Reverberation time

Reverberation time is the time for a broad spectrum sound (a clap) to drop by 60 decibels in an enclosure (to reduce in energy by a factor of 10⁶). A drop of sixty decibels is chosen because 100 dB is the maximum desirable sound level for a full orchestra and choir and 40 dB is the sound level in a normally quiet room.

Reverberation times are ...

... long in cathedrals - up to 10 seconds in places like Notra Dame Cathedral in Paris (8.5 s), aircraft hangers, and Hagia Sophia in Istanbul.

... shorter in school rooms - around one second in lecture theaters and large, hard walled, high ceilinged classrooms. Hanging a dozen 1x2 meter panels covered with egg cartons 20 cm below the ceiling reduced the reverberation time by a factor of 5 in the editor's NZ classroom in the 1980's. The room felt 'dead'. It was difficult to lecture without echo, but the room was more 'student-friendly'.

... very short in elementary classrooms (~0.6 s), and recording studios (~0.4 s).

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