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, important observations are made regarding sound pressure levels and the spatial 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 almost cubic enclosure, both with broadband sound source(s) on an endwall. Source position, relative phasing of multiple sources, level, and placement of absorptive material were variables in the study. The numerical results for 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 absorbed on the first reflection and an approximate formula is given for this correction factor. The reverberant sound field is characterized by a gradual spatial variation in the direction away from the source. This spatial variation scales exponentially with the sidewall absorptivity, as demonstrated by the numerical simulations. An approximate emperical formula is shown to predict this spatial variation fairly well. The computer simulations showed elevated sound pressure levels at the enclosure boundaries, for all cases, and also in the interior, for sound fields excited by a single broadband 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 of the source, whether or not the source is on a line of symmetry.
Franzoni, LP; Labrozzi, DS
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