Abstract:
Recent advances in energetic analysis of sound fields show that three local sound field indicators (eta), (xi), (sigma) accounting, respectively, for the sound radiation, the sound absorption, and the sound energy velocity at any given location of a general sound field can be usefully employed for modeling the reverberation process as a linear feedback system. The input and the output of this black-box model of a general reverberant field are the sound energy density of the associated free-field and the actual sound energy density of the reverberant sound field. It turns out that the energy transfer function of the model system is simply given by the time-average speed of the sound energy at the given location. The local reverberation time formula is obtained from this model by adding up how many ``characteristic times of the acoustic system'' are necessary in order to get an energy feedback contribution 60 dB lower than the steady-state sound energy level of the associated free-field.