| Vol 29 No 2 | CONTENTS |
August 2001 |
Virtual Sensors in Active Noise Control
C.D. Kestell, C.H. Hansen & B.S. Cazzolato
Acoustic Daylight - using ambient noise to see underwater
M.L. Readhead
An approach to estimation of underwater hearing thresholds and noise exposure limits
K. Kuramoto, K. Oimatsu, S. Kuwahara & S. Yamaguchi
Recent developments in the design and performance of road traffic noise barriers
S. Samuels & E. Ancich
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Colin D, Kestell, Colin H, Hansen and Ben S, Cazzolato
Department of Mechanical Engineering,
University of Adelaide SA 5005, Australia
Vol. 29, No. 2 pp 57-61 (2001)
ABSTRACT: Traditional active noise control systems achieve the greatest
noise reduction at the locations of the error sensor(s). In many cases
it is desirable to be able to achieve the maximum noise reduction remote
from an error sensor. One way of doing this is to measure the transfer
function between the desired location of maximum reduction and the error
sensor and incorporate it in the control algorithm. The disadvantage of
this method is that it is not robust to changes in the acoustic
environment. Another method relies on using two or more microphones to
estimate the sound level at a remote location using forward prediction.
This method results in a lower performance but it can be adapted to
changes in the acoustic environment as well as to changes in the
location of the desired pressure minimum. This paper will report on a
study that compares the relative merits of various forward prediction
method in various situations. These commence with a free field
environment (to introduce the concept) and then progress to a more
practical application of an aircraft cabin. Single and multiple control
sources will be considered as will sound pressure sensing and energy
density sensing.
Mark L. Readhead
Maritime Operations Division, Defence Science and Technology Organisation
Vol. 29, No. 2 pp 63-68 (2001)
ABSTRACT: Detection of targets in the ocean using sound is traditionally
achieved with either passive or active sonar. Acoustic daylight is a new
technique being developed, which relies on the ambient noise in the
ocean to provide the acoustic illumination necessary to detect a target.
The presence of a target scatters some of the incident sound which can
be collected by a suitable acoustic lens to produce an image of the
target. An acoustic daylight imaging system developed at Scripps
Institution of Oceanography is described and images obtained of planar,
cylindrical and spherical targets are presented. It was able to image
all targets, with varying resolution and contrast between the target and
background. In some cases it was able to distinguish between different
target compositions through the reflected spectral content. A more
sophisticated imaging system being developed by the DSTO will also be
described.
Kazuoki Kuramoto, Kensei Oimatsu, Shin'ya Kuwahara
Maritime Safety Academy, 5-1 Wakaba, Kure, 737-8512 Japan
Shizuma Yamaguchi
Faculty of Engineering, Yamaguchi University, Tokiwadai, Ube, 755-8611 Japan
Vol. 29, No. 2 pp 69-72 (2001)
ABSTRACT: There are many difficulties to carry out hearing tests in
water, for example, the necessity of preparing audiometric equipment for
underwater measurement and diving equipment (SCUBA) for breathing of
subjects, unavoidable background noise from surrounding and so on. As a
result, there are very few studies on establishing the hearing
thresholds and noise exposure limits in water even though they are
fundamental and important characteristics of underwater hearing in man.
One of the most efficient approaches to acquire these standard values is
through transposition from air to water. We attempted to establish the
relationship between the perceived loudness in water and in air by
conducting hearing tests in a water tank. By applying this relationship
to available data on hearing threshold and noise exposure limit in air,
we have estimated the equivalent thresholds and exposure limits in
water.
Stephen Samuels,
Director TEF Consulting and Visiting Research Fellow UNSW
Eric Ancieh,
Roads and Traffic Authority of NSW
Vol. 29, No. 2 pp 73-78 (2001)
ABSTRACT: This paper deals with some recent developments in the design
and performance of roadside barriers that are applied as a means of
controlling road traffic noise. It is a review paper that is based on
the outcomes of literature and information searches undertaken for and
on behalf of the Roads and Traffic Authority of NSW. Some interesting,
ongoing developments in the design and performance of traffic noise
barriers have been identified. In particular, three types of innovative
barrier designs were identified that appear to offer the potential for
increased attenuation without the need for substantial increases in
barrier height. Each of these developments is considered in some detail
in the paper and recommendations are made for the possibility of
pursuing them further.