Development of software for predicting the acoustic attenuation performance of expansion chambers in duct systems

Noise produced by air duct distribution systems in buildings is always a nuisance to occupants. The expansion chamber is one of major items used by engineers to alleviate duct-borne noise problems. Numerical techniques such as the Boundary Element Method (BEM) are commonly used to predict the performance of mufflers used in duct distribution systems in terms of Transmission Loss (TL). In this paper, computer software based on a 2-dimensional BEM and a 3-point method is developed for calculating the TL of a simple axisymmetric expansion chamber muffler. Computed values of the TL obtained by the software are compared with published experimental data. The effect of the length of the chamber on its acoustic attenuation performance is shown.