An Analytical Method for Expansion Chambers With Continuously Varying Cross-Sectional Area

Abstract

An analytical method is applied to predict the acoustic attenuation performance of expansion chambers with continuously varying cross-sectional area. A feature of the present method is the use of spherical coordinates whose origin is at the top of the cone that is tangent to the wall of the expansion chamber. By this means, the characteristic functions can be analytically determined despite the non-uniform geometry of the expansion chamber. Using the Galerkin method, a variational principle is transformed into linear algebraic equations that are solved to determine the transmission coefficient of the expansion chamber. Numerical results are provided for the case where broadband noise attenuation is achieved.