Compute reverberation time RT60 with both Sabine and Eyring equations from room dimensions, wall/ceiling/floor absorption, occupants, and absorber panel area. Compare against use-case targets from offices to concert halls, recording studios, and cathedrals.
Parameters
Room length L
m
Room width W
m
Ceiling height H
m
Use case
Auto-sets the target RT60
Wall material
Ceiling
Floor
Occupants
ppl
Clothed adult ≈ 0.46 m² Sabin
Absorber panel area
m²
alpha=0.90 (Rockwool / fiberglass)
Results
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Volume V (m³)
—
Total absorption A (m² Sabin)
—
RT60 Sabine (s)
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RT60 Eyring (s)
—
Mean alpha
—
Use-case target (s)
—
Room view — source, reflections, RT60 gauge
Sound from the central source reflects off walls/ceiling/floor and decays by 60 dB over RT60 seconds. Yellow bands are absorber panels; figures are occupants. Gauge color shows deviation from the use-case target.
V: room volume [m³]; A = Σαᵢ·Sᵢ: total absorption [m² Sabin]; mean alpha = A/S; S: total surface area [m²]. Eyring is preferred for highly absorptive rooms.
Sum of wall/ceiling/floor absorption plus occupants Nₚ (≈ 0.46 m² Sabin each) and added absorber panels (alpha ≈ 0.9).
$$\text{STI} \approx \frac{1}{1 + RT_{60}/0.5}$$
Simple speech intelligibility proxy. Lower RT60 pushes STI toward 1 and improves speech clarity.
Room RT60 — Sabine / Eyring Acoustic Design
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Reverberation time RT60 shows up everywhere in acoustics. Is it basically "how long the room rings"?
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Pretty much. Formally, it's the time in seconds for sound energy to drop by 60 dB after the source stops. A handclap dying in 0.5 s gives RT60 = 0.5 s; a cathedral holding for 4 s gives RT60 = 4 s. Wallace Sabine derived the foundational formula RT = 0.161·V/A back in 1898 while fixing Harvard's Fogg Art Museum — and it's still the workhorse equation today.
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Bigger rooms ring longer — that's intuitive. But what exactly is "A"?
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A is the total equivalent absorption, in m² Sabin. You sum α·S over every surface: A = α₁S₁ + α₂S₂ + … Concrete absorbs almost nothing (alpha = 0.02), acoustic tile is 0.7, carpet is 0.4. With the defaults (10×8×3.5 m office) you get A ≈ 108 m² Sabin and V = 280 m³, so RT60 ≈ 0.42 s — right in the sweet spot for an office target of 0.5 s.
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Why does the tool show both Sabine and Eyring side by side?
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Sabine is accurate in live rooms with low alpha, but it overestimates RT60 once mean alpha exceeds about 0.3 — which is the case for a recording studio packed with absorbers. Eyring's equation RT = -0.161·V/(S·ln(1-mean alpha)) keeps the log term so the correction kicks in as the room becomes deader. Pick "Recording studio", switch the walls to wood panel, ceiling to acoustic tile, and crank absorber panels up to 50 m² — you'll see the two values pull apart.
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A classroom that's easy to understand and a concert hall with beautiful reverb need totally different targets, right?
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That's the heart of acoustic design. Speech-driven spaces want short RT60: office 0.5 s, classroom 0.6 s, lecture hall around 1.0 s. Music venues want sustain — Suntory Hall sits at 1.9 s, Berlin Philharmonie at 2.0 s, Carnegie Hall at 1.8 s; the world's great halls all cluster in the 1.8-2.2 s band. Cathedrals routinely exceed 4 s, and Gregorian chant was literally composed for that reverberation. Flip through the use cases to feel the spread.
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When RT60 is too long, where do I start cutting it?
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Absorber panels first — 10 m² of alpha = 0.9 Rockwool adds 9 m² Sabin instantly. Next, swap "exposed" ceiling for "acoustic tile": 80 m²·(0.7 - 0.1) = 48 m² Sabin extra, which is huge. Carpet helps but isn't always allowed for hygiene reasons. Real-world projects revolve around "which surfaces am I allowed to touch?", and this tool lets you dial in materials until the gauge sits at target.
Frequently Asked Questions
Sabine's equation RT = 0.161·V/A is accurate for live rooms with mean absorption coefficient below about 0.2. Above 0.3 (very absorptive rooms like recording studios), Sabine overestimates RT60, so the Eyring equation RT = -0.161·V/(S·ln(1-mean alpha)) is preferred. This tool shows both side by side so you can see them diverge as the room becomes deader.
Common targets: office 0.4-0.6 s, classroom 0.6-0.8 s, conference 0.6-0.9 s, lecture hall 0.9-1.4 s, concert hall 1.8-2.2 s, recording studio 0.2-0.4 s, cathedral around 4 s. The tool auto-applies a target when you pick the use case and displays the deviation from current RT60. Speech intelligibility favors short RT60, while music venues value longer reverberation.
Rockwool or fiberglass panels have roughly alpha = 0.9 at 500 Hz, adding A = 0.9·S_panel to total absorption. For a 280 m³ office at RT60 = 1.2 s with a 0.5 s target, you need to increase A by about 2.4x; divide the missing A by 0.9 to size the panels. Distribute panels across walls and ceiling to avoid concentrated early reflections.
Each clothed adult contributes about 0.46 m² Sabin, so RT60 drops as occupancy rises. Concert halls can see a 0.3-0.5 s difference between empty and full, which is why absorptive seats (cushioned backs) are used to mimic an occupied audience. Slide the Occupants input to compare empty vs full conditions.
Real-world Applications
Offices and coworking spaces: With activity-based working and ubiquitous video calls, office acoustics now matters more than ever. Target RT60 ≈ 0.5 s — usually delivered with acoustic ceiling tile, carpet, and absorber panels on partitions. Try the defaults: office + acoustic tile + carpet lands right inside the target band. Long RT60 hurts meeting intelligibility and concentration, so it must be considered during every fit-out.
Concert halls and theaters: World-class venues like Suntory Hall (1.9 s), Berlin Philharmonie (2.0 s), and Carnegie Hall (1.8 s) all sit between 1.8 and 2.2 s at full occupancy. Detailed studies use ray-tracing tools such as ODEON, CATT-Acoustic, and EASE, but early design is set by Sabine-class calculations of volume and absorption. Select "Auditorium" to see the deviation from a 1.8 s target.
Recording studios and anechoic chambers: Studios aim for RT60 = 0.2-0.4 s, while anechoic chambers approach zero. Rockwool absorbers (alpha = 0.9) cover walls and ceilings, and Eyring becomes mandatory. Try "Studio" with wood-panel walls, acoustic tile ceiling, and 80 m² of absorber: the Sabine-Eyring gap widens, making the case for Eyring on dead rooms.
Classrooms and gyms: ANSI S12.60 caps classroom RT60 at 0.6 s; US studies show that exceeding this hurts vocabulary acquisition and reading. Retrofit projects now routinely add ceiling absorbers and rear-wall panels. Gymnasiums have large volumes that drive RT60 up, so treating the underside of the roof is the most cost-effective intervention.
Common Pitfalls
The biggest trap is "ignoring the frequency dependence of RT60". This tool uses a 500 Hz reference for simplicity, but real RT60 varies strongly with frequency. Most absorbers underperform at low frequencies (125 Hz), so rooms often have a low-frequency RT60 that is 2-3x longer — the classic "boomy" sound. Real designs evaluate six octave bands (125/250/500/1k/2k/4k Hz) and add Helmholtz-style bass traps for the low end. ISO 3382 measurements are also reported per band.
Next, "trusting Sabine for absorptive rooms". Sabine is fine for live spaces but overestimates RT60 once you fill a studio with absorbers; that's why this tool always shows both equations. Use Eyring's value when mean alpha exceeds 0.3. Beyond about 0.5, even Eyring strains and you need to add air absorption / edge effects (Millington-Sette) or use FEM/BEM and ray-tracing tools like CATT-Acoustic.
Finally, "shorter RT60 is always better" is wrong. Speech spaces benefit from short reverberation, but music spaces depend on sustain for impact — over-absorbing music venues produces a dry, lifeless sound and even alters how performers play. Cathedrals have RT60 above 4 s because Gregorian chant and pipe organ literature were composed for that environment. Decide the target with the audience and program in mind, then balance diffusers (QRD/PRD) and absorbers to land on a room that rings just right.
How to Use
Enter room dimensions (length, width, height in meters) to calculate volume and surface area.
Input absorption coefficients for each surface type (walls, ceiling, floor) at your target frequency (125 Hz to 4 kHz bands).
Specify number of occupants; simulator adds ~0.5 m² Sabin absorption per person.
Compare RT60 Sabine (underestimates at high absorption) and RT60 Eyring (more accurate for treated rooms) outputs.
Adjust surface materials iteratively until RT60 matches your use-case target (speech: 0.6–0.9 s; music: 1.2–2.0 s; cinema: 0.8–1.1 s).
Worked Example
Recording studio: 6 m × 4 m × 3 m (V = 72 m³). Walls: drywall α=0.15; ceiling: acoustic tile α=0.80; floor: vinyl α=0.05; two occupants (+1.0 m² Sabin). Total absorption A = (48 × 0.15) + (24 × 0.80) + (24 × 0.05) + 1.0 = 28.2 m² Sabin. RT60 Sabine = 0.161 × 72 / 28.2 = 0.41 s. RT60 Eyring = 0.161 × 72 / (72 − 28.2 × ln(1 − 28.2/72)) ≈ 0.36 s. For voice-over work targeting 0.5–0.7 s, increase ceiling coverage or add wall absorption panels.
Practical Notes
Sabine formula assumes diffuse field and low absorption (α < 0.2); use Eyring at high absorption (treated studios, control rooms).
Occupant absorption varies: seated audience ~0.4–0.5 m² Sabin/person; standing crowds ~0.3 m² Sabin/person.
Measure or source absorption coefficients from manufacturer datasheets (e.g., Owens Corning, Armstrong) for specific frequencies; broadband estimates underestimate in speech range.