A theoretical method has been presented to describe sound decay in building enclosures and to simulate the room impulse response (RIR) employed for prediction of the indoor reverberation characteristics. The method was based on a solution of wave equation having the form of a series whose time-decaying components represent responses of acoustic modes to an impulse sound source. For small sound absorption on room walls this solution was found by means of the method of variation of parameters. A decay function was computed via the time-reverse integration of the squared RIR. Computer simulations carried out for a rectangular enclosure have proved that the RIR function reproduces the structure of a sound field in the initial stage of sound decay suffciently well. They have also shown that band-limitedness of the RIR has evident influence on the shape of the decay function and predicted decay times.

This study presents an analysis of the effect of the concentrated mass on the acoustic power and the resonant frequencies of a vibrating thin circular plate. The fluid-structure interactions and the acoustic wave radiation effect have been included. The eigenfunction expansion has been used to express the transverse displacement of the plate. The appropriate number of modes is determined approximately to achieve physically correct results. Then highly accurate results are obtained numerically. The radiated acoustic power has been used to determine the resonant frequencies. The introducing of the concentrated mass is justified by modelling the added mass of the moving component of the exciter.