Acoustics:

Looking for a sound career move?

Sound, whether music or unwanted noise, affects most of our lives every day. Acoustics is the study of sound. Improving our acoustic environment is a complex and rewarding career requiring skills that span many scientific and engineering disciplines. However, there is much more to sound than meets the ear. Acoustics is responsible for advances ranging from medical diagnosis to understanding climate change.

Often we associate acoustics with music and sound recording or reproduction. Perhaps this is because, for many of us, our most conscious experience of acoustics is via our personal stereos. But audio entertainment is actually only one of many activities that call on the expertise of acousticians. This article explores a few examples to indicate the breadth of opportunity and depth of science that acoustics has to offer as a career.

Recent breakthroughs in audio engineering include the space-saving “flat-panel speaker”. While a conventional speaker has a cone-shaped radiating surface that is stiff and light, the flat-panel speaker is designed to be flexible. Flat panel speakers can be built into ceiling tiles and even talking cereal packets! Interestingly, the idea was conceived from an accidental discovery whilst studying helicopter noise.

Virtual Source Imaging (VSI) is another emerging technology in the multi-media industry. In VSI, the sound appears to originate from a virtual position. This is achieved by introducing time delays between waves propagating from two closely spaced loudspeakers. Already developed for surround-sound in PC applications such as computer games, this technology is set to spread into the rapidly growing market of home cinema.

Although some acousticians do specialise in the field of audio acoustics, many more employment opportunities are associated with reducing unwanted noise. A controversial example is the wind turbine which, after a decade of research by acousticians and other scientists, no longer deserves the reputation for noise it earned for itself in the 1980’s. Aerodynamic noise from the blades is largely at inaudibly low “infrasonic” frequencies and at harmless levels, and mechanical whirring noise from the gearbox and generator has been minimised by vibration isolation measures.

Transportation is perhaps the largest contributor of noise and is the focus of increasingly stringent legislation. Road vehicle noise, for example, is legislated in the European Union through a drive-by test. Of the many sources of noise on a vehicle, it is sound radiated from the tyre that dominates the drone heard from nearby highways. The physical interaction between the tyre and the road is becoming better understood and this has led to developments in quieter road surfaces and designs of tyre.

Rail systems are considered environmentally-friendly, but when a new line is planned it is their noise that often forms the basis of complaints. New techniques to reduce train noise are being developed based on damping out the vibrations of the wheels and rails.

Jet engine noise is a major constraint on the capacity of airports and a blight on local residents, especially in densely populated countries. Aero-engine manufacturers such as Rolls-Royce in the UK invest considerable resources in computational models of flow noise, allowing quieter turbines to be designed. As is often the case in science and engineering, such models should be checked against experiments. Consequently, many leading companies and organisations in the field of acoustics have major experimental facilities. These may include “anechoic chambers” which have highly absorbent walls to reduce sound reflections, “reverberation chambers” and wind tunnels.

Acousticians are also consulted to assess current noise levels and estimate future increases due to proposed new infrastructure. Housing developments, by-passes and airport runways are all likely to affect noise pollution and their impacts must often be predicted before planning consent is given.

Noise is a serious issue for occupants of vehicles as well as residents. In a world shaped by marketing, cars are increasingly designed not only to have quiet interiors but to sound in keeping with the image the manufacturer wishes to portray, e.g. sporty or luxurious. The subjective way in which humans perceive sound is often referred to as psychoacoustics and is becoming a consideration in more of the goods that we buy. For example, when a car door is closed it should sound ‘solid’ not ‘cheap’.

Aircraft cabins are also noisy environments and can cause discomfort and fatigue even on short flights. An approach known as active noise control has been successfully deployed on some turboprop passenger aircraft such as the Bombardier Dash-8 and Saab 2000. Active noise control involves controlling sound with sound. By generating sound waves with opposite phase to what is measured, destructive interference can be obtained in the cabin. Significant noise reductions are possible for a relatively small penalty on the weight of the aircraft. Active noise control technology is also now widely available at airport shops in the form of ‘Noise Cancelling” headsets.

Acoustics also has a very significant contribution to make in gathering information and intelligence for military, geophysical, forensic and medical purposes. Sonar has been used for many decades for marine navigation since only sound waves can travel significant distances underwater. The study of underwater acoustics has led to improved understanding of climate change and marine animal behaviour such as dolphins and whales. In forensic science catastrophic events such as air crashes, explosions and gunfire incidents are frequently captured on audio recordings. By analysing these signals the cause or nature of the event can sometimes be identified from the unique sounds that they make, or their “acoustic signatures”. Using similar signal processing techniques, sensors monitoring the response of a patient can be analysed to infer medical conditions such as susceptibility to a stroke, or the level of consciousness during surgery.

To get into an acoustically related career you will probably need to study for a degree in physics or an engineering related subject at a respected university. In most courses, the number of modules specifically related to acoustics is often fairly limited, although general topics such as electronics, aerodynamics, dynamics and control will stand you in good stead.

You may also like to consider applying to one of the small number of specialist institutions that offer either undergraduate or postgraduate degree programmes in acoustics. Even this would not tie you to a career in acoustics since the multidisciplinary nature of the subject will open doors in many areas of science and engineering.

Dr Tim Walters
ISVR
University of Southampton
www.isvr.soton.ac.uk