RT60

The time it takes for sound to decay by 60 decibels after the source stops.

RT60 (Reverberation Time 60) is the standard metric for measuring how long sound persists in a room after the source stops. Specifically, it measures the time required for sound pressure level to decrease by 60 dB.

This measurement is fundamental to understanding room acoustics because it directly affects speech intelligibility, music clarity, and overall acoustic comfort. A room with a long RT60 sounds "reverberant" or "live," while a short RT60 creates a "dead" or "dry" acoustic environment.

RT60 varies with frequency. Low frequencies typically decay more slowly than high frequencies in untreated rooms. Professional acoustic analysis measures RT60 across multiple frequency bands (typically 125 Hz to 4 kHz) to fully characterize a space.

RT60 is central to room decay, but it isn't a complete diagnosis on its own — especially in small rooms. In studios and critical listening spaces, pair it with frequency response, waterfall/decay plots, and early-reflection timing. The target values below are starting ranges for planning, not fixed standards — actual practice varies by room use and material choices. Field measurements under ISO 3382 often use T20 or T30 (extrapolated decay ranges) rather than a literal 60 dB decay, depending on the room's noise floor.

Formula

RT60 = 0.161 × V / A

V = Room Volume (m³)
A = Total Absorption (Sabins (m²))
0.161 = Constant (seconds/meter)

Practical Example

For a 50 m³ room with 11 Sabins of absorption

RT60 = 0.161 × 50 / 11 = 0.73 seconds

This is too reverberant for mixing (target 0.3-0.4s). Adding absorption panels would reduce RT60.

Standards: ISO 3382-1:2009, ISO 3382-2:2008

Glossary · Diffuser Designer

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