Full Paper(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
ABSTRACT
While research on hearing and perception of room acoustics has produced a great
deal of information concerning the qualitative auditory sensations imparted on
listeners in rooms (reverberance, clarity, etc), little is known about the quantitative
information that listeners obtain concerning the rooms encountered in their everyday
lives. Information about room size, floor construction, room shape, and many other
aspects is transmitted acoustically to listeners in their environments, but it
is the sense of vision that is erroneously assumed to provide all of this information
to humans. A common listening task which has been left behind in research, however,
is the ability of perceiving the size of rooms. In this study, subjective experiments
with blindfolded people were conducted to obtain room size ratings. Anechoic speech
was reproduced over loudspeakers in three small rooms and the relationships between
the room acoustical parameters and the room size judgements were investigated.
The results were compared with results from previous studies where modelled and
measured rooms were used for subjective testing.
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.