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|A Noise Annoys|
Aeroplanes…next door’s stereo… shop musak ….fireworks…roadworks…traffic...babies crying...YOU CAN’T GET AWAY FROM NOISE! But as Quentin Cooper finds out in this week’s Connect, there are some solutions which dramatically help these problems.
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Unlike our eyes, we cannot close our ears, so it can be argued that hearing is one of our most important senses. We are continuously subjected to various types of sound. Some are pleasant and desirable, such as speech and music, whilst some are unwanted and annoying, such as road noise and machinery. Connect looks at and listens to how acoustic technology is helping to control interior and exterior noise, how the less than 'baffling' technology of new materials and structure is providing solutions and how noise engineers can manipulate noise to reflect the car brand - all of which is helping to make the soundtrack to our lives rather quieter.
In reducing noise levels there are Passive and Active methods:
Passive controls are materials that ‘soak’ up unwanted noise, eg covering the walls with absorbing materials like glassfibre coatings. These materials dissipate acoustic energy into heat and so contribute to the noise reduction, but they work best at high frequencies (e.g. above 500 Hz). At the University of Bradford’s Acoustic Group, Dr Kirill Horoshenkov and his team are taking a kitchen sink approach to the problem - literally - by turning industrial waste carpets into environmentally friendly acoustic absorbers. Quentin lends a hand in the kitchen as these carpet ‘pies’ are baked and analyses their performance.
Active controls try to eliminate sound or vibration components by adding the exact opposite sound or vibration. By detecting unwanted sounds with microphones the active noise control system can automatically generate the correct signal to send to loudspeakers which will produce anti-sound to cancel out the original sound and work best with low frequency predictable noise source. Quentin visits Professor Steve Eliott at Southampton’s Institute of Sound and Vibration Research who are developing active solutions to noise problems in aircraft.
|BBC Science & Nature|
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