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Vol 33 No 3


December 2005


Acoustic Systems in Biology: From Insects to Elephants
Neville H. Fletcher

Learning Acoustics through the Boundary Element Method: An inexpensive graphical interface and associated tutorials
Laura A. Brooks, Rick C. Morgans, Cohn H. Hansen

Virtual Acoustic Prototypes: Listening to machines that don’t exist
Andy Moorhouse


What are we doing about exhaust noise?
Neville H. Fletcher

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Acoustic Systems in Biology: From Insects to Elephants

Neville H. Fletcher
Research School of Physical Sciences and Engineering, Australian National University, Canberra 0200, Australia

Vol. 33, No. 3 pp 83-88 (2005)
ABSTRACT: Nearly all animals use sound for communication, for seeking prey, and for avoiding predators. What physical principles govern their choice of frequency? What are their mechanisms of sound production and directional hearing? Why are cicadas so loud? How do birds produce those beautiful, or sometimes not-so-beautiful, sounds? Quantitative analysis of the acoustic mechanisms involved reveals (nearly) all: the action of the sensory hairs on caterpillars, the hollow bodies of cicadas that act as resonators, the horn-shaped burrows dug by crickets and their remarkably human-like auditory anatomy, the inflatable vocal sacs used by “pure tone” songbirds and by frogs, and the chaotic structure of the shrieks of sulphur-crested cockatoos. This lecture will explore all these matters and perhaps some more.

Learning acoustics through the boundary element method: an inexpensive graphical interface and associated tutorials

Laura A. Brooks, Rick C. Morgans, Cohn H. Hansen
School of Mechanical Engineering, The University of Adelaide, Australia

Vol. 33, No. 3 pp 89-95 (2005)
ABSTRACT: The Boundary Element Method (BEM) is a powerful tool which has become an important and useful numerical technique applied to problems in acoustics. It is particularly useful for analysing sound radiation and acoustic scattering problems. Numerous commercial BEM codes with graphical user interfaces (GUIs) and mesh generators exist; however these are relatively expensive, which discourages their use by academic institutions and smaller companies. Helm3D is a three-dimensional BEM code available with purchase of a relatively inexpensive book, but the command file driven interface is difficult to learn and some mechanism to generate the mesh is required. In addition, there is a limited availability of suitable tutorial material, so the uptake of BEM throughout the acoustics community has so far been limited. In this paper, the development of both a mesh generator / GUI interface for the T-lelm3D code and an associated tutorial are described. The interface links the Helm3D code to a freely available numerical simulation pre/post processor. The tutorial demonstrates the capability of BEM in two application areas: interior acoustics and external acoustic radiation. It is envisaged that the availability of the interface and tutorial will accelerate the uptake of BEM by the wider acoustics community.

Virtual acoustic prototypes: listening to machines that don’t exist

Andy Moorhouse
Acoustics Research Centre, University of Salford, Manchester, UK

Vol. 33, No. 3 pp 97-105 (2005)
ABSTRACT: A Virtual Acoustic Prototype (VAP) is a computer representation of a machine (e.g. a domestic appliance), such that it can be heard without it necessarily having to exist as a physical assembly. Whereas visualisation tools are well developed in the field of visual design, the analogous tools for auralisation, such as VAPs, are still in their infancy. Examples of VAPs for a refrigerator, a telecommunications cabinet and a washing machine are presented, through which it becomes clear that considerable sophistication is required to include all the various excitation and transmission mechanisms found in real machines. It is explained that VAPs cannot be purely ‘virtual’ and that some measured data will be needed for the foreseeable future, particularly to characterise active components. Some of the advantages of working with VAPs are outlined.