Reverberation time is how long sound takes to decay in a room. It is the single number behind most complaints that a space is “too loud”, “echoey” or impossible to hold a conversation in — and it is fixable.
Our Room Acoustics Design Report calculates it room by room and specifies the treatment needed, from $545.
What it means
Reverberation time, written T or RT60, is the time in seconds for sound to fall by 60 dB after the source stops. It depends on two things: the volume of the room, and how much absorption the surfaces provide. Hard surfaces — glass, concrete, tile, plasterboard — reflect. Soft, porous and fibrous surfaces absorb.
A restaurant with a concrete floor, glass frontage and a plasterboard ceiling has almost no absorption, so every conversation adds to a rising pool of sound. Diners raise their voices to be heard, which raises the level further. That feedback loop is the Lombard effect, and it is why some rooms become unbearable at half capacity.
Typical targets
| Space | Typical target |
|---|---|
| Restaurant or bar, comfortable conversation | 0.6–0.8 s |
| Open-plan office | 0.4–0.6 s |
| Classroom | 0.4–0.8 s depending on size and use |
| Meeting room | 0.4–0.6 s |
| Sports hall | 1.5–2.0 s |
| Place of worship, speech-led | 0.8–1.2 s |
These are indicative. Schools in the UK are assessed against BB93, healthcare against HTM 08-01, and internationally against ANSI/ASA S12.60 or AS/NZS 2107. Sustainability ratings often set their own criteria.
How it is calculated
The Sabine and Eyring equations relate reverberation time to room volume and total absorption, calculated per octave band because absorption varies enormously with frequency. A material that absorbs well at 2 kHz may do almost nothing at 125 Hz, which is why rooms treated with thin foam still sound boomy.
This calculation needs room dimensions and surface finishes. It does not need a site visit — which is why room acoustics work desk-based with no compromise at all.
What actually fixes a room
- Enough absorption area. The most common error is treating 10% of a room and expecting a transformation. The calculation tells you the square metres required
- The right absorption class. Specified by absorption coefficient across frequency, not by appearance
- The right placement. Ceiling first in most rooms, then upper walls. Absorption behind furniture does little
- Low-frequency performance where the problem is boominess, which usually means depth or an air gap behind the absorber
What will not fix it
- A better sound system. Amplifying into a reverberant room makes intelligibility worse
- Thin decorative foam. It absorbs at high frequencies only
- Soft furnishings alone, in a room of any real volume
- Acoustic panels chosen by looks, with no calculation behind the quantity