Prediction of the performance of the expansion chamber in air ducts

An expansion chamber is frequently used as an acoustics silencer for the control of duct-borne noise in ventilation systems. The flow of air and the effect of sound pressure may cause the vibration of the end plates of the expansion chamber and in turn will influence the performance (usually in terms of the transmission loss (TL)) of the expansion chamber. By combining the plate bending element and the plane stress element, BEM (for acoustics systems) and FEM (for the structure analysis) are applied to predict the performance of the expansion muffler. A method for calculating the TL for acoustics silencer using BEM-FEM coupled model is therefore presented, and an improved method based on the four-pole parameters used in the BEM is obtained.