A study of sound attenuation of duct elements

Pao Yue-kong Library Electronic Theses Database

A study of sound attenuation of duct elements


Author: Li, Yee-cheong
Title: A study of sound attenuation of duct elements
Degree: M.Sc.
Year: 2002
Subject: Hong Kong Polytechnic University -- Dissertations
Air ducts -- Acoustic properties
Air ducts -- Noise -- Measurement
Department: Multi-disciplinary Studies
Dept. of Building Services Engineering
Pages: iii, 89 leaves : ill. (some col.) ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1661015
URI: http://theses.lib.polyu.edu.hk/handle/200/1676
Abstract: This dissertation describes the sound propagation in a rectangular air duct and investigates experimentally the effect of sound attenuation due to the branch duct fitting under either air flow or non-air flow condition. A set of duct models was designed, produced and modified for experiment. Modified Two Microphone Method (1), (2) is adopted for the analysis of the experimental results. Results from the experiment are consistent with the acoustics theories for the branch element, the attenuation effect of a single branch element is frequency dependent. The influence on attenuation performance due to the air steam in the duct models was not significant when the airflow velocity was below 5.0m/s. The influence enlarged dramatically when the airflow was further raised up from 50m/s to 7.2m/s, but, the existing duct models were found to be unsuitable for performing experiment in this high velocity range. Increase in branch duct length or increase in the separation distance between the branch elements induces an increase in overall attenuation performance of the branch elements. Further investigations on other prevalent air duct fittings are recommended for the provision of valuable information to both Acoustic Scientists and HVAC Design Engineers.

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