Reverberation is the sound that persists in an enclosed space due to multiple reflections, even after the source of the sound has stopped.
Reverberation is the sound that persists in an enclosed space due to multiple reflections, even after the source of the sound has stopped.
The reverberation time is defined as the time it takes for the sound level to decay by 60dB after a sound source has been switched off.
Rooms with small amounts of absorbing materials will have longer reverberation times than rooms with more absorbers.
For normal rooms, with reasonable amounts of absorbers, the reverberation time is approximately given by:
T = 0.16 V / T
in which T is the reverberation time in seconds; V is the room volume; A is the absorption of the room and finally 0.16 is an empirical constant determined by Wallace C. Sabine and published in 1898.
This model cannot be used in rooms with excessive amounts of absorbers, such as anechoic chambers.
To measure the reverberation time you will need a sound source and instrumentation able to capture the sound decay.
You have two options with respect to the sound source; impulse excitation or noise excitation. It is important that the noise is broadbanded enough to cover the entire frequency range of interest.
Although the reverberation time is defined as the time it takes for the sound to decay 60dB, this is seldom possible to measure due to the unavoidable background noise. The reverberation time is therefore normally based on the decay rate for a range of 20 or 30 dB starting 5dB below the stationary level. The value is afterwards extrapolated to 60dB assuming that the part of the decay that we used is representative for the entire decay. It is common practise to specify the range used as T20, T30, etc., all having the same numeric value if the decay is linear.