What Is NRC? (Noise Reduction Coefficient)
Advanced Acoustics Admin
We receive numerous emails asking to explain the abbreviation "NRC" so we thought we'd ad an article to our site to help explain it.
'NRC '(Noise Reduction Coefficient) is a number that rates the capability of a material at absorbing sound (absorbing energy). Why would you want to absorb energy?
In an environment where you have reflective surfaces (hard floors, bare walls, long desks, bare ceilings) the sound emitting from a source can reflect and grow in size causing reverberations.
I am not saying that all reverb is bad. For example, a choir singing hymns within a large church takes advantage of this natural reverb and they really complement each other. However, you would not want the same reflections or reverb times in a lecture hall or large office space. It can disrupt conversations between colleagues, lower productivity and learning. This is why we need to place materials around the environment to help absorb some of this energy.
The Noise Reduction Coefficient is calculated by averaging how absorptive a material is at four different frequencies: 250hz, 500hz, 1000hz, and 2000hz. (The lower frequencies are harder to absorb because the wavelengths are so long). The 250 to 2000hz is an average mid-range speech frequency. This implicates that using the NRC value for a product to absorb music (full frequency range) is pointless.
After each material is tested, it is given an NRC rating. This can range from 0 to 1.00. Ratings are rounded to the nearest .05 These values can exceed 1.00 when thick materials or materials with large air spaces are being tested. Also, a test material’s area does not include the sides of the panel, which are exposed to the test chamber. Depending on the thickness of this, NRC results can vary.
However, because the official NRC is an average, two materials with the exact same NRC can perform differently in different circumstances - E.g. Each may absorb better at different frequency levels, but may work differently in alternate environments.
SAA (Sound Absorption Average) is a newer, more precise test method of an NRC. Whereas NRC ratings are rounded to the nearest .05, SAA is rounded to the nearest .001.
NRC should not be confused with STC (Sound Transmission Class). The key difference between NRC and STC is that NRC is used to rate materials that ABSORB sound, while STC is used to rate materials that BLOCK sound.