PEACE is in sight for couples at war because one wants surround sound while
the other threatens to move out if five loudspeakers move in. The answer is a
single speaker panel that can produce up to six separate鈥攁nd
steerable鈥攂eams of sound to create the same effect as speakers spaced all
around a room.
快猫短视频 heard the system in action at a Cambridge lab just
before Christmas. We heard beams so well separated that one listener can be
hearing only a harpsichord while another, just two metres away, is hearing only
a guitar. Or one listener could hear five-channel surround sound while another
listens to a mono radio channel.
And unlike earlier attempts at simulating surround sound, this system doesn鈥檛
rely on ultrasound beams, which produce only low-volume, rather distorted sound
when they interfere
(快猫短视频, 9 September 2000, p 38).
And ultrasound also disturbs pets.
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The inventor of the new system, Tony Hooley of Cambridge start-up 1Limited,
has 拢8 million of development funding to exploit his creation. It produces
sound beams so well separated that, for instance, a PA system could direct
personal messages to selected people in a large audience. Or rock bands could
steer very loud sound into an open-air venue without upsetting neighbours.
Hooley鈥檚 panel鈥攚hich is fed sound from a CD or DVD player, or a TV
set鈥攈as around 250 tiny but conventional moving-coil loudspeakers arranged
in a vertical grid. But the speakers do a very unconventional job. Normally,
speakers are driven by a continuously varying electric current whose waveform
follows that of the desired sound output. This current induces a vibration in
the speaker cones that creates continuous sound waves in the air.
Instead, the tiny speakers in 1Limited鈥檚 Digital Sound Projector receive a
very rapid series of discrete electrical pulses and send a pattern of sound
pulses into the air, each of them 10 nanoseconds long. If all the speaker units
are driven in step, the panel generates a single, mono sound beam. But by
staggering the way pulse trains are applied across the array, the slightly
out-of-phase sounds reinforce and cancel each other out as they mix in the air,
steering beams at different angles.
For surround sound, multiple beams are steered onto different parts of a
room鈥檚 walls, floor or ceiling to bounce back to the listener鈥檚 ears, giving the
illusion that the sound is coming from different places. Using a remote control,
the listener can adjust the system to get the best effect for their position in
a room.
The panel can convert 2.5 kilowatts of electrical power into very loud sound
without the distortion created by current ultrasound-based systems. It has a
frequency range of 150 hertz to 20 kilohertz. But, as with most home
entertainment systems, a separate 鈥渟ub-woofer鈥� is still needed to waft very low
bass frequencies round the room.
1Limited鈥檚 system will be launched next week at the Consumer Electronics Show
in Las Vegas, Nevada. And products from 1Limited鈥檚 patent licensees are expected
to go on sale by mid-2002, says Hooley. The first panels will match large plasma
TV screens in size and cost up to $10,000.
