RT60 · 125 Hz to 4 kHz
Reverb time calculator
How long your room rings after a sound stops, band by band, and how much absorption it would take to tame it.
Your reverb time
- Sabine, 250 Hz–4 kHz
- 0.53 saverage of five octave bands
- Eyring, 250 Hz–4 kHz
- 0.49 sshorter, as Eyring always is
- Your target
- 0.17 sBS.1116-3 for this volume: 0.17 s
- Room
- 34.3 m³1,210 ft³ · surfaces 65.0 m² (700 ft²)
Diffuse-field formulas: in a small room, treat these as rough estimates.
Reverb time by octave band, seconds
Bands, and what the target needs
| Hz | Absorption, m² (ft²) | Mean α | Sabine, s | Eyring, s | Extra for the target, m², Sabine / Eyring | Panel area for the target |
|---|---|---|---|---|---|---|
| 125 | 16.66 (179.3) | 0.256 | 0.33 | 0.29 | 15.8 / 8.9 | none: the panel absorbs less than the surface it covers |
| 250 | 9.48 (102.0) | 0.146 | 0.58 | 0.54 | 23.0 / 16.1 | 37.7 m² (405 ft²) more than the bare walls |
| 500 | 8.43 (90.7) | 0.130 | 0.65 | 0.61 | 24.0 / 17.1 | 22.0 m² (237 ft²) |
| 1k | 9.24 (99.5) | 0.142 | 0.60 | 0.55 | 23.2 / 16.3 | 20.7 m² (223 ft²) |
| 2k | 12.12 (130.5) | 0.186 | 0.46 | 0.41 | 20.3 / 13.4 | 21.4 m² (230 ft²) |
| 4k | 15.00 (161.5) | 0.231 | 0.37 | 0.32 | 17.5 / 10.6 | 19.4 m² (209 ft²) |
Extra absorption is in m² of perfect absorber (metric sabins). The panel column turns the Sabine figure into an area of Glass-fibre board 51 mm (2 in), Owens Corning 703 on the walls, counting only what the panel adds over the surface it covers.
Surfaces counted
- Walls 36.5 m² (393 ft²), 35.3 m² bare · Gypsum wallboard, ½ in on studs
- Floor 14.3 m² (154 ft²) · Heavy carpet on felt backing
- Ceiling 14.3 m² (154 ft²) · Gypsum wallboard, ½ in on studs
- Window 1.2 m² (13 ft²) on the walls · Ordinary window glass
How the estimate works
Every surface soaks up part of the sound that hits it. Its absorption coefficient runs from 0 (reflects everything) to 1 (absorbs everything) and changes with frequency, so the calculator works band by band. Area times coefficient, added up over the room, gives the total absorption A, and Sabine’s formula turns it into a reverb time:
T = 0.161 · V / A (Sabine) T = 0.161 · V / (−S · ln(1 − ᾱ)) (Eyring)
V is the volume in m³, S the total surface area and ᾱ the average coefficient. Eyring always gives the shorter time; the gap grows as the room gets deader.
Treat the results as rough estimates. Both formulas assume a diffuse sound field, with sound arriving equally from every direction. Small rooms don’t behave like that, least of all in the bass, where room modes take over.
Pick materials from the published table, or choose custom coefficients and copy them from your panel’s data sheet. The target starts at ITU-R BS.1116-3’s value for a reference listening room; set your own for a live room or a vocal booth.
Sources
- Sabine’s T = 0.161·V/A and Eyring’s T = 0.161·V/(−S·ln(1 − ᾱ)), and the diffuse-field assumption behind them: A. Nowoświat and M. Olechowska, Investigation studies on the application of reverberation time, Archives of Acoustics 41(1), 15–26 (2016). Originals: W. C. Sabine, Collected Papers on Acoustics (Harvard University Press, 1922); C. F. Eyring, Reverberation time in “dead” rooms, J. Acoust. Soc. Am. 1(2A), 217–241 (1930). Air absorption is left out.
- Absorption coefficients for building materials: D. E. Hall, Musical Acoustics, 2nd edition (Brooks/Cole, 1991), Table 15.1, as reproduced in R. Nave, Modeling Reverberation Time, HyperPhysics, Georgia State University.
- Glass-fibre board: Owens Corning, Fiberglas 700 Series Board product data sheet (Pub. No. 10021736-H), Type 703 unfaced, tested to ASTM C423 with Type A mounting (against a solid backing). Coefficients above 1 come from the test method, not a fault.
- Target reverb time, Tm ≈ 0.25·(V / 100 m³)^(1/3) s averaged over 200 Hz to 4 kHz, for a reference listening room: Recommendation ITU-R BS.1116-3 (02/2015), §8.2.3.1. The averages here use the 250 Hz to 4 kHz octave bands, the nearest octave-band match.
- Feet and square feet: NIST Special Publication 811 (1 ft = 0.3048 m).
| Material | 125 | 250 | 500 | 1k | 2k | 4k | Source |
|---|---|---|---|---|---|---|---|
| Acoustic tile, rigid mount | 0.20 | 0.40 | 0.70 | 0.80 | 0.60 | 0.40 | Hall |
| Acoustic tile, suspended | 0.50 | 0.70 | 0.60 | 0.70 | 0.70 | 0.50 | Hall |
| Acoustical plaster | 0.10 | 0.20 | 0.50 | 0.60 | 0.70 | 0.70 | Hall |
| Ordinary plaster, on lath | 0.20 | 0.15 | 0.10 | 0.05 | 0.04 | 0.05 | Hall |
| Gypsum wallboard, ½ in on studs | 0.30 | 0.10 | 0.05 | 0.04 | 0.07 | 0.10 | Hall |
| Plywood sheet, ¼ in on studs | 0.60 | 0.30 | 0.10 | 0.10 | 0.10 | 0.10 | Hall |
| Concrete block, unpainted | 0.40 | 0.40 | 0.30 | 0.30 | 0.40 | 0.30 | Hall |
| Concrete block, painted | 0.10 | 0.05 | 0.06 | 0.07 | 0.10 | 0.10 | Hall |
| Concrete, poured | 0.01 | 0.01 | 0.02 | 0.02 | 0.02 | 0.03 | Hall |
| Brick | 0.03 | 0.03 | 0.03 | 0.04 | 0.05 | 0.07 | Hall |
| Vinyl tile on concrete | 0.02 | 0.03 | 0.03 | 0.03 | 0.03 | 0.02 | Hall |
| Heavy carpet on concrete | 0.02 | 0.06 | 0.15 | 0.40 | 0.60 | 0.60 | Hall |
| Heavy carpet on felt backing | 0.10 | 0.30 | 0.40 | 0.50 | 0.60 | 0.70 | Hall |
| Platform floor, wooden | 0.40 | 0.30 | 0.20 | 0.20 | 0.15 | 0.10 | Hall |
| Ordinary window glass | 0.30 | 0.20 | 0.20 | 0.10 | 0.07 | 0.04 | Hall |
| Heavy plate glass | 0.20 | 0.06 | 0.04 | 0.03 | 0.02 | 0.02 | Hall |
| Draperies, medium velour | 0.07 | 0.30 | 0.50 | 0.70 | 0.70 | 0.60 | Hall |
| Glass-fibre board 25 mm (1 in), Owens Corning 703 | 0.05 | 0.26 | 0.63 | 0.88 | 0.97 | 0.94 | Owens Corning |
| Glass-fibre board 51 mm (2 in), Owens Corning 703 | 0.15 | 0.71 | 1.14 | 1.16 | 1.02 | 1.00 | Owens Corning |
| Glass-fibre board 76 mm (3 in), Owens Corning 703 | 0.34 | 1.09 | 1.25 | 1.15 | 1.05 | 1.00 | Owens Corning |
| Glass-fibre board 100 mm (4 in), Owens Corning 703 | 0.56 | 1.26 | 1.22 | 1.11 | 1.07 | 0.96 | Owens Corning |
Questions
Why does the bass stay long when I add panels?
Thin panels absorb little low down. In the Owens Corning data, 25 mm board has a coefficient of 0.05 at 125 Hz against 0.56 for 100 mm. Thicker panels, or panels spaced off the wall, reach lower.
Which result should I trust, Sabine or Eyring?
Neither exactly. They agree when a room is fairly live and drift apart as it gets deader, where Eyring is the better model. In a small room, use them to compare one treatment plan with another, and measure for real numbers.
What target should a home studio aim for?
The default is the value BS.1116-3 gives for reference listening rooms, which are built for critical listening tests; in a small room it is short. Use it as a goal for a mixing room, and set your own for a room you want to sound live.