The European Directive on Construction Protection against noise applies to all buildings occupied by people.
A specific paragraph addresses Reverberant Noise and how to handle it. Intesting is the use of equivalent absorption area.
extract from the Directive below:
Protection against excessive reverberant noise
“The noise within a room is a function, on the one hand, of the acoustic power level of the sources and of the geometric characteristics of the room, which are neutral with regard to products, and on the other hand, of the acoustic absorption coefficient of the materials comprising the different walls and the other furniture. This protection is characterised by the reverberation time T of the room or by the equivalent absorption area.
The equivalent absorption area can be calculated by:
sum(Siai) + sum(Aj)
Si : surface areas with subscript i
and by frequency bands:
ai : sound absorption coefficient of the surfaces with the subscript i
Aj : equivalent sound absorption area of other surfaces than Si
This equivalent sound absorption area and the reverberation time T are expressed by their single number ratings or in frequency bands as appropriate.”