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Vol 37 No 2

CONTENTS

August 2009


ARTICLES

Snodar: An acoustic radar for atmospheric turbulence profiling with 1m resolution
C. S. Bonner, M. C. B. Ashley, J. S. Lawrence, D. M. Luong-Van and J. W. V. Storey
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A simple acoustic immersion index for music perfomance spaces
Neville H. Fletcher
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A low cost underwater sound logger using an MP3 player
L. J. Hamilton and C. Lees
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Design and test of a feedback controller for attenuating low frequency noise in a room
C. Bao, R. Paurobally and J. Pan
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SNODAR: AN ACOUSTIC RADAR FOR ATMOSPHERIC TURBULENCE PROFILING WITH 1 m RESOLUTION

C. S. Bonner1?, M. C. B. Ashley1, J. S. Lawrence1,2,3, D. M. Luong-Van1, J. W. V. Storey1
1 School of Physics, The University of New South Wales, NSW 2052, Australia
2 Department of Physics and Engineering, Macquarie University, NSW 2109, Australia
3 Anglo-Australian Observatory, NSW 1710, Australia
Electronic Mail ? This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Vol. 37, No. 2 pp 47 - 51? (2009)
ABSTRACT: Snodar is a 5 kHz monostatic acoustic radar designed to measure the atmospheric turbulence within the first 200 m of the atmosphere with a vertical resolution of 1 m. An in situ calibration target is used to give absolute intensity calibration. The primary motivation for building Snodar is to quantify the site conditions for a future astronomical observatory in Antarctica. Two Snodar instruments are operating at Dome A, Antarctica, during 2009 as part of the completely robotic ?PLATO? facility. The instruments are separated by 20 m and sample from 8 m to 200 m with a resolution of 1 m allowing the spatial and temporal characteristics of the atmospheric boundary layer to be investigated. We present here the acoustic design of Snodar and example data demonstrating the performance of the instrument..

A SIMPLE ACOUSTIC IMMERSION INDEX FOR MUSIC PERFORMANCE SPACES

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

Vol. 37, No. 2 pp 52 - 56 (2009)
ABSTRACT: A simple acoustic immersion index is proposed that compares the reverberant sound pressure level with the prompt sound pressure level, including both direct and once-reflected contributions, for organ music in a hall defined only by its geometrical dimensions and reverberation time. Two versions of the index are considered. In the first version a very simple calculation is proposed that gives a constant index value S1 throughout the hall. The second version of the index separates direct and once reflected sound, with the result that the computed index S2 varies from the front to the rear of the hall. Values of the index S1 are given for several well known halls and are all close to 0 dB. The exact values appear to correlate well with subjective observations on the acoustical character of the halls.

A LOW COST (NEAR EXPENDABLE) UNDERWATER SOUND LOGGER USING AN MP3 PLAYER: TESTING IN SYDNEY HARBOUR

L.J. Hamilton and C. Lees
Maritime Operations Division Defence Science and Technology Organisation (DSTO)
13 Garden Street, Eveleigh NSW 2015

Vol. 37, No. 2 pp 57 - 60 (2009)
ABSTRACT:A low cost, self contained, portable system based around a modified MP3 player has been constructed to record ambient underwater noise. High resolution acoustic data are stored in PCM WAV file format with a depth of 16 bits and 96 kHz sampling. The MP3 player, preamplifier, and battery are mounted in an underwater housing made of PVC pipe to which is attached a hydrophone on a short buoyed cable. This provides a near expendable package suitable for unattended deployments where equipment loss or damage are possible factors. System functioning was verified by several 24-hour deployments in Sydney Harbour, following which it was used for the international KONDARI ports and harbour security trial at Garden Island. Three characteristic sound regimes were observed: (1) a regular succession of ferry passage events from morning till midnight; (2) irregularly occurring high energy vessel events other than ferries; (3) lower sound levels from midnight to six a.m. dominated by snapping shrimp, and by pumps and ancillary engines on moored vessels and dockyards.

DESIGN AND TEST OF A FEEDBACK CONTROLLER FOR ATTENUATING LOW FREQUENCY NOISE IN A ROOM

C. Bao1, R. Paurobally2 and J. Pan2*
1Building A51, DSTO WA, PO Box 2188, Rockingham, WA 6958, Australia
2School of Mechanical Engineering, The University of Western Australia, Crawley, WA 6009, Australia

Vol. 37, No. 2 pp 61 - 66 (2009)
ABSTRACT: A single-channel feedback control system is presented for global noise attenuation inside a room. The controller design is based on the compensation filter approach of classical control theory. To demonstrate the global noise attenuation capability of this simple control scheme experimental results of noise control in an office are presented. They show that the positioning of the error microphone relative to the control loudspeaker greatly affects the global noise attenuation performance. If the microphone is placed too close to the control source, the microphone signal is dominated by the near field and little global noise reduction is achieved. If the error sensor is placed further away where the near field has little effect on the microphone signal, noise reductions of about 10 dB can be obtained over low frequency ranges.

 

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