A list of terms and definitions most commonly used when dealing with acoustics and wall surfaces can be found here.

Daily Personal Noise Exposure

LEP,d: is the average A-weighted noise exposure level for a nominal 8-hour working day, also known as LEX,8h. Used for assessing the noise exposure of a worker during a working day.

Damage Risk Criteria

Recommended maximum noise levels for given exposure periods.


Any means of dissipating vibration energy within a vibrating system. The dissipation of energy with time or distance. The term is generally applied to the attenuation of sound in a structure owing to the internal sound-dissipating properties of the structure or to the addition of sound-dissipative materials. The action of frictional or dissipative forces on a dynamic system causing the system to lose energy and reduce the amplitude of movement. Removal of echoes and reverberation by the use of sound absorbing material.

Noise Reduction Coefficient : NRC

A single-number rating system used to compare the sound-absorbing characteristics of building materials. A measurement of the acoustical absorption performance of a material, calculated by averaging its Sound Absorption coefficients at 250, 500, 1000 and 2000 Hz, expressed to the nearest multiple of 0.05.


Sound that persists in an enclosed space, as a result of repeated reflection or scattering, after the sound source has stopped.

Sound Exposure Level : SEL

The logarithmic measure of the A-weighted , Sound Pressure Level squared and integrated over a stated period of time or event, relative to a reference sound pressure value. The units are the decibel (dBA).

Sound Transmission Class : STC

is an integer rating of how well a building partition attenuates airborne sound.  It is widely used to rate interior partitions, ceilings/floors, doors, windows and exterior wall configurations.