AUDIO & ACOUSTICS

 

ACOUSTICS RESEARCH LABORATORY


 

CONTENTS

 


Updated January 5, 2007 Audio & Acoustics Links

 

INTRODUCTION

The Acoustics Research Laboratory in the Faculty of Architecture, Design and Planning provides substantial infrastructure for research and teaching in acoustics and audio within and beyond the Faculty. The laboratory one of several substantial technical facilities associated with the Architectural Technical Services Centre (ATSC) of the Faculty.

The Laboratory is equipped to do a wide variety of acoustic measurements and procedures including:

  • General measurement of sound
  • Sound absorption coefficients and impedance using impedance tubes
  • Sound transmission using impedance tubes
  • Sound absorption and power level using a reverberant room
  • Sound intensity
  • Speech intelligibility, privacy and security
  • Vibrometry (including single point laser)
  • Air flow resistivity
  • Subjective testing of sound
  • Sound quality and psychoacoustics
  • Source directivity
  • Acoustic scattering
  • Room acoustical measurements
  • Computer modeling of rooms
  • Field airborne and impact sound insulation
  • Sound logging
  • Sound-field spatial distribution
  • Sound-field simulation
  • Binaural recording and reproduction
  • Loudspeaker electroacoustics

LOCATION

The laboratory is located on Level4 of the Wilkinson Building.

STAFF

Densil Cabrera (senior lecturer) is the head of the Acoustics Research Laboratory and coordinator of the graduate program in audio and acoustics.
   
Ken Stewart (senior technical officer) manages the laboratory, including equipment hire.
   
Fergus Fricke (honorary associate professor) founded the current laboratory.

Several other honorary staff are involved with the laboratory, including Neville Thiele, Jingfeng Xu, Joseph Nannariello, Nigel Helyer, Jin Yong Jeon and Dae Up Jeong.

 

EQUIPMENT HIRE AND CONSULTING

Some items of equipment may be hired from the Laboratory on a commercial basis. Tapping machines and sound level meters are among the most commonly hired items.

The Laboratory can perform contract measurements. Common measurements include sound absorption (impedance tube) and field sound insulation using sound intensity.

Members of the Laboratory can perform consulting on a commercial basis through the University's Business Liaison Office. Consulting projects in recent years have been in auditorium acoustics, auditory display, building acoustics, speech intelligibility, and audio systems.

Contact Ken Stewart for more information about equipment hire and routine measurements.

HISTORY OF THE LABORATORY

First Laboratory

The history of the acoustics laboratory dates from 1954 when Professor H. J. Cowan was appointed and the Department of Architectural Science was established in the Faculty of Architecture. A Master of Building Science degree was started in 1961. Initially it was mainly concerned with structural aspects of buildings but it was soon realized that there was a need for other aspects of building science such as lighting, thermal and acoustic design. These and other subjects were incorporated into the Master of Building Science degree and then, because of need and increased knowledge, became postgraduate degree courses in their own right. At the same time there was growing interest in undertaking postgraduate research degrees, especially in acoustics, and a need for acoustics courses in Architecture, Engineering, Physics and Music, all of which required access to an acoustical laboratory.

The first acoustics laboratory was constructed in the late 1960s, partly in an abandoned chocolate factory and partly in a disused ladder factory, in Darlington . It consisted of a large reverberation room, an instrument room/electronic workshop and a small anechoic room. The instrument room contained little more than a reel-to-reel tape recorder, a couple of sound level meters, a calibrator, a measuring amplifier, a couple of frequency filters, a standing wave tube with frequency generator and power amplifier, a white noise generator, paper chart recorder, a couple of condenser microphones and a few loudspeakers. The reverberation room was a very basic 200 m 3 concrete block construction that was mainly used as a venue for parties. The anechoic room could be best described as a large broom cupboard, the walls and ceiling of which had been sprayed with asbestos. The floor had also been sprayed with asbestos, upon which had been laid steel reinforcing mesh that would normally be used for a concrete slab.

 

Despite these limited resources some important research was undertaken, such as the first survey of aircraft noise problems in Australia (Mather 1971) and on the propagation of sound in urban areas (Bullen 1978) before the anechoic room was permanently sealed up because of the danger it posed to students and staff, and the reverberation room (and the building it was in) were demolished as the building was in danger of collapsing if the white-ants decided to move out.

The plans on the left show the location of components of the first laboratory in the old factory buildings.

Right - t he first stage of the new building (1975) is shown under construction.

 

Below - Images of the first laboratory, including instruments and the reverberant room.

Right - Students working in the first anechoic room.

Left - Instruments and a scale model reverberant room.

 

Second Laboratory

A temporary acoustics laboratory was established on the fifth level of the first stage of the existing Architecture building. A small reverberant room (approx 80 m 3 ), an even smaller hemi-anechoic room (approx 35 m 3 ) and an instrument room were fitted out using existing spaces. By this time there was considerably more instrumentation and, because most of the work at this stage involved field measurements, such as measuring sound transmission in buildings (Lim, 1982), much time and effort was spent in carrying equipment up and down four flights of stairs, there being no lift.

Right - images of the temporary laboratory, showing the window into the reverberant room.

 

Third Laboratory

In 1984 the acoustics lab moved into the newly constructed and purpose designed facility (space limitations however were a major constraint on the design). This laboratory included an anechoic room with a useable volume of 56 m3 and a reverberant room with a volume of 130 m3. Studies involving subjective assessments in anechoic conditions could be carried out for the first time. Before the fire both the anechoic and reverberant rooms were heavily used for research (eg Madry (1990), Wu (1991), Jeon (1994), Wendolowski (1995), Field (1998), Jeong (1998), Cabrera (2001) and Xu (2005)), teaching (especially after the audio and acoustics postgraduate coursework program started in 1995) and for final year and honours year projects carried out by students from Physics, Psychology, Mechanical Engineering and Electrical Engineering. Nineteen PhD students and seventeen Masters students completed their degrees in the period 1984 to 2005 and over 150 journal and conference papers were published. Since the laboratory did not have a transmission suite and the reverberant room was not full size, commercial work in the facility was not routine, tending to be of a specialist nature.

Many items of equipment were specifically made for research and teaching activities, eg an airflow resistance rig, two microphone impedance tube, Kundt's tube, computer operated positioning apparatus which could position hot-wire anemometer probes and microphones to 0.5 mm accuracy and specialised loudspeakers. The first computer was introduced into the lab in 1986 and by 2005 most measurement, analysis and recording was undertaken digitally.

Many memorable activities were undertaken in this lab over the years, not the least of which were yelling competitions in the reverberant room on University open days (throat lozenges were freely available for the overzealous participants).

 

Above - views of the anechoic room of the third laboratory

 

Left - views of the reverberant room prior to the fire
Left - views of the 'bar area' and control room prior to the fire

 

Acoustics Lab Fire

In October 2005 a fire destroyed much of the facility through smoke and heat damage. 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 temporarily 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, with research and teaching severely affected. No matter where its location within the laboratory (even in the dome at the far end of the laboratory), only equipment sealed in airtight cases was saved from the hot corrosive smoke. Loudspeakers throughout the laboratory were damaged or destroyed, sometimes through the melting of their suspension, or else through corrosion. Most of the sensitive electronic equipment throughout the lab was damaged. About half of the microphones were damaged.

Throughout 2006 and the first half of 2007, laboratory equipment was temporarily housed in other rooms of the Architecture building. While there were no testing rooms available during this period, equipment such as impedance tubes and a scale model reverberation room could be used effectively. A loudspeaker testing rig was constructed for research on box absorption, using electrical, laser vibrometry and near-field acoustic measurements (this also did not require a special test room). Other research conducted included field measurements in other parts of the building, at other locations, and at other laboratories. We are particularly thankful to National Acoustic Laboratories for providing access for some research work. Nevertheless, research during this period has been severely affected by the lack of testing rooms in the Architecture building.

 

2007 Rennovation

The rennovated laboratory opened in February 2008. The most important change from the pre-fire laboratory is the larger anechoic room.

One of the issues that needed to be addressed in reconstructing the acoustics laboratory was the performance of the anechoic room lining. The original room had flat layers of “graded-density”, fibrous, lining. The design was determined using the work undertaken by the CSIRO (Davern 1980) which involved extensive trial and error testing in an impedance tube. Information on the materials in the three layers and thicknesses of the layers in the destroyed room was lost but the resultant room lining had a low frequency cut-off of approximately 315 Hz. The flat layer graded density (or more correctly graded flow resistance) type construction is far less costly than the anechoic wedge construction and, for a given thickness (length of wedge) can be made anechoic to a lower frequency than the wedge linings. In the past the difficulty with this type of construction has been to determine the optimum airflow resistance and thicknesses of the layers of sound absorbing material to achieve a required cut-off frequency. While it was known that the layer of material nearest the wall had to have the highest airflow resistance and the layer on the room side the least airflow resistance, the thickness of the layers, the airflow resistance values of them and the number of layers was largely a matter experimentation. There was also another constraint; the limited materials available and their thicknesses. Fortuitously, work on this topic had recently been successfully completed for a PhD dissertation at Sydney University (Xu 2006a). The theory, which involved an optimisation technique using evolutionary algorithms, was published (Xu 2004), used in a design (Xu 2006b) and evaluated (Xu 2006c) in an anechoic room at the University of Western Sydney , with a low cut-off frequency of 250 Hz (300 mm lining thickness). Another semi-anechoic room, in the School of Electrical and Information Enginnering at Sydney University , has also been designed, contructed and successfully tested, with an anechoic cut-off frequency of 100 Hz (790 mm lining thickness). This research has established that there is little performance advantage to be gained using more than three different layers of absorbing material, and that optimised designs can be achieved using unmodified commercially available materials. The anechoic lining of the restored laboratory has a low cut-off frequency of 200 Hz (thickness of 430 mm).

Further improvement to the anechoic performance of the room is achieved by a better selection of metal grid for the raised floor. The observation window was removed, replaced by closed circuit television monitoring – which has a much smaller acoustic impact on the room. The luminaires (which were bare Par-38 sources) were replaced with much smaller tungsten-halogen light sources, again reducing acoustic impact. This is also supported by the Fire Department's recommendations, since lighting was a possible cause of the fire. Beyond the anechoic room changes to the laboratory are minor, such as bench reconfigurations, changes to fire escape routes, and improvement of the electrical system and other cabling. We considered the possibility of expanding the reverberant room to 200 m 3 , but this was deemed to be too expensive, since it probably would have involved raising the roof of the concrete shell that encapsulates the laboratory.

 

GALLERY

 

 

 

   

REFERENCES

  • Bullen, R. B. 1978, Sound propagation in urban areas , Thesis (PhD), University of Sydney
  • Cabrera, D. 2001, A psychoacoustical study of resonating sound art , Thesis (PhD), University of Sydney
  • Davern W. A. 1980, “Flat-walled graded density anechoic lining,” Proceedings of 10th International Congress on Acoustics , Sydney , Australia
  • Ferguson , S. and Cabrera, D. 2005, “Vertical localization of sound from multiway loudspeakers,” Journal of the Audio Engineering Society 53(3): 163-173
  • Field, C. D. 1998, The attenuation of noise entering build-ings through ventilation openings , Thesis (PhD), University of Sydney.
  • Jeon, J. Y. 1994, Perception and production of tonal sounds: duration studies ,Thesis (PhD), University of Sydney
  • Jeong, D. 1998, Just noticeable differences in tonal quality as a measure of room acoustics , Thesis (PhD), University of Sydney
  • Lim, C. H. 1982, Some aspects of acoustical privacy in dwellings , Thesis (PhD), University of Sydney
  • Madry, A. J. 1990, Aspects of outdoor sound propagation , Thesis (PhD), University of Sydney
  • Mather, C. E., 1971, Some aspects of the aircraft noise problem in the vicinity of Sydney (Kingsford-Smith) Airport . Thesis (PhD), University of Sydney
  • Wendolowski, J. C. 1995, Applications of Green's functions to acoustic ducts and cavities with rigid boundaries , Thesis (PhD), University of Sydney
  • Wu, Q. and Fricke F.R. 1991, Determination of the Size of an Object and its Location in a Rectangular Cavity by Eigenfrequency Shifts. J. Sound and Vibration, 144, 131-147
  • Xu J., Nannariello J., and Fricke F. R. 2004, “Optimising flat-walled multi-layered anechoic linings using evolutionary algorithms,” Applied Acoustics 65: 1009-26
  • Xu J. 2006a, Applying Artificial Neural Networks and Evolutionary Algorithms ro Architectural and Building Acoustics , PhD Dissertation, Faculty of Architecture, University of Sydney
  • Xu J., Buchholtz J. M., and Fricke F. R. 2006b, “Application of multi-layered polyurethane foams for flat-walled anechoic linings,” Applied Acoustics 67: 476-485
  • Xu J., Buchholtz J.M., and Fricke F.R. 2006c, “Flat-walled multilayered anechoic linings: Optimization and application,” J. Acoust. Soc. Am. 118: 3104-3109