Enter room and material data
The page stays in a single-column flow, while the calculator fields adapt to three columns on large screens, two on medium screens, and one on mobile.
Example data table
Use this example to test the calculator quickly or compare your own room against a realistic classroom-style setup.
| Input | Example value | Notes |
|---|---|---|
| Length × Width × Height | 10 m × 8 m × 3 m | Rectangular teaching room |
| Floor / Ceiling α | 0.08 / 0.65 | Hard floor with acoustic ceiling |
| Front / Back wall α | 0.25 / 0.30 | Moderately treated teaching surfaces |
| Left / Right wall α | 0.18 / 0.18 | Painted wall plus partial panels |
| People count | 20 | Typical occupied lesson |
| Absorption per person | 0.45 sabins | Approximate mid-band value |
| Furniture or extras | 6.50 sabins | Desks, chairs, and window dressing |
| Directivity factor Q | 2.0 | Teacher or loudspeaker near a wall |
| Example output | Value |
|---|---|
| Volume | 240.00 m³ |
| Equivalent absorption | 97.90 sabins |
| RT60 Sabine | 0.395 s |
| RT60 Eyring | 0.317 s |
| Critical distance | 1.00 m |
| Schroeder frequency | 81.11 Hz |
Formula used
1) Room volume and boundary area
V = L × W × H and S = 2(LW + LH + WH). These geometric values drive most acoustic decay estimates for rectangular rooms.
2) Equivalent absorption area
A = Σ(Si × αi) + N × aperson + Aextra. The total is measured in sabins and combines surfaces, occupants, and added absorbers.
3) Reverberation time
Sabine: RT60 = 0.161V / A
Eyring: RT60 = 0.161V / [-S ln(1 - ᾱ)], where ᾱ = A / S. Eyring is usually better when average absorption is not small.
4) Room constant and critical distance
R = A / (1 - ᾱ)
Dc = 0.057√(Q × R). Critical distance estimates where direct and reverberant sound energy become similar.
5) Mean free path and Schroeder frequency
Mean free path = 4V / S
fs = 2000√(RT60 / V). This frequency marks a rough transition between modal behavior and diffuse-field assumptions.
How to use this calculator
- Enter the room length, width, and height in meters.
- Assign absorption coefficients for each major surface. Use area-weighted averages when a surface has mixed finishes.
- Add people count, a realistic per-person absorption value, and any extra absorption from furniture, curtains, or treatment.
- Choose a source directivity factor Q. This affects critical distance calculations only.
- Select the room use type to compare the predicted reverberation against a practical target range.
- Press Calculate acoustics to display the results above the form. Then use the CSV or PDF buttons if you want a saved copy.
Why these results matter
A room with too much reverberation can reduce speech intelligibility, smear transient detail, and make amplified systems harder to control. A room with too little reverberation may sound unnaturally dry, especially for music. By comparing Sabine and Eyring predictions, checking the room constant, and reviewing the critical distance, you get a broader picture than RT60 alone.
This tool is especially useful for classrooms, meeting spaces, rehearsal rooms, project studios, and small halls during early design or retrofit planning. It is a simplified broadband model, so frequency-by-frequency design, strong room modes, scattering, and non-rectangular geometries should still be checked separately for final engineering work.
FAQs
1) What does RT60 mean?
RT60 is the time needed for sound energy to decay by 60 decibels after the source stops. It is one of the most common indicators of room reverberation.
2) Should I trust Sabine or Eyring more?
Sabine works well in lightly absorptive rooms. Eyring usually becomes more reliable when average absorption is higher, because it better handles stronger attenuation at boundaries.
3) Why include people in the calculation?
Occupants absorb sound, especially in mid and high frequencies. A full classroom or audience can noticeably reduce reverberation compared with the same empty room.
4) What is a sabin?
A sabin is a unit of equivalent absorption area. One square meter with an absorption coefficient of 1.0 contributes one square meter sabin of absorption.
5) What does critical distance tell me?
Critical distance estimates where direct sound and reverberant sound are roughly equal. Closer than this point, clarity usually improves because the direct field is stronger.
6) Why is Schroeder frequency useful?
It marks a rough crossover between sparse room modes and a more diffuse sound field. Below that region, modal behavior can dominate what listeners hear.
7) Can I use this for non-rectangular rooms?
Yes, as a quick approximation if you use equivalent dimensions and averaged surfaces. For complex shapes, professional modeling or measurement is still recommended.
8) Does this calculator replace acoustic testing?
No. It is ideal for planning and comparison, but final decisions should be confirmed with frequency-specific design methods, simulations, or on-site acoustic measurements.