THE microphones and speakers attached to office PCs could form the heart of a
cheap, wireless network. While the computers communicate by exchanging squawks,
people won鈥檛 hear a thing from the chattering hardware, according to its
inventors.
A sound pitched slightly higher and quieter than normal conversation is
inaudible if it is only a few milliseconds long, explains John Harris, an
engineer at the University of Florida in Gainesville. Although people are good
at hearing frequencies between 1 and 20 kilohertz, we find sounds in this range
harder to hear when they are very short-lived.
Unlike directional ultrasound or infrared beams, which need to be aimed
carefully to ensure a clear signal, sounds in the 1 to 20 kHz range bounce
easily around a room. Alternative wireless systems based on radio waves, such as
Bluetooth, constantly have to hop frequencies so they don鈥檛 interfere with each
other. But Harris says his system allows many computers to operate
simultaneously at the same frequencies, as long as they are near one
another.
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The system will also cope with open-plan offices and apartments where several
computers run simultaneously. 鈥淲e build rooms and walls so that sounds stay
localised,鈥� says Harris. By contrast, radio waves can travel up to 100 metres
through walls and floors. A mobile phone company is now interested in using the
idea to transfer text from phone to PC.
One concern, however, is that pets could be disturbed by the computer
chatter, because they may be more sensitive to short pulses than humans are. But
the sounds are fairly low-intensity, so Harris doesn鈥檛 think they鈥檒l bother Spot
or Fluff.