How to use the sabine reverberation time calculator
- Choose meters or feet, then enter the room volume in cubic meters or cubic feet.
- List each surface of the room with its area and its absorption coefficient, a number from 0 for a surface that reflects all sound to 1 for one that absorbs all of it.
- Add any extra absorption from people, seats or furniture in the advanced options.
- Read the reverberation time, the time in seconds for sound to fall by 60 decibels, with the total absorption and a breakdown by surface.
Formula
total absorption A = sum of (area x absorption coefficient) + extra
RT60 = 0.161 x V / A with V in cubic meters and A in square meters
RT60 = 0.049 x V / A with V in cubic feet and A in square feet
The constant comes from 24 x ln(10) / c with the speed of sound c near 343 m/s, which is 0.1611. The imperial constant is the same relation in feet. Both can be changed in the advanced options.
A small room of 60 cubic meters
Take a room of 60 m3 with 20 m2 of carpet (coefficient 0.3), 20 m2 of acoustic ceiling tile (0.6), 54 m2 of painted plaster wall (0.05) and 4 m2 of window glass (0.1). The absorptions are 6.0, 12.0, 2.7 and 0.4 square meters, a total of 21.1. RT60 is 0.161 x 60 / 21.1 = 0.458 seconds.
Doubling the absorption would halve the reverberation time to 0.229 seconds. The same room worked out in feet and square feet with the imperial constant gives 0.457 seconds, a difference of about 0.15 percent that comes from rounding the two constants.
What reverberation time tells you
A long reverberation time makes speech muddy because each syllable still rings when the next arrives. A short time makes music sound dry. Rooms for speech usually aim for a shorter time than rooms for orchestral music, but the right figure depends on the room size and the use, so this tool reports the number and leaves the target to you.
Where the formula is weak
Sabine's formula assumes sound spreads evenly through the room and that no surface absorbs most of the energy. In a very absorbent room it gives times that are too long. Coefficients also vary with pitch, so a single figure for a surface is an average. For important work, measure the room with a meter and use frequency-by-frequency coefficients from the material maker.
More waves and light tools
For related tools on sound and light, try the Thin Lens Calculator, Telescope Magnification Calculator and Doppler Effect Calculator.
Assumptions and limits
- Sound is spread evenly through the room.
- Each coefficient is a single average figure that does not vary with pitch.
- Every surface of the room is listed, or the unlisted ones are covered by the extra absorption.
- The coefficients in the form are examples for the sample materials, not data sheet values.
- The room volume and areas use the same unit system you chose.
Frequently asked questions
What does RT60 mean?
It is the time for the sound level to drop by 60 decibels after the source stops. That is a fall to one millionth of the original sound energy, which is roughly the point where a loud sound has died away into the background.
Where do I find absorption coefficients?
Acoustic material makers publish them on data sheets, often per octave band. A coefficient near 0.05 is a hard painted wall and near 0.9 is thick porous absorber, and the real values depend on the product.
Why does the page ask for extra absorption?
People, seats and furniture soak up sound but are awkward to list as surfaces. Work out their total absorption from a table you trust and enter it as one number.
Is a short reverberation time always better?
No. Too short a time makes a room sound lifeless and tiring, especially for music. The right time depends on what the room is used for.