Abstract
Higher-order mode sound waves in an infinite rectangular straight duct can be attenuated using a thin flat plate parallel to the duct axis inserted in the duct. The performance of the plate has been confirmed experimentally by the authors for the (1, 0) mode sound wave in the duct. The property of the plate varies according to the length and position of the plate. In this study, the sound field in the duct is numerically calculated using the boundary element method (BEM) for revealing how the plate affects the sound. After the analytical model for BEM appropriately representing the (1, 0) mode wave propagation in the duct is constructed, the reliability of the calculation is confirmed by comparing the calculated results to the measured ones showing the amount of sound reduction by the plate. Then the mechanism of sound attenuation is considered by studying the calculated sound fields (sound pressure distributions) in the duct. The frequency of the sound reduction seems to depend on the relation between the plate length and the axial wavelength of the (1, 0) mode in the area where the plate is inserted.
