Reverberation:

• Reverberation means the prolonged reflection of sound from walls, floor or roof of a hall.
• In simple words, it means persistence of sound even after the sources of the sound has stopped caused by multiple reflection of the sound within a closed space.

Reverberation time:

• The time gap between the initial direct note and the reflected note upto a minimum audibility level is called reverberation time.
• The interval of time taken by a sustained or continuous sound to fall to an intensity level equal to one millionth of its original value. (that is fall by 60 db in loudness) is called reverberation time.
• In a good auditorium it is necessary to keep the reverberation time as small as possible.
• When a source emits sound, the waves spread out and the listener is aware of the commencement of sound when the direct waves reach his ears. Subsequently the listener receives sound energy due to reflected waves also.
• If the note is continuously sounded, the intensity of sound at the listener’s ears gradually increases. After sometime, a balance is reached between the energy emitted per second by the source and energy lost or dissipated by walls or other materials.
• The resultant energy attains an average steady value and to the listener the intensity of sound appears to be steady and constant.
• When intensity of sound falls below the minimum audibility level, the listener will not get the sound. When a series of notes are produced in an auditorium each note will give rise to its own intensity curve with respect to time.
• In order to maintain distinctness in speech it is necessary that each separate note should give sufficient intensity of sound in every part of the auditorium and each note should die down rapidly before the maximum average intensity due to the next note is heared by the listener.

Reverberation time role in acoustics:

• Reverberation time must be maintained in such a that it does not remain too short or too large that is nearly 0.5 seconds for lecture hall, around 1.2 for concerts hall and around 2 for cinema halls.
• Proper use of absorbing materials, sufficient people as audience, presence of open windows presence of furniture etc are the major components which can decide the reverberation time.
• Calculated use of such components will be helpful to either increase or decrease the reverberation time.