Quiet please! Fighting noise pollution in Australian citiesIncreases in the density of residential and commercial buildings, more traffic on the roads, and out-dated building regulations are all contributing to serious noise pollution in our cities.
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Key textNoise is an inescapable part of modern life. Traffic on the road, low-flying aircraft, dogs barking, lawn mowers, and music blaring from ghetto blasters are some of the noises polluting our cities.Judging by the number of complaints made to authorities, Australians are becoming increasingly irritated by urban noise. In Sydney there are over 100,000 noise complaints a year, most of which relate to noisy neighbours. Similarly, in one of Melbourne’s inner city councils, complaints about noise more than doubled in 2000 after higher density housing was permitted. Even in thinly populated Tasmania, approximately half the environmental complaints relate to noise. But it is not just the number of complaints that is on the rise. There has also been a sharp increase in noise litigation, with people prepared to take legal action to protect their peace and quiet. Of even greater concern is the effect excessive noise can have on the physical and psychological well-being of people (Box 1: Health issues related to noise pollution). Sounds of the city Noise pollution can be defined as any unwanted or offensive sounds that unreasonably intrude into and disturb our daily lives (Box 2: What is noise?). Noise originates in all sorts of ways, but, in general, increasing noise pollution is primarily the result of the increasing population of cities. More people mean more road, rail and air traffic, more industrial noise, and more neighbourhood and recreational noise. A contributing factor to the rise of noise pollution is the increase in high- to medium-density housing. People are leaving the traditional quarter-acre block in the suburbs and moving into apartments, town houses and converted warehouses in the central and inner city areas. Australians are now living and working physically closer to each other than ever before. And people are noisier now than they were a generation ago. Most homes now boast at least one television, one radio, a thumping stereo system and a range of noisy household appliances. Controlling noise pollution There is no single government authority in Australia with overall responsibility for controlling or reducing noise pollution. The Commonwealth government takes responsibility in areas such as aircraft noise (Box 3: Planning to reduce airport noise) and emission standards for new motor vehicles (Box 4: Traffic noise – sources and solutions), while an environment protection agency regulates environmental noise in each State. The National Occupational Health and Safety Commission has a national code of practice that provides advice on management of noise in the workplace. Neighbourhood and recreational noise issues are usually the domain of the police and local councils. Guidelines for the sound insulation and acoustic properties of walls between adjoining units in multi-residential buildings are set out in the Building Code of Australia (BCA). The number of complaints from unit owners indicates that these guidelines are too lenient, and moves are underway to improve the building code. Currently the Australian Building Codes Board, which administers the BCA, is considering strengthening the present sound insulation provisions in the code. This will lead to a rationalisation of the present tangle of different standards and set new regulations that can be easily understood and applied by the building industry (Box 5: Soundproofing noisy buildings). Sound design While tougher regulations are one way to combat noise pollution, smarter urban planning and improved building design will also help to create a quieter environment. Steps that can be taken include:
Quiet buildings Noise inside a building can be reduced if both the external and internal walls have high sound reduction. Heavy, dense materials such as masonry or brick walls are better for sound reduction, but there are also lightweight solutions. For example, interior walls that have layers of plasterboard with sound-control material in the cavity can be very effective in reducing noise. Windows and doors are often the weakest link in sound insulation. Double glazing is particularly effective for windows, especially if the airspace between the two panes is as wide as possible. Solid-core doors are best, particularly for those that open on to external areas. All gaps and openings around both doors and windows should be well sealed – even the smallest openings can leak significant amounts of noise. Sound versus noise Sound is an important part of everyday life: for communication, for enjoyment or for alerting us to danger. But when sound becomes noise, we like to know there are regulations protecting us from its harmful effects. Related Nova topics:
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Extreme noise At its most extreme, loud noise can cause instant and permanent hearing loss. Normal hearing depends on the three components of the human ear: the outer, middle and inner ear. The inner ear or cochlea is the most susceptible to damage by loud noises. It contains thousands of tiny hair cells that transmit sound impulses to the auditory nerve. Explosive sounds with peak noise levels of 140 decibels (dB) or more can destroy these cells and cause permanent deafness. Extended exposure to loud noise can also lead to long-term hearing loss. A sound level meter is used to measure the decibel levels of sound. Usually the sound level meter has a filter that has a frequency response similar to the human ear. These levels are known as dB(A) or A-weighted decibels. Like the ear, this filter reduces the sound levels in the lower frequencies (below 1000 hertz) and in the higher frequencies (above 5000 hertz). Worksafe Australia recommends that a noise level of 85 dB(A), sustained for no more than 8 hours a day, should be the maximum to which a worker is exposed. This is about the same as the noise level in a street with heavy traffic. Higher noise levels can cause permanent hearing loss unless protective measures are taken. Damage to more than hearing Aside from contributing to hearing loss, too much noise can affect human health in many other ways. Research has shown that people living near airports or busy roads have a higher incidence of headaches, take more sleeping pills and sedatives, are more prone to minor accidents, and are more likely to seek psychiatric treatment. Exposure to high noise levels has also been shown to lead to a range of physical symptoms such as accelerated heartbeat, high blood pressure, gastro-intestinal problems and chronic fatigue. Some of these problems are relatively easy to treat medically, but other psychological effects such as insomnia, nervousness, anxiety and depression can be longer lasting. Related sites
Sounds can be characterised by their frequency (or pitch) and intensity (or loudness). The vibrations producing the sound are cyclical and are measured in hertz (Hz), which gives the number of cycles that occur per second. An adult with good hearing can hear frequencies in the range 20 to 15,000 Hz, while children can hear frequencies above 20,000 Hz. The sound pressure level is measured in decibels (dB). For example, a whisper is in the range 20-30 dB, normal conversation about 60 dB, while someone shouting in your face can easily exceed 80 dB. A sound level meter is used to measure the decibel levels of sound. Usually the sound level meter has a filter that has a frequency response similar to the human ear. These levels are known as dB(A) or A-weighted decibels. Like the ear, this filter reduces the sound levels in the lower frequencies (below 1000 hertz) and in the higher frequencies (above 5000 hertz). The correspondence between decibel levels and perceived loudness is fairly simple. A difference of 3 dB in noise level is barely noticeable, yet it represents a doubling of the acoustic energy involved. For a noise to sound twice (or half) as loud, a difference of about 10 dB is required. For example, a lawn mower measured at 80 dB will sound about twice as loud as a hair dryer at 70 dB. When sounds become noise People react to sounds in different ways. We take most sounds for granted, but in some situations a sound can distract us and break our concentration. When this happens, the sound becomes unwanted noise. Often it is not the pitch or the loudness that makes a sound an annoying noise. Sometimes it is the repetitive nature of the sound and our inability to control it that makes it annoying. Car alarms and the seemingly endless barking of a dog are good examples. Related sites
Aircraft noise in Sydney is a major environmental concern, particularly since the opening of the third runway at Kingsford Smith. To cope with the increased noise levels, soundproofing costing several millions of dollars has been installed in thousands of homes near the airport. Three approaches to solving the problem of airport noise Noise complaints from people living beneath flight paths have reached record levels, not just in Sydney but in cities across Australia. Authorities have adopted a ‘three-legged stool’ approach to the problem. The first leg is to ensure that aircraft emit the lowest possible noise levels, compatible with airline safety. Aircraft such as the Boeing 727 and 757 are as much as 20 dB quieter than the Boeing 747 recorded over Sydenham. The second leg is to impose controls on airport operations, such as restricting the number of arrivals and departures, imposing night curfews, and minimising flight paths over populated areas. The third leg of the stool is to control urban development near existing airports and the site of future airports. Homes, schools, hospitals, commercial and public buildings all need protection from excessive aircraft noise. Australian Noise Exposure Forecast system Urban planners use a scheme known as the Australian Noise Exposure Forecast (ANEF) system to determine noise levels near airports. The system does not rely on decibel levels alone, but draws up ‘noise contours’ around airports. The contours are based on additional factors such as the projected volume of flights and the time of day they occur.
Australia has close to 13 million registered motor vehicles, about two vehicles on the road for every three people. Passenger vehicles make up the great majority (80 per cent), followed by light commercial vehicles, trucks, motorcycles and buses. Traffic noise has become a serious problem now because of inadequate urban planning in the past. Homes, schools, hospitals, churches, libraries and other community buildings were routinely built on main roads without buffer zones or adequate soundproofing. The problem has been compounded by increases in traffic volumes far beyond the expectations of our early urban planners. Sources of traffic noise At low speeds, most traffic noise is caused by vehicle engines, transmissions, exhausts and brakes. The stop-start braking and acceleration during peak-hour congestion also increases noise levels. On freeways where speeds are high and relatively constant, most noise is caused by a combination of tyre contact with the road and aerodynamic drag over the vehicle. Trucks and motorcycles combine to make up 7 per cent of vehicles on our roads, but they are largely responsible for the peak noises that stand out from the steady background rumble. It is these sharp and intermittent noises that are more likely to cause sleep disturbances and to contribute to other physical and psychological problems. Solving the problem of traffic noise A 2001 report by the National Road Transport Commission (NRTC) found that, in comparison with Europe, Japan and the United States, Australian regulations permit up to double the noise emission levels from some vehicles. The report recommends adopting new noise levels in line with international standards and, tougher regulations to control the performance of exhaust systems. Another recommendation is to provide more resources to local authorities to ensure that owners, particularly those of older cars, comply with the new regulations. One target of the NRTC report is the excessive noise from trucks that use engine braking as a backup to conventional wheel braking. While engine braking is an indispensable safety device, fitting trucks with improved and relatively inexpensive mufflers can significantly reduce the noise levels. The installation of noise barriers along major roads and freeways is another way to combat traffic noise. The barriers deflect noise from adjoining urban areas and can be made from relatively light and inexpensive materials such as timber, fibro-cement sheet or Perspex. An effective barrier needs to be long enough and high enough to deflect noise from the area that is to be protected. Usually this means that the barrier blocks the line of sight to the noise source. Any gaps in the barrier (eg, driveways) decrease its effectiveness. A combination of strategies that include noise barriers, lower vehicle noise levels and better urban planning will help reduce the impact of traffic noise in the future. Related sites
Structure-borne and airborne noise Noise can pass from one room to another either through the building structure itself (structure-borne noise) or through the surrounding air (airborne noise). Airborne noise is the more common and occurs, for example, when loud music in a living area interferes with people sleeping in bedrooms. Airborne noise can pass from one room to another along a variety of paths such as open doors and windows, openings in walls separating the rooms, stairwells, or heating and air-conditioning ducts. Structure-borne noise occurs when the building structure itself is made to vibrate; for example, a washing machine in contact with a wooden floor, a saucepan falling to the kitchen floor, and the impact of footsteps on hard floors. Soundproofing guidelines The guidelines for soundproofing in the Building Code of Australia (BCA) date back to a time when most Australians were leading a much quieter life in the suburbs. At least four significant failings have been identified with the present BCA:
Currently the Australian Building Codes Board is considering strengthening the sound insulation provisions of the BCA. Any changes would almost certainly strengthen the sound insulation requirements for internal walls of buildings. How well a wall insulates sound is measured by the weighted sound reduction index. The minimum allowable value of the index for internal walls in the current building code is 45 decibels (dB). Increasing the index to 55 dB would approximately halve the amount of unwanted sound leaking through a wall. It would also bring Australia into line with building codes in countries such as Germany, Denmark, Great Britain and New Zealand. The new code would also need to recommend a minimum requirement for 'impact sound insulation' of floors. Currently there is no requirement, because the code assumes that carpet will be used as a general floor covering, ignoring the fact that homeowners are turning to hard floor coverings such as polished boards and ceramic tiles. Good sound insulation is expensive. The proposed changes are expected to add an extra 2 per cent to the construction costs of a building. Also, the extra thickness of walls, floors and ceilings would mean that 3 per cent fewer dwellings could be fitted onto a development site. Developers would therefore need to charge more for each dwelling to maintain their profit margins. Nationally, the changes could cost the building industry an estimated $115 million a year. Related site
Materials (for each person) 1 plastic ruler Procedure
Teachers notes Students should observe the following: Flicking the ruler resulted in an up and down motion (vibration). The second distance (15 centimetres) produced a faster vibration and should have generated a sound that was easier to hear.
Further readingAustralasian Science November/December 2004, page 13 Fresh air without the noise (by Stephen Luntz) A high-tech window delivers fresh air into a building while keeping out noise.
Ecos No. 108, 2001, pages 32-33 Sound standards (by Steve Davidson) Covers proposed changes to sound insulation standards in Australia.
New Scientist 22 August 2007, pages 6-9 Dying for some quiet: The truth about noise pollution (by Andy Coghlan) Reports on research linking noise pollution to premature death and illness.
13 December 2003, pages 28-31 The shape of wings to come (by Paul Marks) Discusses approaches being investigated for the development of quieter aircraft.
22 November 2003, pages 26-27 Smooth approach cuts noise pollution (by Paul Marks) Noise nuisance from aircraft can be reduced significantly by changing the way planes come in to land.
23 March 2002, pages 32-35 Sculpted sound (by Philip Ball) Describes how large structures called sonic crystals can block out sound.
17 March 2001, page 5 Sounds alarming (by Duncan Graham-Rowe) An Austrian study has shown that children living in noisy neighbourhoods had raised levels of blood pressure, heart rates and stress hormones.
8 September 1998, page 7 The sound of silence (by Mick Hamer) Describes ways of minimising train noise.
5 July 1997, page 12 What did you say? (by Dan Charles) Discusses the effect of loud music on hearing.
10 May 1997, page 5 Noise pollution robs kids of language skills (by Vincent Kiernan) Discusses the links between poor reading skills where children live.
16 November 1996, pages 14-15 Plagued by noise (by Michael Bond) Discusses noise pollution guidelines and the effects of noise on human health.
research*eu January 2008 Wings of silence (by Delphine d’Hoop) Evaluates noise reduction technology in aircraft.
Discusses environmental noises, how they can be measured
and why their measurement is not straightforward.
Australia's vehicle noise limits too loud: NRTC report (National Road Transport Commission, Australia) Summarises the findings of a report on vehicle noise regulations. The
full report can be access by clicking on 'A review of the noise related
Australian design rules and engine brake noise' at the end of the article.
Noise and vibration (WorkSafe, Western Australia) Provides information on workplace hazards relating to noise and vibration. Click on 'Education' for articles about noise and vibration.
Australian Broadcasting Corporation
Information from each State.
New South Wales
Northern Territory
Queensland
South Australia
Tasmania
Victoria
Western Australia
deafness. There are two types of deafness: sensori-neural and conductive. In sensori-neural deafness, the defect lies in either the cochlea (the organ that converts vibrations to nerve impulses) or in the transmission of the sound signals to the brain once they have left the cochlea. This form of deafness tends to occur with age, and is accelerated by exposure to loud sounds (eg, at a disco, from a ghetto blaster, from a portable radio used with earphones, from construction projects). Workers on noisy building sites wear ear protectors, as do sporting-rifle shooters and army personnel on a rifle range. Conductive deafness occurs when something prevents the sound vibrations from reaching the inner ear. This could merely be wax in the ear canal, but it could also occur if infection has caused the ear drum to become perforated so that it does not move normally under the influence of sound pressure. Alternatively, the ossicles (the tiny bones connecting the ear drum to the cochlea) might become stiff so that they lose their 'lever' action. With conductive deafness, the hearing organ is basically normal, and the problem lies in getting sound to the cochlea. decibel (dB). A logarithmic scale used to denote the intensity, or pressure level, of a sound relative to the threshold of human hearing. A step of 10 dB is a ten-fold increase in intensity or sound energy and actually sounds a little more than twice as loud. The quietest sound we can hear is 0 dB; a soft whisper has about 100 times more sound energy and so is about 20 dB. A power lawn-mower has a factor of 109 more sound energy and is about 90 dB. A rock band may be as high as 110 dB. Above 120 dB the sound produces discomfort and even pain. The scale is often adjusted to take account of the reduced sensitivity of human hearing to high and low frequencies and is then specified as dB(A). On this adjusted scale (the A-weighted scale), the range of human hearing is about 3 to 140 dB(A). For more information see What is a decibel? (How Stuff Works, USA); What is a decibel? (University of New South Wales, Australia); and Intensity and the decibel scale (The Physics Classroom, USA). frequency. A measure of how frequently an electromagnetic wave goes up and down (oscillates) or the number of waves passing by in a second. A hertz is a unit of frequency – 1 oscillation per second; a kilohertz (kHz) is 1000 hertz – 1000 oscillations per second; a megahertz is 1 million hertz – 1 million oscillations per second. For more information see Sound properties and their perception – pitch and frequency (The Physics Classroom, USA). reflection, scattering, absorption. Sound waves can be reflected by hard surfaces, scattered by rough surfaces, or absorbed by soft porous surfaces, in much the same way as light waves. Because the wavelength of sound ranges from centimetres to metres, smoothness must be judged on a similar scale. When sound meets with a large surface, the sound may be absorbed or reflected depending on the nature of the surface. Hard, glossy surfaces such as glass, bricks and ceramic tiles are efficient reflectors; porous surfaces such as carpets and curtains are good absorbers. These differences are important in the design of living rooms, recording studios and concert halls. For more information see Behavior of sound waves – reflection, refraction and diffraction (The Physics Classroom, USA). weighted sound reduction index. A single-number rating of the sound reduction through a wall or other building element. Since the sound reduction may be different at different frequencies, test measurements are subjected to a standard procedure which yields a single number that is about equal to the average sound reduction in the middle of the human hearing range.
Posted June 2002. The Australian Foundation for Science is also a supporter of Nova. This topic is sponsored by the bequest of J S
Anderson, FAA.
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