Sabineformelen

Sabineformelen, or the Sabine formula, is a cornerstone of room acoustics. It relates the reverberation time of a closed space to its size and to how its surfaces absorb sound. In SI units, the standard form for the RT60 is T = 0.161 V / A, where T is the reverberation time in seconds, V is the room volume in cubic metres, and A is the total absorption in sabins.

Total absorption A is the sum over all surfaces: A = Σ S_i α_i, with S_i the surface area in square metres and α_i the average absorption coefficient of that surface over the relevant frequency range. Absorption coefficients range from near 0 for highly reflective surfaces to near 1 for very absorptive ones.

The formula assumes a diffuse sound field, uniform absorption, and that air absorption is negligible at the considered frequencies. It is most reliable for mid frequencies (roughly 500 Hz to 2 kHz) in rooms that are not too small or irregular. In highly absorbing spaces or at extreme conditions, alternative models may be preferred.

Historically, it was introduced by Wallace C. Sabine around the turn of the 20th century and first quantified the relation between architecture and acoustics in concert halls. It remains widely used by architects and acousticians to estimate and adjust reverberation time during design, often by adding or removing absorptive materials such as panels, curtains, or upholstery.

Variations exist, notably the Eyring formula, which can yield better estimates in highly absorptive rooms. The Sabine formula provides a transparent, first-order link between room geometry, surface treatment, and acoustic decay.