The reverberation time is larger for an empty hall than for a crowded hall. Why ?

A hall has a volume of 10000 m^(3) . Its total absorption is equivalentto 400sq. M of an open window. What will be the effect ona reverberation time if audience fills the hall and increases the absorption by another 400sq. Metre of an open window?

What is reverberation? What will happen if the reverberation time in a big hall is too long?

(7)/(9) of the people present in a hall are sitting in (9)/(13) of the chairs available and the rest are standing. If there are 28 empty chairs, how many chairs would have been still empty if everyone in the hall was sitting?

Area related to a square or rectangular room/hall

What do you mean by reverberation and reverberation time ? How is reverberation controlled ?