Reverberation
The persistence of sound in an enclosed space caused by multiple continuous reflections from room boundaries after the original source stops.
Governing formula
RT60 = 0.161 V / A (Sabine's Formula)
SI unit
s
In depth
Reverberation time (RT60) is the time required for sound intensity to decay by 60 dB. Concert halls optimize RT60 to ~1.5 - 2.0 seconds for warm musical acoustics.
Examples in the real world
Echos lingering in large stone cathedrals vs short reverberation in carpeted living rooms.