RT60 is the time it takes for sound in a room to decay by 60 dB after the source stops. Long times make speech blur; very short times make rooms feel dead. It depends on room volume and how much absorption is in the room.
| RT60 | How the room feels |
|---|---|
| Under 0.3 s | Very dry: studios, vocal booths |
| 0.4–0.6 s | Clear and comfortable for speech |
| 0.8–1.2 s | Lively: restaurants, lecture halls |
| 1.5–2.5 s | Reverberant: churches, concert halls, gyms |