Methodology & sources
Every number this site produces comes from a published formula and sourced data. Here is exactly what we use, so you can check our work.
Reverberation time (RT60)
Sabine (1900): RT60 = 0.161 · V / A, where V is room volume (m³) and A is total absorption in metric sabins (Σ area × absorption coefficient). The constant 0.161 follows from the speed of sound at 20 °C.
Eyring–Norris: RT60 = 0.161 · V / ( −S · ln(1 − ᾱ) ), where S is total surface area and ᾱ = A / S is the mean absorption coefficient. We recommend Eyring when ᾱ ≳ 0.2 (treated rooms), where Sabine over-predicts.
We do not currently add an air-absorption (4mV) term; its effect is small in small rooms below 2 kHz.
Room modes
Rigid-wall modal frequencies of a rectangular room (Rayleigh):
f(p,q,r) = (c / 2) · √[ (p/L)² + (q/W)² + (r/H)² ]
with c = 343 m/s, and L, W, H the room dimensions. A mode is axial when one of p, q, r is non-zero, tangential when two are, and oblique when all three are. Axial modes are strongest. We compute indices up to 4 and report modes below your chosen cut-off.
Room ratio rating
We normalise your dimensions to height = 1 and compare against published "preferred" small-room ratios (Sepmeyer, Louden, and a mid-point of the Bolt area). The rating reflects how close your ratio is to the nearest preferred set — a proxy for how evenly the low-frequency modes are spread.
Panel coverage
We compute wall + ceiling area, apply the coverage range recommended for your use-case (e.g. 30–40% for critical listening), reserve four floor-to-ceiling corner bass traps, and convert the remaining target area into a panel count for your panel size. These are planning estimates; verify the result with the RT60 calculator.
Absorption data
Coefficients are random-incidence octave-band values measured per ISO 354 / ASTM C423, compiled from the references below and from manufacturer datasheets. NRC is the average of the 250/500/1000/2000 Hz coefficients, rounded to the nearest 0.05. Browse or download the full dataset (CC BY 4.0).
- Cox, T. J. & D'Antonio, P. — Acoustic Absorbers and Diffusers (CRC Press).
- Vorländer, M. — Auralization (Springer).
- Bies, D. & Hansen, C. — Engineering Noise Control.
- Owens Corning 700-series and mineral-wool manufacturer datasheets.
- Standard ISO 354 / ASTM C423 coefficient tables.