Measurement of total structure-borne sound power transmission from a building services machine by direct and indirect methods

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Measurement of total structure-borne sound power transmission from a building services machine by direct and indirect methods


Author: Lau, Ka-chi James
Title: Measurement of total structure-borne sound power transmission from a building services machine by direct and indirect methods
Degree: M.Eng.
Year: 2011
Subject: Vibration--Measurement.
Noise-- Measurement.
Architectural acoustics-- Measurement
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: xii, 86, [30] leaves :ill. (some col.) ;30 cm.
Abstract: The concern of aural comfort in buildings is growing in recent decades in both air-borne and structure-borne noise. In structure-borne noise control, vibration isolators are widely used in building services machines. However, the traditional performance indicator - Force Transmissibility (T) for vibration isolator selection may result inaccurate isolator selection since floor mobility is neglected in the calculation. Therefore, researchers [6-8] proposed using Power Transmissibility (γ) as an indicator for the selection of vibration isolator that is defined as the ratio of structure-borne sound power transmitted to floor with and without the installation of vibration isolator. Unlike the well-developed air-borne sound measurement, there are still no practical methods available for building services engineers to predict or measure the structure-borne sound generated from machines. The theoretically direct measurement method is not practical in reality as it requires to insert force transducers under the contact points of a heavy machine during measurement period. Therefore, an indirect measurement method is proposed in this dissertation in order to circumvent this practical problem. The main objective of this study is to investigate the accuracy of indirect measurement method, and act as a preliminary study on indirect structure-borne sound power measurement for future development. A single-phase small size induction motor was considered as multi contact-point vibration sources in a building to evaluate the accuracy of the proposed indirect method by comparing with the measurement results obtained from direct measurement method in same situation. The data in this study were collected by means of site measurement in the acoustic chamber in The Hong Kong Polytechnic University to minimize the effects from other vibration sound sources. The measurement error of indirect measurement method in total structure-borne sound power was around 20% comparing with direct measurement method under same measurement condition, and the accuracy of structure-borne sound power measurement in both total and single contact point measurement can be increased by shorten the distance of indirect measurement points. The measurement results indicate that the indirect measurement method can provide reasonable accurate measurement results in both total and single contact point structure-borne sound power measurement in close range. Large-scale building services machine such as air handling unit on concrete plinth is recommended to use in future studies to justify the accuracy and feasibility of indirect measurement method in real cases.

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