Acoustic attenuation analysis of expansion chambers with extended inlet/outlet

Numerical mode matching (NMM) method is developed to predict and analyze the acoustic attenuation performance of expansion chambers with extended inlet/outlet. The two-dimensional finite element method is employed to extract the transversal eigenvalues and eigenvectors, and the mode matching technique is used to determine the modal amplitudes and transmission loss of expansion chamber silencers by combining the boundary conditions at inlet and outlet. The transmission loss results from the NMM method, three-dimensional finite element method (FEM), and experiment showed good agreements for circular expansion chambers with extended inlet and outlet ducts, which verified the accuracy of the present NMM method in calculating the acoustic attenuation performance of expansion chamber. Then the NMM method is used to investigate the effects of arrangements, extended lengths and locations of inlet and outlet ducts on the acoustic attenuation performance of elliptical expansion chambers. (C) 2013 Institute of Noise Control Engineering.