Reverberation time

In closed spaces (enclosures) reflections cause the sound to reverberate. The reverberation time is defined as the time that is required for the intensity of a given sound source to decay 60 dB assuming that the room was in steady-state when the sound source was turned off. There is another article in the IA Knowledge Base which deals in the term "logarithms". Basically, a logarithm is a mathematical exponent, and the notion of reverberation time dropping by 60 dB is the equivalent of the acoustic sound pressure dropping to one-millionth of its starting sound pressure (loudness) level.

The reverberation time in a diffuse sound field (where the sound energy density is equal everywhere) is independent of the physical location (is equal everywhere). In real world room spaces, the reverberation time may differ from place-to-place, but in well-behaved rooms, this variation in reverberation time varies only slightly. In coupled spaces, or curved tubes, multiple slope decays can be experienced -- so it might not be adequate to characterize the reverberation time as only a single value.

The reverberation time is dependent of the frequency; usually longer for low frequencies and shorter for high frequencies to decay by 60dB. Think about this the next time you hear the low frequencies of thunder rumbling in the distance: you mainly hear the lowest frequencies rumbling away. Some large and damped rooms may have very short or no reverberation time at very high frequencies, since the sound may be attenuated completely by the air attenuation even before reaching the listener or before reaching the reflective surfaces.