RT60 Decay (Sabine) for Music

Reverberation time RT60 (Sabine): formula and example

RT60 is how long a sound takes (in seconds) to fall 60 dB once the source goes quiet. Sabine wrote it as RT60 = 0.161 · V / A, with V the room volume in m³ and A the total absorption in sabines (add up each surface area times its absorption coefficient). Run a 100 m³ room with 25 sabines through it and you get RT60 ≈ 0.644 s. Where do you usually want to land? A pop recording studio sits below 0.3 s, a classical concert hall around 1.8-2.2 s, and big churches drift out to 3-4 s.

Applications

Acoustic designers lean on RT60 when they size absorbers, diffusers and bass traps for home studios, listening rooms and concert halls. Bach famously wrote with the long reverb of Lutheran churches in mind, and modern halls like Sala São Paulo (RT60 ~1.8 s, adjustable) earn praise for their classical balance. A home theater aims for roughly 0.3-0.4 s so dialogue stays clear, while clubs and karaoke rooms nudge RT60 in a direction that flatters vocals.

FAQ

Is Sabine accurate for very absorbent rooms? Not really. Once a room gets very absorptive (mean coefficient > 0.2), reach for the Eyring or Millington formulas instead.

Why 0.161? The number falls out of the speed of sound (~343 m/s) plus constants that W. C. Sabine pinned down in his Harvard experiments around 1900.

Does RT60 vary by frequency? It does. Bass tends to hang around longer, which is why serious acoustic reports break RT60 out per octave band, from 125 Hz up to 8 kHz.

What's "good" RT60 for vocals? It depends what they're doing. Spoken word wants 0.3-0.5 s, choral music likes 1.5-2.0 s, and opera lands near 1.4 s.