Transfer matrix of curved duct bends and sound attenuation in curved expansion chambers

Abstract

An explicit formula of the transfer matrix is derived for evaluating the acoustic performance of the chamber including curved duct bends. Based on the derived transfer matrix, the reactive sound attenuation of the chamber can be easily calculated by using an empirical formula for estimating the normalized maximum radial pressure of the fundamental mode in the curved duct bend. Predicted results are compared with experimental ones and they show good agreements. It is found that the classical plane wave theory for the straight duct of equivalent length to the curved duct bend is not applicable if the normalized maximum pressure is greater than 1.3. In addition, the sound attenuation in curved expansion chamber is investigated by studying the effect of geometrical parameters. The derived transfer matrix for the curved duct bend can be easily incorporated as a basic module into any existing computer programs dealing with four-pole parameters for predicting the acoustic performance of HVAC and other silencing systems. (C) 1998 Elsevier Science Ltd. All rights reserved.