The effect of modal localization on reverberant energy decay in a case of two acoustically coupled rooms

In the paper a modal analysis was used to describe a reverberation phenomenon in an
irregularly shaped room. A theoretical model was limited to low sound frequencies, when
eigenmodes are lightly damped, thus they may be approximated by normal acoustic modes
of a hard-walled room. A utility of this method was demonstrated in a numerical example
where the room in a form of two acoustically coupled rectangular subrooms was considered.
A reverberation time was evaluated individually for each subroom from time decay of acoustic
pressure amplitude for different distributions of absorbing materials of room walls and various
positions of sound source under the condition that a total room absorption remained constant.
Calculation results have shown a great influence of modes localization on a reverberant energy
decay for a large difference between the absorption coefficients of walls in subrooms, because
in this case for frequencies of some localized modes a substantial increase in the reverberation
time was observed.