RT60

RT60 is the time in seconds for sound to decay by 60 decibels after the source stops. It is the single most important metric in room acoustics, defined in ISO 3382-2:2008 Annex A. A longer RT60 means more reverberation, which can enhance music but degrade speech intelligibility. Typical targets range from 0.4 s for classrooms (per ANSI S12.60) to 2.0 s or more for concert halls. RT60 is measured across octave bands from 125 Hz to 4000 Hz. The mid-frequency average (500–1000 Hz) is commonly used as a single-number descriptor. RT60 is predicted using the Sabine or Eyring equations and verified through impulse response measurements.