Australian IT..
New directions in sound
Ian Grayson
AUGUST 17, 2004
HAVE you ever tried to talk to someone in a crowded room? By cocking your head and listening intently, it's usually possible to ignore other speech and background noise so you can make out what's being said.
This happens because your brain is able to filter out the sounds you want to hear from everything else in the room.
The same trick enables you to listen to a television or public-address announcement in a bar or airport terminal.
Wouldn't life be a whole lot easier if sound could be aimed directly at those who wanted to hear it? Just as a torch can focus a beam of light in a single direction, wouldn't being able to do the same thing with sound be pretty useful?
Well, as a result of some clever audio developers, such feats are possible.
They have designed a system that directs sounds in a narrow beam that can be aimed at a particular spot, or even an individual in a crowd.
Beams of sound can be narrowly focused and sent over far greater distances than conventional speakers allow, and still be heard above ambient noise.
The company leading the charge on this development, American Technology, has been enthusiastically demonstrating the system, dubbed the HyperSonic Sound system, to anyone who will listen, and responses have been encouraging.
The technology underpinning HSS has been known for years, but hasn't made it out of the research labs, and complex electronics and expensive equipment made it little more than a plaything for audio scientists.
The system uses a highly directional beam of ultrasonic sound, which is outside human hearing range.
Because of the nature of ultrasonic wavelengths, such beams remain far more focused and can, therefore, travel greater distances than audible sounds.
Researchers say careful modulation of the ultrasonic beam enables it to generate audible sound out of the air through which it travels.
Essentially, the beam causes the air to vibrate at frequencies humans can hear.
Using some very clever mathematics, the ultrasonic beam can be modulated to faithfully reproduce anything from spoken words to classical music.
Conventional sounds (recorded or live) are fed into an HSS signal processor, which converts them into pulses of ultrasonic sound before they are amplified and fed to an emitter device, which creates the concentrated beam.
Anyone standing in the path of the ultrasonic beam will hear whatever is being broadcast, but if they step just outside it they will hear nothing.
Because the audible sounds are not actually created until they hit something (such as the ear), users report the effect is more like wearing headphones than listening to a distant speaker. If the beam is bounced off a wall or other surface, the sound will seem to come from that place.
Researchers are confident ultrasonic broadcasts can be projected more than 100m without any noticeable drop-off in sound level or quality. Applications of this exciting technology are vast.
Supermarket operators will be able to direct advertising messages to people standing in front of a product display, and banks like the idea of being able to play advertisements to people standing at an ATM, without annoying others walking by. In the consumer world, cars could be fitted with the technology to allow one music CD to be heard in the front while another is playing in the back.
The same principle could be used in hospitals or waiting rooms so some people can watch television while others sleep undisturbed, or in conferences so different sections of an audience can hear translations without needing headphones.
In home cinemas, different audio channels could be directed to different parts of the room, without the need for extra speakers and wires, or an audio zone could be created for listening to loud CDs. Step outside the zone and the sounds of the latest band would fade to nothing.
Emergency services groups also are excited by the possibilities for directing voices over long distances in noisy conditions when co-ordinating rescue missions.
Military forces would be able to bounce sound off objects, potentially fooling the enemy into thinking an attack was coming from a different direction.
Some audio experts say the technology could replace conventional speakers as the dominant means of listening to recorded and amplified sounds.
Those behind HSS are, however, more intent on getting their invention into niche areas first, before tackling the speaker industry.
There is little doubt this technology could revolutionise the way sounds are created and shared.
Many experts say it is the biggest step since the invention of the cone speaker, a mainstay of audio reproduction for more than 70 years. |
