Analysis of broadband reverberant fields in terms of time-averaged energy and intensity variables using a boundary element formulation

Abstract

In practice, reverberant sound fields often exhibit significant spatial variation in time-averaged sound pressure level and intensity. In this theory for steady-state, high-frequency, broadband, diffuse sound fields, the enclosure boundaries are replaced by a continuous distribution of broadband uncorrelated sources, each of which provides a constituent field expressed in terms of time-averaged energy and intensity variables. Superposition of these fields leads to the overall time-averaged acoustic energy and intensity as a function of position. Boundary conditions for radiating and absorbing surfaces are also recast in terms of energy and intensity variables. The use of these averaged variables, which vary slowly in space, allows direct and efficient calculation of important sound field characteristics. The approach is implemented as a boundary element formulation for efficient evaluation of the pressure and intensity fields in enclosures. Application of the method is illustrated by the solution of model problems, which are also solved by classical means for comparison. The approach is much more efficient than a full frequency-dependent calculation, but it also provides more detailed information than is available from other simple theories. An application is the analysis of moderately absorptive enclosures, such as vehicle interiors.