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Open toolReverberation Time Calculator (Sabine & Eyring RT60 Acoustic Formula)
Compute room reverberation time (`RT60`) in seconds from room volume (`m³`) and surface absorption coefficients (`alpha`): compare **Sabine** (`0.161 V / A`) and **Norris-Eyring** decay times, total metric Sabins, critical distance (`d_c`), and extra acoustic treatment needed.
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How Sabine & Norris-Eyring RT60 Calculations Work
Every time a sound wave strikes a wall, ceiling, or floor of area `S_i`, a fraction `alpha_i` of its acoustic energy is absorbed and `1 - alpha_i` is reflected back into the room.
A = sum(S_i * alpha_i); T60_Sabine = (0.161 * V) / A; T60_Eyring = (-0.161 * V) / (S * ln(1 - A / S)); Extra Sabins for Target T* = (0.161 * V / T*) - A.
The constant `0.161 s/m` derives from `24 * ln(10) / c` at standard room temperature (`20 °C`, speed of sound `c = 343 m/s`).
Acoustic Absorption Coefficients & Default 180 m³ Room RT60 Table
Typical `500 Hz / 1 kHz` absorption coefficients (`alpha`) and exact breakdown for the default `180 m³` room (`198 m²` total boundary surface).
| Room Surface / Acoustic Metric | Area (S_i) & Alpha (α_i) | Absorption Area (A_i) | RT60 & Acoustic Interpretation |
|---|---|---|---|
| **Gypsum Board Walls** | `108.0 m²` × `α = 0.06` | `6.48 m² Sabins` | Reflective boundary (`94%` energy reflected) |
| **Smooth Concrete Floor** | `45.0 m²` × `α = 0.02` | `0.90 m² Sabins` | Hard floor surface (`98%` energy reflected) |
| **Acoustic Ceiling Tile** | `45.0 m²` × `α = 0.65` | `29.25 m² Sabins` | Provides `79.9%` of total room absorption |
| **Total Room (`V = 180 m³`)** | `S = 198.0 m²`, `ᾱ = 0.1850` | **`36.63 m² Sabins`** | **Sabine `0.79 s`** • **Eyring `0.72 s`** (`d_c = 0.86 m`) |
How to Calculate Room RT60 in 3 Steps
Measure your room volume and list its major boundary surfaces.
Enter total room air volume V in cubic meters (m³)
Multiply length × width × height in meters (for example, `7.5 m × 6.0 m × 4.0 m = 180 m³`).
Add each boundary surface area (m²) and absorption coefficient (alpha)
Enter one row per surface (`name, area_m2, alpha`), such as drywall (`0.06`), glass windows (`0.10`), carpet (`0.25`), or 50 mm fiberglass acoustic panels (`0.85`).
Select your target room use (Studio, Classroom, Lecture Hall, or Concert Hall)
Compare your Sabine and Eyring `RT60` values against the target range and check the exact additional `m² Sabins` required to reach the upper target limit.
Worked Room Acoustics & Treatment Examples
See how adding broadband acoustic panels brings an echoey room into ANSI/ISO compliance.
Default 180 m³ Classroom Before Wall Panels (Sabine 0.79 s)
With `108 m²` gypsum walls (`0.06`), `45 m²` concrete floor (`0.02`), and `45 m²` acoustic ceiling tile (`0.65`), total absorption is `36.63 m² Sabins` (`Sabine RT60 = 0.79 s`, `Eyring RT60 = 0.72 s`). To reach the `0.60 s` ANSI classroom ceiling, the room needs `+11.67 m² Sabins` (about `14 m²` of `alpha = 0.85` wall panels).
Adding 16 m² of Broadband Fiberglass Wall Panels (alpha = 0.85)
Adding `16 m²` of `0.85` panels contributes `+13.60 m² Sabins`, raising `A` from `36.63` to `50.23 m² Sabins` and dropping Sabine `RT60` to `0.58 s` (Eyring `0.51 s`), meeting ANSI S12.60.
Small Voiceover / Podcast Booth (30 m³, Heavily Treated)
In a `30 m³` room where mean absorption `alpha_bar = 0.35`, Sabine estimates `0.26 s` while Norris-Eyring gives `0.21 s` because Eyring accounts for rapid discrete reflection loss.
How to Interpret Sabine vs. Eyring & Critical Distance
Knowing both `RT60` and `Critical Distance (d_c)` tells you where to place microphones and acoustic absorbers.
In the default `180 m³` room (`Sabine RT60 = 0.79 s`), the omnidirectional critical distance is `d_c = 0.86 m` (`~1.5 m` for a directional cardioid microphone or human voice). Listeners seated beyond `1.5 m` hear more room reflection than direct voice energy unless absorption `A` is increased.
If you are also configuring digital audio interfaces for a studio, pair your acoustic decay check with our Audio Latency Calculator (/tools/audiolatencycalculator) to keep round-trip monitoring below 10 ms.
Diffuse-Field Assumptions & Input Boundaries
Sabine and Eyring equations assume an approximately diffuse sound field.
A = sum(S_i * alpha_i); T60_Sabine = (0.161 * V) / A; T60_Eyring = (-0.161 * V) / (S * ln(1 - A / S)); Extra Sabins for Target T* = (0.161 * V / T*) - A. The constant `0.161 s/m` derives from `24 * ln(10) / c` at standard room temperature (`20 °C`, speed of sound `c = 343 m/s`).
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Open toolFrequently Asked Questions About RT60 Reverberation Time
Answers about using Reverberation Time Calculator (Sabine & Eyring RT60 Acoustic Formula) and understanding its results.
What is RT60 reverberation time and how does Sabine's formula calculate it?
RT60 is the time in seconds required for the sound pressure level in an enclosed room to decay by 60 decibels (to one-millionth of its initial acoustic energy) after a sound source stops. Wallace Clement Sabine's formula calculates RT60 as T_60 = 0.161 * V / A, where V is room volume in cubic meters and A = sum(S_i * alpha_i) is the total equivalent absorption area in metric Sabins (m²).
What is the difference between the Sabine and Norris-Eyring RT60 equations?
Sabine's equation assumes a continuous, low-absorption sound field and over-predicts reverberation time in heavily treated rooms (In fact, as alpha approaches 1.0, Sabine fails to reach 0 seconds). The Norris-Eyring equation replaces alpha_bar with -ln(1 - alpha_bar), correctly approaching T_60 = 0 in an anechoic chamber (alpha_bar -> 1). Whenever mean absorption alpha_bar exceeds 0.20, acoustic engineers prefer Eyring RT60.
What is a good RT60 target for a classroom, podcast studio, or conference room?
ANSI/ASA S12.60 recommends RT60 <= 0.60 seconds for core learning classrooms and conference rooms so consonant sounds do not blur across syllables. Podcast, voiceover, and mixing studios target 0.25 to 0.40 seconds, whereas concert halls target 1.40 to 2.00 seconds for musical envelopment.
What is Critical Distance (d_c) in room acoustics?
Critical distance d_c = 0.057 * sqrt(Q * V / RT60) is the distance from a speaker where the direct sound level equals the reflected reverberant field level. Sitting closer than d_c ensures high speech clarity; beyond d_c, room reflections dominate.
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