Reverberation

Reverberation is the collection of reflected sounds from the surfaces in an enclosure like an auditorium. It is a desirable property of auditoriums to the extent that it helps to overcome the inverse square law dropoff of sound intensity in the enclosure. However, if it is excessive, it makes the sounds run together with loss of articulation - the sound becomes muddy, garbled. To quantitatively characterize the reverberation, the paramater called the reverberation time is used.

Reverberant sound is the collection of all the reflected sounds in an auditorium.

Reverberant Sound Field

The sketch below depicts the sound received by a single listener as a function of time as a result of a sharp sound pulse some distance away. The direct sound received is followed by distinct reflected sounds and then a collection of many reflected sounds which blend and overlap into what is called reverberation. The delay between the direct sound and the first reflected sound is a significant characteristic for an auditorium, though not as important as the overall reverberation time.

Reverberant Sound Decay

	Whether from a sound impulse or a steady sound which ceases, the reverberant sound in an auditorium decays in an approximately exponential fashion.
Sample measurements show a straight line decrease of the decibel level, which permits determination of the reverberation time.

Sound Decay Measurements

Measurements of sound decay in a classroom (Jesse, see ref) showed that the sound intensity in decibels dropped off linearly with time. Since decibels are a logarithmic quantity, this implies an exponential decay of the sound. These plots can be extrapolated to give reverberation times for the room, which amount to about 0.5 s for the empty room and about 0.4 s for the occupied room.