Reverberation absorption coefficient

Professional Definition

The reverberation sound absorption coefficient (often denoted as αs) is a value determined by the formula αs = A / S, where S is the surface area of the tested sample (in m²), and A is the equivalent sound absorption area of the tested sample (in m²).

In engineering practice, this parameter is determined in a reverberation chamber according to ISO 354 standards. The value of A is calculated based on the difference in reverberation times in the empty chamber and in the chamber with the material sample installed. Importantly, due to diffraction effects at the edges of the sample, the measured value of this coefficient may exceed the theoretical unity (1.0) in certain frequency bands, which is a physical phenomenon rather than a measurement error.

Acoustics in Simple Words

Imagine that sound is a stream of tennis balls thrown against a wall. If the wall is made of concrete, almost all the balls bounce off and come back into play—then the absorption coefficient is close to 0. However, if we cover the wall with a thick layer of soft sponge, most of the balls get stuck in it and lose energy—the coefficient approaches 1.

The best analogy for the value 1.0 is an open window. The sound that comes in through it flies out and does not return—it has been 100%