Replacing average absorption with summed open-window area handles mixed materials.

Evidence

The denominator in the Sabine reverberation equation, Equation 6.19, is also equivalent to the open window area of the room but has been calculated using the average absorption coefficient in the room. It is therefore easy to incorporate the effects of different materials by simply calculating the total open window area for different materials, using the method described earlier, and substituting it for S α in Equation 6.19. This gives a modified equation that allows for a variety of frequencydependent materials in the room as: where αi ( f ) = absorption coefficient for a given material For the Norris-Eyring reverberation time equation, the situation is a little more complicated because the equation does not use the open window area directly. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1891

Categorization

• XREF: Links to the earlier derivation of the Sabine equation and its average-absorption simplification.