Reverberation means the prolonged reflection of sound from walls, floor or roof of a hall. In simple language it is nothing but persistence of sound even after the sources of the sound has stopped.

Reverberation time: The time gap between the initial direct note and the reflected note upto a minimum audibility level is called reverberation time.

Sabine’s formula:

Prof. W.C. Sabine observed the concept of reverberation time for varieties of conditions like empty room, furnished room, small room, auditorium etc.

He concluded the following,

(a) Reverberation time depends upon reflectivity of sound form various surfaces available in side the hall. If the reflection is good, reverberation time of the hall will be longer as sound take more time to die out.

(b) Reverberation time depends upon volume of the hall.

                                     i.e. TµV

(c) Reverberation time depends upon coefficient of absorption of various surfaces present in the hall. For shorter reverberation, absorption should be more.

(d) As absorption coefficient is found to be increased with increase in frequency, reverberation time decreases with frequency.

$\therefore$ Reverberation time

$T\propto VA $

where,

$V=$ Volume of hall

$A=$ Absorption

or

$T=K\dfrac{V}{A}$

where,

$K=$ Proportionality constant

It has been further observed that is all the parameters are taken in SI then, proportionality constant is found to be 0.161.

$\therefore T= 0.161\dfrac{V}{A}$…..(1.8)

Equation (1.8) is Sabine’s formula.

Absorption A given in Equation (1.8) represents overall absorption which is given as

$A=\displaystyle\sum_{i=1}^naS=a_1S_1+a_2S_2+.....+a_nS_n$