Tomorrows World BBC Television
January 12th 2000

Sound Beam:
Transmits sound in a straight line.

The sound beam is a new device which sends sound in a straight line - like a spotlight. It could be used to talk to just one person in a crowd, from a distance of up to 200m. Or, to beam music to individuals on a cinema or plane, instead of headphones.

It's made by Joe Pompei, a researcher at MIT media lab in Boston. Joe had the idea of using ultrasound, those frequencies that are beyond our hearing, to act like a 'carrier' for audible sound.


Sound Beam Explained

Animation (real video player)

Normal sound is rather like a lightbulb, flooding a room. What Joe has done is extraordinary: making sound that's more like a spotlight. He makes use of high frequency ultrasound waves, beyond our hearing, which travel in straight lines. What Jo does first is combine music with ultrasound: this recreates the complex wave patterns of the music at a much higher frequency that can't be heard. He uses a specially designed speaker to send out this high frequency ultrasound beam.

Physical properties of the air then distort the beam producing a range of frequencies including audible sound. As Jo knows exactly how much distortion the air causes, he can predict how to combine the music with the ultrasound to get the music out again.

The ultrasound transmits audible sound in a long thin beam, just half a metre wide. The sound quality isn't strong enough yet to cover very long distances, but once it is, it could be used to pick out just one person in a crowd: a personal message system in public places like airports and stations, or even a personal speaker for music.

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