Strutt|Building Acoustics|Alpha from RT back-calculates the average room absorption coefficient `bar alpha` from the reverberation time in the room, using either the Sabine or Eyring formulae.
Using the Sabine formula, the average absorption is calculated as follows:
`bar alpha = (55.3 V)/(c T S) - (4mV)/S`
where:
`V` is the room volume (m³)
`c` is the speed of sound (m/s). When using 343 m/s the constant term `55/c` reduces to the more-familiar 0.161
`T` is the reverberation time (s)
`m` is the air absorption coefficient
Using the Eyring formula, the average absorption is calculated as follows:
`bar alpha = 1-e^((55.3 V)/(c T S)) - (4mV)/S`