A study of damping effects on spatial distribution and level of reverberant sound in a rectangular acoustic cavity

Based on computer simulations of sound fields in rectangular enclosures, im portant observations are made regarding sound pressure levels and the spati al variation of the broadband reverberant field. From these observations an empirical formula is deduced that describes the slow spatial variation of the broadband reverberant mean-square pressure in one lengthwise direction. Two room shapes were studied: an elongated rectangular enclosure and an al most cubic enclosure, both with broadband sound source(s) on an endwall. So urce position, relative phasing of multiple sources, level, and placement o f absorptive material were variables in the study. The numerical results fo r the spatially averaged mean-square pressure in the reverberant field were often not in very close agreement with values predicted from a traditional Sabine approach. The prediction was improved by accounting for the power a bsorbed on the first reflection and an approximate formula is given for thi s correction factor. The reverberant sound field is characterized by a grad ual spatial variation in the direction away from the source. This spatial v ariation scales exponentially with the sidewall absorptivity, as demonstrat ed by the numerical simulations. An approximate emperical formula is shown to predict this spatial variation fairly well. The computer simulations sho wed elevated sound pressure levels at the enclosure boundaries, for all cas es, and also in the interior, for sound fields excited by a single broadban d source on an endwall. These intensification zones occur along a plane in front of the source and along a plane which corresponds to the reflection o f the source, whether or not the source is on a line of symmetry. (C) 1999 Acoustical Society of American. [S0001-4966(99)00608-6].