How can you cut out noise from an outside source such as a noisy road

asks modge:
A. There may be a way. A new invention was reported in New Scientist recently. It's called the Silence Machine and may be the answer to the sound of a road drill or thumping bass from a party.

Q. How does it work
A. It works by analysing the stream of sound waves coming from an outside noise source and generating sound that is exactly out of phase with it, thereby neutralising the incoming sound waves.

Q. Eh
A. Apparently this technique is already being used commercially in planes - in noise-cancelling headphones which cancel out the sound of the jet engine and let you hear the in-flight movie in peace. But the Silence Machine is the first system that can block out a particular source of noise so that everything but the unwanted noise will still be audible.

The device has microphones for sound sampling, a computer for generating anti-noise, and loudspeakers for blasting that anti-sound at the incoming noise. The size of the affected area can be varied by altering the number of loudspeakers or their positions, according to inventor Selwyn Wright, an engineer at the University of Huddersfield in Yorkshire.

Q. Where can the Silence Machine be used
A. It's designed for using with continuous predictable noise - the sort of thing you'd find in factories. A more sophisticated version to deal with unpredictable noises such as music is in the pipeline. It needs different software and won't be available for a year.

Q. How much does it cost
A. An industrial-scale Silence Machine will cost around 10,000, and smaller domestic versions will be about 1000.

That's a lot of money for peace and quiet...
A. It is, but it could prove invaluable for those who live near motorways or air routes, creating quiet spots in the garden, for example.

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By Sheena Miller