Efficient calculation of vehicle interior noise is a challenging task. Classical acoustic boundary element calculations become costly at high frequencies due to the very large number of elements required and must be solved repeatedly for broadband applications. An alternative energy-intensity boundary element method has been formally developed that employs uncorrelated broadband directional intensity sources to predict mean-square pressure distributions in enclosures. The boundary source directivity accounts for local correlation effects and specular reflection. The method is applicable to high modal density fields, but it is not restricted to the usual low-absorption, diffuse, and quasi-uniform assumptions. The approach can accommodate fully specular reflection, or any combination of diffuse and specular reflection. This new method differs from the classical version in that the element size is large compared to an acoustic wavelength and equations are not solved on a frequency-by-frequency basis. These differences lead to an orders-of-magnitude improvement in computational efficiency. In vehicle interiors the sources are typically the vibrating walls of the enclosure. A special treatment for wall vibration sources has been developed for use with the new boundary element method. Calculations of spatially varying mean-square pressures agree well with computationally intensive modal solutions.

In the high-frequency limit, vibrating panels subject to spatially random, temporally broadband forcing are shown to have broadband power and directivity properties than can be characterized by a limited set of parameters, based on numerical simulations. The radiated pressure field is parametrized in terms of direction, wave speed ratio, panel damping, and dimensionless frequency. A source directivity equation dependent on these variables is presented. The radiation properties of this equation are incorporated to simulate vibrating wall panels in an energy/intensity–based boundary-element method (BEM) developed for the prediction of steady-state, broadband, reverberant sound fields in enclosures having either diffusely or specularly reflecting boundaries. The BEM method uses uncorrelated broadband directional intensity sources to construct the source and reflection sound fields and predict mean-square pressure distributions in enclosures. Because uncorrelated broadband directional intensity sources are used, the system does not require a frequency-by-frequency-based solution, thereby reducing computational expense. Simulations are compared to exact solutions obtained by computationally expensive frequency-by-frequency modal methods. When fully developed, the directed application of this method is aircraft interior noise caused by exterior boundary layer excitation on fuselage panels.