Noise reduction coefficient

The noise reduction coefficient (commonly abbreviated NRC) is a single-number rating intended to describe the average sound absorption performance of a material, derived from reverberation-room measurements. In common usage it is reported on a scale from 0.0 (very low absorption) to 1.0 (very high absorption), though values greater than 1.0 can occur in reverberation-room testing due to measurement effects such as edge diffraction and non-ideal diffuse-field conditions rather than “more than 100%” absorption.

NRC should not be confused with the sound transmission class (STC), a single-number rating derived from laboratory measurements of airborne sound transmission loss through building elements (for example walls, doors and windows). In general terms, STC relates to sound transmission loss through a construction element, while NRC relates to sound absorbed within a room by surfaces and treatments, such as to dampen echos and reverberations.