What Is Reverberation Time?
Reverberation time (RT60) is how long it takes sound to decay by 60 dB after a source stops — in plain terms, how long an echo lingers in a room. It's driven by a space's geometry and surface materials: hard, reflective surfaces (glass, concrete, tile) extend RT60, while soft, absorptive materials (carpet, curtains, acoustic panels) shorten it.
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60 dB
The standard decay threshold RT60 measures — the time for sound to drop to one-millionth of its original intensity
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By Ear
Subjective impressions of an "echo-y" room are inconsistent between listeners and can't be reliably compared over time or between venues
How RT60 Is Actually Calculated
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Sound Decay
The physical phenomenon being measured — how quickly acoustic energy dissipates as it reflects around a room after the source stops.1 -
T20 / T30
In practice, the true 60 dB tail is often masked by background noise, so a shorter segment of the decay (25–5 dB or 35–5 dB) is measured and extrapolated.2 -
Octave-Band Analysis
RT60 varies by frequency, so results are reported across the 125 Hz–4 kHz range rather than as one single figure for the whole room.3 -
RT60 Result
The mathematically extrapolated time for a full 60 dB decay, calculated from the measured decay slope at each frequency band.4
Room type |
Typical RT60 target | Why |
|---|---|---|
| Classroom / lecture hall | 0.4 – 0.6 s | Speech clarity is the priority; longer decay blurs consonants for students further from the speaker |
| Courtroom / conference room | < 1.0 s | Testimony and discussion must stay intelligible without amplification for the full room |
| Open-plan office | 0.5 – 0.8 s | Balances speech privacy between desks against an overly "dead," uncomfortable acoustic |
| Recording / broadcast studio | 0.2 – 0.4 s | A near-neutral acoustic prevents the room itself from coloring a recorded or broadcast signal |
| Concert hall (orchestral) | 1.6 – 2.2 s | Longer decay is wanted for warmth, blend, and fullness of unamplified music |
| House of worship | 1.0 – 2.0 s | Depends on whether the space prioritizes spoken word, music, or a mix of both |
The Role of Reverberation Time Measurement
Built for This Workflow: AWA6292
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1
What's a "good" reverberation time?
It depends entirely on room use — see the target table above. There's no single universal figure; the right target is set by the room's purpose, not the instrument.
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2
Do I need T20, T30, or full RT60?
T20 and T30 are standardized ways of estimating RT60 from a shorter, cleaner segment of the decay curve when background noise would otherwise mask the full 60 dB tail — in practice, most field measurements report T20 or T30 rather than a directly observed 60 dB decay.
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3
How many measurement points does a survey need?
ISO 3382 generally calls for multiple source and receiver position combinations distributed through the room — for a mid-size room, 2–3 source positions with 3 or more receiver positions each is typical, with larger or more complex spaces needing more.
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4
Can this be measured in an occupied, furnished room?
Yes, but results will differ from an empty shell — furniture, curtains, and people absorb sound and lower RT60. Testing should generally match the room's real, in-use condition for results that reflect what occupants actually experience.
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5
How is this different from just measuring background noise?
Background noise (dB level) and reverberation time measure different things — a quiet room can still have poor speech intelligibility due to excessive echo. Both are often assessed together for a full acoustic compliance picture.