|
Material
|
Noise Reduction Coefficient
|
| Fiberglass (2″) |
0.89
|
| Carpet (heavy foam-backed) |
0.74
|
| Concrete (coarse) |
0.36
|
| Gypsum Board (on studs) |
0.07
|
The Noise Reduction Coefficient (NRC) is an average rating of the absorptive quality of a material across mid-frequencies. Values of NRC range from zero to one. A rating of zero indicates that the material is entirely reflective, whereas a rating of one indicates that the material is entirely absorptive.
Materials exhibit different absorption characteristics at different frequencies. For instance, wallpapered plaster has an absorption coefficient of 0.03 at the 250 Hz octave band, 0.04 at the 500 Hz octave band, 0.05 at the 1000 Hz octave band, and 0.07 at the 2000 Hz octave band. To obtain the NRC, the absorption coefficients at the 250, 500, 1000, and 2000 Hz octave bands are averaged together. In our example of wallpapered plaster, the NRC would be:
NRC = (0.03 + 0.04 + 0.05 + 0.07)/4 = 0.0475
Information taken from Reference #14.