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Vol 38 No 2

CONTENTS

August 2010


ARTICLES

Acoustical background to the many varieties of birdsong
N. H. Fletcher
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Monitoring aircraft noise levels to the side of flight paths
Marion Burgess and Matthew McCarty
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Prediction of the acoustic performance of small poroelastic foam filled mufflers: A case study
P. W. Jones
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Multiple-leaf sound absorbers with microperforated panels: An overview
Kimihiro Sakagami, Motoki Yairi and Masayuki Morimoto
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Vibrational characteristics of roll swage jointed plates
Mauro Caresta and David Wassink
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TECHNICAL NOTES

Note on the applications of a simple acoustic immersion index
Cameron M. Hough
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Modelling soundscapes
Rob Bullen
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Implications of updating the vibration assessment methodology of BS6472 from the 1992 to the revised 2008 version
M. Allan, D. Duschlbauer and M. Harrison
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Letter to the Editor
News
New Products
Meeting Report
Standards Australia
FAST
FutureConferences & Workshops
Diary
Sustaining Members
Graham Thirkell Obituary
Advertisers Index


Acoustical background to the many varieties of birdsong

N.H. Fletcher
Research School of Physics and Engineering, Australian National University, Canberra ACT 0200 This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Vol. 38, No. 2 pp 59 -62? (2010)
ABSTRACT: Birdsong can be broadly classified into two categories: biphonic in which two different notes can be sung simultaneously, and monophonic in which only one note is sung. Monophonic song can be further divided into rich harmonic song, single- frequency song, and chaotic song. While some of these distinctions arise from clear anatomical features of the bird, others are more subtle and pose problems for physical scientists working in collaboration with biologists. This paper provides information on the physics and acoustics underlying these differences and shows how quantitative predictions can be made.

Monitoring aircraft noise levels to the side of flight paths

Marion Burgess and Matthew McCarty
Acoustics and Vibration Unit, University of New South Wales at the Australian Defence Force Academy, Canberra, ACT 2600

Vol. 38, No. 2 pp 63 - 68 (2010)
ABSTRACT: Assessment of aircraft noise levels near to the main flight paths has been successfully implemented at many airports and a good indication of the aircraft noise levels at those locations is obtained. Monitoring of aircraft noise levels away from the main flight paths is sometimes required to meet community demands and is more challenging as the aircraft noise may not be clearly defined above the background noise level in the area. This paper reviews the recommendations for monitoring aircraft noise in such ?acoustically unfavourable? locations with particular reference to the findings from analysis of data from such a placement. The outcomes indicate that more sophisticated analysis is required for such placements to achieve a fair and accurate assessment of the aircraft noise levels.

Prediction of the acoustic performance of small poroelastic foam filled mufflers: A case study

P. W. Jones
School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney NSW 2052, Australia

Vol. 38, No. 2 pp 69 - 75 (2010)
ABSTRACT: The acoustic performance of small, irregularly shaped mufflers in continuous positive airway pressure (CPAP) devices is often enhanced by the inclusion of dissipative materials. In this study, the acoustic properties of two polyurethane foams were determined using a two-cavity method. Acoustic models of two CPAP device muffler designs incorporating a foam insert have been developed using a commercial finite element analysis software package. Experimental results for the mufflers have been obtained using the two-microphone acoustic pulse method. Results of the transmission loss of the muffler designs obtained from the finite element models are presented and validation of the computational results is discussed.

Multiple-leaf sound absorbers with microperforated panels: An overview

Kimihiro Sakagami1,**; Motoki Yairi2; Masayuki Morimoto1
1 Environmental Acoustics Lab., Graduate School of Engineering, Kobe University, Rokko, Nada, 657-8501 Kobe, Japan
2 Kajima Technical Research Institute, Chofu, 182-0036, Japan
** This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Vol. 38, No. 2 pp 76 - 81 (2010)
ABSTRACT: Since the pioneering work by Maa, multiple-leaf microperforated panel (MPP) sound absorbers of various configurations with different materials have been studied. Multiple-leaf structures are primarily employed to obtain wideband sound absorption. The authors have proposed double-leaf microperforated panel space absorbers (DLMPP), which consist of two MPPs and an air-cavity in-between, without a back wall. A DLMPP is a wideband sound absorber, which is also effective at low frequencies. However, an MPP is still expensive. If one of the MPPs in such a structure can be substituted with another material, such as a permeable membrane, it can be effective and also economical. The authors, therefore, have been exploring various multiple-leaf structures including both MPPs and permeable membranes. This paper gives an overview of our studies on such multiple-leaf sound absorbing structures with MPPs, including a DLMPP, a triple-leaf MPP space absorber, a space sound absorber consisting of an MPP and a permeable membrane. Also it includes a multiple-leaf structure with MPPs and membranes backed by a rigid wall.

Vibrational characteristics of roll swage jointed plates

Mauro Caresta: School of Mechanical and Manufacturing Engineering, University of New South Wales (UNSW), Sydney, NSW 2052, Australia
David Wassink: Australian Nuclear Science and Technology Organisation (ANSTO), Lucas Heights, NSW 2234, Australia

Vol. 38, No. 2 pp 82 - 86 (2010)
ABSTRACT: The aim of this work is to model the vibrational behaviour of thin plates joined to a stiff orthogonal side plate using the technique of ?roll swaging?. Swage joints are typically found in plate-type fuel assemblies for nuclear reactors. Since they are potentially liable to flow-induced vibrations, it is crucial to be able to predict their dynamic characteristics. It is shown that the contact between the plates resulting from the swage can be modelled assuming a perfect clamp of all the degrees of freedom except for the rotation around the axis parallel to the swage which is elastically restrained with a torsional spring. A modal analysis was performed on different specimens and the values of the first natural frequencies are used to find the equivalent stiffness of the torsional spring restraint by matching these frequencies with the results obtained from a finite element model (FEM).

Note on the applications of a simple acoustic immersion index

Cameron M. Hough
Arup Acoustics, Sydney NSW Australia

Vol. 38, No. 2 pp 87 - 93 (2010)
ABSTRACT: The applicability of a simple acoustic immersion index for halls is investigated by calculating the values of the index for many well-documented halls and theatres. Correlations between the immersion index S1 and other auditorium acoustic parameters are investigated, as well as the effectiveness of the index in describing subjective evaluations of halls. The index S1 appears to broadly correspond to subjective ratings of halls, both from published data and from experiences in Australian halls, but is only weakly correlated with technical parameters describing the immersion of the sound field. However, the index appears to be reasonably correlated with Binaural Quality Index (BQI), and therefore may be useful as a ?spaciousness index? as a means of estimating BQI during the early design of a hall.

 

Newsflash

PROPOSED INTERNATIONAL YEAR OF SOUND 2019

Let's make 2019 the International Year of Sound!

Click here to see draft prospectus. Suggestions for major activities that would be truly international to strengthen the application are welcomed.

 

ACOUSTICS 2017

Perth, Western Australia 19-22 November 2017