RT60

RT60, or reverberation time, is the time required for the sound pressure level in a room to decay by 60 decibels after the source stops emitting. It is frequency dependent and is commonly reported for standard octave or third-octave bands to reflect how quickly different frequencies die away.

Measurement of RT60 involves exciting the space with an impulse or noise, recording the room’s impulse response, and analyzing the decay of the reverberant sound. Techniques such as Schroeder integration or decay-slope analysis are used to estimate the time it takes for the response to drop by 60 dB. Measurements are typically made at key listening positions and in a diffuse portion of the room, following established standards.

The Sabine equation provides a widely used estimate of RT60 in a diffuse, evenly absorbing room: RT60 = 0.161 V / A, where V is the room volume in cubic meters and A is the total absorption in sabins (A = sum of absorption coefficients α_i times surface areas S_i). For rooms with higher absorption or non-ideal diffusion, the Eyring form can be more accurate: RT60 ≈ -0.161 V / [S ln(1 − ᾱ)], where ᾱ is the average absorption coefficient.

Typical RT60 values vary with room type: small, acoustically controlled spaces may have RT60s around 0.3–0.6 s, while concert halls may range from about 1.8 to 2.5 s or more depending on design and frequency. RT60 is frequency dependent and is not a single universal parameter; it is used alongside other metrics to characterize room acoustics.

Standards such as ISO 3382 and IEC 60268-16 govern measurement procedures and reporting in professional acoustics.