Absorption Coefficient

The absorption coefficient (α) is the fraction of incident sound energy absorbed by a surface, ranging from 0 (perfect reflection) to 1 (perfect absorption). Measured according to ISO 354:2003 in a reverberant chamber, it is reported per octave band from 125 Hz to 4000 Hz. Random-incidence absorption coefficients can occasionally exceed 1.0 due to edge diffraction effects in the test specimen, which is physically valid for the test method. The absorption coefficient is the primary input for reverberation time calculations using the Sabine or Eyring equations. Different mounting conditions (A, E, D per ISO 354) significantly affect measured values, particularly at low frequencies. Designers must match the mounting condition in the data sheet to the intended installation method.