Ideal Reverberation Times (RT60) & Early Decay Time (EDT)
Mid-frequency (500 Hz – 1 kHz) targets for RT60 and EDT by room type. Values represent best-practice ranges from: ISO 3382, Beranek, and IEC standards.
Categories:
- Music performance
- Speech/intelligibility
- Multi-purpose Large / sports venues
- Specialist / controlled
| Space | Volume range | RT60 target (s) | EDT target (s) | EDT / RT60 ratio | Design notes |
| Music performance | |||||
| Chamber music hall | 1 000 – 5 000 m³ | 1.4 – 1.8 s | 1.3 – 1.7 s ≈ 0.90 – 0.95 × RT₆₀ | 0.90 – 0.95 | EDT should track RT₆₀ closely; shoebox or fan shape preferred. |
| Concert hall (symphonic) | 10 000 – 25 000 m³ | 1.8 – 2.2 s | 1.7 – 2.1 s ≈ 0.92 – 0.98 × RT₆₀ | 0.92 – 0.98 | High EDT ≈ RT₆₀ signals envelopment; bass warmth (RT rise at 125 Hz) desirable. |
| Opera house | 8 000 – 18 000 m³ | 1.2 – 1.6 s | 1.1 – 1.5 s ≈ 0.90 – 0.95 × RT₆₀ | 0.90 – 0.95 | Shorter RT₆₀ aids sung diction; pit volume affects total RT. |
| Organ / choral church | 5 000 – 50 000 m³ | 2.5 – 5.0 s | 2.0 – 4.5 s ≈ 0.85 – 0.95 × RT₆₀ | 0.85 – 0.95 | Gothic cathedrals can exceed 8 s; polyphonic music designed for these spaces. |
| Jazz / intimate club | 300 – 1 500 m³ | 0.6 – 1.0 s | 0.5 – 0.9 s ≈ 0.85 – 0.95 × RT₆₀ | 0.85 – 0.95 | Low RT preserves rhythmic clarity; early reflections add intimacy. |
| Recording studio (live room) | 50 – 500 m³ | 0.2 – 0.5 s | 0.1 – 0.4 s ≈ 0.70 – 0.90 × RT₆₀ | 0.70 – 0.90 | EDT often intentionally below RT₆₀; variable absorption panels used. |
| Speech / intelligibility | |||||
| Lecture theatre / classroom | 100 – 500 m³ | 0.4 – 0.7 s | 0.35 – 0.65 s ≈ 0.85 – 0.95 × RT₆₀ | 0.85 – 0.95 | STI > 0.60 target; avoid rear-wall flutter echoes. BB93 in UK. |
| Conference / boardroom | 50 – 200 m³ | 0.3 – 0.5 s | 0.25 – 0.45 s ≈ 0.85 – 0.90 × RT₆₀ | 0.85 – 0.90 | Video-conferencing systems benefit from RT₆₀ < 0.5 s. |
| Courtroom | 300 – 1 200 m³ | 0.5 – 0.8 s | 0.45 – 0.75 s ≈ 0.88 – 0.95 × RT₆₀ | 0.88 – 0.95 | Speech intelligibility is a legal requirement; ADA compliance. |
| Open-plan office | 500 – 5 000 m³ | 0.3 – 0.5 s | 0.25 – 0.45 s ≈ 0.85 – 0.95 × RT₆₀ | 0.85 – 0.95 | Low RT₆₀ + acoustic screens reduce speech propagation distance. |
| Multi-purpose | |||||
| Multi-purpose auditorium | 3 000 – 12 000 m³ | 1.2 – 1.8 s | 1.0 – 1.6 s ≈ 0.85 – 0.92 × RT₆₀ | 0.85 – 0.92 | Variable absorption (banners, retractable panels) allows mode-switching. |
| School hall / assembly | 500 – 3 000 m³ | 0.8 – 1.2 s | 0.7 – 1.1 s ≈ 0.88 – 0.95 × RT₆₀ | 0.88 – 0.95 | Occupied RT₆₀ is typically 0.1–0.3 s shorter than unoccupied. |
| House of worship | 800 – 8 000 m³ | 1.0 – 1.8 s | 0.9 – 1.6 s ≈ 0.88 – 0.95 × RT₆₀ | 0.88 – 0.95 | Contemporary worship favours lower end; traditional liturgical favours upper. |
| Large & sports venues | |||||
| Gymnasium (school / club) | 1 000 – 5 000 m³ | 1.5 – 2.5 s | 1.2 – 2.2 s ≈ 0.80 – 0.90 × RT₆₀ | 0.80 – 0.90 | Hard parallel surfaces cause flutter; cloud baffles or perforated panels recommended. Speech intelligibility poor above 2.0 s. |
| Indoor arena (multipurpose) | 80 000 – 300 000 m³ | 3.0 – 6.0 s | 2.0 – 5.0 s ≈ 0.70 – 0.85 × RT₆₀ | 0.70 – 0.85 | PA system design critical; directional delays required. EDT often well below RT₆₀ due to large absorptive crowd areas. |
| Sports stadium (covered) | 200 000 – 800 000 m³ | 4.0 – 8.0 s | 2.5 – 6.0 s≈ 0.65 – 0.80 × RT₆₀ | 0.65 – 0.80 | Intelligibility relies entirely on distributed PA with delay towers. Retractable roof significantly raises RT₆₀ when closed. |
| Natatorium (indoor pool) | 2 000 – 20 000 m³ | 2.0 – 4.0 s | 1.5 – 3.5 s ≈ 0.75 – 0.90 × RT₆₀ | 0.75 – 0.90 | Water surface is almost perfectly reflective; moisture-resistant absorption essential. |
| Ice rink / hockey arena | 15 000 – 60 000 m³ | 3.0 – 5.0 s | 2.0 – 4.5 s ≈ 0.75 – 0.90 × RT₆₀ | 0.75 – 0.90 | Ice and boards are highly reflective; acoustic treatment above ice level needed. |
| Specialist & controlled environments | |||||
| Anechoic chamber | 10 – 200 m³ | < 0.1 s | < 0.05 s ≈ 0.50 × RT₆₀ | ~ 0.50 | Free-field conditions; wedge absorbers from 80–250 Hz upward. Not a usable space. |
| Control room / mix suite | 30 – 150 m³ | 0.15 – 0.3 s | 0.1 – 0.25 s ≈ 0.70 – 0.85 × RT₆₀ | 0.70 – 0.85 | LEDE or RFZ design; tight EDT for near-field accuracy. |
| Home cinema / screening room | 40 – 300 m³ | 0.2 – 0.4 s | 0.15 – 0.35 s ≈ 0.75 – 0.90 × RT₆₀ | 0.75 – 0.90 | ITU-R BS.1116 guidance; Dolby Atmos rooms target ≤ 0.3 s. |
| Broadcast studio (radio/TV) | 60 – 400 m³ | 0.2 – 0.4 s | 0.15 – 0.35 s ≈ 0.70 – 0.90 × RT₆₀ | 0.70 – 0.90 | EBU Tech 3276 specification; coloration from room modes a concern. |
Notes:
RT₆₀ — time for sound pressure level to decay 60 dB after the source stops. The primary room-acoustics metric per ISO 3382-1.
EDT (Early Decay Time) — derived from the first 10 dB of decay, extrapolated to 60 dB. Correlates more strongly with perceived reverberance than RT₆₀.
EDT / RT₆₀ ratio < 1 indicates a diffuse, absorptive room. Ratio ≈ 1 indicates highly diffuse or reverberant conditions (desirable in concert halls).
All values are mid-frequency (500 Hz – 1 kHz). RT₆₀ rises at lower frequencies in most naturally hard spaces (bass warmth) and falls at high frequencies due to air absorption in large volumes.
Occupied vs. unoccupied: audiences absorb ~0.1–0.4 s of RT₆₀. Large-venue values shown are for occupied conditions.
Sources: ISO 3382-1:2009, Beranek (2004) Concert Halls and Opera Houses, IEC 60268-16, BB93 (UK DfE), ITU-R BS.1116, EBU Tech 3276.
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