RT60: Sound Decay in Enclosed Spaces
Reverberation time (RT60) is the time for sound to decay 60 dB after the source stops. Sabine's formula RT60 = 0.161V/A relates room volume V to total absorption A (Sabins). It governs speech intelligibility and music quality.
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Sabine assumes diffuse field; Eyring improves for ฮฑ > 0.2. Schroeder frequency fs = 2000โ(RT60/V) marks modal/diffuse transition. Critical distance dc = 0.057โ(V/RT60) where direct = reverberant. Mean free path ฮป = 4V/S for average reflection spacing.
Ready to run the numbers?
Why: RT60 determines how 'live' or 'dead' a room sounds. Too long: muddled speech; too short: dry, lifeless. Studios need ~0.3 s; concert halls ~2 s.
How: Enter room dimensions and surface absorption coefficients. Total absorption A = ฮฃ(Sแตข ร ฮฑแตข). Sabine works best for low absorption; Eyring for higher ฮฑ.
Run the calculator when you are ready.
๐ Room Dimensions
๐งฑ Surface Materials
โ Additional Surfaces (windows, doors, seats)
โ Frequently Asked Questions
What is RT60 and why is it important?
RT60 (reverberation time) is the time required for sound to decay by 60 decibels after the source stops. It's a fundamental measure of how "live" or "dead" a room sounds and critically affects speech intelligibility, music quality, and acoustic comfort. Different room types require different RT60 values for optimal acoustics.
What's the difference between Sabine, Eyring, and Millington methods?
The Sabine formula is simplest and best for low absorption rooms. The Eyring method is more accurate for rooms with higher absorption (ฮฑ > 0.2). The Millington-Sette method accounts for individual surface absorption coefficients and is most accurate for detailed analysis.
What RT60 is ideal for different room types?
Recording studios: 0.2-0.4s, Conference rooms: 0.4-0.6s, Classrooms: 0.4-0.7s, Lecture halls: 0.6-1.0s, Concert halls: 1.5-2.5s, Churches: 1.5-3.0s. Speech requires shorter RT60 (0.4-0.8s) while music benefits from longer RT60 (1.5-2.5s).
How do I reduce RT60 if it's too high?
Add absorptive materials: acoustic panels, carpet, curtains, upholstered furniture, or acoustic ceiling tiles. The calculator shows how much additional absorption (in Sabins) is needed to reach your target RT60.
What is the Schroeder frequency?
The Schroeder frequency (fs = 2000 ร โ(RT60/V)) marks the transition from modal (low frequency) to diffuse field (high frequency) behavior. Below this frequency, room modes dominate; above it, sound behaves diffusely.
What is critical distance?
Critical distance (dc = 0.057 ร โ(V/RT60)) is where direct sound and reverberant sound are equal in level. Closer to the source, direct sound dominates; farther away, reverberant sound dominates. This is important for microphone placement.
How accurate are RT60 calculations?
Calculations provide theoretical estimates. Actual RT60 depends on frequency, source position, measurement method, and environmental conditions. For critical applications, always verify with acoustic measurements using calibrated equipment.
๐ Official Data Sources
ISO 3382 Acoustics
International standard for measurement of room acoustic parameters including RT60
Last Updated: 2026-02-07
Acoustical Society of America
Professional acoustics organization providing standards and research on room acoustics
Last Updated: 2026-02-07
Audio Engineering Society
AES standards and publications on studio acoustics and reverberation time
Last Updated: 2026-02-07
Engineering Toolbox Acoustics
Engineering reference for room acoustics calculations and absorption coefficients
Last Updated: 2026-02-07
โ ๏ธ Disclaimer: This calculator provides theoretical RT60 estimates based on room dimensions and material properties. Actual reverberation time varies with frequency, source position, measurement method, and environmental conditions (temperature, humidity). Absorption coefficients are approximate and may vary with installation, frequency, and material age. For critical applications such as studio design or architectural acoustics, always verify calculations with professional acoustic measurements using calibrated equipment following ISO 3382 standards.
For educational and informational purposes only. Verify with a qualified professional.
๐ฌ Physics Facts
Sabine derived RT60 in 1900 for Boston Symphony Hall.
โ ASA
Speech intelligibility best at RT60 0.4โ0.7 s.
โ AES
Concert halls target 1.5โ2.5 s for orchestral music.
โ ISO 3382
Eyring formula more accurate for highly absorptive rooms.
โ Engineering Toolbox
What is Reverberation Time (RT60)?
Reverberation time (RT60) is the time required for sound to decay by 60 decibels after the source stops. It's a fundamental measure of how "live" or "dead" a room sounds and critically affects speech intelligibility, music quality, and acoustic comfort.
Sabine Method
Classic formula by Wallace Sabine. Best for low absorption rooms.
Eyring Method
More accurate for rooms with higher absorption (ฮฑ > 0.2).
Target Values
Optimal RT60 depends on room use. Studios: 0.3s, Halls: 2.0s.
Recommended RT60 by Room Type
| Room Type | Min RT60 | Ideal RT60 | Max RT60 |
|---|---|---|---|
| recording studio | 0.2 s | 0.3 s | 0.4 s |
| home theater | 0.3 s | 0.4 s | 0.5 s |
| conference room | 0.4 s | 0.5 s | 0.6 s |
| classroom | 0.4 s | 0.6 s | 0.7 s |
| lecture hall | 0.6 s | 0.8 s | 1 s |
| concert hall | 1.5 s | 2 s | 2.5 s |
| church | 1.5 s | 2.2 s | 3 s |
| gymnasium | 1 s | 1.5 s | 2 s |
| office open | 0.4 s | 0.6 s | 0.8 s |
| restaurant | 0.5 s | 0.7 s | 1 s |
Applications of RT60 Calculation
Recording Studios
Control room design, vocal booths, mixing environments
Concert Halls
Optimize acoustics for orchestral and chamber music performance
Office & Education
Speech intelligibility in classrooms, conference rooms, open offices
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