Equivalent sound-absorbing surface area of the room, acoustic absorption of the room (A)

Professional Definition

The equivalent sound-absorbing surface area of a room (marked with the symbol A) is a hypothetical surface of material with an absorption coefficient equal to 1 (total absorption), which would absorb the same amount of acoustic energy as the actual room with all its elements.

This value is expressed in square meters [m²]. It is calculated as the sum of the products of the area of individual materials and their sound absorption coefficients, taking into account the absorption of freestanding objects (e.g., chairs) and damping by air.

Acoustics in Simple Words

The best analogy for parameter A is an open window. If a room has an acoustic absorption A = 10 m², it behaves as if we have cut a hole in the walls with an area of 10 m², through which sound escapes outside and does not return (is not reflected). The greater the value of A, the larger the “hole” through which noise escapes, resulting in a shorter reverberation and greater tranquility inside. A small value of A means that sound is trapped inside and bounces off the walls multiple times, creating noise.

Summary

The acoustic absorption of a room (A) is a cumulative measure of how much the interior “drinks” sound. It is a key parameter used to calculate reverberation time and to design acoustic adaptations to improve speech intelligibility or reduce noise.