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In 1898, Wallace C. Sabine (Sabin) (1868 - 1919) came up with the reverb time formula, but
the article "Collected Papers on Acoustics" appeared in print 1922: Don't be shocked by this early date from 1898. His formula is still unchanged very much in use. Reverberation time RT60 = k · V / A with the factor k = (24 · ln 10) / c20 = 0.049 (feet) and with k = (24 · ln 10) / c20 = 0.161 (meter) V = room volume in m3 A = α · S = equivalent absorption surface or area in m2 α = Absorption coefficient or attenuation coefficient RT60 = reverberation time in s S = absorbing surface in m2 A = α1 · S1 + α2 · S2 + α3 · S3 + ... c20 = Speed of sound is 343 m/s or 1126 ft/s at 20°C |
| Sound engineers and "ear people" mostly use the usual sound field quantity, they therefore state: RT60 is the reverberation time, when the sound pressure level is decreased to (−) 60 dB, this is the thousandth part (10−3) of the initial sound pressure. Acousticians and "people fighting sound" like more the sound energy quantity. They express this differently: RT60 is the reverberation time, when the sound intensity level is decreased to (−) 60 dB, this is the millionth part (10−6) of the initial sound intensity. |
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Reverberation time (RT) is a measure of the amount of reverberation in a space and equal to
the time required for the level of a steady sound to decay by 60 dB after the sound has stopped. The decay rate depends on the amount of sound absorption in a room, the room geometry, and the frequency of the sound. RT is expressed in seconds. k is a constant that equals 0.161 when the units of measurement are expressed in meters and 0.049 when units are expressed in feet. A = S × α is the total surface absorption A of a room expressed in sabins. It is the sum of all the surface areas in the room multiplied by their respective absorption coefficients. The absorption coefficients α express the absorption factor of materials at given frequencies. V is the volume of the enclosure. The figures used in this calculator come from the table of absorption coefficients for various materials which can be found in any book that talks about room acoustics. |
Enter the measurements of the room
and make sure to specify the units.
Absorption Coefficients α of Building Materials and Finishes
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| The reverberation time is the time interval within which the sound level in a room has faded away by 60
dB. Note: This sound pressure is the thousandth part of the initial sound pressure and the sound intensity is the millionth part of the initial sound intensity. Often this is confusing, because the sound pressure as a sound field quantity is mixed with the sound intensity as a sound energy quantity. Notice: I ~ p2. |
Calculating the three room modes − eigenmodes or eigenfrequencies
Standing waves (acoustic resonances)
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