Full Paper(1) School of Mechanical Engineering, the University of Adelaide, Adelaide, SA, Australia (2) Departamento de Engenharia Mecânica, UFSC, Florianopolis, SC, Brasil
ABSTRACT
An unusual ANC approach using structural sensors and actuators is investigated for its effectiveness in actively attenuating the sound radiation from an irregular enclosure excited by an internal sound field. The intention of the control strategy is to control the enclosure vibrations in such a way that the radiated sound field is minimized. For the case considered here the interior noise spectrum has most of its energy below the first enclosure structural resonance frequency, thus complicating the control design. Here the design of a suitable control system for this problem is described. This is followed by a discussion concerning the type and reliability of the equipment which is most appropriate, after which experimental results illustrating the performance of this approach are presented. The experimental data show a direct correlation between the reduction in enclosure surface vibration and the reduction in noise radiation.
(1) School of Mechanical Engineering, the University of Adelaide, SA 5005 Australia (2) Department of Systems Design Engineering, Tokyo Metropolitan University, 6-6 Asahigaoka, Hino-city, Tokyo 191-0065 Japan
ABSTRACT
The work is aimed to investigate the method to create a zone of quiet (vibration) on a structure by modifying its vibration power flow. Since the vibration behaviour can be related to how the vibration power flows, it is possible to control the vibration profile by forcing the power to flow to a certain direction over the structure. Therefore, it should also be possible to vary the location for the zone of quiet by redirecting the power flow. Numerical simulations on a panel structure are performed to investigate the effect of redirecting the power flow to change the structural vibration behaviour, where it is found that it is possible to achieve a zone of quiet by power flow modification.
(1) School of Mechanical Engineering, the University of Adelaide, SA 5005 Australia (2) Department of Systems Design Engineering, Tokyo Metropolitan University, 6-6 Asahigaoka, Hino-city, Tokyo 191-0065 Japan
ABSTRACT
The work is aimed to develop a strategy for controlling general multi-objective functions using a cluster control method. A set of multiple quadratic objective functions is described as a set of clusters, in which each cluster represents a particular objective function. The proposed clustering method will thus allow a simple control procedure since only the associated cluster needs to be controlled. This general cluster control method can be used for a variety of vibration and structural-acoustic control, such as for vibration or acoustic control at varying locations yielding a multi-objective control problem. An optimisation procedure is developed to simultaneously determine the locations of sensors used and the clustering parameter. A case study on a structural-acoustic system is provided to demonstrate the effectiveness of the proposed cluster-control method to target the sound power contributed by a particular set of structural modes.
School of Mechanical Engineering, the University of Adelaide, SA 5005 Australia
ABSTRACT
The focus of the paper is to control the far-field sound radiation from an arbitrary planar structure using multiple structural sensors, particularly for broadband applications. A number of structural velocity sensors are distributed over the structure for sensing the sound radiation at a particular far-field region for control purposes. Spatial control of structural sound radiation is achieved by constructing a frequency-independent spatial filter that reflects the spatially-weighted sound radiation energy. Thus, the signal produced by the spatial filter can be used as an error signal to be minimised by standard active control methods. A numerical case study on the sound radiation of a flat panel structure is performed to investigate the control performance using the developed frequency-independent spatial filter.
School of Mechanical Engineering, the University of Adelaide, SA 5005 Australia
ABSTRACT
The aim of the work is to develop a practical active control strategy in which vibration of an arbitrary structure can be spatially-weighted for achieving a vibration reduction at the structural region of interest. Multiple sensors are used to sense the vibration of the entire arbitrary structure and a filtered-reference Least Mean Square (FX-LMS)-based adaptive control strategy is used to minimise the instantaneous error energy representing the spatially weighted vibration energy of the structure. A numerical study for spatial vibration control of a plate structure is discussed to demonstrate the control effectiveness of the adaptive spatial controller for tonal and broadband cases.
(1) School of Mechanical Engineering, University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Australia (2) State Key Laboratory of Modern Acoustics, The Institute of Acoustics, Nanjing University, 210093, China
ABSTRACT
This paper deals with the evaluation of power radiated by two monopoles located near a reflective surface, especially in the case when one monopole-strength is actively controlled for the minimization of total radiated power. The radiated power and the optimal input for the controlled monopole are derived analytically. It is found that the power output of an active noise control system consisting of two point sources and located near a reflective surface is dependent upon the system orientation angle. Based on the mechanism that the reflecting surface can convert a dipole vertical to the surface into a longitudinal quadrupole, we demonstrate that the introduction of a reflecting surface to the active noise control system could further enhance the total power reduction. Experimental results are also included to demonstrate that the effect of a reflecting surface on the sound radiation of a dipole is still significant even though the size of the surface is much smaller than the wavelength of the sound radiation.
Active Noise and Vibration Control Group, University of Adelaide, Adelaide, Australia
ABSTRACT
Global control of sound at audio frequencies in large spaces is challenging and has been a sticking point for the development of active systems for noise control in areas such as factory floors or public spaces. Combining highly directional sound sources and virtual sensing techniques is proposed as a possible solution. Such a system would create localised zones of quiet that can follow an individual through a space. The application of a parametric array as a sound source is discussed in this paper. The parametric array creates an audible directional sound source due to the non-linear interaction of two ultrasound waves. A beamwidth of the order of a few degrees is possible at audio frequencies, however the sound levels produced are quite low. The properties of the source in regard to active control are discussed. Virtual sensing uses an array of microphones to predict the sound field at a remote point. It has been shown that active control of the sound field at a moving virtual error sensor is possible. The criteria for control performance in a 1D sound field using such a sensor are outlined. The advantages and disadvantages of the combination of these two advanced transducers for use in active noise control are discussed in this paper.
School of Mechanical Engineering, The University of Adelaide, Adelaide, S.A. 5005, Australia
ABSTRACT
One of the problems associated with the use of Helmholtz resonators to control tonal noise propagation inside a pipe or duct is that any slight frequency changes in the tonal noise as a result of environmental changes or load changes on the device generating the noise will severely compromise the performance of the resonator. Thus, it is desirable to use an adaptive resonator whose volume or neck length can be adjusted to maintain optimal tuning as the excitation frequency or environmental conditions change. The ideal cost function would be a measure of the sound power propagating down the duct so the control system could minimise this quantity by driving motors that change the geometry of resonator. In practice, it is highly desirable to have available a self-contained adaptive resonator that does not need any external inputs or measures of quantities outside the resonator package. A cost function based on pressure measurements in the resonator, which corresponds to sound power in the duct has been found and verified experimentally and numerically. The effect of resonator damping on the cost function and a method to correct for the effect is also discussed.
School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney, NSW2052, Australia
ABSTRACT
This paper presents the optimization of the location and feedback gains of active bar in a closed loop control system for stochastic piezoelectric smart truss structures under stationary random excitation. The mathematical model with reliability constraints on the mean square value of the structural random dynamic displacement and stress response is developed based on maximization of dissipation energy due to the control action. The randomness of the structural physical materials and geometric dimensions are included in the analysis, and the applied forces are considered as stationary random excitation. The numerical characteristic of the stationary random responses of stochastic piezoelectric smart structures is developed by the random factor method. Numerical examples of piezoelectric truss structures are presented to demonstrate the rationality and validity of the active control model.
VIPAC Engineers & Scientists, Adelaide, South Australia
ABSTRACT
The Department of Transport and Regional Services is overseeing a $63 million federally funded sound insulation program for residential and public buildings surrounding the Adelaide Airport. VIPAC was engaged by the project manager (Clifton Coney Stevens) as the acoustic consultant to design the treatments for the buildings, to oversee the installation of the treatments and to verify its performance.
This paper presents a review of the noise insulation treatment works at St. George College. An analysis of the noise reduction gained within the different buildings of the college (based on pre and post-construction measurements) is presented as well as a comparison with the noise reduction achieved and the noise control treatments utilised in other types of public buildings included in the noise insulation program.
(1) Senior Consultant, Savery & Associates Pty Ltd, Brisbane, Australia (2) Director, Savery & Associates Pty Ltd, Brisbane, Australia
ABSTRACT
Research was conducted into the aircraft noise reduction achieved by an outdoor recreation structure compared to a free-field control measurement location. The outdoor test structure was modified to simulate a building facade with an external overhead verandah or balcony. The test structure was located under the flight-path of the main runway at Brisbane Airport. The structure was configured with three alternative roof-ceiling constructions, including a bare metal option, a transmission loss option and a transmission loss/absorptive ceiling option. Four partial wall configurations/orientations, including the fully-open situation (i.e. no walls) were investigated. For each test configuration, the LAmax,slow flyover was sampled for nominally 10 jet aircraft flyover events and then averaged. The noise level of each flyover event was measured under the centre of the shelter, and at a free-field position 10 m from the edge of the structure. The averaged measured level under the shelter for the various test scenarios ranged from a 1 dB(A) increase compared with the free-field position to a 6.5 dB(A) decrease.
Marshall Day Acoustics, Sydney, Australia
ABSTRACT
The introduction of a third runway at Sydney’s Kingsford Smith Airport and the increased pressure to develop inner city land for residential purposes has resulted in residential development in areas which would usually be considered unsuitable. Recent measurements were conducted at a development located under the flight path which required a glazing specification usually reserved for high performance commercial applications, such as recording studios. This paper examines the requirements of Australian Standard AS2021, the predicted versus the actual onsite glazing performance and the onsite conditions limiting glazing performance.
The Acoustic Group. Sydney, Australia
ABSTRACT
Validation of INM predictions finds agreement when the monitoring position is close to or directly underneath the flight track. At locations to the side of the flight track where the angle from the receiver point to the aircraft is less than 20o, INM underestimates the noise level. With the need for inclusion of helicopters operating at Australian Defence establishments in ANEF contours, investigations have revealed a major component of the aforementioned anomaly to be associated with an incorrect application of lateral attenuation. Correcting the NPD data curves to exclude lateral attenuation found agreement between measurement and predicted results. Following communication with the FAA and presentation of research material to the US Standards committee for Aircraft Noise (SAE-21) an acknowledgement of lateral attenuation discrepancies has resulted in INM version 6.2 having the capability of turning lateral attenuation off. The lateral attenuation difficulties/effects and our procedure for correcting the INM database is discussed.
The Acoustic Group, Sydney, Australia
ABSTRACT
The standard procedure used in the US for derivation of aircraft noise power distance (NPD) curves is to conduct a measurement at one position and extrapolate those results by general acoustic formula with corrections for atmospheric attenuation at standard atmospheres. Initial work undertaken for helicopters operating from military bases in Australia found different rates of attenuation for slant distances less than 1,000ft versus that for slant distances greater than 2,000ft. The position of the aircraft when creating the maximum level at a receiver location is not physically at the slant distance used on an NPD curve for that same position. SAE/FAA procedures for conducting/calibrating NPD curves from field measurements do not exist and from FAA advice, no such work has been carried out. Examination of military jet aircraft and military helicopter operations in Australia, with DGPS positioning and atmospheric attenuation corrections identified in the previous papers has resolved this issue. The NPD derivation investigations are discussed.
The Acoustic Group, Sydney, Australia
ABSTRACT
In relation to predicted aircraft noise levels and derivation of the EPNL for aircraft operations by INM, reliance is placed upon attenuation for atmospheric absorption based on distance, temperature and relative humidity. Measurements of military aircraft (helicopters and fixed wing) for the purpose of deriving noise power distance curves to be used in INM have revealed significant anomalies with measured and theoretical results. Standard practice in the US for deriving NPD curves is to utilise measurements in relatively close proximity to the aircraft, extrapolate a 6 dB per doubling of distance and provide standard atmospheric attenuation. Working backwards from field measurements utilising aircraft distances greater than that used for certification assessments has consistently revealed significant discrepancies. Specific testing in the South Australian desert utilising a twin engine military jet on full afterburners to a height of 5,500m above monitoring microphones has revealed the atmospheric attenuation over distance is not a dB per 100 metres linear rate. The basis of deriving atmospheric attenuation from field measurements, rather than laboratory measurements with dimensions significantly less than 100 metres, is explained.
School of Physics, Monash University, Clayton, Victoria, AUSTRALIA
ABSTRACT
Gaps occur in many acoustic barriers and buildings, allowing sound to pass from one side to another. But exactly how does sound pass through a gap? Measuring the transmitted energy when continuous wave (CW) sound is incident on one side allows an estimate to be made of the energy passing through the crack, but does not permit a detailed analysis of the mechanisms involved. However, if a short duration pulse of sound is used, the transmitted sound exhibits a sequence of pulses in time, obviously linked in some way to various possible paths through the crack. At first sight it is tempting to associate these peaks with a set of modes, similar to those set up in an organ pipe. Unfortunately, simple calculations of path lengths and pulse delays demand an embarrassingly large speed of sound. Moreover, some of the transmitted pulses are significantly narrower than the incident pulse. Perhaps the gap is simply filtering out the lower frequencies - but then why are some pulses broader? A full explanation requires the use of a diffraction theory that provides both magnitude and phase information.
(1) School of Mechanical Engineering, The University of Adelaide, Adelaide, S.A. 5005, Australia
ABSTRACT
A theoretical model is developed to predict the transmission loss of a clamped rectangular plate with an array of lumped masses attached, and is compared with experimental measurements. An increase in the transmission loss of the plate was observed over approximately two octaves, in excess of that expected due to the effect of the ‘smearing’ the added mass over the plate, and these results compared well with a theoretical model. A laser vibrometer was used to measure the average velocity of the plate and the measured results compared favourably with theoretical predictions.
University of Auckland, New Zealand
ABSTRACT
Recently both Australia and New Zealand have felt the need to revise the noise control sections of their building codes. The focus for these codes is the protection of the quality of domestic environments in high density living conditions because of the increasing numbers of people choosing – or being forced into – city living. The success of these revisions depends on the appropriateness of the metrics used for the building insulation performance, the dependability of the way we make and use the measurements and any remaining uncertainties or omissions from the codes. The issues will be reviewed from a New Zealand perspective including - (i) the need for greater recognition of noise sensitivity, privacy sensitivity and social responsibility with respect to noisy behaviour and the use of loudspeakers, (ii) the relationship of measurements to the subjective assessment of building performance, and (iii) recent research on new techniques for conducting field measurements.
(1) Sustainable Consumer Products, Scion, Rotorua, New Zealand. (grant.emms@scionresearch.com) (2) Mathematics Department, University of Auckland, New Zealand. (3)McGunnigle Ltd, Auckland, New Zealand. (4) Acoustics Research Centre, University of Auckland, New Zealand.
ABSTRACT
One of the major problems with the impact insulation of lightweight floors is that they are lightweight, giving problems with impact insulation in the low-frequency region. This paper outlines the results of a New Zealand and Australian project which has been looking at which techniques may be useful in reducing the above problem in lightweight floors, particularly light timber-framed floor systems. Floor designs were produced, incorporating techniques from around the world, and then evaluated in a laboratory setting. The particular emphasis has been to produce floor designs which can be easily built in New Zealand and Australia.
Acoustics Research Centre, The University of Auckland, New Zealand
ABSTRACT
This talk presents a mathematical model of light weight timber floor/ceiling structures. The structures studied here consist of three basic components, upper plate, joist beams and ceiling. The shape of the whole structure is rectangular with the edges simply supported. Connections between the joist beams, the upper plate and the ceiling are considered. This connection conditions include the slippage and the springs. The configuration of the structure is made progressively more complex by adding more components such as cavity air and stiffening battens.
(1) School of Applied Sciences, RMIT University, GPO Box 2476V Melbourne Victoria 3001, Australia (2) CSIRO Manufacturing & Infrastructure Technology, PO Box 56 Highett Victoria 3190, Australia (3) Watson Moss Growcott Acoustics Pty Ltd, 7/696 High Street East Kew Victoria 3102, Australia
ABSTRACT
This paper describes a theoretical method for predicting the directivity of the sound radiated from a panel or opening excited by sound incident on the other side. The method uses a two dimensional strip model and the low frequency result for a square piston. A cosine squared weighting function with a weighting angle parameter is used to account for the angular distribution of the incident sound. The method is compared with published results. The values of the weighting angle parameter which give the best agreement with each set of published results are determined. The directivity depends strongly on the length of the radiating object in the direction of the observer and only slightly on the width of the object at right angles to the direction of the observer. Above its critical frequency a panel radiates strongly at the angle at which coincidence occurs.
Faculty of Architecture, University of Sydney, NSW 2006, Australia
ABSTRACT
In October 2005, the University of Sydney’s Acoustic Research Laboratory experienced a fire, which destroyed much of the facility through smoke and heat damage. This paper tells the story of the fire and its consequences. While the cause of the fire remains undetermined, it seems likely that it started in the lighting system of the anechoic room. The presence of some flammable material in the room, the high degree of thermal insulation, and a compressed air supply to the room established the fire in that room, with hot smoke filling the rest of the laboratory. Laboratory restoration is a slow process, and we report on how teaching and research has been affected. We also describe the features of the restored laboratory, including architectural modifications and a systems-based approach to equipment.
Day Design Pty Ltd, Sydney, Australia www.daydesign.com.au
ABSTRACT
Airborne sound transmission through a masonry wall (150 mm thick clay bricks with 13 mm thick cement render on both sides) changes during the early curing period. Australian Standard AS1191-2002 states: “…masonry walls…should not be tested until after an adequate drying out period.” However the ‘adequate drying out period’ or ageing period is not quantified. Reference may be made to ASTM E90 which recommends a minimum ‘aging period’ of 28 days before a masonry wall's sound transmission loss properties should be tested. However in the building industry, “time is money” and there are significant cost penalties in waiting 28 days before carrying out acoustical testing.
This paper provides support to reduce the accepted 28 days curing period to a much shorter period while still achieving a stable sound transmission loss.
Acoustic Division, NDY Sound, Auckland, New Zealand
ABSTRACT
This paper presents horizontal impact noise test results collected over the last five years during the Auckland ‘Apartment boom’ and aims to improve the industry’s ‘information base’ when considering horizontal impact noise transmission in multistorey apartment buildings. This topic is particularly relevant to the New Zealand building industry today in light of the likelihood that the revised Building Code that is under consideration will include objective horizontal criterion. Horizontal impact insulation test results on various types of concrete floor systems (precast, post-tensioned, etc) are presented. Results observed with commonly utilised impact treatments below tiled floor systems have been included and compared. Based on the field results presented possible horizontal impact noise criteria are considered.
Department of Building and Housing, New Zealand
ABSTRACT
The Building Act 2004 took effect from 30 November 2004. Provisions in the new Act are aimed at having our buildings built right first time. It introduces provisions to review the whole process of building looking at each of the different stage's - design, consenting, construction, and inspection. It also requires the Building Code to be reviewed. It is the first substantive review of the Code since it was introduced in 1991. In the intervening 15 years our needs and expectations as building users have changed dramatically. So too have building technology and building systems. We expect a lot more from buildings now and the technologies used in construction have advanced considerably. The review provides the opportunity to take a fundamental look at how we design and build, and how our built environment works for us as people and communities. It will enable technical, environmental, and societal needs to be considered together. This will involve considering a broad range of issues such as what does sustainability and energy efficiency mean in the context of buildings and houses, the impacts of our changing population on the type of buildings we need, and how to balance short-term cost with long-term benefits. There is also a need for performance standards to be set clearly so they can be easily understood and achieved. This paper presents an overview of the issues being addressed in the review of the Building Code.
Department of Building and Housing, New Zealand
ABSTRACT
Excessive noise is widely recognised as being detrimental to human health. More generally, there is considerable evidence that excessive noise can reduce the wellbeing of those subject to it, and reduce productivity in the workplace. It is important that people within a building have appropriate safeguards through the design and construction of that building from illness or loss of amenity as a result of noise intrusion. The current requirements relating to insulation from airborne and impact sound are set out in Clause G6 of the Building Code and the associated Acceptable Solution G6/AS1. Key weaknesses identified in the current Building Code, and the experiences of people living in multi-unit housing developments and high-rise apartments, initiated changes to update the Building Code. The part of the Purpose of the new Building Act 2004 relating to “promoting sustainable development” provided further impetus to revising the noise provisions of the Building Code. Predictions of further intensification of some of New Zealand’s urban areas provide additional impetus to ensure the Building Code provides properly for the sustainable development of those areas. The paper describes how the Building Code works to promote sustainable development through its provision for an acceptable indoor noise environment. It outlines the proposed revised requirements for noise in the Building Code, and associated Compliance Documents.
University College London, United Kingdom
ABSTRACT
Building regulations in England and Wales have consistently failed to ensure that domestic dwellings are built to standards where occupants are satisfied with the level of sound insulation. Recent judgments have left owner/occupiers exposed to noise without a legal remedy. If occupants complain about noise they risk reducing the selling price of that dwelling.
Dwellings are often marketed on visual aspects rather than performance, people view property but they test drive cars. Lessons from the car industry suggest how a media focus on testing and comparing performance can help drive up standards of features that are not immediately visible such as CO2 emissions and safety.
This paper will present results from surveys of both builders and occupants to show their current attitudes towards sound insulation and regulation. Drawing upon empirical evidence from other industries this paper puts the case that effective rating systems improve performance of products for consumers more effectively than regulation. Looking at successful rating systems in other areas and current noise/acoustic comfort ratings, which have been in existence for over a decade, this paper asks the questions what makes a rating system successful? and what should a noise/acoustic comfort rating system look like in 2006?
Faculty of Architecture, University of Sydney, NSW 2006, Australia
ABSTRACT
The reliable field measurement of airborne sound insulation between rooms in the very low frequency range (20 Hz – 100 Hz) presents a substantial challenge for several reasons. Sound source and microphone placement can have a strong effect on the transmission, and diffuse field conditions are usually not possible to establish in medium-sized rooms. In this study we compare three methods that have been proposed previously for transducer placement with each other, and with mass law theory. Our results show that substantially different values may be obtained from each method of measurement. Furthermore, we examine the influence of the test signal on the measurement, and find that non-linearities in the building fabric can also substantially affect the apparent sound reduction index in the very low frequency range. We discuss how measurement techniques might be refined to increase their reliability.
(1) Marshall Day Acoustics Ltd, Auckland t.scelo@auckland.ac.nz (2) Department of Mechanical Engineering, University of Auckland, New Zealand Private Bag 92019, Auckland
ABSTRACT
The insulation performances of floor/ceiling systems are yet to be fully understood as the mechanisms responsible for the transmission of sound are complex. An analytical model predicting the performances of such systems has been developed in order to develop and explain structures with improved insulation. The paper presents briefly the modelling approach and the accuracy of the predictions. The model, by focusing on the low frequencies range, employs a modal decomposition method. The solution relies neither on the periodicity of the stiffened ceiling panels or suspension system nor on the infinite extend of the floor. The quadratic vibration velocity of the ceiling panel is predicted. Comparisons are made between measurements and prediction.
(1) School of Electrical, Energy and Process Engineering, Murdoch University, Murdoch 6150, Australia (2) School of Electrical, Energy and Process Engineering, Murdoch University, Murdoch 6150, Australia
ABSTRACT
A method for the design of arbitrary minimum or linear phase FIR filters is developed for audio applications by using the Tuneable Approximate Piecewise Linear Regression (TAPLR) method to smooth the required FIR magnitude frequency response from a prototype Bode plot model. The TAPLR method incorporates a set of contiguous piecewise linear (affine) sections, which are coupled and smoothed by a single tuning parameter associated with a set of amplitude weighted Radial Basis Functions (RBFs) assigned to each linear section. The Bode plot also consists of a set of contiguous linear asymptotes plotted on a log-log scale, which makes it a perfect candidate for modelling and smoothing by the TAPLR method. The TAPLR smoothing turns the artificial asymptotic magnitude plot into a realisable magnitude response curve, which can be made to be band-limited with a finite impulse response by the appropriate degree of smoothing. A typical FIR filter design example for audio system equalisation is provided to show the value and versatility of the method. Also, two Bode plot filter prototypes are presented to show how well the new modelling approach can capture them and adapt them to suitable band-limited FIR filter designs.
Marshall Day Acoustics, New Zealand, Marshall Day Acoustics, New Zealand, Futureworks, New Zealand
ABSTRACT
For more that twenty years the congregation of The Cathedral of St Paul in Wellington have complained about poor speech intelligibility. A recent suggestion from the client team, to resolve this long-standing issue was to increase the absorption in the space to make it more suited for speech communication. This approach would have resulted in destroying one of Wellington's highly desired venues for Choral and Organ Music. Using simulations of organ and choral music as well as speech in different reverberant conditions, we demonstrated to the client team that it is possible to provide adequate speech intelligibility, whilst preserving the conditions desired for Choral and Organ music. The result is a new sound system using highly directional loudspeakers that provide intelligible speech throughout the Cathedral. The methodologies used will be discussed in the paper.
Industrial Research Ltd, PO Box 31310, Lower Hutt, New Zealand
ABSTRACT
Electronic enhancement systems are being increasingly used to provide control of the acoustics of multipurpose venues. Since the acoustics of a venue is governed by the power and spatial properties of the early and late sound, enhancement systems must also provide control of these properties. The Variable Room Acoustics System is one product which offers this control. The principles of the VRA system are presented here and its ability to independently control early and late energy is discussed. Two examples of installations are given.
Noise and Sound Services, St Ives, NSW 2075, Australia.
ABSTRACT
According to data given by the Australian Council of Trade Unions there are about 1.5 million Australian children under the age of five. Every year 250,000 new babies are born and by the time a child is in his or her second year, 57% of mothers are back in the workforce and by the time children turn three, 68% of mothers are back in the workforce. Many new childcare facilities have recently been constructed in the built environment in many parts of Australia and New Zealand to cater for this growing demand. The proposed location of childcare facilities is highly important because of the noise impact they will have on the surrounding neighbours. However, in many cases childcare facilities are being proposed in normal residential roads with as many as five neighbouring residential properties at their boundaries. Often childcare proprietors would like to accommodate as many children as practicable. This can be as many as 50 to 60, or even 90 children in the age group 2 to 5 years.
(1) Ron Rumble Pty Ltd, 96 Petrie Terrace, Spring Hill, Queensland, Australia 4004 (2) Division of Mechanical Engineering, The University of Queensland, St Lucia, Queensland, Australia 4072
ABSTRACT
The prediction of crowd noise is a problem faced by acoustic consultants. Although consultants are frequently required to predict noise emissions from activities involving crowds of people, there are no prediction methodologies available. When the consultant is required to evaluate whether a proposed outdoor facility such as a sports ground, school or alfresco eating area will adversely affect the amenity of nearby noise-sensitive premises, the normal approach is to use data from measurements at similar existing facilities. Difficulties arise when the test crowd differs in size or some other characteristic from the proposed crowd being modelled. Prediction errors can be as large as 10 to 15dB(A). The purpose of this paper is to present a systematic analysis and evaluation of the factors influencing crowd noise. Factors such as the situation in which the crowd occurs, size of crowd and crowd composition and their influences on the overall sound power emissions are discussed. Prediction equations for several different crowd types are presented, based upon the results of experiments and measurements
conducted by the authors.
(1) Environmental Resources Management Australia Pty Ltd 33 Saunders St Pyrmont, NSW Australia 2009 najah.ishac@erm.com (2) Wilkinson Murray Pty Ltd 201 Willoughby Rd Willoughby, NSW Australia 2065
ABSTRACT
Noise propagation is significantly affected by prevailing meteorological conditions, leading to variations in received noise levels. Several standard modelling methods rely on measured meteorological data and estimation techniques. Rather than accept the uncertainty of modelling methods, we decided to obtain realistic and actual noise level data including the effect of atmospheric conditions by conducting a year long experiment on sound propagation. Loud speakers were placed at a central location on a site, to be used as an artificial sound source. A constant sound signal of a set of pure tones with varying sound intensity levels between each frequency is triggered every hour, for one minute, twenty four hours per day and for a year. The primary frequencies in the source signal were chosen to adequately simulate the main frequency range of typical mechanical plant. The transmitter consists of a CD player with a CD containing the source noise, a timer to trigger playback, a power amplifier and loud speakers. The arrangement is powered by solar panels and housed in a wire mesh and roofed compound. The sound bursts were recorded by loggers at distant offsite locations, as well as at an intermediate position near the speakers. Each logger contains a calibrated measurement microphone and a Digital Audio Tape (DAT) recorder. The loggers are pre programmed to record the received noise levels. Meteorological data is continuously collected by a weather station. Each monitor’s DAT was then analysed using narrow band spectral analysis to filter the discrete pure tones from the ambient noise recorded. In the first instance the fluctuation of sound at each monitoring site is quantified. The meteorological and noise data is correlated and analysed to quantify the effects of weather on noise propagation. The results are encouraging with significant differences in noise levels being recorded, attributed to weather influences.
CRC for Railway Engineering and Technology (Rail CRC), School of Engineering, University of Queensland, Brisbane, Qld 4072, Australia
ABSTRACT
A feedback model for wear-type rail corrugation has been modified to account for vehicle speed variations over successive passages, so that the effect on corrugation amplitude growth can be investigated. The feedback model encapsulates the most critical interactions occurring between the wheel/rail structural dynamics, rolling contact mechanics and rail wear. Using this model, numerical and analytical investigations are performed to quantitatively identify the effect of deliberately changing the speed of successive vehicle passages in a statistically controlled manner. The effect of different initial track profiles on the results is also investigated. The results provide insight into a possible alternative means of retarding wear-type corrugation growth.
Maunsell Limited (in association with Bassett Acoustics, Australia), Auckland, New Zealand
ABSTRACT
A substantial portion of the work undertaken by acoustic consultants in both Australia and New Zealand involves the assessment of noise in the environment – be it from general industry, commerce, domestic, road/rail/aircraft traffic or a myriad of other sources. This paper provides a brief comparison of both statutory regulations and general duties of care applicable in the two countries. The paper also investigates the implications these have not only on the approach to objective assessment of environmental noise, but also a comparison of the impact on the various parties involved in the process – the generator of the noise, the receiver of the noise, and the requirements and responsibilities of the acoustic consultant.
University of Adelaide, Australia
ABSTRACT
Mechanical engineers for a long time have realized the advantages of balancing Fan impellors and other rotors; increased power efficiency, increased bearing life, reduced probability of unplanned failures and an increase in rotor and shaft life. Most Condition Monitoring practitioners, who use vibration as the primary monitoring tool, regularly balance rotors in-situ using single or two plane balancing techniques. This paper will present an alternative primary method to vibration measurements; it is particularly useful for drum impellors commonly found in cooling water systems and for medium size fans mounted on isolation mounts. The author is an experienced condition monitoring engineer with many, many year’s field experience.
Day Design Pty Ltd, Acoustical Consultants, Sydney, Australia www.daydesign.com.au
ABSTRACT
This paper investigates the directional properties of sound emitted from the end of a long straight duct and has practical applications for the acoustic modelling of exhaust and ventilation systems. It is known that the level of sound at a point remote from the open end of a duct is dependent on frequency, duct area, distance and direction.
As the angle between the duct centreline and a remote point increases the sound level decreases. This loss due to directivity is termed ‘directivity loss’. By understanding directivity loss, the modelling and assessment of noise from such ducts and the design of noise control may be conducted with increased accuracy.
At present the quantitative analysis of directivity loss is not well established. The NSW Environment Protection Authority published directivity loss curves in the “Environmental Noise Control Manual” however this data is based on limited testing.
This study has been undertaken to provide a more detailed assessment of duct borne directivity loss. Testing has been conducted using several different diameters of steel duct and the directivity loss at octave band frequencies has been quantified. Charts relating directivity loss to duct area and frequency have been developed for reference. These directivity loss charts have been compared to the EPA directivity loss chart and the results discussed.
Energy Research Group, University of Waikato, Hamilton, New Zealand
ABSTRACT
The flow induced noise from a two stage expansion of a round air jet has been investigated experimentally, with specific application to high velocity HVAC systems. The two stage expansion consists of an enclosed primary conical diffuser connected to a straight outlet duct section of arbitrary length followed by a secondary expansion of the jet into open space. The experimental analysis compares the effect of varying the angle of the primary conical diffuser and the length of the subsequent straight outlet duct length. A constant expansion area ratio of 9 was used. The optimum diffuser angle and duct length is determined for both minimum noise and minimum space constraints. The total sound power, octave sound power and 1/3 octave sound power levels are all consistent to within 2 to 3 dB. The acoustic effects of fitting HVAC air diffuser grills onto the outlets of each of the experimental cases presented is also documented to demonstrate the potential application of these results to HVAC installations.
School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney NSW 2052, Australia
ABSTRACT
Two matters which may be important in the modelling of small mufflers for Continuous Positive Airway Pressure devices are the effects of mean flow and of compliant walls. A preliminary experimental investigation using a simple expansion chamber muffler has been undertaken to assess the likely importance of these matters and the results are presented in this paper. The frequency dependent sound transmission loss of the expansion chamber muffler in the presence of mean flow and when it was fitted with compliant walls, was measured using a novel technique involving passing transient acoustic waves through long conduits attached to the muffler. The validity of the measurement technique was demonstrated. Results show that at the low mean flow velocities of interest, the mean flow has little effect but wall compliance can be significant.
School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney 2052, Australia
ABSTRACT
Excessive noise radiated by pipes consisting of air or steam are often lagged using porous materials of high flow resistivity and impervious sheets usually made from metals and plastics. This paper looks at the prediction of insertion loss associated with the lagging of cylindrical pipes. A method is described and a program to efficiently calculate the predicted insertion loss as a function of frequency is developed. Predicted values of the insertion loss are compared with measured values found in past literature. Accompanying this is a comparison of the predicted values compared with current recognised theoretical results. Finally an indepth parametric study is presented.
Physics Department, University of Auckland, New Zealand
ABSTRACT
Underwater sound has many practical applications and some of these will be reviewed. The ocean forms a complicated waveguide for sound and there are a variety of methods of calculating the sound field. Nevertheless the theoretical description of underwater sound propagation still presents some challenges. Wavefront modelling has recently been developed to give efficient evaluation of the sound field including the field near the foci and caustics that are common in both deep water and shallow water with surface waves. Many applications of underwater acoustics are well established but others such as large scale oceanography and large scale fish monitoring are under development. Underwater sound is also of great interest in marine biology. Whale sounds are routinely recorded at Great Barrier Island and are probably due to a resident population. The larval stages of some marine species appear to use sound to find suitable reef habitat to continue their life cycle. Current research is investigating what features of the sound field can give the required orientation cues.
Institute of Technical Acoustics, RWTH Aachen University, Aachen, Germany
ABSTRACT
Following the processes of international harmonization, measurement methods for sound insulation material and prediction models for characterization of field situations were recently reviewed. In the area of prediction, a great step was made towards a physically sound and practical method for describing noise sources of airborne and structure-borne sound in buildings, the transmission in the building structure and radiation into the receiving room. The subsystems of a building, its beams, plates and cavities can be assumed to show statistical modal behaviour. Hence the modal density is sufficiently large for purely energetic considerations using, for example, statistical energy analysis. On the basis of this prediction model and its results in frequency bands, an algorithm of digital signal processing can be added which enables modelling of the sound signal flowing through the building and to the receiver. The auralized sound can be used in various applications: The method opens the possibility to demonstrate effects, also in teaching, to investigate sound effects and annoyance, by variation of construction parameters and systematic listening tests or psychoacoustic analysis.
School of Mechanical Engineering, University of Western Australia, 35 Stirling Highway, Crawley WA 6907, Australia
ABSTRACT
Workers were exposed to excessive noise when working in the sample preparation room of ALCOA Kwinana Refinery. The noise was mainly from the four BICO disk mills located side by side in the centre of the room. High noise level from each mill affected its operator and operators of other mills. The airgun used for cleaning sample residues further increased the workers’ noise exposure level. The sample preparation practice also generates dust. Workers had to use earmuffs on top of other bulky safety equipment, which made the job quite awkward. A simple noise control solution involving noise absorption treatment, noise transmission blockage and vibration damping, was proposed and implemented for this noise problem. After the treatment, the noise exposure level was significantly reduced to the level below the exposure standard for ten-hour shift, making the use of hearing protection unnecessary.
UNSW@ADFA,Australia, National Acoustics Laboratory, Australia
ABSTRACT
Currently in both New Zealand and Australia the criteria for exposure to noise are based on two single values, namely the LAeq,8hr of 85 dB for continuous noise and LCPeak of 140 dB for impulse noise. Recently the European Directive on Occupational Noise introduced the requirement of two ‘action levels’ below the criteria or exposure limits. The concept of legislated action levels and the requirements for workplaces once action levels are exceeded will be discussed. The benefits to Australia and New Zealand of such a stepped approach to occupational noise management will also be presented.
Research Section, National Acoustic Laboratories, 126 Greville Street, Chatswood, NSW, 2069, Australia
ABSTRACT
Currently there has been and is a lot of discussion generated by articles in the popular press concerning the possible future hearing loss developed by individuals who listen to personal stereo players (PSP). How much of this concern is real and how much is unreal perception from media publicity? In this work PSP users were approached in their natural environment and questioned about their use while the equivalent at ear LAeq was measured. From this information an LAeq,8h was calculated for comparison to the workplace noise exposure regulations commonly in place in New Zealand and Australian jurisdictions. The results indicate that approximately 25% of a cross section of typical users could be considered to be at risk. Is this significant and how does this compare to workplace noise exposure?
Principal Policy Advisor, Department for Transport, Energy and Infrastructure, South Australia, Australia
ABSTRACT
Higher traffic densities and community expectations for a clean environment have resulted in jurisdictions developing and adopting more stringent standards for motor vehicle emissions. This includes motor vehicle drive-by noise and noise generated by heavy vehicle engine brakes. To date, enforcement of in-service motor vehicle noise standards has been limited to stationary noise testing. This method of enforcement is labour intensive, disruptive to conforming motorists and does not correlate well with drive-by noise levels. The South Australian Department for Transport, Energy and Infrastructure has undertaken to develop an automated system called a noise camera to identify noisy vehicles in the traffic stream. The noise camera, believed to be a world first, is capable of recording noisy vehicles based on user programmable sound characteristics. Designed primarily to identify noisy engine brakes in accordance with Engine Brakes Noise Standards, currently being developed by the National Transport Commission, the camera can also identify noise from individual vehicles during acceleration. This paper describes the drivers behind the development of the camera, the design of the technology, its capabilities and data collected to date.
Planning, Design & Operations Division, Queensland Department of Main Roads, Brisbane, Australia
ABSTRACT
Queensland Department of Main Roads (QDMR) regularly receives complaints about the annoyance of road traffic noise. The purpose of this paper is to provide an overview of the revised Code of Practice (revised CoP) (QDMR.2006) that aims to guide and instruct the user in the assessment, design and management of the impact of road traffic noise.
The CoP was first released in June 1999. Some minor revisions were made and Version 2 was released in January 2000. Due to experience with the use of the CoP over the past six years, it has become necessary to undertake a revision in order to clarify a number of issues and include new issues that have developed. Some of the issues are related road traffic noise assesment, district noise management strategies, development applications, construction noise and vibration, community engagement, managing noise complaints and engine compression braking.
(1) Marshall Day Acoustics, Melbourne, Australia (2) Marshall Day Acoustics, Christchurch, New Zealand
ABSTRACT
Partial enclosures have been used for the control of road traffic noise in Europe and have been considered for some road projects in Australia. However, the Calculation of Road Traffic Noise (CRTN) method has no algorithms for estimating the insertion loss of partial enclosures. In particular, CRTN does not consider the effect of multiple reflections within the enclosure. Also, environmental noise modelling software packages cannot always estimate the barrier attenuation as the edge of the enclosure is not necessarily between the noise source line and the receiver. This paper describes a simple modification to CRTN that can be implemented in a software package such as SoundPLAN which estimates effects. The risks associated with such a simple modification are estimated.
Bassett Acoustics, Sydney, Australia
ABSTRACT
Traffic noise is generated from the network of roads forming the matrix of an urban environment and impacts residents everywhere. As a result of the gradual tightening of noise limits imposed by legislation tyre/road noise has become the dominant traffic noise source particularly in free-flowing traffic at speeds above 40-50 km/h. Numerous factors affect the production of tyre/road noise - speed and weight of vehicle, wear, tread and structure of the tyre and the road surfacing. Previous studies have concluded that there is greater scope for reducing tyre/road noise by redesign of the road surfacing than by redesign of the tyre. The main characteristics determining noisiness of road surfacings are geometrical features, acoustical and mechanical properties of the pavement. Two generation processes have been identified; one in the low frequency range is roughness induced vibration; the other in the high frequency range is ‘air-pumping’. Certain road surfacings such as Stone Mastic Asphalt (SMA) have modified surface textures which bring about reductions in noise however major concerns have been raised regarding the early life skidding resistance. This paper examines the acoustical benefits of the use of surfacings such as SMA and reviews evidence for the purported associated reduction in skidding resistance.
Managing Director, Sound Barrier Solutions Ltd, Market Harborough, United Kingdom Chair CEN TC226/WG6/TG1 for Road Traffic Noise reducing Devices
ABSTRACT
There is a general lack of confidence in the noise barrier industry in the design and specification of effective noise barriers. There is also a need for clear guidance in the application of appropriate standards. The aim of this paper is - To enable informed choices to be made using best practice in the detailed design and specification of noise barrier systems both for industrial and transport noise and to give an update of the latest developments in noise barrier design standards and technology to the benefit of the future Australasian Market.
Managing Director, Sound Barrier Solutions Ltd, Market Harborough, United Kingdom
ABSTRACT
There is a general lack of confidence in the noise barrier industry in the design and specification of effective noise barriers. There is also a need for clear guidance in the application of appropriate standards. The aim of this paper is to give practical case studies of real-life noise barrier projects for roads and industry to show how barrier design theory and specifications can be applied effectively.
ASK Consulting Engineers, Brisbane, Australia
ABSTRACT
Road Traffic is the major environmental noise source impacting on numerous people in Australia. The main component of this noise is caused by the interaction of the road surface and the vehicle tyres. Current approved road surface noise test methods include static measurements (i.e. fixed microphone location beside the road) and dynamic measurement (i.e. microphone located on a moving vehicle). Currently, only the static measurement approach is widely used in Australia. ASK have developed and tested a dynamic test rig which can be used to gain a further understanding of tyre/road noise; provide details on variation in tyre-road noise level by road or air temperatures, and aging of the road surface; be used in the development of low noise road surfaces and low noise tyres; for cataloguing road surface types and their noise level emissions; post construction compliance testing of new roads; and mapping of road noise levels for integration into road authority databases or similar.
(1) Manager Environmental Monitoring, RTA NSW, Australia. (2) Principal, TEF Consulting and Visiting Research Fellow, UNSW, Australia.
ABSTRACT
This paper deals with a Roads and Traffic Authority of NSW funded study of the resultant incabin noise levels generated by a passenger vehicle travelling under controlled conditions. The objective of the study was to investigate the relationship between externally and internally measured noise levels and to compare the internally measured noise levels with those recorded in overseas studies. The study investigated 20 pavement surfaces that represented a wide range of construction materials and techniques and surface textures adopted in NSW.
A range of purportedly low noise asphalt and a dense graded asphalt were found to return the lowest overall noise levels followed by a concrete pavement that had minimal surface texture. A stone mastic asphalt along with an exposed aggregate concrete were found to perform better than randomly transverse tyned concrete pavements. Uniformly tyned concrete pavements and chip seal pavements were found to be amongst the loudest pavements.
The present study found that generally, trends in internal noise levels followed those measured externally; however there were some exceptions such as chip seal pavements that recorded higher internal noise levels than did concrete pavements with comparable external noise levels.
(1) Manager Environmental Monitoring, RTA NSW, Australia. (2) Principal, TEF Consulting and Visiting Research Fellow, UNSW, Australia.
ABSTRACT
A study of the tyre/road noise generated by 20 pavements surfaces representing a wide range of construction materials, techniques and surface textures constructed in NSW was undertaken and compared against the results of similar studies of 75 pavements constructed overseas. A range of more than 14 dB in passby noise levels was reported over the pavement types investigated with the NSW data being consistent with international data for similar pavement types. In general a range of low noise asphalts were found to return the lowest overall noise levels followed by concrete pavements that had minimal surface texture. Dense grade and stone mastic asphalts, and exposed aggregate concrete were found to perform better than randomly transverse tyned concrete pavements. Longitudinally tyned concrete pavements are not a design that is used in NSW however in international studies they were found to return noise levels similar to that of dense graded asphalts. Uniformly tyned pavements and those which generate acoustic energy in discrete frequency bands were found to be amongst the loudest pavements.
Transit New Zealand
ABSTRACT
Transit New Zealand (Transit) is the Crown Entity responsible for state highways - the strategic roads and motorways that are about 12% (10,894 km) of all New Zealand's roads. The state highway network carries about half of the 36 billion vehicle kilometres travelled on New Zealand roads every year. The management of noise from the state highway network requires a variety of approaches to reflect Transit’s duties under the Resource Management Act 1991, the Land Transport Management Act 2003 and the New Zealand Transport Strategy.
Transit currently has three distinct approaches for managing noise around the state highway network. These are:
(1) TEF Consulting and Visiting Research Fellow, University New South Wales, Sydney, Australia (2) Planning, Design and Operations Division, Queensland Department of Main Roads, Brisbane, Australia
ABSTRACT
This paper presents a substantial investigation of the road traffic noise attributes of five types of pavement surface currently in service in Queensland. The investigation was configured to examine the acoustic performance of the set of pavement surfaces and how these performances varied over time. To do this, a considerable set of roadside noise data, measured according to the statistical passby technique, was collected at 29 sites in 2002, 2003 and 2005. These data were collected at 21 sites in South East Queensland and at 8 sites in North Queensland in the Townsville environs. 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 and to exploring how they varied over time. The paper presents and discusses the acoustical attributes of the five types of pavement surfaces studied. It then goes on to set out and consider how the acoustical attributes of the pavement surface types varied over time. Some of the pavement surfaces exhibited very stable acoustical performance over the 2002 to 2005 period while the acoustical performance of others varied somewhat.
Central Laboratories, Opus International Consultants, Lower Hutt, New Zealand
ABSTRACT
New Zealand has a wide range of road surface types, ranging from large to small chipseals, and bituminous mixes ranging from 10mm asphaltic concrete to deep depth open graded porous asphalt. This paper describes first the measurement of the noise effect of these surfaces, by a variant of the cruise-by technique. The findings describe how the road surface type had a significant effect on traffic noise at urban driving speeds, and that the effects differed for light and heavy vehicles. The paper then links these findings to previous work on how the change in noise caused by resealing with different surface types could have significant effects on how adjacent communities perceived this noise environment, to produce a guideline of when worthwhile gains in noise environment improvement could be achieved by using a surface type with lower noise levels. This guideline required a new descriptor of community impact, “acutely affected”, be derived. The effect that a change in noise has on the percentage of the population that is “acutely affected” was calculated for three characteristic street-noise groupings of suburban streets, distributor roads, and major arterials and an indicative guideline for Road Managers developed.
(1) Faculty of Architecture, University of Sydney, NSW 2006, Australia (2) Faculty of Architecture, University of Sydney, NSW 2006, Australia * Currently with Renzo Tonin & Associates, Level 1, 418a Elizabeth Street, Surry Hills, NSW 2010, Australia (3) Department of Architectural Engineering, Chonbuk National University, Jeonju, Korea
ABSTRACT
Binaural reproduction without head-tracking or head-related transfer function individualization is used widely for auralization in architectural acoustics. Using headphones, this technique conveys an impression of an acoustic space, and allows comparison between spaces. Problems commonly encountered with headphone reproduction include the sound-field being locked to the head, no frontally located auditory image, and generally vague image locations except for nearby, lateral or moving sources. Some studies have shown that loudspeaker-based reproduction can provide greater realism. In this paper we compare subjective room size judgments made in real rooms (blindfolded subjects) and simulations of those rooms using binaural headphone reproduction and a loudspeaker-based binaural reproduction (the stereo dipole technique). Results indicate that room size judgments are affected by similar acoustic factors in the three listening conditions, but that the stereo dipole technique provides a better reproduction than headphones.
Faculty of Architecture, University of Sydney, NSW 2006, Australia
ABSTRACT
In this paper we develop examples of how the understanding of acoustic and audio phenomena can be enhanced through sonification, especially with a view to application in education. The term sonification refers to the process of converting data into non-speech audio, and is distinct from auralization in that the process does not aim to simulate an actual or imagined sound environment. Measurements of audio and acoustical systems are most commonly represented numerically and graphically, and these two methods each have distinct advantages. However, display of such data using sound not only conveys important information, but also may provide an experience of important aspects of the phenomenon under consideration. When used in an education context, this method of data display should improve listening skills. We demonstrate various data transformations that allow a sonification of acoustical measurements or phenomena to bring out features of interest. We also demonstrate more abstract sonifications (auditory graphs) that can be usefully applied to this context.
(1) Faculty of Architecture, University of Sydney, NSW 2006, Australia (2) Architectural & Building Acoustics, Renzo Tonin & Associates, Surry Hills NSW 2010, Australia
ABSTRACT
This paper looks at what information is needed to give concert hall acoustic design a firmer scientific basis: whether there is sufficient, and sufficiently reliable, subjective and objective data on concert halls and whether good halls can be distinguished from poor halls on the basis of geometric or acoustic qualities. In particular, existing indicators of acoustic quality, used in the early stages of a design, are investigated to see whether their use can be justified. Based on limited subjective assessments of concert hall acoustic quality, objective acoustical measurements and geometrical parameters it is shown, using a statistical test, that commonly used parameters such as the volume per seat are not statistically significant indicators of acoustic quality while the most reliable indicators are still reverberation time and sound strength, Gmid, (and variants on these). These two parameters can be simply and accurately calculated using neural networks with very limited input data. Some “geometric” parameters are also significant, the best of these being width, W, for rectangular halls.
(1) Marshall Day Acoustics, Auckland, New Zealand (2) Acoustics Research Centre, University of Auckland, New Zealand
ABSTRACT
New Standards for classroom design indicate that classrooms for young children should be built to criteria which in some respects – e.g. reverberation time – differ markedly from the traditional criteria for adults. Research in New Zealand has investigated the reasons for these differences. To identify why the reverberation needs of children and adults for speech perception are so different we have measured speech integration times for adults and children using a novel technique of reversed-segmented speech to obviate the confounding effects of differing language abilities in children. The values found for the two groups are significantly different. Background noise is a critical feature in classrooms and, with present day teaching emphasizing interactive learning; it is the activity noise of the children which is the main component. When groups of children are working independently in the same classroom the "cafe effect" produces a rising noise level as children compete to be heard. We suggest this results from the Lombard effect. From measurements of this effect in children and adults we have been able to successfully predict the activity noise measured in a classroom, and compare differences in susceptibility and magnitude between these two groups.
Acoustics Research Centre, University of Auckland, New Zealand
ABSTRACT
This paper will present a (mostly) non-technical overview of the research undertaken for my thesis. The work was a study of piano vibrations, to find whether improvements may be achieved by altering the piano case materials. Modal analysis and sound level measurements showed that because of the manner in which sound is radiated by the piano, the tone does not change significantly when typical materials are used in the case. A new method was developed for analysing recorded notes; it showed differences in vibrations between upright and grand pianos. A finite element model of a piano suggested that changing one component (the keybed) of the upright would reduce the key vibration level, and make the upright feel more like a grand. These changes were made to one of a pair of pianos, which were subjectively compared by a group of pianists; the results showed that the upright piano had been improved.
Laboratorium Auditionis, Acoustic Consultant, ul. Mietowa 3B 7, Gdynia 81-589, Poland
ABSTRACT
Typically, the design of a modern auditorium hall starts with the architect’s vision of the whole building. Architects rarely allow acousticians to interfere with the shape and interior design of their work as they are responsible for the whole project. Better or worse compromises are achieved during the design process, and sound system planning usually comes after, only to fit in the previously developed space. To satisfy the architect’s intentions, the acoustician proposed an interesting solution of the shape and structure of the ceiling of the auditorium hall in Wyzsza Szkola Menedzerska in Warsaw bearing in mind the importance of its modern appearance. The GRG ceiling was intended to function as a “wavy sound transporter-projector” capable of directing a non-amplified human voice from the lecturer’s platform and spreading it evenly over the audience. Moreover, it was to serve as a horn-like enclosure to accommodate custom-built loudspeakers. Two speaker clusters were designed as a multiarray construction working as a point source so that each listener would have the impression that the speaker addressed him/her directly. The economic aspect of the design, besides its assumed functionality, was also important. This paper describes the design and acoustic results achieved after the completion of the auditorium hall.
Marshall Day Acoustics
ABSTRACT
The Café & Restaurant Acoustical Index (CRAI) hit the public arena in the December 2003 issue of New Zealand Acoustics. The aim of the rating is to allow diners to have a say in the acoustical environment in eating establishments, and in time provide the ability for intending patrons to make an educated choice of where to eat, based on the type of environment they want. For three years, CRAI ratings have struggled to gain recognition, confined to the back of a quarterly journal and unknown outside of the New Zealand acoustics fraternity. Then, the power of the press takes hold, courtesy of the National Foundation of the Deaf. A press release issued to coincide with Deaf Awareness Week resulted in a flood of publicity and "vast numbers" of emails and completed rating forms. This presentation takes a broad look at the CRAI rating system; why it began, what it aims to do, how it's progressed, and where it might go from here. It also looks at some of the press articles which have recently appeared, and examines alternative views on the issue of noise in the eating environment.
Department of Architectural Engineering, Chonbuk National University, JeonJu, Korea
ABSTRACT
The present work tries to investigate the problems and uncertainties of measuring random-incidence scattering coefficients in a reverberation room based on ISO 17497-1. A 1:5 scale model of the reverberation room, which has a volume of 2.4 m3, was employed to measure the random-incidence scattering coefficient for periodic battens. In the present work, three factors, the turntable diameter, the air gap below the turntable and the absorption of test sample were considered. The influence of each factor on the scattering coefficients was measured and analysed. It was found that the turntable diameter influenced the scattering coefficient of the baseplate at frequency bands, 1 kHz to 5 kHz, although the values are within the ranges specified in the ISO standard. An air gap of 50 mm below the turntable results in a high scattering coefficient for the base plate and in a low scattering coefficient for the periodic battens at 1 kHz to 5 kHz. Varying the absorption of the test sample has no significant effect on the scattering coefficients.
School of Mechanical Engineering, The University of Adelaide, Adelaide, South Australia, Australia
ABSTRACT
A thermoacoustic air conditioner that utilises a branched duct network is described in this paper. It was found that the standard four-pole methods to describe the acoustics in the branched duct did not match the predictions from finite element analyses. Additional correction terms to describe lumped inertances at the branch connection are required to properly describe the acoustic behaviour of the system. Branched ducts of square, rectangular, triangular, and semi-circular shapes are considered, and the corresponding terms for the lumped impedances are given.
School of Mechanical Engineering, The University of Adelaide, Australia
ABSTRACT
Thermoacoustic devices may use high-amplitude sound waves to serve a variety of purposes such as cryogenics, domestic refrigeration, electricity generation or warning siren systems. In all designs, there is a transfer of acoustic power between the various ‘sources’ and ‘sinks’, especially at very high acoustic pressure levels (170dB+) and velocity amplitudes (which are significant fractions of the local Mach number). Inertance segments, in which the oscillatory flow is accelerated, represent a design challenge in balancing frictional or viscous losses with improvements to the compactness, weight and performance of the overall system. This paper considers optimisation of an inertance segment used in a standing-wave type heat-driven thermoacoustic device and compares experimental data with results obtained from numerical finite element modelling, acoustic transmission line theory and linear thermoacoustic formulations.
(1) Maritime Operations Division, Defence Science and Technology Organisation, Australia, adrian.jones@dsto.defence.gov.au (2) Centre for Marine Science and Technology, Curtin university of Technology, Australia, a.maggi@cmst.curtin.edu.au
ABSTRACT
DSTO possesses a data set of sound pressure time series received at a number of ranges from small explosive detonations along a number of tracks in shallow oceans in the Australian region. In recent years, these time series data have been under study by DSTO and Curtin University in relation to the potential impact of underwater explosions on marine fauna, in particular, marine mammals. Past work had shown that the characteristics of waveforms received at medium ranges might be simulated closely if bathymetry and sound speed data were known, and if the seafloor reflectivity was known at relevant frequencies. Sound pressure peaks were, however, overpredicted by the modelling, unless time spreading effects attributed to reflections from non-smooth ocean boundaries were included.
This paper reviews this past work and shows the results of more recent analyses in which data along a much greater number of ocean tracks have been studied. It does appear from this analysis of the extended data set that if the sound transmission from an explosive detonation is via bottom bounces, or via surface reflections from a rough surface, the peak level received is considerably less than the value expected from weak shock theory for a single arrival in a uniform ocean of infinite extent. However, if transmission is via surface reflections from a nearly smooth surface, the measured peak level is closer to the theoretical value. This conclusion is illustrated with a presentation of atsea data and comparison with modelled time series.
Centre for Marine Science and Technology, Curtin university of Technology
ABSTRACT
A number of underwater acoustic propagation modelling programs have been placed in the public domain by their authors. Different programs are required for different situations, but together they can perform the majority of common modelling tasks. All these programs are input file driven, but with different file formats, and each requires considerable time and effort to be expended in order to work out its specific requirements. The programs also generate output data in a number of different formats, making the setting up of software for visualisation or further processing a time consuming process. Several years ago the Centre for Marine Science and Technology publicly released a free Graphical User Interface (GUI) that provides a simple, consistent interface for running the various propagation routines in the Acoustic Toolbox, a collection of underwater acoustic propagation modelling programs written by Mike Porter from HLS Research. The GUI is written in Matlab, and also provides a variety of output data visualisation tools. It provides ready access to programs for acoustic field calculation by normal modes, wavenumber integration, and ray and beam tracing, and can also compute reflection coefficients for complicated layered seabeds. These codes are only suitable for modelling range-independent environments, with the exception of the ray code which can handle range-dependent bathymetry. An expanded version of this interface has recently been released and can be downloaded for free from CMST's web site. The primary enhancement is to provide fully range-dependent modelling through the inclusion of support for the RAM family of parabolic equation codes written by Mike Collins at the US Naval Research Laboratory. This paper describes the capabibilities of this new version of the GUI, and provides examples of its use.
(1) Centre for Marine Science & Technology, Curtin University of Technology, Perth, Australia
ABSTRACT
Rifting and breaking of ice shelves and icebergs in Antarctica produce intense pulse-like acoustic noise in the surrounding ocean, which can be detected thousands of kilometres away at the hydroacoustic receive stations deployed in the Indian Ocean as part of the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). A number of the most intense signals from Antarctic ice events observed at two IMS stations were selected to analyse their individual spectral characteristics and correlation and to verify the acoustic propagation model. The location of ice events derived from the back-azimuth estimates for signal arrivals at two stations was used to numerically predict the signal travel times using the seasonal temperature and salinity field from the World Ocean Atlas, and to compare the modelled and observed travel time differences. In most cases, the discrepancy in the even location derived from back-azimuth estimates and that derived from the travel time difference did not exceed 50 km, which justified the accurate location of events and verified the acoustic propagation model. Effects of normal mode coupling and transmission loss were also investigated through numerical modelling for different acoustic paths from Antarctica and compared with those observed experimentally.
(1) National University of Singapore, 21, Lower Kent Ridge Road, Singapore 119077 (2) Acoustic Research Laboratory, National University of Singapore, 12A Kent Ridge Road, Singapore 119223 (3) DSO National Laboratories, 20, Science Park Drive, Singapore 118230
ABSTRACT
Very shallow water acoustic communication channels are known to exhibit fading due to time-varying multipath arrivals. This is further complicated by impulsive snapping shrimp noise that is commonly present in warm shallow waters. This paper will present a communication channel model simulation for such a channel. The paper also presents results from the use of single-carrier differential phase shift keying (DPSK) modulation which does not require an elaborate method for estimating the carrier phase. The receiver designs in simulation and trial data analysis are based on the least mean square (LMS) adaptive linear equalizer (LE) and decision feedback equalizer (DFE). Multichannel combining and forward error correction (FEC) schemes such as turbo product codes (TPC) are employed to improve performance. We will present performance results based on simulated data as well as for real data collected from the sea.
Defence Science and Technology Organisation, A-51, HMAS Stirling, Rockingham, WA 6958, AUSTRALIA
ABSTRACT
A baffled arc array (BAA) comprises a circular array of sensors surrounding a cylindrical metal baffle, and beam-forming is carried out by processing sensors on an arc centred on beamsteer. It is widely used in sonar for passive underwater surveillance. An important factor that limits the performance of the array at high frequencies is the appearance of grating lobes in the beamformer response. This occurs when sensor separation is greater than half a wavelength, and leads to masking of weak signals by the grating lobes of strong signals. In the case of the BAA, the grating lobes are imperfect as a consequence of the circular geometry; there is a mismatch between array responses to signals arriving from the beamsteer and grating lobe directions. Adaptive beamforming is sensitive to this mismatch, and suppress the grating lobes, thus extending the frequency range of the BAA beyond its design frequency. The purpose of this paper is to demonstrate the effectiveness of adaptive beamforming for suppressing grating lobe effects in the BAA.
(1) Defence Science and Technology Organisation and University of Sydney Institute of Marine Science, Sydney, Australia (2) Centre for Marine Science and Technology, Curtin University, Perth, Western Australia (3) Australian Marine Mammal Research Centre, Zoological Parks Board of NSW and University of Sydney, Sydney, Australia (4) School of Veterinary Science, University of Queensland, Brisbane, Australia
ABSTRACT
Pioneering recordings of underwater sounds off New Zealand showed a wide range of high level sounds from marine animals, particularly whales [Kibblewhite et al, J. Acoust. Soc. Am. 41, 644-655, 1967]. Almost 40 years later, a much greater amount of data is available on marine animal sounds and there is now considerable interest in using the sounds to monitor the animals for studies of abundance, migrations and behaviour. Passive acoustic monitoring shows much promise because the animal vocalisations are usually detectable over long distances, allowing a large area to be surveyed. Marine mammals are detectable acoustically at much greater distances than they are visible and passive acoustics has the potential to fill in the gaps in open ocean surveying. There are however challenges, and this paper discusses progress and the steps needed to develop robust methods of surveying the abundance and migrations of marine animals, illustrated by studies in our region. Effective use of passive monitoring requires an understanding of the acoustic behaviour of the animals, a knowledge of the acoustic propagation and ambient noise at the time of the survey and a rigorous statistical analysis.
(1) School of Mechanical Engineering, The University of Adelaide, Australia (2) Maritime Operations Division, DSTO, Edinburgh SA 5111, Australia
ABSTRACT
The determination of seabed properties from interference patterns (or striations) in frequency versus range spectrograms of shipping or other noise, depends on successful identification of these patterns. Within this paper, new local and global techniques for the extraction of the waveguide invariant from spectrogram striations are presented. The waveguide invariant relates the modal group and phase velocities of a medium and can be used as an input to an inversion model of the environment. The model can then be used to estimate seabed properties. The proposed methods apply to range-independent environments, such as continental shelves, and assume that the spectrogram data set is collected in the far field. By minimising the variance of the sound pressure level along the striations corresponding to assumed values of the waveguide invariant, the best fit with the actual waveguide invariant value is found. This paper compares the proposed striation determination methods and discusses the implementation aspects and robustness to noise of the new algorithms.
School of Earth and Ocean Sciences, University of Victoria, B C, Canada
ABSTRACT
This paper describes a computationally efficient inversion technique for determining the depth and speed of a sound source that is emitting a set of high signal-to-noise ratio tones. It is assumed that the source is moving at constant heading, speed and depth in shallow water, and passes close by a bottom moored hydrophone. At short ranges, the acoustic field consists of a dominant signal from the direct and surface reflected Lloyd mirror (LM) component, and a series of bottom reflected paths that modulate the LM signal. A computationally efficient propagation model based on the method of images is developed to calculate modelled fields for the inversion. The matched field inversion method for inferring the source depth, speed, and closest point of approach from a single hydrophone is demonstrated using data an experiment carried out in shallow water off the east coast of Canada. The results from the experimental data for the individual hydrophones were combined to give information about the source track. These results are compared with independent measurements of the track geometry that were taken at the time of the experiment.
SonarData Pty. Ltd., GPO Box 1387, Hobart, Tasmania, 7001, Australia
ABSTRACT
In fisheries acoustics, the scientific echo sounder is the typical instrument for estimating the biomass of aquatic organisms and for studying their ecology. There are key technologies of analysing acoustic data from echo sounders as follows: 1) Fish tracking techniques for counting the number of fish especially in rivers and lakes, and also to provide behavioural characteristics such as fish speed and direction, and their depth distribution. 2) School detection techniques allow fish schools to be detected automatically for obtaining morphological, bathymetric, and energetic characteristics. 3) Acoustic species identification techniques use various characteristics of aquatic organisms, such as the frequency-dependence of their backscatter (dB difference and three-colour techniques), and geometric and energetic characteristics. The use of scientific echo sounders has been expanding. For example, seabed classification techniques place the focus on acoustic characteristics of the seabed to categorize fish habitat and to search for mineral resources. Meanwhile, there is a movement towards the use of new instruments such as mutibeam and scanning sonars for the same purposes as echo sounders. Sonars cover a wider area and provide higher resolution compared to conventional echo sounders, and provide one more dimension to observe schools in various ways. For example, 4D display gives changes of morphology and behaviour of 3D detected schools according to time. Inspection technique (a view of cross section of the school) provides a hint of the internal structure of schools. A combination of 3D schools and 3D sea bottom (generated either from the sonar data set or from electronic charts such as C-map) gives improved overall understanding. Quantitative morphologic and energetic school parameters can be generated and exported to text formats for quantitative study. Echoview has been developed to provide access to the latest technologies. In this paper, representative examples of above techniques are introduced using Echoview.
(1) School of Earth and Ocean Sciences, University of Victoria, BC, Canada (2) Defence Technology Agency, Auckland Naval Base, Auckland, New Zealand
ABSTRACT
Acoustic transients radiated from undersea earthquakes were recorded in an experiment carried out using a towed horizontal line array operating in the South Fiji Basin. The transient signals consisted of P-, S- and T-phases, with strong spectral content in each phase to frequencies as high as 70 Hz. The directionality of the T-phase signal was determined to high spatial resolution by processing the array hydrophone data with a cross spectral beamformer. The T-phase signal was highly directional, and the directivity pattern was different for earthquake events at different sites. For deep earthquakes originating in the fore-arc trench at the northern boundary of the basin, the strongest T-phase components arrived from different directions much farther south of the source, in a region where a number of sea-mounts and ridges rose within the sound channel. For events originating along the subduction zone arc, the T-phases radiated from slope sites along the ridge to the north. A simple model based on ray path travel times for elastic wave travel in the earth and acoustic wave propagation in the water suggests that the components of the T-phase signal were radiated into the water by downslope propagation from the seamounts and ridges.
Centre for Marine Science and Technology, Curtin University of Technology, Perth, Australia
ABSTRACT
The seabed type of most shallow water areas is very often not homogenous but patchy in space and changeable with time. Recent studies have shown that statistics of acoustic backscatter from an inhomogeneous seabed deviate significantly from a conventional Rayleigh model and may show distributions with multiple modes and heavier tails. In this work, seabed backscatter statistics are analysed using the data collected with a RESON SeaBat 8125 multibeam sonar system (operating at 455kHz) in the regions of Recherche Archipelago and Cockburn Sound in Western Australia. The 455kHz acoustic backscatter data were collected over areas consisting of different seabed types, including sand, rhodolith, seagrass and bedrock. Statistical models of backscatter intensity from these different seabed types were investigated for different values of the incident angle. The goodness of fit for the model with the experimental distributions was assessed with the nonparametric Kolmogorov-Smirnoff (KS) test statistic. Before compensation for the angular dependence of backscatter, the Rayleigh mixture probability distribution function provides the best fit to all experimental distributions at near-nadir angles of incidence. Within moderate and oblique angle intervals, the log-normal distribution fits experimental distributions best around the centre of the distributions and the Rayleigh 3-component mixture distribution in most cases provides the best fits to the tail of the distributions. After the angular correction, the log-normal distribution fits empirical distributions best in all cases, but the Rayleigh mixture distribution offers the best fits to the tail of distributions for seagrass and bedrock seafloors.
(1) Centre for Marine Science and Technology, Curtin University of Technology, Perth, WA, Australia (2) Department of Fisheries, Government of Western Australia, North Beach, WA, Australia
ABSTRACT
In comparison with many complex mammal vocalisations, most fish sounds are relatively simple pulsed broadband or tonal sounds where pulse rates and/or dominant frequencies are species-characteristic, resulting in several advantages and disadvantages for call classification. Mulloway (Argyrosomus japonicus) is a member of the sciaenid family, a group of fish containing several soniferous species. One suggested reason for vocalisation by the family is the attraction of female fish for the spawning process and that a spawning ground populated by ‘chorusing’ males increases the ‘catchment’ area of females in the vicinity. The location of one such area has been identified in the Swan River at Mosman Bay, Perth, Western Australia. Hydroacoustic recordings of vocalisations in the bay, made by several individuals during reproductive periods, were taken and characteristic parameters analysed. Acoustic features of individual callers were discrete enough to distinguish between fish, whilst also comparable to suggest they were of the same species. The regularity of individual callers and their specific frequencies have also been analysed.
School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney NSW 2052, Australia
ABSTRACT
Modelling the vibro-acoustic responses of vehicles in the mid to high frequency range is particularly difficult. This is due in part to the structural and acoustic responses of sections of a vehicle being highly sensitive to uncertainties arising from the assembly process and manufacturing tolerances. For example, the dynamic response of body panels can be greatly altered by small variations in spot welds. This leads to significant variation in interior noise levels of successive vehicles from a production line. This paper investigates the use of techniques for predicting the responses of structures with inherent uncertainties in the medium frequency range. The dynamic characteristics and responses of an ensemble of coupled plate structures are examined, where uncertainty is generated by adding small masses at random locations. A measure of the uncertainty is obtained by observing the variation in the natural frequencies of an ensemble member from their mean value across the ensemble. An ergodic hypothesis is used to compare the frequency averaged response of a single member in the ensemble with the ensemble averaged response. Finally, structure-borne sound pressure levels obtained experimentally are compared with results obtained from an SEA model.
School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney 2052, Australia
ABSTRACT
Dynamic simulations of gears and rolling element bearings have previously been made separately, but cases have been experienced in practice where bearing faults show up only because they modulate the gearmesh signal in a way that is different from the effects of gear faults. A combined gear/bearing model has been made to obtain a better understanding of the interaction of the two components. Results have previously been published for simulated local faults in the bearings. The simulation model has now been modified to model extended faults of the type that do not necessarily produce high frequency impact responses, but do modulate the gearmesh signals. This simulation model will be useful to test new diagnostic algorithms, as well as prognostic algorithms by varying the size of the simulated faults. A third application is to use the simulated signals to train neural networks to recognize the various faults without having to experience large numbers of failures. The paper compares simulated and actual signals (localized and extended inner race faults) from a gear/bearing test rig, and in particular demonstrates that they react similarly to existing diagnostic techniques.
Marshall Day Acoustics Pty Ltd, Collingwood, Australia
ABSTRACT
Structural engineers frequently use the prediction method developed by Murray to estimate the natural frequency and response of building floors to foot fall vibration.
The Murray method was developed over a long period has had several revisions and is widely used. The ASI (Australian Steel Institute) has published a design guide for common floor scenarios that enables standard floor designs to be checked for compliance against Murray’s acceptability criteria of 0.5%g (0.5m/s2) at frequencies between 4 and 8Hz.
The assumptions and simplifications in Murray’s method are sometimes criticized. In addition, perceptible and potentially annoying floor vibrations have been found in floor systems that, according to his method, are deemed to be acceptable.
Consequently, field tests have been performed on three long span floor systems, including two new composite construction buildings. Measured natural frequencies and vibration amplitudes have been compared against the Murray predictions and the reasons for any discrepancies are evaluated and discussed.
Hatch, Sydney, NSW, Australia
ABSTRACT
Wind farms are a growing form of energy supply in Australia and New Zealand. Wind farm development in Australia has grown significantly since 1999. From 2003 to 2005, there were several proposals submitted for approval with numbers of turbines ranging from 30 to over 100. Noise impacts from wind farms remains a contentious issue for the community and statutory authorities in the planning stage, but there is no nationally agreed approach to assessment. A recent Swedish study identified a dose-response relationship for noise from wind farms that was significantly higher than that obtained for general industrial noise. This paper attempts to compare the incidence of complaints in Australia and New Zealand, about noise from wind farms and complaints about noise in general. Data on complaints or objections from planning and approval stages is compared with those from the operating phases of wind farms. Understanding of any dose response to wind farm noise is likely to be a key factor in their future approval conditions, siting and operation.
CEO, Windflow Technology Ltd, Christchurch, New Zealand
ABSTRACT
The wind energy industry is booming in New Zealand and presents a new set of challenges to the acoustics industry. The NZ Standard NZS 6808:1998 ‘Acoustics – The Assessment and Measurement of Noise from Wind Turbines’ provides guidelines on the way in which sound from wind turbines should be measured and assessed and the levels of sounds that are acceptable. As part of its resource consent conditions for a New Zealand designed and manufactured 500 kW wind turbine at Gebbies Pass near Christchurch in July 2003, Windflow Technology offered to do better than the guidelines and be no louder than 30 dBA at the boundary (including tonal penalty). This paper outlines the process of estimating the sound levels in the area, determining the sound source when the turbine was found to be over the limit, and the results from implementing the solution. The paper also raises other unique issues in measuring sound levels in different wind conditions and topography, and low frequency/infrasound concerns that are arising.
Principal, L Huson & Associates Pty Ltd, PO Box 290, Woodend, VIC, Australia
ABSTRACT
NZS6808 : 1998 “Acoustics - The Assessment and Measurement of Sound from Wind Turbine Generators” has been applied in various forms across Australia for wind farm projects. This paper reviews license conditions issued by authorities when granting approval for wind farms in Australia and provides a detailed analysis of data from one such wind farm in Victoria where NZS6808 has been referenced in conditions of approval. The analysis shows confidence levels associated with the measurement of sound from a wind farm when NZS6808 is applied and concludes that the use of this standard in approval conditions for testing compliance is ill advised. An alternative method to test compliance is proposed.
(1) Vipac Engineers & Scientists Ltd., Adelaide, SA, Australia (2) Bassett Acoustics, Maunsell Pty Ltd, Auckland, New Zealand
ABSTRACT
The assessment of noise from wind farms is a significant element of the development approval process for proposed wind farms in Australia. This paper addresses the current requirements for acoustic measurement, modelling and reporting for wind farm developments in Australia and relevant issues arising from these requirements. In particular, the practical application of the assessment requirements is discussed, and the implications of these for new wind farm proposals are investigated. Lessons which have been learned through experience with wind farm noise assessments have been used to provide a practical perspective.