If this works, it would really be nice to shut out the sound of your lawn
mower while you are mowing so you could hear other things running across
your yard like neighborhood kids or the neighbor's dog.

THIS WEEK:                                                       p19 30 Mar
02
 #10  The art of noise
          Hear only what you want to hear with the Silence Machine

 Marina Murphy

THE deafening racket of a road drill, the thumping beat from a
nightclub or the thunderous snoring of a partner-you'll soon be
able to silence them all, while the sounds you want to hear come
through loud and clear.

That at least is the claim of Selwyn Wright an engineer at the
University of Huddersfield in Yorkshire, who 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
Britain'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 GBP
10,000, while smaller domestic versions will sell at about GBP
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.


____________________________________________________________
Copyright 2002 New Scientist, Reed Business Information


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