- Sound produced in an enclosure does not die out immediately after the source has ceased to produce it. A sound produced in a hall undergoes multiple reflections from the walls, floor and ceiling before it becomes inaudible. A person in the hall continues to receive successive reflections of progressively diminishing intensity. This prolongation of sound before it decays to a negligible intensity is called reverberation.
- Reverberation time is defined as the time interval between the initial direct note and the reflected note up to a minimum audibility level.
- More precisely, Reverberation time is defined as the time required, in seconds, for the average sound in a room to decrease by 60 dB after a source stops generating sound.
Reverberation role in acoustics
- If a hall is to be acoustically satisfactory, it is essential that it should have the right reverberation time.
- The reverberation time should not be either too long or too short. A very short reverberation time makes a room 'dead'.
- On the other hand, a long reverberation time renders speech unintelligible. The optimum value for reverberation time depends on the purpose for which the hall is designed.
- A reverberation time of 0.5 secs is acceptable for speeches and lectures, while a reverberation time of 1 to 2 secs is satisfactory for concerts.
- In case of theatres, the optimum value varies with volume. 1.1 to 1.5 secs is suitable for small theatres, whereas for large theatres it may go up to 2.3 sees.