Case study: Acoustic attenuation performance of circular expansion chambers with extended end-inlet and side-outlet

The acoustic attenuation performance of circular expansion chambers with ex tended end-inlet and side-outlet is investigated. Three approaches are empl oyed to determine the transmission loss: (1) a one-dimensional analytical a pproach based on axial plane wave propagation for long chambers and diametr al plane wave propagation for short chambers; (2) a three-dimensional compu tational technique based on the boundary element method (BEM); and (3) expe riments on an extended impedance tube set-up. The transmission loss results from the BEM show good agreement with the experiments for the selected con figurations over the frequency range of interest, whereas the plane wave th eory may be used for a reasonable estimate at low frequencies. The effect o f chamber length and relative inlet/outlet location on multidimensional wav e propagation and acoustic attenuation performance of expansion chambers wi th end-inlet and side-outlet is discussed in detail. (C) 2000 Institute of Noise Control Engineering.