C-32 · ACOUSTICS · ROOMS
Room acoustics
Draw the room, put in its windows, doors, furniture and finishes, and see how long it rings: reverberation time in every octave band by four formulas, against the target for what the room is for, with its modes and the absorption it needs.
Changing a wall's length stretches the room on that side. Split a wall to add a corner, then drag it on the plan.
A panel, rug or curtain covers part of a surface: its area takes the place of the surface under it.
Furniture marked ≈ has no measured data of its own: it uses the nearest published material, named in the absorption table.
Enter a product's measured absorption coefficients (from its data sheet, ISO 354) to use it anywhere in the room.
Tm = 0.25·(V/100 m³)^⅓ = 0.20 s, within ±0.05 s from 200 Hz to 4 kHz.
What this room shows
- Reverberation time 0.81 s at 500–1000 Hz (Eyring), 0.86 s by Sabine.
- Too reverberant for Listening room, home cinema (ITU-R BS.1116) in the 250, 500, 1000, 2000, 4000 Hz bands.
- Fitzroy differs from Eyring by up to 29 %: the absorption sits mostly on some surfaces, so the parallel bare ones will decay more slowly (flutter echo risk).
- Below about 260 Hz (Schroeder frequency) the room behaves as separate modes, not as a reverberant field: look at the mode list there.
- Mode spacing meets Bonello's criterion up to 300 Hz.
- 29.0 m² of Glass wool 50 mm, on the wall brings the 500–1000 Hz time to 0.20 s.
| What | Published | This calculator | |
|---|---|---|---|
| Room 7 × 5 × 3 m, first six modes (Long 2014, Table 8.1) | 24.6 · 34.5 · 42.4 · 49.2 · 57.4 · 60.1 Hz | 24.6 · 34.4 · 42.3 · 49.1 · 57.3 · 60.0 Hz | agrees |
| Same room, modal density at 1 kHz (Long 2014, §8.3) | 34 /Hz | 34.3 /Hz | agrees |
| Air absorption, 20 °C, 50 % RH, 1 kHz (ISO 9613-1, as tabled by Piercy & Daigle 1998) | 4.7 dB/km | 4.66 dB/km | agrees |
| Air absorption, 30 °C, 50 % RH, 4 kHz (same table) | 25 dB/km | 24.6 dB/km | agrees |
| Uniform absorption: Fitzroy and Arau-Puchades equal Eyring (identity) | equal | equal | agrees |
| Small absorption: Eyring tends to Sabine (Long 2014, eq. 8.62) | ln(1 − ᾱ) ≈ −ᾱ | within 0.5 % at ᾱ = 0.01 | agrees |
- Statistical room acoustics: right for ordinary rooms above the Schroeder frequency. Concert halls, coupled spaces and strongly uneven rooms need a ray-tracing or wave model.
- Sound fields, early reflections and low-frequency modes of any shape are the kind of simulation we build Tessera for. See Tessera →
HOW IT'S CALCULATED · WITH YOUR NUMBERS
Step by step, with your numbers
References: Long, Architectural Acoustics, 2nd ed. (2014), ch. 7 and 8; Cox & D'Antonio, Acoustic Absorbers and Diffusers, 3rd ed. (2016), App. A; Fitzroy, JASA 31 (1959); Arau-Puchades, Acustica 65 (1988); ISO 9613-1:1993; DIN 18041:2016; ANSI/ASA S12.60-2002; ITU-R BS.1116.
BEYOND THE DIFFUSE FIELD