Reverberation time is defined as a 60-decibel energy decay

Evidence

W. C. Sabine, the acoustician, has defined reverberation time technically. It is the time that elapses from the instant a sound source is switched off until its energy decays to one millionth of its original strength (a drop of 60 decibels). As far as the ear is concerned, it is the time it takes for a sound to melt and be lost in the ambient noise. Echo differs from reverberation in that it is a repetition or partial repetition of a sound, due to reflection off a distant surface. Reverberation is also reflected sound but no separate repetitions of the original are distinguishable. — Schafer, Murray R, The Soundscape- Our Sonic Environment…, 446

It would be better to call a soundboard reverberant, and to characterize it in the way we will characterize concert halls, by the reverberation time, T60, which is the time it takes sound or vibration energy to decay by 60 dB. — Eric J. Heller, Why You Hear What You Hear- An…, 1176

Equation A4.8 gives a relationship between the ratio of sound energy decay and the time it takes and so can be used to calculate this time. There is an infinite number of possible ratios that could be used. However, the most commonly used ratio is that which corresponds to a decrease in sound energy of 60 dB, or 106. When this ratio is substituted into Equation A4.8, we get an equation for the 60 dB reverberation time, known as T60, which is: where T60 = the 60 dB reverberation time (in s) Thus the reverberation time is given by: where T60 = the 60 dB reverberation time (in s) Equation A4. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2834

Categorization

• DEFINE: Technical definitions of reverberation time and its distinction from echo.
• corroborated: 5 independent passages support this claim — Schafer, Murray R, The Soundscape- Our Sonic Environment…, 446; Eric J. Heller, Why You Hear What You Hear- An…, 1176; David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2834
• XREF: connects to: Sabine experimentally verified exponential sound decay in a reverberant room; A single slope measurement of dB decay directly yields the reverberation time; Recommendable reverberation times range from 2 seconds down to 0.35 seconds by room type (+4 more)