Improvement of sound quality through accurate acoustic diagnostic boundary element analysis

Abstract

The boundary element method (BEM) has long been used effectively in the prediction of sound-pressure levels in acoustic cavities and surrounding vibrating bodies. While this is an important capability in the design of structures for noise constraints, it does not point the engineer to the appropriate remedial action if the noise is found to be excessive. This paper presents a discussion of ‘‘acoustic diagnostic analysis,’’ which is an analytical extension to the BEM which traces the source of any noise to its root cause. The impact of a design change can be seen immediately through the use of sensitivity computations, which clearly show the most effective modifications which can be made for noise reduction. The technique works by calculating the contributions made by each portion of the surface area to the sound-pressure level at an internal point. This allows an accurate evaluation of the contribution made from each part of the panel to the noise experienced at that point. The paper discusses some issues involved in performing the boundary element analysis for sound-pressure level prediction and calculating the panel contributions accurately. The paper also describes recent extensions to the method which allow acoustic diagnostic analysis of multidomain problems, and also how more accuracy can be obtained for problems including sound absorbing materials. Both of these developments have important consequences, in particular in automotive noise reduction. A test example shows how the technique locates the structural panels which are the major contributors to a noise problem, and which are therefore the panels which offer the most noise reduction effect for a given remedial action.