It is desirable that the reverberation time in a sutdio or sound control room should be reasonably constant when measured in the 1/3 octave frequency bands of the audio frequency range.(reverberation time is usually measured over the range 50 to 10 000 hz.)measurements of reverberation time in such areas often show a ‘bass rise’ with reverberation time increasing at low frequencies. An example of this is shown in fig.1