Reverberation time equations must incorporate frequency-dependent absorption coefficients

Evidence

In order to take account of the frequency variation of the absorption coefficients, we must modify the equations used to calculate the reverberation time as follows: where α( f ) = frequency-dependent absorption coefficient for the Norris-Eyring reverberation time equation and: for the Sabine reverberation time equation. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1881