reverberationtime

Reverberation time, denoted T60, is the time required for the sound pressure level in a space to decay by 60 decibels after the sound source has stopped. It is a key measure of how reverberant or “live” a room sounds and depends on room geometry, surface materials, occupancy, and air properties. In practice, RT60 varies with frequency, and is often specified for octave or fractional-octave bands.

In the Sabine model for a diffuse sound field, T60 is approximately 0.161 times the room volume V (in cubic meters) divided by the total absorption A (in sabins): T60 ≈ 0.161 V / A. Absorption A is the sum over all surfaces of their area S_i multiplied by their absorption coefficient α_i (A = ∑ α_i S_i). If the field is not diffuse or low-frequency behavior dominates, alternative formulas such as Eyring’s may be more accurate.

Measurement typically uses an impulse or a swept sine/MLS signal to generate an impulse response. The decay portion is analyzed (often by Schroeder integration) to extract T60 for one or more frequency bands. Standards such as ISO 3382 describe procedures for room acoustics measurements.

Typical RT60 values vary widely by space type and frequency. Small rooms may be around 0.3–0.6 s, offices about 0.4–0.6 s, lecture halls around 0.8–1.2 s, and concert halls commonly in the 1.8–2.2 s range. RT60 is a fundamental parameter in acoustical design and is influenced by material choices, absorbers, diffusers, and room use.