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Vol 26 No 1


April 1998


Non-destructive testing of composites using long waves
S. Thwaltes and N.H. Clark
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Noise reduction for friction saws
M A Burgess, H M Williamson and S Kanapathipillai
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Workers compensation for Industrial Deafness
J H Macrae
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Broadband microphone arrays for speech acquisition
Darren B. Ward, Robert C. WIlliamson and Rodney A. Kennedy
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Sound Proofing a Forge
Steven Cooper
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Non-destructive testing of composites using long waves

S. Thwaites and N.H. Clark
CSIRO National Measurement Laboratory,
P.O. Box 218 Lindfield NSW Australia

Vol. 26, No. 1 pp 5-8 (1998)
ABSTRACT: A new technique for detecting faults in composite panels has been developed based on measurements ofthe local phase velocity of low frequency flexural waves. Broadband excitation is used so the method includes source configurations and software to reduce the effect of the reverberant field. An X-Y scanning version has been built employing non-contact methods and a handheld version based on a note book computer has also been constructed. The method has been used on multi-ply panels to determine stiffness matrix elements and lay-up errors. Delaminations and core damage in honeycomb sandwich panels have also been detected via scattering of the waves.

Noise reduction for friction saws

M A Burgess, H M Williamson1 and S Kanapathipillai2
Acoustics and Vibration Unit,
University College, University of New South Wales,
Australian Defence Force Academy,
Canberra, ACT Australia 2600

Vol. 26, No. 1 pp 9-12 (1998)
ABSTRACT: Friction saws are used extensively in industry to cut steel and aluminium pipes and structural sections. In many ClIses they may be the only type of saw which is suitable for the task or because of their speed. The noise levels from friction sawing are such that there is a high potential for hearing damage for the operator and for others in the area. The findings from an investigation of methods for noise reduction for a friction saw are presented. The potential for noise reduction by changing various parameters associated with the sawing process and by the application of damping to the saw and to the product is discussed.

Workers compensation for Industrial Deafness

J. H. Macrae
Hearing Assessment Research
National Acoustic Laboratories
126 Greville Street, Chatswood Australia 2067

Vol. 26, No. 1 pp 13-16 (1998)
ABSTRACT: In 1997, the final report of the Heads of Workers Compensation Authorities made the following recommendations: a percentage loss of hearing (PLH) threshold of 10% will apply for compensability but a PLH of 5% or greater will trigger rehabilitation for the worker and workplace assessment as a preventive initiative; where the threshold for compensability is attained, the full PLH will be compensated; and subsequent claims must demonstrate at least a further 5% deterioration from the previous PLH. The relationship between PLH and requirement for hearing aids and the retest variability of PLH were investigated in order to obtain information that could be used to assess these recommendations. Requirement for hearing aids begins at a PLH of about 5% for some clients and approximately 16% of claimants with a PLH between 5 and 9.9% will require hearing aids. It seems more reasonable, therefore, to set a PLH threshold for compensation of 5% rather than 10%. The standard deviation of the retest variability of PLH was found to be 1.94%. This means that a change in PLH of 4.5%, or 5% when rounded to the nearest whole percentage point, is significant at the 1% level. The recommendation that an increase in PLH of 5% must occur before any subsequent claim can be made therefore seems reasonable.

Broadband microphone arrays for speech acquisition

Darren B. Ward;*1 Robert C. Williamson* and Rodney A. Kennedy2.
*Dept of Engineering, FElT
2Telecommunications Engineering, RSISE
Australian National University
Canberra, ACT 0200


Vol. 26, No. 1 pp 17-20 (1998)
ABSTRACT: A microphone array provides an effective means of hands-free speech acquisition, rmding application in large-room video-conferencing, desktop teleconferencing, and hands-free telephony. Unlike a single omni-directional microphone, the array provides high spatial directivity, allowing it to attenuate room reverberation and other unwanted noise. In this paper, we give an overview of the techniques available for speech acquisition using microphone arrays. In particular we will focus on methods of frequency-invariant bearnforming, in which the array maintains the same spatial response over a wide frequency range.

Sound Proofing a Forge

Steven Cooper,
Steven Cooper Acoustics pty Ltd
28A Woolwich Road, Hunters Hill NSW 2110

Vol. 26, No. 1 pp 21-23 (1998)
ABSTRACT: A major forging company in Sydney was required by the NSW EPA to achieve a substantial noise reduction or be closed down. This paper sets out the acoustic solution developed for the company using a light weight multiple layered construction that achieved the stringent noise limits imposed by the NSW EPA. TIlis noise control solution has been tested and proven to be most effective in achieving an outstanding environmental goal that has also resulted in a significant improvement in the occupational environment for air, noise, light and heat of employees working in the forge.




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