Editing Reverberation (section)

=== Sabine equation ===
[[Wallace Clement Sabine|Sabine]]'s reverberation equation was developed in the late 1890s in an [[empirical]] fashion. He established a relationship between the ''T''<sub>60</sub> of a room, its volume, and its total absorption (in [[Sabin (unit)|sabin]]s). This is given by the equation:

:<math>T_{60} = \frac{24 \ln 10^1}{c_{20}} \frac{V}{Sa} \approx 0.1611\,\mathrm{s}\mathrm{m}^{-1} \frac{V}{Sa}</math>.

where ''c''<sub>20</sub> is the speed of sound in the room (at 20&nbsp;°C), ''V'' is the volume of the room in m<sup>3</sup>, ''S'' total surface area of room in m<sup>2</sup>, ''a'' is the average absorption coefficient of room surfaces, and the product ''Sa'' is the total absorption in sabins.

The total absorption in sabins (and hence reverberation time) generally changes depending on frequency (which is defined by the [[acoustics|acoustic properties]] of the space). The equation does not take into account room shape or losses from the sound traveling through the air (important in larger spaces). Most rooms absorb less sound energy in the lower frequency ranges resulting in longer reverb times at lower frequencies.

Sabine concluded that the reverberation time depends upon the reflectivity of sound from various surfaces available inside the hall. If the reflection is coherent, the reverberation time of the hall will be longer; the sound will take more time to die out.

The reverberation time ''RT''<sub>60</sub> and the [[volume]] ''V'' of the room have great influence on the [[critical distance]] ''d''<sub>c</sub> (conditional equation):
:<math>
d_\mathrm{c} \approx 0{.}057 \cdot \sqrt \frac{V}{RT_{60}}
</math>

where critical distance <math>d_c</math> is measured in meters, volume <math>V</math> is measured in m³, and reverberation time ''RT''<sub>60</sub> is measured in [[second]]s.