RT60 Sabine

Reverberation time (RT60) — Sabine formula

Sabine's equation estimates how long sound takes to fall off by 60 dB: RT60 = 0.161 · V / A, with V the room volume in m³ and A the total absorption in sabins (each surface area multiplied by its absorption coefficient α, all summed). Run a 100 m³ room with 25 sabins of absorption through it and you land near RT60 ≈ 0.64 s. What you aim for depends on the space. Cathedrals > 2 s give you that lush choral wash; living rooms ~0.5 s keep speech comfortable; recording studios < 0.3 s stay dry and neutral. Wallace Sabine worked the equation out around 1900 while wrestling with the Fogg Lecture Hall at Harvard, and in doing so launched modern architectural acoustics.

Applications

Acoustic design for churches, theatres and concert halls. Tuning home studios with bass traps, panels and diffusers. Meeting NR-15 (the Brazilian occupational noise rule) and NBR 10152 in classrooms, hospitals and offices. And predicting speech intelligibility (STI) and music clarity (C80) before a single brick is laid.

FAQ

When does Sabine break down? It leans on a diffuse field and α < 0.3. Once a room gets very absorbent, switch to Eyring or Norris-Eyring.

Does RT60 depend on frequency? It does, because α shifts with frequency. Measure RT60 at 125, 250, 500, 1k, 2k, 4k Hz if you want the full picture.

How do I measure RT60 in practice? Grab the free REW (Room EQ Wizard) software, a calibrated mic, and an impulse response from a balloon pop or a swept sine.