One of the most important quantities that characterizes an environment in terms of sound is the *reverb time*,
[Reverb
]
and the standard unit used for this evaluation is the *RT _{60}* (Reverb Time). By definition the RT

_{60}is the time taken by an amplitude to decrease by 60 dB from the initial amplitude. This quantity depends on the dimensions of the room's surfaces and their absorption coefficient, and is calculated using the following equation (Sabine equation):

Equation 15.3. Sabine equation for the calculation of the RT_{60}

where:

V is the total volume of the room (measured in m

^{3}).S

_{i}is the area of the i-th surface (measured in m^{2}).a

_{i}is the absorption coefficient of the i-th surface^{[21 ]}.The value 0.161 is a constant multiplying factor.

^{[21
] }
A number that varies between 0 and 1. The 0 value indicates lack of absorption (in other words the surface is totally reflectant), the value 1 indicates total absorption (lack of reflection). Clearly 0 and 1 are theoretical values in that no surfaces that are either completely absorbing or totally reflectant actually exist. In the theoretical case of totally reflectant surfaces we'd have: a_{i} = 0, which, if substituted into the Sabine equation would give an infinite reverb time.