NRC评级
What is an NRC Rating?
Noise reduction coefficient, or NRC, is a rating used to measure how effective a material is at absorbing sound. NRC ratings are calculated by taking the arithmetic averages of a material’s sound absorption coefficients at 250, 500, 1000, and 2000 Hz and then rounding it to the nearest 0.05. Even though standard testing procedures will measure the absorbing efficiency at 125 Hz and 4000 Hz, those values are NOT used to calculate the NRC.
NRC is a good approximation of frequency at the middle frequencies, making it good for most situations but not all. It’s easiest to think of sound absorption coefficients and NRC ratings as percentages. If the material you’re working with has a 0.9 NRC rating, it’s roughly 90% absorptive. But again… the exact absorption will vary depending on the sound’s frequency. The higher the NRC rating, the better a material is at absorbing sound.
Another commonly used measurement in the sound world is sound transmission class, or STC, which is a measurement of how well a material or structure is at blocking sound from passing through it. These two ratings are not related, but each has its place in telling you about the sound quality in a space.
What Goes Into an NRC rating?
We’ve already talked a bit about sound absorption coefficients. To understand NRC, you have to understand the sound absorption coefficient. The coefficient describes how much sound energy that a material absorbs. Theoretically, a coefficient will vary from 0 (100% of sound is reflected) to 1.0 (perfect absorption). In practice though, labs report coefficients higher than 1.0 all the time due to the testing methods and sound diffraction. It’s normal, and not something to worry about.
Materials with coefficients of 0.50 and higher are generally classified as “sound absorbing”, while those with coefficients at or below 0.20 are “sound reflecting”. There can be a wide variety of materials in a single room, all with different coefficients. As a general rule, for a human to be able to tell a difference at all between two materials, the sound absorption coefficient must be at least 0.10 different. By the time the difference is 0.40 or greater, you
