In reverberation sound produced in an enclosure continues to be heard for some time. A sound produced in a room undergoes multiple reflections from the walls, the floor and the ceiling before becoming inaudible. The prolongation of sound in an enclosed place even when the sound source has stopped is called reverberation.

The time taken by the sound to fall from its average intensity to inaudibility is called the reverberation time. It is also defined as time during which the sound intensity falls from its steady state value to its one-millionth value after the source is shut off

∴ $I/I_0 = 10^{(-6)}$

And from equation it, is found as ,

L = -60 dB

Thus during reverberation time the intensity level drops by 60 dB.