ABCs of Noise Control Materials
Sound absorbers are soft, porous, open-celled materials such as foam sheets or fiberglass blankets and baffles that reduce the reflection of sound waves. Their sound absorption efficiency is rated by an “NRC” number – Noice Reduction Coefficient*. The HIGHER the NRC rating, the more EFFICIENT the product is at absorbing noise.
*NRC is a sound absorption rating. Noise control materials measure a percentage of how much sound will not be reflected back from where it came. Based on a range from .05 to 1.0, where an NRC of 1.0 means that all the sound energy that hits that product passes through it and does not “bounce” back to its source. An NRC of .60 would reflect 40% of the sound back to the source and let 60% of the noise pass through it.
Noise Barriers combine mass, flexibility, and limpness to block noise from transmitting from one area to another. Flexible mass-loaded vinyl sheeting has replaced thin lead sheets as the noise barrier of choice. Noise Barriers are rated by an “STC” number – Sound Transmission Classification. The HIGHER the STC rating**, the more EFFICIENT the product is at blocking noise.
**STC Sound Transmission Class: Single-number rating of airborne sound insulation of a partition, derived by fitting a reference rating curve to the sound transmission loss values measured for the 16 contiguous 1/3 octave frequency bands with nominal mid-band frequencies of 125 Hz to 4000 Hz inclusive, by a standard method. The standard method typically used is ASTM Standard E90. This test is valid for single homogenous layers, multiple layers, or complete assemblies. A higher STC rating typically represents a better ability to stop the noise, frequency notwithstanding.
Noise control materials are products that combine both Noise Barrier & Sound Absorber materials. Typically, they offer the most significant overall noise reduction. Acoustical Composites are rated in both “NRC”* and “STC”** numbers. Sound Seal uses composite materials such as Panels, Acoustical pipe & duct Lagging, or Acoustical Curtain Systems.