RT60 and absorption: Sabine and Eyring
Reverberation time (RT60) is the time it takes for sound to decay by 60 dB after the source stops. It is the most widely used single number to describe how "live" a room is.
Sabine's equation
T = 0.161 · V / A
where V is the room volume in m³ and A is the total absorption in m² Sabine: the sum of each surface's area multiplied by its absorption coefficient α. Doubling the absorption halves the reverberation time.
Eyring's equation
T = 0.161 · V / ( −S · ln(1 − ᾱ) )
S is the total surface area and ᾱ the average absorption coefficient. For small ᾱ the two equations agree. Eyring is more accurate in heavily damped rooms such as studios, where Sabine overestimates RT60.
The RT60 calculator gives both.
Absorption coefficients
α runs from 0 (perfect reflector) to 1 (perfect absorber) and depends on frequency. A concrete wall absorbs very little at any frequency, while a thick porous absorber absorbs well at mid and high frequencies but little in the bass. Use values for the frequency band you care about.
Typical targets
| Room | Typical RT60 |
|---|---|
| Control room, small studio | about 0.2 to 0.4 s |
| Classroom or conference room | about 0.4 to 0.8 s |
| Concert hall | about 1.5 to 2.2 s |
Targets depend on use, volume and standard. Speech needs less reverberation than orchestral music.
Limits
These equations assume a diffuse sound field. In small rooms at low frequencies, modes dominate, and RT60 per octave band is better measured than calculated. See Room modes explained.
Draft: written by an AI assistant, awaiting technical review.
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