Absorption Area

Absorption area (A) is the total equivalent absorption in a room, measured in square metres of perfect absorption (metric sabins). It is calculated by summing the product of each surface’s area and its absorption coefficient: A = Σ(S_i × α_i). Additional absorption from furniture, occupants, and air absorption at high frequencies is added to the surface contributions. The absorption area is the denominator in the Sabine equation (RT60 = 0.161V/A) and directly determines the reverberation time. Doubling the absorption area halves the reverberation time. Per-person absorption values are typically 0.4–0.6 m² (seated audience). Air absorption at 4000 Hz adds approximately 0.01 m² per cubic metre of air at standard conditions. Absorption area is the primary design variable in room acoustics: specifying acoustic treatment involves determining how much additional absorption area is needed per frequency band to achieve target reverberation times.