Investigation of higher order mode transmission loss in a rectangular air duct with no flow

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Investigation of higher order mode transmission loss in a rectangular air duct with no flow


Author: Leung, Kwan-hao
Title: Investigation of higher order mode transmission loss in a rectangular air duct with no flow
Degree: M.Eng.
Year: 2008
Subject: Hong Kong Polytechnic University -- Dissertations.
Sound -- Transmission.
Air ducts -- Noise control.
Department: Dept. of Building Services Engineering
Pages: xvi, 84, xiii leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record:
Abstract: This dissertation examined, experimentally and theoretically, the higher order mode sound power transmission losses of single branching installed along a rectangular duct in stationary medium. Special efforts were made to develop the high order sound attenuation model, mathematically, which based on the predications of sound power transmission loss by plane wave theory. A set of duct together with single branch and anechoic terminations were designed and produced for experimental purpose. Using the advanced equipment such as frequency pulse analyzer and conditioning amplifier, measurement were conducted in the laboratory of Department of Building Services Engineering at The Hong Kong Polytechnic University. The transmission loss effect of the single branching duct was investigated experimentally. The study found that higher order sound transmission resulted more transmission loss than that on low frequency sound transmission. It has been showed that the single branching took away more acoustical energy at high order mode, and thus reduction of sound power transmission to downstream of the main duct occurred. Further investigations on high order transmission in flow condition should recommend for the provision of accurate and comprehensive information of this behavior for ductwork designers in reality.

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