Room acoustics
NRC (Noise Reduction Coefficient)
A single-number rating of how much sound a material absorbs, averaged over 250 Hz to 2 kHz, from 0 (fully reflective) to 1 (fully absorptive).
NRC averages a material's absorption coefficients at 250, 500, 1000, and 2000 Hz, rounded to the nearest 0.05. A coefficient of 1.0 means all incident sound in that band is absorbed; values above 1.0 appear in tests because of edge diffraction on finite panels.
It is a quick way to compare panels for treating reflections and reverberation in the midband, where voices live. It is also easy to misuse, since it says nothing about performance below 250 Hz, where home theater rooms have their biggest problems.
A 2 inch mineral wool panel scores about 0.95 to 1.0, heavy drapes about 0.5, and bare drywall roughly 0.05. For bass, read the full absorption table rather than the NRC number.
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