Define Noise Reduction Coefficient
Used as a way of comparing the sound absorbing characteristics between materials, the Noise Reduction Coefficient (NRC) is an average of the four absorption coefficients spread across a large spectrum of sound waves. A noise reduction coefficient would represent a perfect reflection of sound, while an NRC of 1 would represent a 100% absorption of sound into a material.
Simply put, the noise reduction coefficient is a value given to sound absorbing products between 0 and 1. The higher the number (closer to 1) the better that material is at absorbing sound. For those building a recording studio, or engineering an auditorium, acoustic foam panels with a high NRC are best.
When To Use The Noise Reduction Coefficient
A common misconception is that the noise reduction coefficient determines how well a product or material will soundproof a room. There is a big difference between sound blocking and sound absorption. A material with a high NRC will not necessarily block sound better than a material with a low noise reduction coefficient. In fact, quite the opposite. The best sound blocking materials are heavy and dense, while the best sound dampening products are thick and airy. Products like acoustical foam are lightweight and uncompressed allowing the sound waves to get trapped inside.
In practice, sound blocking products are used to eliminate the transmission of sound from one room to another. For example, you have neighbor who’s dog barks all night long. You want to block that sound from entering your room. Putting products on the wall with a high NRC will not give you peace and quiet. However if you are building a small home vocal studio and are having trouble with echos in the booth, covering the walls with sound dampening foam will improve the quality of sound in the room.
Comparing Noise Reduction Coefficient Values
The noise reduction coefficient offers consumers a way of comparing different sound dampening products. A rough guide to judging which sound dampening materials are best is by determining how much sound control you need. As a rule of thumb, a product with an NRC of .5 will absorb about 50% of the sound that hits it, one with a value of .62 will absorb 62% of sound. Most professional quality sound dampening foam will have an NRC rating between .7 and .85. Higher end professional sound panels can have a noise reduction coefficient as high as 1, representing a 100% absorption of sound.
If you are interested in temporary sound dampening for a mobile studio or event, acoustical blankets can offer an NRC rating of over .5. Acoustical blankets are great for speaking engagements in open rooms where the existing noise reduction coefficient is not substantial enough to absorb the echos.