Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/12634
Title: Transmission characteristics of a tee-junction in a rectangular duct at higher-order modes
Authors: Lau, SK
Leung, KH
Issue Date: 2009
Source: Journal of the Acoustical Society of America, 2009, v. 126, no. 6, p. 3028-3039
Abstract: Numerical and experimental studies were undertaken to characterize the noise transmission and scattering properties in higher-order modes across the tee-junction of a rectangular duct used in ventilation and air-conditioning systems. To measure these properties, a formulation of a transmission matrix based on the transfer function and a two-microphone method was devised. The measurement of modal sound transmission and scattering coefficients is demonstrated for a duct element in a rectangular duct. The results of numerical simulations were verified by experiments. The results show that sound transmissions of fundamental mode and higher-order modes across the main duct are high at the eigen-frequencies of the main duct and sidebranch. Weak modal coupling of the branch-modes and the traveling wave in the main duct is observed at or very close to the eigen-frequencies of the sidebranch, which shifts excitation of the higher-order branch-modes at higher frequencies. A decrease in sound transmission and increase in sound scattering into higher-order modes occur with excitation of the axial branch-mode. Excitation of the longitudinal branch-mode due to branch-end reflection also results in lower sound transmission of higher-order modes across the junction along the main duct.
Publisher: Acoustical Society of America
Journal: Journal of the Acoustical Society of America 
ISSN: 0001-4966
EISSN: 1520-8524
DOI: 10.1121/1.3257209
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