Table of Contents
(1) Acoustics Research Centre, University of Salford, Manchester, UK
ABSTRACT
The concept of Virtual Acoustic Prototypes (VAPs) is explained and is
illustrated with examples. A VAP is a computer representation of a
machine (e.g. a lawnmower), such that it can be heard without it
necessarily having to exist as a physical assembly. It is argued that,
whereas visualisation tools are well developed in the field of visual
design, equivalent tools for auralisation, such as VAPs, are still in
their infancy. Examples of VAPs for a fridge, a telecommunications base
station and a washing machine are presented, through which it becomes
clear that considerable sophistication is required to include all the
various excitation and transmission mechanisms found in real machines.
It is explained that VAPs cannot be purely
‘virtual’ and
that some measured data will be needed for the foreseeable future,
particularly to characterise active components. Some of the advantages
of working with VAPs are outlined.
SSC San Diego, c/o Naval Postgraduate School, Physics Department, Monterey, CA 93943, United States
ABSTRACT
Seaweb networks interconnect fixed and mobile nodes distributed across
a wide area in the undersea environment. Acoustic communications
between neighboring DSP-equipped telesonar modems is the basis for the
physical layer. Node-to-node ranging is a by-product of telesonar
signaling, permitting localization of sensor nodes and navigation of
mobile nodes such as submarines and autonomous vehicles. The unusual
characteristics of the physical-layer medium constrain the design of
the link and network layers. Seaweb data-packet communications are
achieved through the ancillary use of compact channel-tolerant utility
packets. Measuring the available acoustic channel permits link
optimization by adapting the data-packet signal parameters to the
prevailing channel attributes. Link-layer methods including forward
error correction, handshaking, and automatic repeat request provide
reliability. Network-layer mechanisms such as distributed routing
tables, neighbor-sense multiple access, packet serialization, and
return receipts enhance quality of service. This paper reviews the
concept of operations for undersea networks with illustrative examples
of actual Seaweb deployments.
Research School of Physical Sciences and Engineering, Australian National University, Canberra 0200, Australia
ABSTRACT
Nearly all animals use sound for communication, for seeking prey, and
for avoiding predators. What physical principles govern their choice of
frequency? What are their mechanisms of sound production and
directional hearing? Why are cicadas so loud? How do birds produce
those beautiful, or sometimes not-so-beautiful, sounds? Quantitative
analysis of the acoustic mechanisms involved reveals (nearly)
all: the action of the sensory hairs on caterpillars, the
hollow bodies of cicadas that act as resonators, the horn-shaped
burrows dug by crickets and their remarkably human-like auditory
anatomy, the inflatable vocal sacs used by “pure
tone” songbirds and by frogs, and the chaotic structure of
the shrieks of sulphur-crested cockatoos. This lecture will
explore all these matters and perhaps some more.
Acoustics and Vibration Unit, UNSW@ADFA, Canberra, ACT 2600
ABSTRACT
The Australian Acoustical Society is a professional society with
membership from all aspects of acoustics (including vibration). One
important concern, from an investigation of the top ten issues for the
Membership, was the future for acoustics in Australia as a whole. This
was further investigated and two major areas were identified: changes
in the approach of the government regarding support for publicly funded
facilities and opportunities for education in acoustics. This paper
provides an overview of the findings thus far and is intended to be an
introduction to the workshop discussion on this topic.
School of Mechanical Engineering, The University of Adelaide, Australia
ABSTRACT
Conventional Active Noise Control (ANC) systems that minimise pressure
at a point in space have typically used loudspeakers as control
sources, which are virtually omnidirectional within the low frequency
range of interest. One obvious disadvantage of this is that locations
remote from the desired control point may actually experience an
increase in sound pressure level. The parametric array is capable of
producing a highly directional beam of low frequency sound via the
nonlinear interaction of emitted ultrasonic waves with air. Although
significant research and development of the parametric array for use in
audio systems has been undertaken, the feasibility of using a
parametric array as the control source in an ANC system has not yet
been fully investigated. Within this paper, the theory governing the
operation of the parametric array and the resulting restrictions upon
the production of low frequency sound are discussed. Experimental
testing of a commercially available parametric array indicates that
although highly directive low frequency noise of sufficient amplitude
for some ANC applications can be produced, there are a number of
practical concerns. The noise floor of the parametric array is high at
low frequencies, resulting in a poor signal to noise ratio. The
nonlinear nature of the sound production process means that the precise
control in amplitude and phase required for ANC cannot, as yet, be
achieved. In addition, there are concerns regarding the safety of the
high amplitudes of ultrasound emitted by the parametric array. These
limitations would all need to be overcome before the parametric array
could be successfully implemented as a control source in an ANC system.
Maritime Platforms Division, Defence Science and Technology Organisation, P0 Box 4331, Melbourne, Victoria 3001, Australia
ABSTRACT
A theoretical analysis of the active modal control of radiated pressure
from a finite cylindrical pressure hull is presented. The control
action is implemented through a Tee-sectioned circumferential stiffener
driven by a pair of PZT stack actuators. The actuators are located
under the flange of the stiffener and are driven out of phase to
produce a control moment. This paper examines the effects of control
actions, both structurally and acoustically, for a control moment
applied around the circumference of the hull. The model considered is a
water-loaded finite stiffened cylindrical shell with rigid ends caps.
One end of the shell is excited by an axial force while the other end
is free. Control action is achieved by using the PZT actuators and
stiffener to minimize the structural response and radiated pressure. It
was found that the control system was capable of reducing the radiated
pressure by approximately two-thirds for the first three axial modes.
Vibration and Acoustics Laboratory, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, 24061
ABSTRACT
Adaptive tuned vibration neutralisers are common solutions to
controlling a single but variable frequency disturbance, such as the
interior sound field in a turbo prop aircraft. This paper presents a
study of feedback control of several adaptive vibration neutraliser to
minimize tonal sound radiation from a modally dense rectangular plate.
It is shown that several adaptive vibration neutraliser's using local
feedback loops can be managed by a simple global algorithm to minimize
the sound radiation from a plate. As an adaptive passive approach is
used, each individual adaptive vibration neutraliser can be constrained
to be stable and the resulting global system is also stable. Spatially
averaged single frequency reductions of up to 22dB are experimentally
demonstrated in the radiated field.
Maritime Platforms Division, Defence Science & Technology Organisation, PO Box 4331, Melbourne VIC 3001, Australia. Email: james.forrest@dsto.defence.gov.au
ABSTRACT
One source of structural vibration in a submarine is the fluctuating
axial thrust force applied to the thrust block by the propeller shaft.
This paper describes the initial stages of experimental work being
undertaken to validate an existing mathematical model for the sound
radiation from a submarine excited by this mechanism. A thin
cylindrical shell 1500mm long and 400mm in diameter made of 2mm thick
steel with its ends capped by 20mm thick steel discs is examined. The
shell was suspended from eyelets welded at either end and was excited
axially by a modal shaker mounted inside the cylinder on one of the end
caps. The first few modes with significant axial content were extracted
from frequency-response functions measured at a number of points on the
surface of the cylinder and the end caps and are described. This work
will lead into the development of a sound radiation model suitable for
use in the active vibration control of the cylinder.
(1) School of Mechanical Engineering, the University of Adelaide, SA 5005, Australia
ABSTRACT
The aim of the paper is to develop a robust virtual sensing method
where dynamic variations in the actual acoustic system would not
degrade the sensing performance. The approach here is to consider the
possible uncertainties in the systems and to take into account this
information to develop a virtual sensing method that is robust against
these uncertainties. A certain sensing performance can be enforced and
the task is formulated as an optimal robust control problem that
includes uncertainty modelling. Numerical studies are performed on an
acoustic duct system with varying properties, which show a satisfactory
performance of virtual sensing when the system varies within a
particular range. The proposed approach guarantees a certain level of
performance robustness for virtual sensing when the systems are
expected to vary during operations. Therefore, the approach can be used
for practical implementation in actual acoustic systems where it is
possible that the systems might vary during the sensing and control
operation.
(1) School of Mechanical Engineering, the University of Adelaide, SA 5005, Australia
ABSTRACT
The aim of the research presented in this paper is to actively control
broadband vibration on panel structures using multiple sensors. The
broadband vibration profile of a panel structure is estimated by using
spatial interpolation functions and vibration measurements from the
surface mounted sensors. The control objective is then achieved by
deriving ‘spatial’ error signals whose energy
represents the spatially-weighted vibration energy over the structure.
An optimal H-2 control design using this spatial control approach is
discussed to demonstrate the effectiveness of the broadband spatial
control on a panel. Numerical results show that the broadband vibration
profile can be spatially controlled, not just by minimising the
strength of each vibration mode, but also by controlling the relative
strength of each mode.
(1) School of Mechanical Engineering, The University of Adelade, Adelaide, S.A. 5005, Australia
ABSTRACT
A transducer is described which can be used to measure the
translational and rotational vibratory power transmission from a source
to a receiving structure. A description of the procedure used to
calibrate the device is also included. The results from the calibration
show that whilst the amplitude of the forces, moments, translational
and rotational displacements can be measured accurately, it is the
phase accuracy of these measurements that limit the accuracy of
measurements of vibratory power transmission. The transducer was used
in active vibration isolation experiments to reduce the vibration
energy transmitted into a beam from a vibrating rigid mass. The results
show the occurrence of vibratory power circulation where translational
vibration is converted into rotational vibration.
(1) School of Mechanical Engineering, the University of Adelaide, SA 5005, Australia
ABSTRACT
The paper proposes a beam steering method for regulating sound
radiation from flat panel structures using multiple structural velocity
sensors. Velocity measurements from the structural sensors are used to
estimate the velocity profile of the panel, which is then used to
estimate the acoustic beam pattern of radiated sound. An objective
function is defined for active beam steering purposes, representing the
spatially-averaged error between the reference beam pattern and the
estimated beam pattern of sound radiation in the far-field. Numerical
studies on a rectangular flat panel are used to demonstrate the ability
of the proposed method to regulate a beam pattern of sound for steering
a beam to different directions in the far-field. It is demonstrated
that the proposed method can modify the beam pattern of tonal sound
radiation by modifying the vibration velocity profile of the panel.
School of Mechanical Engineering, Adelaide University, Adelaide, SA5005, Australia
ABSTRACT
Sandwich beam structures constructed with MR fluids can be implemented
as distributed vibration absorbers to suppress unwanted vibrations.
This paper introduces an analytical model for MR structures based on
the Kelvin-Voigt model and Hamilton principle. The relationship between
the magnetic field and the complex shear modulus of MR sandwich beam in
the pre-yield regime is presented. The governing partial differential
equations describing the dynamics of MR sandwich beam are derived and a
model analysis is performed. An active vibration controller based on
Lyapunov stability theory is designed. Simulations show the stable
response and improved transient performance provided by the control
system.
(1) School of Mechanical Engineering, The University of Adelaide, SA, 5005, Australia (2) Phone-Or Ltd, 17 Hataasia St., or-Yehuda 60212, Israel
ABSTRACT
In this paper, an optical sensor capable of measuring pressure and the
three orthogonal particle velocities at a point is presented. This
sensor can be used to measure three-dimensional sound intensity or
energy density in the presence of strong electro-magnetic and
radio-frequency fields. The benefits of the sensor compared to
traditional p-p intensity probes is discussed, as well as the design,
construction and performance of the sensor. It will be seen that this
new type of sensor has many advantages compared to traditional sensors.
School of Engineering, University of Tasmania, Private Bag 65, Hobart, Tasmania 7001
ABSTRACT
Present road traffic noise prediction models, such as TNOISE, use
semi-empirical adjustments to account for factors that influence the
noise level impacting a receiver. Most adjustments are based on actual
sound level measurements, for example of noise attenuation by different
ground types, and hence present models perform satisfactorily for the
simple situations in which the measurements were made. However,
accurate noise prediction in more complex situations is beyond the
ability of such models, because determination of a comprehensive set of
adjustments is defeated by the numerous possible variations in terrain
characteristics, building geometries, and so forth. This paper
describes how this problem can be overcome using a neural network
approach to road traffic noise prediction. We demonstrate how a simple
neural network easily mimics one of the present road traffic noise
models, and how neural networks trained on grid-based data can learn to
predict road traffic noise in complex situations.
(1) Faculty of Architecture, University of Sydney, NSW 2006,
Australia
(2) Faculty of Architecture, University of Sydney, NSW 2006, Australia
Faculty of Architecture, University of Sydney, NSW 2006, Australia
ABSTRACT
This paper reviews techniques for the recording and reproduction of
room sound fields used by the author in a variety of room acoustics
research projects. The paper approaches this first through discussion
of various criteria for assessing the usefulness of sound-field
reproduction/simulation systems. The paper highlights issues in the
recording of impulse responses for audio reproduction (through
convolution) including in the design of the sound source, the design of
microphone arrays, measurement signals, treatment of impulse responses
and larger problems with this process. The greatest focus of this paper
is on audio reproduction methods, with an emphasis on
non-individualized two-channel techniques.
School of Engineering, Murdoch University, Rockingham, 6168, Australia
ABSTRACT
A practical loudspeaker frequency response interpolation model is
developed using a modification of the Tuneable Approximate Piecewise
Linear Regression (TAPLR) model that can provide a complete magnitude
and phase response over the full frequency range of the loudspeaker.
This is achieved by first taking standard one-twelfth octave frequency
interval acoustic intensity measurements at a one meter distance in
front of the loudspeaker. These measurements are inserted directly into
the formulation, which then requires only minimal tuning to achieve a
magnitude response model to better than +/- 1 dB error as compared with
the magnitude of the Fourier transform of the impulse response for
typical hi-fi loudspeakers. The Hilbert transform can then be used to
compute the corresponding phase response directly from the resulting
magnitude response. Even though it is initially based on consecutive
piecewise linear sections this new model provides a continuous smooth
interpolation between the measured values that is much more
satisfactory than normal piecewise linear segment interpolation and
much simpler to do than polynomial interpolation. It only requires the
tuning of a single parameter to control the degree of smoothness from a
stair step response at one extreme to a straight mean horizontal line
at the other. It is easy to find the best tuning parameter value in
between these two extremes by either trial and error or by the
minimisation of a mean squared interpolation error.
Faculty of Electrical Engineering, University of Ljubljana, Trzaska 25, Ljubljana, Slovenia
ABSTRACT
Head Related Transfer Function (HRTF) libraries enable the generation
of virtual acoustic sources in arbitrary spatial positions. In
experiments with a large number of test subjects, general or
non-personified HRTF libraries are used, measured with human-shaped
dolls. The resolution of azimuth in the frontal area is much better
than in lateral areas. To improve resolution in lateral areas,
Principal Component Analysis (PCA) on 37 HRTF magnitudes at elevation
0° was performed. The 1st and, in part,
the 2nd weight were found to be monotonic
functions of azimuth, with greater slope at an azimuth of around
0° and smaller in lateral areas. To enhance resolution in
lateral areas, the weights were linearly interpolated and the slope was
increased to become constant over all azimuths in the median plane
(from -90° to 90°) and reconstructed HRTFs using those
modified weights. Localization tests performed with original and
modified HRTFs showed that resolution in the frontal area remains the
same, while there is a noticeable improvement of resolution in the
lateral areas (azimuths ±90° and
±45°).
Faculty of Electrical Engineering, University of Ljubljana, Ljubljana, Slovenia
ABSTRACT
Spectral features of sound are believed to be the primary cues for the
human perception of spatial sound elevation. It has also been observed
that people connect higher frequencies of sound with a higher elevation
of the sound source and lower frequencies with lower elevations. The
most common approach to creating an acoustic image delivered by
headphones is to use Head Related Transfer Functions (HRTFs).
Unfortunately, satisfactory perception of elevation can only be
achieved with personalized HRTFs which are impractical to measure. This
paper describes an alternative method of sound coding for
representation of the virtual sound source elevation in an acoustic
image. Our method is based on coding particular elevations with sound
stimuli which differ in spectral content. Sound stimuli were created by
various signal processing techniques (e.g. filtration, modulation).
Experiments show that, in certain cases, test subjects were able to
perceive up to 60 different elevations in the range of
–40° to 90°.
Day Design Pty Ltd, Acoustical Consultants, Sydney, NSW
www.daydesign.com.au
ABSTRACT
This paper discusses the general principles of muffler design and
explains the main advantages of various styles of mufflers. When
designing a muffler for any application there are several functional
requirements that should be considered, which include both acoustic and
non-acoustical design issues as detailed in this paper.
(1) Active Noise and Vibration Control Group, Dept. Mechanical Engineering University of Adelaide SA 5006.
ABSTRACT
Radiation of noise from exhaust stacks is a significant source of
community disturbance. In this paper an exhaust stack with an adaptive
length is proposed. The effective length of the stack is changed by
altering the level of water in a sump at the base of the stack, this
level is controlled as a function of the radiated noise from the top of
the stack. The system is modelled as a pipe with an adaptive side
branch. A gradient descent algorithm is used to minimise the radiated
sound. The response to a step change in frequency and a chirp signal is
shown. A simple heuristic controller is compared to the performance
obtained with the gradient descent algorithm and is shown to be
acceptable and computationally simpler.
School of Mechanical Engineering, The University of Adelaide, Adelaide, SA 5005, Australia
ABSTRACT
Numerical optimisations were conducted to reduce the noise levels
inside the payload bay of a rocket by using vibration and acoustic
absorbers attached to the fairing walls. The vibration absorbers act in
both translational and rotational axes. The acoustic absorbers were
modelled as simplified Helmholtz resonators. A Finite Element model of
the vibro-acoustic system was created in ANSYS and the uncoupled
structural and acoustic modal responses were calculated. The combined
response of the acoustic and vibration absorbers, the acoustic cavity
and structural modal responses were coupled using modal coupling theory
in Matlab. The optimisation of the parameters and locations of the
absorbers were conducted using a semi-synchronous parallel genetic
algorithm and a large number of networked desktop computers.
School of Mechanical Engineering, The University of Adelaide, Adelaide, SA 5005, Australia
ABSTRACT
A distributed computing network was created
using the software called Condor and a large number of networked
desktop
computers. This computational tool was used to optimise the design and
location of passive vibration and acoustic absorbers attached to the
payload
fairing of a rocket launch vehicle. This paper describes a mathematical
model to
calculate the coupled vibro-acoustic response of a system from the
uncoupled
structural and acoustic modal responses obtained from finite element
analysis. A
genetic algorithm was used in conjunction with the distributed
computing
network to optimise the parameters of the absorbers. The optimisations
using the
computing network could be completed in significantly less time
compared to a
single desktop computer.
School of Mechanical and Manufacturing Engineering, University of New South Wales, Sydney, NSW 2052, Australia
ABSTRACT
This work is concerned with defining a methodology for adjusting the
design of gearbox casings so that the radiated noise for constant speed
operation is minimised. A baffled rectangular plate having a dimension
similar to that of radiating surface of the gearbox casing was used in
the study to develop the technique. Structural changes such as the
number and arrangement of stiffening ribs were simulated on the plate
and the differences in the radiated sound studied. A valid modal model
of the plate was developed by correlating experimental data with
numerical results. The same updating technique can later be used on the
gearbox model with internals. Pseudo-inverse method was used to
determine the excitation force from the measurement of the surface
vibration and the updated FE model. The same forcing function was used
in the subsequent optimisation studies for which an optimal stiffener
layout was sought for minimising the weighted vibration energy. The
optimisation was performed over a band of frequencies centred on the
dominant excitation frequencies in order to make it less sensitive to
the accuracy of the model as well as the variations from one unit to
another. A procedure for determining an optimal configuration using
genetic algorithm was proposed.
School of Mechanical Engineering, The University of New South Wales, Sydney NSW 2052, Australia
ABSTRACT
The effectiveness of a reactive muffler results from the destructive
interference of acoustic waves travelling within the device.
Cross-sectional area changes within the device produce the interfering
acoustic waves. In this paper, plane wave transmission line theory is
used to predict the acoustic performance of simple expansion chamber
mufflers. The performance is quantified by the frequency-dependent
sound transmission loss. The presence of dissipative materials has also
been considered by the inclusion of a simple model describing wave
propagation in porous materials. The predicted acoustic performance is
obtained for various mufflers and compared with results obtained
experimentally.
(1) Acoustic Group, Hyder Consulting Pty Ltd, Sydney, 141
Walker St, North Sydney, NSW 2060, Australia
(2) Faculty of Engineering, University of Technology, Sydney, POBox
123, Broadway, NSW 2007, Australia
ABSTRACT
An aseismic hybrid control system was employed to protect a five-storey
benchmark-building model against strong earthquakes. The hybrid control
system consists of a base isolation system (laminated rubber bearings)
connected to an active control system (a tuned mass damper and an
actuator). A five-storey benchmark model is developed to study the
effectiveness of the hybrid control system against different ground
motions: El-Centro 1940, Hachinohe 1968, Kobe 1995, and Northridge 1994
earthquakes. It was found from the numerical results, that the rubber
bearing system alone can perform well against Hachinohe and Northridge
ground motions, but not well enough to protect the lower floors of the
model against El-Centro and Kobe ground motions. After an active
control system was implemented to the rubber-isolated model, further
improvements in earthquake resistance against these four earthquakes
were obtained, especially against the El-Centro and Kobe. It is shown
that a combined use of active and passive control systems, (referred to
as hybrid control system), is more effective in reducing the building
response under strong earthquakes.
(1) School of Mechanical Engineering, The University of
Western Australia, Crawley, WA
(2) WorkSafe, Western Australia
(3) Ayers Composite Panels, Western Australia
ABSTRACT
Honeycomb panels are commonly used in ship, aircraft and building
industries because of their lightweight, high-stiffness and
non-combustibility properties. However, they provide very little
absorption to sound approaching to them. This paper reports a
significant improvement of the sound absorption in a broad frequency
range when one of the surface sheets of honeycomb panels is
micro-perforated. Acoustical analysis and test have been used to select
the panel parameters for achieving the optimal sound absorption
performance of the perforated honeycomb panels. One practical outcome
of this study is a new type of micro-perforated honeycomb panels, and
their successful test results for noise reduction in ship building
industry is also presented.
Environmental Resources Management Australia Pty Ltd, Brisbane, Australia
ABSTRACT
Brisbane’s Fortitude Valley is an inner city area combining
retail, commercial, residential, and entertainment uses. For many years
it has been the melting pot for new groups and has been the starting
point for several major Australian bands. The Valley has seen a large
increase in the number of residential apartments over recent years as
part of Brisbane’s inner city urban renewal, which has led to
concerns regarding the impact this may have on the future of live music
in the Valley. To address this issue, the Brisbane City Council is
developing the Valley Music Harmony Plan that includes entertainment
precincts with specific noise criteria within the Valley, and will
allow informed decisions to be made regarding future development while
minimising potential noise conflicts. A picture of the existing noise
climate in the Valley was required to provide background information
for the project. The aim of the study was to provide a noise contour
map of the Fortitude Valley Local Plan area for the day, evening and
night time periods, and to determine suitable times for these periods
given the different nature of the noise climate within the Valley (eg.
traffic jams at 1am, evening and night time levels higher than day time
noise levels). Modelling and monitoring approaches were considered to
produce the noise contours, however monitoring was chosen as the
preferred approach as it would incorporate sporadic sources such as
people’s voices, music, and randomly located mechanical
plant. A monitoring strategy was developed and implemented, including
safety procedures. Measurements were taken at over 330 locations. The
resulting data was used to produce dB(A) and dB(C) contours and provide
specific levels outside venues, which provided a clear indication of
hot spots and areas to be considered for the entertainment precinct.
The work concluded that: road traffic noise dominates the ambient
levels in many areas; the Valley Heart Precinct has the largest number
of entertainment venues and experiences the highest noise levels; in
areas with live entertainment the evening period may effectively extend
to 1.00am; and patrons and pre-recorded music venues may maintain
relatively high ambient noise levels for several hours after the live
music has finished. The noise mapping work has proved an invaluable
tool in the development of the Valley Music Harmony Plan, which was
released in draft form in 2005 by the Brisbane City Council.
WorkSafe Division, Department of Consumer and Employment Protection, Government of Western Australia, Westcentre 1260 Hay Street, West Perth WA 6005, Australia
ABSTRACT
Noise exposure to people working in the music entertainment industry
has long been recognized as a workplace hazard in Western
Australia. The Occupational Health, Safety, and Welfare
Commission of Western Australia first issued a Code of Practice
“Control of Noise in the Music Entertainment
Industry” in 1992. This has been updated several
times, most recently in 2003. To promote the use of this Code
of Practice and noise control in the music entertainment industry, an
inspection project was carried out in late 2004/early 2005 by
WorkSafe. This was a follow-up of a previous project
conducted in 2000. In this present study, a total of 17 music
entertainment venues were visited, 3 of which had been inspected during
the previous project. In each venue, employees’
noise exposures were assessed and noise-related information was
collected via a questionnaire. Information on noise control,
hearing protectors and the Code of Practice were provided to management
at each venue and some law-enforcement actions were taken where
required. Results were analysed and compared to those
obtained in 2000. It has been found from this study that
although the awareness of noise and need for hearing protection has
increased in the industry, noise is still a major
hazard. More work is required to promote practical
noise controls, select suitable hearing protectors and ensure that
these are worn.
(1) Ron Rumble Pty Ltd, Brisbane, Australia (2) Division of Mechanical Engineering, The University of Queensland, Brisbane, Australia
ABSTRACT
Liquor licensing authorities across Australia typically require an
entertainment noise test to be conducted before a venue can host
amplified entertainment. The purpose of this test is to simulate live
entertainment in order to determine the maximum permissible noise
source limits allowed for the venue. In this paper, several
disadvantages of the current method used for entertainment noise
testing are identified and discussed. It was found that the choice of
music can affect the resulting source noise level limits. An
alternative approach has been suggested which involves playing
band-limited pink noise across the 63 to 2kHz octave bands. A
correction is then applied to determine the source noise level limits
associated with different genres of music. The advantages of this
method are that it reduces the time required to conduct the test, the
nuisance caused to neighbouring premises is reduced and the variance in
source noise level limits caused by different choice of test music is
eliminated.
Massey University Wellington, New Zealand
ABSTRACT
Many changes have occurred in the last seventy years, not least of
which are the changes in our environment and
interdependently our intellectual and technological development. The
problems that faced our predecessors at that time were quite different
from those of today, perhaps not as great but, with the limited tools
at their disposal, no less demanding - particularly so in the economic
and political situation of the time. The difficulties they faced were
mainly technological. It was the developmental period of acoustical
measurement and assessment, and they provided the basis on which we
rely for our present day work. The one thing technologically that was
not solved is the lack of accuracy in the measurement of sound. No
doubt this too will be solved in time but a still greater challenge
faces us today - perhaps the most difficult acousticians have ever had
to face. Our problems not only involve sound, but also culture,
possibly genetics, and the side-effects of developments in
communication and mobility.
School of Architecture, Design Science and Planning, University of Sydney, Sydney, Australia jbassett@mail.usyd.edu.au
ABSTRACT
In a changing urban environment the tradition of ringing bells in
church bell towers has, in some circumstances, been significantly
curtailed by the complaints of residents. This paper examines some of
the issues involved in treating bell towers in order to balance the
longstanding tradition of change ringing against the need to minimise
neighbourhood complaints.
(1) Environment Division
(2) Threatened Species Unit
Both within Department of Primary Industries, Water and the
Environment, Tasmania, Australia
ABSTRACT
The Orange-bellied Parrot Neophema chysogaster (OBP) is a threatened,
obligate migrant. The species breeds in south west Tasmania (Oct-Feb)
and migrates along the Tasmanian west coast and western Bass Strait to
South Australia and Victoria where it spends the winter months foraging
in a range of coastal habitats. A method to estimate the total
population and habitat usage during migration and at wintering sites is
difficult for this mobile species which often frequents rugged and
remote areas. The possibility of using long-term audio recording at
various strategic locations throughout the OBP’s range is
being investigated as a survey technique. At this stage it is believed
that long-term recording followed by laboratory-based signal analysis
offers significant advantage over, and is a precursor to, a
call-triggered data logger approach. If successful, the method has the
potential to greatly extend the data collection effort compared to
direct observer methods. The acoustic method can operate at night (OBPs
are known to fly at night) and can be used where continuous observation
is beyond personnel resource availability. Preliminary field trials
indicate that the flight call of the OBP, at between 6 and 8.5 kHz, can
be successfully recorded and subsequently identified by a skilled
ornithologist. The next stages of the investigation are an assessment
of the ‘uniqueness’ of the OBP call compared to
closely related species; development of recording devices and power
supplies suitable for operation in remote locations; and a review of
field trials to determine the potential for development of
call-triggered data loggers.
(1) Belleng Pty Ltd – Water and Environmental
Scientists and Engineers, VDM Group, Gold Coast, Australia
(2) Belleng Pty Ltd – Water and Environmental Scientists and
Engineers, VDM Group, Gold Coast, Australia
ABSTRACT
New residential development was recently established in Coomera at the
Gold Coast to Brisbane urban corridor. The development has an extensive
frontage to a sub-arterial road with an ultimate capacity of 14,000
vehicles per day (Annual Average Daily Traffic - AADT). The houses in
the first row along the road were affected by traffic noise exceeding
the free-field traffic noise criterion of 60dB(A)L10(18 Hour).
The
design of the dwellings (all low-set houses) includes large patios with
pergolas facing the traffic noise source. Considering that the
elevation of the dwellings was at least 2 metres higher than the
elevation of the road it was considered impractical to construct a
noise barrier fence along the property boundary. Instead, acoustic
screens (1.8m high) were recommended along the perimeter of the patios.
Post construction investigation of the efficiency of one of the
acoustic screens was carried out. The aim was to determine the noise
reduction achieved as well as to determine the compliance with the
relevant free-field traffic noise criterion for formal open space of
60dB(A)L10(18 Hour) considering ultimate traffic
flow of 14,000
vehicles AADT. The investigated 1.8m high acoustic screen has
attenuated the traffic noise to below the free-field criterion of
60dB(A)L10(18 Hour) . The noise reduction
achieved for the L10
parameter is 6dB(A), as expected from similar noise barrier fence. It
is considered that an acoustic screen, not higher than 1.8m, can be
viable alternative to standard noise barrier fences to provide noise
protection for the formal open spaces of dwellings along sub-arterial
roads with a maximum design traffic flow of not more than 15,000
vehicles AADT.
(1) University of Zagreb, Faculty of Civil Engineering,
Kaciceva 26, 10000 Zagreb, Croatia
(2) Modern Technologies of Building, Puskariceva 1a, 10000 Zagreb,
Croatia
ABSTRACT
Noise is one of the main causes of reduced quality of life, especially
in urban environments, where noise is constantly present. Complaints
from citizens living and working in urban zones near traffic routes
with intense road and tram traffic are more and more frequent. A study
on the impact of tram traffic, which is one of the greatest generators
of increased noise levels in the City of Zagreb (Croatia), is presented
in this paper. According to data from the International Union of Public
Transport, tram traffic is much more intense in Zagreb than in other
European cities where trams form the backbone of the municipal public
transport system. Since the interaction of the wheel and rail has the
highest impact on the noise levels, the impact of the geometry of rail
welds as a noise contributing factor was studied. Measurements of noise
levels were performed in two phases. The first phase addressed noise
measurements for tracks with irregularities at the weld zone. The
geometry of the irregularities section was first recorded. The second
phase involved measuring noise levels at the same locations, but after
the irregularities of the rail running surfaces were repaired. The
measurements took the tram type and travelling speed into account. That
way it was possible to analyse the results to determine to what extent
tram type and speed influences increased noise levels. This study was
conducted in cooperation with the Zagreb Streetcar Company, the company
in charge of reconstruction and maintenance of the tracks in Zagreb.
The study results helped to define the impact of the rails running
surface geometry in the weld zone on the increased noise levels, and
also to determine permissible tolerances for weld geometry on tram
tracks in Zagreb.
(1) TEF Consulting and Visitng Research Fellow, University New
South Wales, Sydney, Australia
(2) Planning Design and Environment Division, Queensland Department of
Main Roads, Brisbane, Australia
ABSTRACT
This paper presents a follow up investigation of the noise attributes
of several pavement surfaces currently in service in and around
Townsville. The investigation aimed to examine the acoustic performance
of the set of pavement surfaces over time. A previous similar
investigation, which was reported to the 2004 AAS Annual Conference,
involved two extensive data collection exercises which were conducted
in 2002 and 2003. In the present investigation more data were collected
in 2004. Analyses of the data produced values of a parameter known as
the Statistical Passby Index which was applied to quantifying the
acoustic performance of the pavement surfaces over time. It was found
that the acoustic attributes of most of the pavement surfaces remained
reasonably stable over the two year period from 2002 to 2004. This was
not, however, always the case and some explanations for variant
behaviour are presented in the paper. In further exploring these
observations, a subset of the 2004 data set was compared to a
theoretical model of pavement surface noise generation developed by the
first Author several years ago. In addition this data set was compared
to some empirical data also previously collected by the first Author
elsewhere in Australia. These comparisons facilitated explanations of
the acoustical attributes of the Townsville pavement surfaces.
(1) Planning Design and Environment Division, Queensland
Department of Main Roads, Brisbane, Australia
(2) TEF Consulting and Visitng Research Fellow, University New South
Wales, Sydney, Australia
ABSTRACT
Since road pavement surface type is such an important factor in the
generation of traffic noise, much research has been conducted in
Australia and internationally on this topic. Over the last several
years, the Authors have collaborated on a series of investigations for
the Queensland Department of Main Roads (QDMR), which have been
directed at determining the acoustic attributes of various Queensland
pavement surface types. Some of these investigations have been
presented at recent AAS Annual Conferences. The conduct and outcomes of
these investigations, along with their applications, have been brought
together in a document known as the QDMR Pavement Surface Noise
Resource Manual (PSNRM). Throughout the investigations, collection of
the required pavement surface noise data was undertaken according to
the statistical passby technique. In total, 33 Sites of varying
pavement surfaces were included in the investigations and of these 24
were in South East Queensland and 9 were in the Townsville environs.
These data have been analysed to determine the values of the
Statistical Passby Index for the each of the pavement surfaces. The
Statistical Passby Index may be used to quantify the overall effects of
pavement surface type on traffic noise. Thus the paper introduces the
QDMR Pavement Surface Noise Resource Manual, presents some of its key
contents and explains some of its applications.
(1) Manager Environmental Monitoring, RTA NSW
(2) Principal, TEF Consulting and Visiting Research Fellow, UNSW
ABSTRACT
As part of a continuing program of investigations into roadside traffic
noise barrier optimisation, the NSW Roads and Traffic Authority (RTA)
funded a research and development study to develop and evaluate several
full size prototype barrier designs. Of particular interest to this
study was a design known as a Random Edge Profile Barrier since there
was a body of published evidence which indicated that a barrier of this
type can cause a substantial degradation of the noise diffracted over
the barrier edge. As a consequence, it has been suggested that such
barriers are capable of providing improved traffic noise attenuation
compared to conventional barriers. The present study involved an
empirical evaluation of a prototype Random Edge Profile Barrier and the
comparison of its performance with that of conventional barriers and
also with that which is known as a T-Top barrier. In total four
barriers types were constructed alongside a major rural freeway in NSW
and were 80m long by either 2.4m or 3.0m high. A substantial body of
empirical data were collected at various receiver locations in front
of, behind and adjacent to each barrier. Analyses of these data showed
that for the receiver locations investigated, the random edge barrier
out-performed the conventional barrier of the same nominal height for
most frequencies associated with broadband tyre/road noise. The T-Top
barrier was found to perform the best for frequencies greater than 3.15
kHz whilst the conventional barrier offered the most practical solution
for attenuation of low frequency noise.
Department of Environment and Conservation, Sydney, Australia.
ABSTRACT
Maximum LA, (Max) Traffic Noise Events are
reported in the literature as contributing to sleep disturbance in the
community. The New South Wales Department of Environment and
Conservation (DEC) has undertaken a noise monitoring program to measure
maximum traffic noise levels at night using specialised “Mad
Max” Noise Monitoring Equipment. The aim of the study is to
better understand the characteristics of maximum noise events at night
for selected roads and to investigate the behaviour of the Sleep
Disturbance Index (SDI) as proposed by Bullen et al (1996) in these
situations. The noise monitoring program involved selection of six
noise monitoring sites, two sites each for low, medium and high
anticipated maximum noise impacts. Maximum noise levels were measured
in conjunction with concurrent traffic counts and classifications,
using an Acoustics Research Laboratories EL215 data logger and Hewlett
Packard Personal Data Assistant (PDA) configured with “Mad
Max” software. The instrumentation and measurement
methodology is explained to indicate how the SDI is evaluated using
this system. SDI values calculated from the monitoring program are
discussed with observations on what road traffic components appear to
be significant in changing SDI values. Prediction approaches are
discussed to indicate how SDI values may be evaluated as part of an
impact assessment process.
Air Traffic Management, Airservices Australia, Canberra, Australia
ABSTRACT
Airservices Australia (AA) and its predecessors have provided air
traffic control services throughout Australia since the late
1930’s. In 1995 Airservices Australia was established when
the air traffic control functions were separated from the Civil
Aviation Authority. In addition to operating throughout Australia AA
now provides air traffic control services to other countries.
Internationally there is a push to reduce the number of air traffic
service providers as a more efficient system is constantly being argued
by the airline industry. When AA was formed in 1995 it had clear
environmental responsibilities and specific environmental regulatory
functions. AA has established a comprehensive Environmental Management
System which runs parallel with the Safety Management System. Managing
the environmental impact is considered a core AA function, crucial to
this is the ability to report and disseminate useful information on the
impacts of aircraft operations. This paper discusses how AA performs
these tasks with respect to aircraft noise. Recent developments of
credible environment performance metrics to enable AA to report on its
environmental performance will also be discussed.
Dombivli, Maharashtra, India
ABSTRACT
Author worked for three years on resolution of human ear. The
resolution was defined as “just noticeable
difference”
detected at a given base frequency. Large numbers of observations
(10299 no of observations of 522 persons) were segregated into two
groups, musicians and non-musicians. Statistical analysis showed
‘significant’ difference between the two groups.
This gave
the clue to define, formulate, and establish a quotient –
Musical
Notes Quotient (MNQ). Later, after defining MNQ author identified a
method of training, which improved this MNQ considerably, in a very
short period. The subjective opinion that participants (116 &
3079
no of observations) started singing better after the training programme
was tested objectively. The statistical analysis confirmed the
subjective opinion of better singing. The MNQ showed
‘significant’ improvement, which established the
usefulness
of MNQ as a measure of progress in music.
(1) School of Architecture Design Science & Planning,
University of Sydney, Sydney, Australia.
(2) Victorian College of the Arts, University of Melbourne, Melbourne,
Australia.
audiodarnok@yahoo.com
densil@arch.usyd.edu.au
ABSTRACT
A singer's vocal output has to vary depending on the musical work being
performed, the size of the auditorium used for the performance and
other factors. In the work reported on in this paper the small hall and
the large hall voices of professional opera singers were investigated
to determine the spectral and temporal changes in their vocal output.
Recordings of 8 opera singers were made in an anechoic chamber. Singers
were asked to imagine they were in a small hall for one set of
recordings and in a large auditorium for another set. The recordings
were then analysed to determine spectral changes between the large hall
and small hall renditions. Temporal changes were investigated looking
at performance timings of the songs (under different projection
conditions). Psychoacoustical models were also used to evaluate the
recordings.Overall, it was found that large hall song renditions
produced greater amplitude in the 1kHz-4 kHz region as well as faster
tempos compared to small hall performances.
School of Physics, University of NSW, Sydney NSW 2052
ABSTRACT
The different vowel sounds in normal speech are produced by adjusting
the position of tongue, lips and teeth so that the vocal tract
resonates at certain specific frequencies. In voiced speech, these
resonances interact with the harmonics of the lower frequency signal
from the vibrating vocal folds to produce associated peaks, or
formants, in the output spectrum. Singers sometimes use these
resonances in musical rather than linguistic ways. For sopranos, the
vibration frequency of their vocal folds may be much higher than the
normal values for the lowest resonance, and consequently a reduced
interaction would cause a loss of power. Direct measurements of the
resonance frequencies of the vocal tract of classically-trained
sopranos during singing show that they consistently increase them to
match the frequency of their singing. This significantly increases the
loudness and the uniformity of tone, at the expense of
comprehensibility. The fundamental frequency of other singers is
usually less than the value of the lowest resonance and so they would
experience no advantage in tuning this resonance. However the power
could be increased if the resonance frequency were tuned to a harmonic
of the fundamental frequency. Our measurements indeed show that some
altos, tenors and baritones use this strategy when appropriate. The
role of the vocal tract resonances is quite different when playing a
wind instrument. The sound is then generated by the vibrating lip or
reed valve rather than by the vibrating vocal folds. The frequency of
vibration is then primarily determined by one of the strong resonances
of the wind instrument itself. Our measurements show that varying the
resonances of the vocal tract can then still slightly alter the
vibration frequency and change the harmonic structure or timbre of the
produced sound. The described research has involved several members and
associates of our Acoustics Laboratory.
School of Mechanical Engineering, The University of Adelaide, Australia
ABSTRACT
The Boundary Element Method (BEM) is a powerful tool which has become
an important and useful numerical technique applied to problems in
acoustics. It is particularly useful for analysing sound radiation and
acoustic scattering problems. Numerous commercial BEM codes with
graphical user interfaces (GUIs) and mesh generators exist; however
these are relatively expensive, which discourages their use by academic
institutions and smaller companies. Helm3D is a three-dimensional BEM
code available with purchase of a relatively inexpensive book, but the
command file driven interface is difficult to learn and some mechanism
to generate the mesh is required. In addition, there is a limited
availability of suitable tutorial material, so the uptake of BEM
throughout the acoustics community has so far been limited. In this
paper, the development of both a mesh generator / GUI interface for the
Helm3D code and an associated tutorial are described. The interface
links the Helm3D code to a freely available numerical simulation
pre/post processor. The tutorial demonstrates the capability of BEM in
two application areas: interior acoustics and external acoustic
radiation. It is envisaged that the availability of the interface and
tutorial will accelerate the uptake of BEM by the wider acoustics
community.
(1) Department of Mechanical Engineering, University of
Melbourne, Parkville, 3010, Australia
(2) Maritime Platforms Division, Defence Science Technology
Organisation, Fishermans Bend, 3207, Australia
(3) Manufacturing & Infrastructure Tech., Commonwealth
Scientific and Industrial Research Organisation, Highett, 3190,
Australia
ABSTRACT
An upstream turbulence/fluctuation has been shown to increase the
unsteadiness in the wake of a three-dimensional bluff body (Mittal,
2000). This inevitably will influence the radiated acoustic waves in
the far field. In this paper, the effects of fluctuating freestream
disturbances on the wake structure and sound radiation from a
two-dimensional flow over a circular cylinder are investigated. The
flow field is obtained by numerically solving the incompressible
Navier-Stokes equations. At a Reynolds number of 40, the addition of
fluctuating disturbances in the freestream causes the otherwise steady
wake to oscillate at the frequency of the disturbance. This oscillation
is enhanced with increasing energy and frequency of the fluctuations.
The corresponding acoustic field is obtained by using an Expansion
about Incompressible Flow (EIF) method. The computed acoustic field
shows a dipole directivity, which is similar to that of a natural
vortex shedding. Moreover, using the rms plot of the fluctuations of
the EIF source terms, the location of the dipole source in the wake of
the cylinder is accurately identified.
Mechatronics and Intelligent Systems Group, Faculty of
Engineering,
University of Technology Sydney, PO Box 123, Broadway NSW 2007,
Australia
ABSTRACT
Gone are the days when children’s playgrounds were erected on
concrete and asphalt. Impact attenuating playground surfacing has been
common place in most children’s playgrounds for many years.
Unfortunately there is not a strong correlation between the expected
reduction in the frequency and severity of playground injuries. Until
recently testing of playground undersurfacing was restricted to the
laboratory. This paper details the development and description of a
portable data acquisition system for use in playgrounds.
Standards Australia Limited, 286 Sussex Street, Sydney NSW 2000
ABSTRACT
Acoustic standards produced by Standards Australia are developed under
set procedures and policies. My presentation aims to clarify Standards
Australia’s procedures and policies as well as provide
information on current acoustic projects at Standard Australia. General
information regarding Standards Australia will be provided. The
following list questions that will be answered in the presentation:
what is a standard?, who develops the standards?, why are standards
important?, are standards mandatory?, how are standards funded?. The
steps that apply in creating a new Australian standard will be spelled
out. For example, the rules required for a draft to be published - that
is, there must be no major sectional interest maintaining a negative
vote and there must be 80% agreement from committee members. The
periods for committee comment and public comment will also be detailed,
as well as, how the public is encouraged to actively participate in the
commenting process. Statistical information on Standards Australia will
also be listed - for instance; how many standards are published, what
percentage of standards published are made mandatory etc. Logistical
information such as how does someone become a committee member, and how
can someone request for a new standard to be developed, will be
explained. Current acoustic projects at Standards Australia will also
be provided. This will include the name of existing committees and some
of the projects that are currently being undertaken by those
committees.
Workplace Health and Safety Queensland, Level 4 / 543 Lutwyche Road, Lutwyche Qld 4030, Australia
ABSTRACT
An estimated 220,000 telephone headset using workers are employed in
about 4000 Call Centres across Australia. Call Centres annual
attrition- and average turnover rate (23%), is higher than the general
industry average of 18%. This has been attributed to poor working
conditions, health and safety issues, and stress. Occasionally Call
Centre telephone operators experience acoustic incidents such as a
sudden loud shriek or piercing tone through their headsets. Where these
cause symptoms like; a startle reflex, tingling, dizziness and nausea,
headaches, fullness of hearing or tinnitus, the operator has
experienced an acoustic shock. The sounds originate either from line
faults, misdirected faxes, power supply failures, or manmade sources,
e.g. frustrated customers. Despite these sounds seldom being loud
enough to cause physical damage to the inner ear’s hair cell
structures, their effects on the operator can be devastating and
considered directly related to the level of stress the operator
experiences. Effects range from simple annoyance to incapacity to
continue work or never again being able to work with headsets. Audits
of Call Centres revealed inadequate (acoustic) environments, and
acoustic incident protection, follow up measures and training. Call
Centre managements must ensure that adequate control measures are in
place.
School of Mechanical Engineering, The University of Adelaide, Adelaide, SA 5005, Australia
ABSTRACT
The standards for airborne ultrasound exposure limits were derived from
research conducted by three independent groups in the late 1960s.
Recently,
a regulatory body in the USA has proposed increasing the generally
accepted
exposure limits by 30dB. This paper contains a review of the literature
concerning
the effects of exposure to airborne ultrasound impinging on human ears
and the
suggested exposure limits that are used in several countries.
(1) Noise and Vibration Measurement Systems, Leederville,
Perth, Australia
(2) SVT - Engineering Consultants, Leederville, Perth, Australia
ABSTRACT
There are two methods for evaluating noise exposure in the workplace:
dosimetry using a Personal Sound Exposure Meter (PSEM) and sampling
using a sound level meter (SLM). This paper discusses the advantages
and disadvan-tages of both methods in the context of the fundamental
objectives of an occupational noise survey, i.e. identification of
exposed workers, determination of exposure magnitude, and
identification of the noise sources, processes and ac-tivities that
contribute to exposure. Exposure evaluation using a sound level meter
is quick and reliable when noise levels are relatively low and when
exposure varies little as a function of time. When noise levels are
very high, how-ever, even very small changes in assumed exposure
duration can have a significant effect on the calculated exposure. On
the other hand, dosimetry avoids having to estimate exposure durations
but can take much longer to assess an en-tire workforce. These aspects,
as well as equipment and measurement considerations are discussed and
it is concluded that a well designed measurement strategy is likely to
incorporate both methods.
National Acoustic Laboratories, 126 Greville Street, Chatswood, NSW, 2067, Australia
ABSTRACT
A variation in the method of calculating the attenuation performance of
hearing protectors can produce a simple relation between overall
performance and a single standard deviation. This outcome facilitates
easier comparison of the statistical performance between hearing
protectors and allows for a less complex error analysis procedure. For
example, one such comparison reveals a strong negative correlation
between attenuation and standard deviation which has important
implications on the perceived performance of hearing protectors for the
end user and may partially explain why, particularly in
‘low’ noise environments, hearing protector
programs are not as successful as they should be. This method of
analysis is compatible to any single number rating such as NRR, SNR or
SLC80.
School of Mechanical Engineering, The University of Adelaide, Australia
ABSTRACT
The design and functionality of thermoacoustic refrigerators has been
the focus of considerable attention from the re-search community since
the 1980’s. This environmentally friendly technology has the
potential to become another option for refrigeration, as improvements
in the design and technology are realised. Heat-exchangers are used to
in-crease the efficiency of thermoacoustic systems, however they are
typically complex to manufacture, expensive, and limitations of
heat-exchangers exist in terms of efficiency and durability. Reducing
or eliminating the use of heat-exchangers through the use of
flow-through designs dramatically reduces the cost and complexity of
thermoacoustic systems, potentially with minimal efficiency loss. In
this review paper of flow-through thermoacoustic refrigeration, the
developments of flow-through design and its potential benefits will be
discussed.
School of Mechanical Engineering, The University of Adelaide, South Australia
ABSTRACT
Concerns regarding the environmental impact associated with the use of
current vapour-compression refrigeration systems in automobiles have
led to the investigation of alternative ‘green’
technologies. Thermoacoustic refrigeration, an emerging
‘green’ technology based upon the purposeful use of
high-pressure sound waves to provide cooling, is the most promising
replacement investigated so far. Thermoacoustic refrigerators use
environmentally benign gases, are relatively simple and inexpensive to
manufacture and can operate using a heat source, which leads to their
appeal as a sustainable waste heat recovery device. In this paper, the
feasibility of a thermoacoustic refrigerator driven by recovered heat
from the waste exhaust gases of an automobile is investigated.
Practical considerations and calculations incorporating typical
performance characteristics indicate that an automotive waste-heat
driven thermoacoustic air-conditioner is potentially feasible and
warrants further investigation.
School of Mechanical Engineering, The University of Adelaide, Australia
ABSTRACT
Thermoacoustic refrigeration is an emerging ‘green’
technology based upon the purposeful use of high-pressure sound waves
to provide cooling. This paper describes the development of a
thermoacoustic refrigerator built with the aim of using domestic
‘off the shelf’ parts where possible. The key
considerations and tools used in the design and development of the
thermoacoustic refrigerator are discussed, and results detailing the
performance of the device obtained from direct measurements and
computer modelling are compared.
(1) School of Environmental Science, Murdoch University,
Perth,
Western Australia
(2) Centre for Marine Science and Technology, Curtin University, Perth,
Western Australia
(3) Department of Animal Biology, University of Western Australia,
Perth, Western Australia
ABSTRACT
A number of ambient sound recordings took place in three clear-water
wetlands in Perth, Western Australia for one month in summer, 2003. The
wetlands differed in terms of their degree of enrichment, habitat
structure, substrate material and water depth. Temporal and spatial
variations were evident in the macroinvertebrae distributions and the
biologic calling activity, with seven distinct calls recognised in this
study. Noise levels were greatest at dusk and to a lesser extent at
midnight with chorusing only evident at the most enriched wetland.
Biologics used frequencies ranging from 3 kHz up to around 14 kHz with
the exception of the ‘bird-like song’ which
extended from 500 Hz up to around 10 kHz. There was negligible sound
contribution to ambient noise at low wind speeds of Beaufort Wind Scale
0,1 & 2.
School of Physics, University of Western Australia, Perth, Australia
ABSTRACT
Geographe Bay, south-western Australia has been host to several past
mass live cetacean (whale and dolphin) strandings. It is noticed that
the majority of stranded whales tend to be healthy, toothed cetaceans
(Odontoceti) which employ echolocation as a method of navigation. This
paper explores a bioacoustic mechanism known as sonar termination as a
major factor in the occurrence of these strandings in Geographe Bay.
Sonar termination occurs when a navigational echolocation click
projected towards the coast critically attenuates to a point where it
is not detectable. The paper proposes two mechanisms contributing to
sonar termination: first, the presence of a gently sloping shore and
second, the presence of continuously created stagnant micro sized
bubbles (microbubbles). By depicting a wedge shaped coastline as a
perfect flat reflector the attenuative effect of multiple reflections
and resident microbubbles in a coastal water column on a cetacean
echolocation signal is calculated, and a limiting distance that a
cetacean may be able to detect the presence of a shoreline is
determined from these results. A brief review of the most recent mass
strandings at Dunsborough (03/04/05, 02/06/05) is presented and the
plausibility of the bioacoustic mechanism’s role in the
strandings is investigated.
(1) MOD, Defence Science and Technology Organisation, HMAS
Stirling, Australia
(2) CMST, Curtin University of Technology, Bentley, Australia
(3) School of Engineering Science, Murdoch University, Rockingham,
Australia
(4) MOD, Defence Science and Technology Organisation, Edinburgh,
Australia
ABSTRACT
Snapping shrimp are a well known interference source for underwater
sonar and communication systems, particularly in shallow and harbour
waters. The noise produced by snapping shrimp is highly impulsive and
the amplitude statistics are non-Gaussian. Impulsive noise is most
often modelled in a way that implicitly assumes that the temporal
statistics are Poisson. The Poisson assumption implies that a snap from
any shrimp is completely independent of snaps from other shrimp. This
paper reports on an exploratory analysis of non-Poisson temporal
behaviour in snapping shrimp noise using real acoustic data from
different geographic locations in Australian coastal waters. The
analysis makes use of various statistical techniques applied to snaps
detected in high-pass filtered data using a threshold technique.
Attempts are made to eliminate multi-path effects, which can introduce
correlations between snap arrivals, from other possible effects such as
interactions between shrimp. The results are compared and contrasted
between different geographic locations.
(1) Centre for Marine Science and Technology, Curtin
University, GPO Box U1987, Perth, WA 6845, Australia
(2) Department of Fisheries, Government of Western Australia, PO Box
20, North Beach, WA, 6020, Australia
ABSTRACT
Coastal waters of Western Australia and their associated habitats are
home to many species of demersal fish that migrate to form short-lived
aggregations in order to spawn. These spawning aggregations form at the
same sites over successive, predictable spawning seasons. Due to the
exploitation of demersal finfish spawning aggregations within the West
Coast Bio-region, recent attention has been paid to using acoustic
techniques for assessments of these aggregations, to help evaluate
their sustainability. This management process has been raised as an
important issue. A well established tool for biomass estimates, used in
these evaluations, is single-beam echosounding. As part of the
Management and Monitoring of Fish Spawning Aggregations project of the
Department of Fisheries, acoustic data on fish aggregations have been
recorded during 2004 and 2005, using a SIMRAD EQ60, single-beam
echosounder, operating at frequencies of 38 kHz and 200 kHz. These
recordings were made at various locations around Rottnest Island, where
recurring spawning aggregations have been reported. At selected sites,
towed video and physical sampling techniques were employed to
ground-truth acoustic results. Initial analysis of acoustic backscatter
measurements from selected sites is presented, and possible
correlations between targets and individual species are discussed.
Preliminary conclusions are drawn in respect to the use of a
single-beam echosounder for estimating fish stocks within dense and
sparsely populated aggregations.
(1) CSIRO Marine Research, Floreat, WA, Australia
(2) CSIRO Marine Research, Hobart, TAS, Australia
ABSTRACT
As
part of a multi-disciplinary research effort off the West Australian
coast,
acoustic methodologies are being developed to characterise fine
scale vertical distributions of mesoplankton
(0.1 to 20 mm in length)
using high frequencies: 265,
420, 700, 1100, 1800, 3000 kHz. This
study combines the use of multi high frequency acoustics with discrete
biological samples and physical water column parameters (temperature,
salinity,
fluorescence) over a multi year period. The physical samples were
obtained with
a specially designed Discreet In-situ Plankton Sampler (DIPS) that
collects 6
samples within the water column at targeted depths. The Tracor Acoustic
Profiler System (TAPS) attached to DIPS was operated at a fixed range
of 1.5 m
with a 5 litre sampling volume. We present our initial investigations
of comparing the plankton samples
to the observed values of acoustic reverberation (Sv dB re 1 m. We
examine both the affect of system noise and
low
densities of plankton and how they might
affect our strategy for estimating distribution based
on acoustic models.
This comparison highlights limitations in the
methodology due to the low densities of plankton generally obtained in
the
oligotrophic waters off Western Australia>,
their patchy distribution and potential
heterogeneity of scattering types.
(1) Defence Science and Technology Organisation, and University of Sydney, Sydney, NSW
(2) University of Queensland, Brisbane, QLD,
(3) Scripps Institution of Oceanography, San Diego, CA, USA
(4) University of St. Andrews, St. Andrews, UK
(5) Woods Hole Oceanographic Institution, MA, USA
(6) University of Newcastle, Newcastle, NSW
(7) Brisbane, QLD
ABSTRACT
While there is concern about the potential effects of noise from human
activities on marine mammals, it is very difficult to determine whether
a particular noise exposure has an effect, and if it does, to assess
the long term consequences. So many variables affect the behaviour of
marine mammals in relation to the use of sound that it is difficult to
distinguish behavioural reactions in response to a particular noise
exposure from unrelated behaviour. A lot is known about the sounds
produced by marine mammals, but much less is known about how these are
used, particularly for baleen whales. This paper describes the
methodology and some results of “Controlled Exposure
Experiments” developed by the Humpback Whale Acoustic Research
Collaboration (HARC), a multinational project studying the effects of
noise on humpback whales migrating along the Queensland coast. It
combines the different methods of experimental control used in the
physical sciences with those of the biological sciences. Part of the
methodology is to minimise the effects of as many variables as possible
by choice of the conditions of experiment, and to allow for the effects
of other variables by establishing baseline knowledge of their effects
on normal acoustic behaviour and then to measure these variables during
noise exposure. This involves a wide range of multidisciplinary and
multiplatform measurements and observations, including the behaviour at
and below the surface of subject animals, the movements and vocal
behaviour of all other conspecifics in the area, as well as the
environmental acoustic conditions (propagation, ambient noise)
affecting the use and reception of sound.
DSTO, Adelaide, Australia
ABSTRACT
We study the efficacy of a generalised form of differential encoding of
binary phase shift keyed (BPSK) signals transmitted through a shallow
underwater acoustic communication channel. Using simulations involving
a fixed source and a receiver moving about with the surface waves, we
show that no advantage arises from using the generalised differential
encoding methods. On the contrary, the best results in our study arise
from simple second-order differential BPSK (DBPSK) signalling. This is
in contrast to an earlier study that showed the promise of the
generalised differential encoding methods via simulations. The previous
study did not address the issue of inter-symbol interference (ISI),
whereas we include ISI. It appears that the added complication of
removing ISI significantly reduces the benefits of generalised
differential encoding.
DSTO, Adelaide, Australia
ABSTRACT
A low probability of intercept (LPI) underwater acoustic telemetry
system (UATS) is proposed to transmit sonar products from seabed arrays
to submarines and surface relay buoys. A UATS simulator has been
developed to implement all the steps in the processing chain.
Underwater LPI systems have low transmitter power and hence low data
rates. Techniques have been developed in DSTO to compress sonar
products (2D images) to enable transmission at lower data rates without
significant degradation. This paper studies bit error rates (BERs) and
achievable bit rates for transmitting random messages and compressed
sonar products (CSPs) from the standard UATS, with no channel coding,
through Gaussian and fading channels. It also assesses the quality of
the received and uncompressed CSP images. The effects of applying two
types of forward error correction (FEC) - convolutional and turbo
coding - in Gaussian and fading channels are then evaluated. A
significant improvement in performance for both random messages and
CSPs and hence data rates arises from using convolutional coding in
Gaussian channels, but this improvement is lost in some fading
channels. A greater improvement arises from using turbo coding in
Gaussian channels. For fading channels, this improvement is less but
still significant.
Centre for Marine Science and Technology, Curtin University of
Technology, GPO Box U1987, Perth WA 6845, Australia
CRC for Coastal Zone, Estuary and Waterway Management, Indooroopilly
Sciences Centre, Indooroopilly, Queensland, Australia
ABSTRACT
Multibeam systems are capable of recording acoustic backscatter signals
received from a wide swath of the seafloor. Backscatter characteristics
are well correlated with morphological and physical properties of the
seabed. Thus, a multibeam sonar system is a potentially useful tool for
seafloor characterisation work. As part of the Coastal Water Habitat
Mapping project, a subproject of the CRC for Coastal Zone, Estuary and
Waterway Management, multibeam data and ground-truthing video data have
been collected from various sites around Australia, including Cockburn
Sound in Western Australia. One of the aims of the project is to
investigate the capability of multibeam systems to map seafloor
habitats. Initial work has concentrated on the processing of the
backscatter pulse form. However, for the backscatter to be a useful
tool in tracking changes in seafloor habitats it needs to be invariant
to system settings, oceanic conditions and beam geometry. Most of these
parameters can be easily corrected for, except for angular dependence
of backscatter. Variation in backscatter due to incident angle is
commonly seen in swath sonar images, typically as higher intensities at
nadir angles than for oblique incidence, which can be hard to
compensate. Here a new angular dependence correction algorithm,
developed by the CWHM project, is examined to see how effective it is
at correcting for this phenomenon. The results have implications for
the use of multibeam sonar in seabed classification, which are
discussed.
Centre for Marine Science and Technology, Curtin University of Technology, GPO Box U1987, Perth WA 6845, AUSTRALIA
ABSTRACT
Global warming induced by the greenhouse effect will affect the
Antarctic ice sheet primarily in the form of disintegration of the ice
shelves surrounding the continent. Calving of large icebergs can be
observed post factum from satellites, whereas numerous ice shelf breaks
of smaller volumes and ice rifting processes that precede the calving
events are not well monitored and analysed. Detection and localization
of acoustic signals emitted by ice rifting and calving in Antarctica,
using remote hydroacoustic receive stations in the ocean, can be an
efficient and cost-effective way to monitor disintegration of the
Antarctic ice sheet. An analysis of acoustic noise recordings at the
hydroacoustic listening station installed off Cape Leeuwin, Western
Australia as part of the International Monitoring System of the
Comprehensive Test Ban Treaty, has shown that the majority of the
signals arriving from Antarctica have a pulse-like waveform, a
frequency band limited within 5 - 30 Hz, and spectrograms that reveal
strong waveguide dispersion typical for long-range propagation in the
Polar environmental conditions. The azimuthal location of the detected
events is not uniformly distributed along the observed sector of the
Antarctica coast, and the rate of events varies with the seasons of
year. The results of numerical modelling of acoustic propagation from
Antarctica to the Cape Leeuwin station show that the origin of the
observed signals is short, pulse-like physical processes on the
Antarctic shelf, which are most likely ice rifting and calving events.
(1) School of Mechanical Engineering, The University of New
South Wales, Sydney NSW 2052, Australia
(2) Maritime Platforms Division, Defence Science and Technology
Organisation, Fishermans Bend VIC 3207, Australia
ABSTRACT
This paper examines the reduction of the low frequency acoustic
signature of a submarine by optimal passive tuning of a resonance
changer. The propeller-shafting system is modelled with a combination
of lumped parameter and continuous parameter systems utilising the
transmission matrix method. The submarine hull is modelled as a ring
stiffened finite cylindrical shell submerged in a fluid undergoing
axial excitation from the propeller-shafting system. The total sound
pressure radiated into the far-field from the hull is obtained by using
an approximate closed form solution to the Helmholtz integral equation.
Optimal parameters for the resonance changer are obtained by minimising
the maximum far-field radiated sound pressure using a genetic algorithm.
Nautronix Ltd, Fremantle, Australia
ABSTRACT
A methodology is proposed for the measurement of submarine target
strength whilst in transit, utilising submarine navigation systems and
sonobuoys. Direct sequence spread spectrum signals are transmitted via
VHF to a telemetry relay sonobuoy, which re-transmits the signal
acoustically. A standard sonobuoy receives the signal and relays it to
the data recorder. Using high stability clocks for the synchronisation
of the transmitter and receiver, accurate time-of-flight measurements
can be made between sonobuoy transmitters and receivers via direct and
reflected acoustic paths. The positions of the three objects need to be
known to discriminate between target and surface reflections and to
measure the bistatic angle between the source, target and receiver. The
positions of the target are estimated by the submarines inertial
navigation system, and the positions of the other objects are estimated
using the submarine position as a reference, and constructing a
baseline over time as the submarine moves. Target strength is
calculated by comparing the correlation of the signals received from
the direct path and reflected paths, with reference signals. This
technique enables target strength measurements in negative SNR
environments. The implementation of this methodology is described and
the results of a simulation of an operational scenario are presented.
Emeritus Scientist, DSTO Sydney, Pyrmont NSW, Australia
ABSTRACT
Oceanic sound velocity profiles can vary so as to change important
characteristics of transients propagated over long distances. Staff of
the Scripps Institution of Oceanography fired a series of deep shots
during a transit across the Indian Ocean in 2003. The shot to be
considered was a Signal Underwater Sound (SUS), fired on 29 May at a
depth of 0.9 km in the middle of the ocean. The acoustic signals were
recorded with hydrophones south of Diego Garcia (DGS), and off Cape
Leeuwin (CL). These hydrophones were respectively 1600 km and 4260 km
from the shot. It was noted that the DGS signal had its peak near the
start, whereas the peak of the CL signal was at the end. For a
frequency of 100 Hz, the mode travel times and attenuations along each
path have been computed, using sound velocity profiles based on average
temperature and salinity profiles. Since the source and receivers were
near the SOFAR axis, the transmission losses of the modes generally
increase as the mode number increases. Along the path to DGS, the sound
velocity profile is relatively blunt. As a result, the low-order modes
travel faster than the contributing (non-attenuated) modes of somewhat
higher order. Along the path to CL the sound velocity profile is
relatively sharp and Mode 1 is slow, regardless of seafloor depth. The
difference between the signals can thus be attributed to the different
sound velocity profiles along the respective paths.
(1) Program Office, DSTO Edinburgh, SA 5111, Australia
(2) Centre for Marine Science & Technology, Curtin University
of Technology, Perth WA 6845, Australia
(3) Maritime Operations Division, DSTO Edinburgh, SA 5111, Australia
ABSTRACT
The sound pressure time series received at medium ranges from small
underwater explosives, known as "SUS" charges, have been under close
study in recent years in relation to the potential impact of the use of
such devices on marine fauna, in particular, marine mammals. Past work
has centred on investigations of time series measured in shallow oceans
in the Australian region. Here, at-sea measured data showed,
consistently, received peak levels which were considerably less than
published weak shock theory would have suggested. This paper shows the
results from the analysis of an extended data set, which includes
measurements of SUS signals received along a shallow ocean track in an
additional ocean region. Further, this paper shows the results of
simulations of the time series received along all these tracks. These
simulations of received SUS waveforms, carried out at Curtin
University, have been obtained by generating an inverse Fourier
transform of the product of the oceanic transfer function and the
Fourier transform of an input SUS waveform. The oceanic transfer
function has been based on the use of the SCOOTER model at low
frequencies and a ray model (BELLHOP gaussian beam ray model) at
remaining frequencies. By simulating the received time series in this
way, reasons for the discrepancies between measured peak data and
expectations based on weak shock theory have been investigated and are
presented in this paper.
Emeritus Scientist, DSTO Sydney, Pyrmont NSW, Australia
ABSTRACT
Long-range hydroacoustic propagation at low frequencies is determined
by: (a) the sound velocity profile (SVP) of the ocean as a function of
depth and position on the spheroidal geoid, (b) seafloor topography,
and (c) the acoustic properties of the seabed. Neglecting transverse
refraction, an acoustic path follows a great ellipse on the geoid. The
Antarctic Convergence Zone (ACZ) defines a front between two water
masses with different types of SVPs. It is circumpolar and its latitude
varies between –60° and -50°. The path from
an acoustic pulse
emitted in high southern latitudes to a hydrophone at a temperate
latitude is likely to cross the ACZ. This is expected to change the
shape of the signal and increase its dispersion and complexity. For
Transmission Loss (TL) along a path that crosses the ACZ, it is
expected that there would be no discontinuity in TL at the ACZ, but
there would be a discontinuity in the rate of change of TL with range.
There have been three major experiments that have involved propagation
through the ACZ: (1) Perth to Bermuda in March 1960, (2) Project
Neptune (Cape Town to New Zealand) in April 1964, and (3) the Heard
Island Feasibility Test in January 1991. For the first two, which
involved the firing of shots, both the sources and receiver were north
of the ACZ so there were two crossings of the zone. For the third, the
projector (which emitted tones near a frequency of 57 Hz) was located
within the ACZ, so there was a partial one-way crossing. The results of
these experiments have been reviewed, and it is concluded that the
observed signal shape and TL are broadly consistent with the
expectations listed above.
Defence Science Technology Organisation, A-51, HMAS Stirling, Rockingham, WA 6958, AUSTRALIA
ABSTRACT
Sonar audio is a major tool used by sonar operators to assist in
classifying acoustic contacts. In this paper we discuss some issues
that arise when adaptive beamforming is used for sonar audio. Frequency
domain beamforming is used to reduce computational cost, and diagonal
loading of the cross-spectral matrix is used to obtain the best quality
out-put. The effectiveness of a robust Capon beamformer (RCB) with
nonuniform loading is compared with that of a minimum variance
distortionless response beamformer with uniform loading (MVDRUL). For
the tests described in this paper, which involve a signal together with
a strong interference and background noise, RCB produced the high-est
quality output and was more robust than MVDRUL. On the other hand,
conventional beamforming (CBF) failed to provide a satisfactory output
for any test.
(1) Maritime Operations Division, DSTO, Edinburgh SA
(2) Department of Electrical and Electronic Engineering, University of
Melbourne VIC
ABSTRACT
The use of high bandwidth pulses in active sonar systems can reduce
interference from reverberation and variability due to channel fading.
However, the matched filter detection performance is degraded more by
acoustic multipath when the bandwidth is increased. The performance
degradation due to multipath distortion results when the destructive
interference of the paths cancels some frequencies reducing the
similarity between the echo and the transmitted pulse required for
matched filter operation. Increased bandwidth means that more
frequencies are cancelled so distortion and degradation increases. If
the acoustic properties of the channel are known well enough to predict
the acoustic multipath characteristics, detection can be improved by
matched filtering for the distorted signal rather than the transmitted
signal. In cases where the channel properties are unknown, acoustic
path delays and amplitudes must be estimated from the data itself. In
this paper the acoustic path delays and amplitudes are first estimated
using the Expectation Maximisation (EM) algorithm. The estimates are
then used to integrate the return from each path recovering part of the
loss caused by multipath distortion.
National Key Lab of Underwater Technology, Harbin Engineering University， Harbin, China
ABSTRACT
Two inspecting sonar-High Resolution Multi-beam Sonar (HRMS) and
Profiling Sonar (PS) - mainly presented in this paper. The ROV which
carries them will also be briefly described. Some experimental results
have shown that the ROV equipped with the developed sonars under
control of the movement programs can give accurate maps for either the
surface shape or the internal structure of underwater objects, so it is
applicable for many underwater engineering cases.