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"Silence machine" zaps unwanted noiseApril 6 2002 at 1:11 AM
Johnny Bob (Login jbob)
from IP address 184.108.40.206
"Silence machine" zaps unwanted noise
11:17 28 March 02
Exclusive from New Scientist Print Edition
You will soon be able to silence the deafening racket of a road drill or the thumping beat from a nightclub without blocking the sounds you want to hear, according to Selwyn Wright, an engineer at the University of Huddersfield in Yorkshire, UK.
He has developed what he calls the Silence Machine. It works by analysing the stream of sound waves from a noise source, and generating sound that is exactly out of phase and neutralises the incoming sound waves.
The concept is already in use commercially in noise-cancelling headphones to wear in passenger aircraft. These cancel out the jet engine noise and let you hear the in-flight movie in peace. And flat-panel speakers that produce anti-noise have been fitted to fighter plane cockpits to make them more comfortable for pilots.
But Wright's system is the first that can block out a particular source of noise to produce a personal "sound shadow" in which everything but the unwanted noise will still be audible.
His patented Silence Machine comprises microphones for sound sampling, a powerful computer for generating anti-noise, and loudspeakers for blasting that anti-sound at the incoming noise.
The size of the shadow areas where the sound and anti-sound waves cancel each other can be varied by changing the number of loudspeakers or their positions. Any microphones or loudspeakers will work, says Wright, but the more directional they are in terms of sensitivity the better the result.
Signal processors in the computer measure the frequency of every component in the noise signal, and use this information to create the anti-noise-sound with an identical frequency but the opposite phase. This means that a peak in the noise wave meets a trough in the anti-noise, cancelling out the sound.
A Silence Machine suitable for use in factories is ready for commercialisation, says Wright, who has spent two years developing the machine with the help of a "smart award" from the UK's Department of Trade and Industry.
While this machine is aimed at cancelling continuous, predictable noise - such as that produced by compressors, drills and generators - a more sophisticated version is also on the way. This will require different software to cope with unpredictable noises such as speech and music. "We are pretty close, but it will be a year before you can buy it in the shops," Wright says.
He expects an industrial-scale Silence Machine to cost around £10,000, while smaller domestic versions will sell at about £1000. It could be used to create quiet zones in a garden, for example, or around your house, blocking out railway, aircraft and motorway noises, without affecting pleasant sound such as birdsong.
If the machine can be proved to work, "it probably will have some applications," says Tim Williamson of Britain's National Society for Clean Air and Environmental Protection. But perhaps there are simpler ways to make life quieter. "It would seem far easier and more sensible to avoid making noise in the first place," he says.
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