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Vol 25 No 1

CONTENTS

April 1997


ARTICLES

Wavelets and Heart Sounds
RJ Alfredson
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Application of Active Noise Control to Noise Barriers
J Guo and J Pan
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Impact Sound Insulation of Building Partitions: Its Measurement and inherent Difficulties
K Cook
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Design of a Test Facility for Vibration Isolator Characterisation
J D Dlckens and C J Norwood
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Acoustic Design at RMIT University
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AAS Membership Grading
K Cook
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Wavelets and Heart Sounds

R.J. Alfredson
Department of Mechanical Engineering
Monash University, Clayton, Vic.

Vol. 25, No. 1 pp 5-10 (1997)
ABSTRACT: Simple quantitative procedures for analysing heart sounds have been investigated. They are based on the discrete wavelet transfonn. DWT, particularly those developed within the past decade or so. The early indications are that these transfonns are particularly useful in being able to identify clearly the presence of munnur and of some low frequency phenomena associated with abnonnal heart sounds. While the origin of the first is well understood, the source of the latter requires further investigation. It occurs at frequencies well below the audio-frequency range and would not be detected with normal auscultatory procedures. The work is continuing.

Application of Active Noise Control to Noise Barriers

Jingnan Guo and Jie Pan
Department of Mechanical and Materials Engineering
University of Western Australia, Nedlands, WA 6907

Vol. 25, No. 1 pp 11-16 (1997)
ABSTRACT: Previous work has shown that active noise control technology may improve the low frequency performance of noise barriers. In this paper, such a possibility is confirmed. A multi-channel active control system has been used to create quiet zones on the top of a barrier in order to reduce the diffraction along the top, and to increase the insertion loss of the barrier. Both the simulation and experimental results obtained showed that a barrier assisted with an active noise control device achieves extra noise attenuation when the control system is optimally arranged. The results also demonstrate that active noise control is particularly effective at low frequencies in increasing the insertion loss of a noise barrier. This feature of active noise control overcomes the weakness of noise barriers at low frequencies.

Impact Sound Insulation of Building Partitions: Its Measurement and inherent Difficulties

Ken Cook
Department of Applied Physics, RMIT,
GPO Box 2476V, Melbourne, Vic 3001

Vol. 25, No. 1 pp 17-21 (1997)
ABSTRACT: Part F5 of the Building Code of Australia 1990 contains performance requirements in relation to the resistance of building partitions to the transmission of impact sounds. The Code specifies the method required under laboratory conditions. The construction is deemed-to-satisfy if it is no less resistant to impact sound than one of three specified walls. Measurements have been carried out on a number of commercial partitions. Great difficulties are experienced so far as details/requirements are concerned, and even more in the interpretation of results. In this paper these difficulties are pointed out, with suggestions for modification of the Code and possible adoption of a means of the expression of results by a single number. Some alarming errors in measured values due to unexpected flanking paths have been detected. Accordingly it has been decided to eliminate the reporting of actual measured values of impact insulation.

Design of a Test Facility for Vibration Isolator Characterisation

J. D. Dickens, and C. J. Norwood
Ship Structures and Materials Division
Aeronautical and Maritime Research Laboratory, DSTO
506 Lorimer Street, Fishermens Bend, 3207

Vol. 25, No. 1 pp 23-28 (1997)
ABSTRACT: Vibration isolators are an important element in the reduction of structure-borne noise transmission. The dynamic properties need to be determined at the pre-load and over the frequency range experienced in normal operation. The four-pole parameters description of the isolator dynamic properties is independent of the testing arrangement. A test facility has been designed to measure the four-pole parameters of vibration isolators with pre-loads up to 30 kN and over a frequency range from 10Hz to 2000 Hz. This paper describes the dynamic design of the test facility using modal analysis and harmonic response analysis.

Acoustic Design at RMIT University

Robyn Lines and Neil McLachlan
Faculty of Environmental Design and Construction
RMIT, Melbourne

Vol. 25, No. 1 pp 29-30 (1997)
ABSTRACT: The Australasian Soundscape Project in the Faculty of Environmental Design and Construction at RMIT University has introduced a new minor study in acoustic design for architecture and design students. The study seeks to emphasise the contribution of sound to the experience of space through a series of practical and theoretical design and analysis subjects.

AAS Membership Grading

Ken Cook
Chairman of CSCM

Vol. 25, No. 1 pp 31-32(1997)

 

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ACOUSTICS 2017

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