Sabine’s equation is a hundred years old and still the fastest gut-check we have

Wallace Sabine derived his reverberation-time formula at Harvard at the turn of the twentieth century, by moving organ pipes and a stopwatch between lecture halls until the pattern in his numbers stopped looking like noise. The formula that came out of it — reverberation time proportional to room volume, divided by total absorption — still gets used on the first day of nearly every project we take on.

It is not the most accurate model available. It assumes a diffuse sound field and an even distribution of absorption, both of which are approximations in any real room. But it is fast, it requires nothing more than a floor plan and a materials list, and it is accurate enough to tell you, on day one, whether a room is going to be a ten-minute fix or a six-month problem.

We still reach for the full octave-band version of Sabine’s formula, sometimes the Eyring variant for rooms with lots of absorption, on every commissioned project. The version running in the browser on our homepage is the same equation, single-band, doing the same first-pass job it did in 1900.