| Vol 33 No 3 | CONTENTS | 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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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.
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.
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.