as music or controlling mechanical noise."

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