Sound produced in auditorium or any big hall persists for sometime due to multiple reflection from the wall and ceiling. This phenomenon is termed as reverberation.
One can keep hearing the sound till the sound reaches inaudible level.
Many times we hear thunder sound from clouds persisting for sometime due to multiple reflection at various layer inside clouds. Also in big halls or auditorium or theaters, we use sound absorbing material in walls, roofs, seats to reduce reverberation in hall.
Reverberation time is obtained by Sabine's Formula, i.e
t = 0.161V / Σ as
where, V = Volume of hall
a = absorption coefficient for various objects in auditorium
s = Surface Area of various objects on which the sound waves fall
