Modeling Reverberation TimeSabine is credited with modeling the reverberation time with the simple relationship which is called the Sabine formula: where V is the volume of the enclosure and and a is the absorption coefficient associated with a given area S.

Index Auditorium acoustics  

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Sound Absorption CoefficientWhen a sound wave in a room strikes a surface, a certain fraction of it is absorbed, and a certain amount is transmitted into the surface. Both of these amounts are lost from the room, and the fractional loss is characterized by an absorption coefficient a which can take values between 0 and 1, 1 being a perfect absorber. Effective absorbing area = aS The effective absorbing area is a factor in determining the reverberation time of an auditorium. The absorption coefficient of a surface typically changes with frequency, so the reverberation time is likewise frequency dependent. A table of absorption coefficients can be used in calculations of reverberation time with the Sabine formula.

Index Auditorium acoustics  

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Sabine Formula DiscussionThe Sabine formula works reasonably well for medium sized auditoriums but is not to be taken as an exact relationship. It tends to overestimate the reverberation times for enclosures of high absorption coefficient. A better approximation for such enclosures utilizes an overall average absorption coefficient: Note that this reduces the calculated reverberation time. The Sabine formula also neglects air absorption, which can be significant for large auditoriums.

Index Auditorium acoustics  

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Table of Absorption Coefficients
Data from Hall, 2nd. Ed., Table 15.1

Index Auditorium acoustics Reference Hall  

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Air AbsorptionAir absorption is usually neglected in calculations of reverberation times for auditoriums, but for large enclosures it may become significant. Air absorption is greater for high frequencies and is dependent upon air temperature and relative humidity. Rossing reports the following values and the modification of the Sabine formula:

Index Auditorium acoustics Reference Rossing Science of Sound  

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