-Caveat Lector-
http://www.popsci.com/popsci/science/article/0,12543,351353,00.html
We've heard hypersonic sound. It could change everything.
by Suzanne Kantra Kirschner
It's the most promising audio advance in years, and it's coming this fall:
Hypersonic speakers, from American Technology (headed by the irrepressible
Woody Norris, whose radical personal flying machine appeared on our August
cover), focus sound in a tight beam, much like a laser focuses light. The
technology was first demonstrated to Popular Science five years ago ("Best
of What's New," Dec. '97), but high levels of distortion and low volume kept
it in R&D labs. When it rolls out in Coke machines and other products over
the next few months, audio quality will rival that of compact discs.
The applications are many, from targeted advertising to virtual rear-channel
speakers. The key is frequency: The ultrasonic speakers create sound at more
than 20,000 cycles per second, a rate high enough to keep in a focused beam
and beyond the range of human hearing. As the waves disperse, properties of
the air cause them to break into three additional frequencies, one of which
you can hear. This sonic frequency gets trapped within the other three, so
it stays within the ultrasonic cone to create directional audio.
Step into the beam and you hear the sound as if it were being generated
inside your head. Reflect it off a surface and it sounds like it originated
there. At 30,000 cycles, the sound can travel 150 yards without any
distortion or loss of volume. Here's a look at a few of the first
applications.
1. Virtual Home Theater
How about 3.1-speaker Dolby Digital sound? With hypersonic, you can
eliminate the rear speakers in a 5.1 setup. Instead, you create virtual
speakers on the back wall.
2. Targeted Advertising
"Get $1 off your next purchase of Wheaties," you might hear at the
supermarket. Take a step to the right, and a different voice hawks Crunch
Berries.
3. Sound Bullets
Jack the sound level up to 145 decibels, or 50 times the human threshold of
pain, and an offshoot of hypersonic sound technology becomes a nonlethal
weapon.
4. Moving Movie voices
For heightened realism, an array of directional speakers could follow actors
as they walk across the silver screen, the sound shifting subtly as they
turn their heads.
5. Pointed Messages
"You're out too far," a lifeguard could yell into his hypersonic megaphone,
disturbing none of the bathing beauties nearby.
6. Discreet Speakerphone
With its adjustable reach, a hypersonic speakerphone wouldn't disturb your
cube neighbors.
TARGETED SOUND
Unlike ordinary speakers, which disperse sound in all directions, American
Technology's speakers emit ultrasonic frequencies in a focused cone, like a
flashlight. Only when you disrupt the sound beam or reflect it off a surface
do you hear it. So audio can be pinpointed to reach an individual or widened
to target a larger group.
Illustrations by Stephen Rountree (on website)
--
http://www.atcsd.com/tl_hss.html
HyperSonic Sound
What is HSS?
HyperSonic Sound Technology is simply the most revolutionary sound
reproduction system of this century. Not since the development of the "cone"
loudspeaker more than 75 years ago has any technology provided such
significant departure from conventional loudspeakers and such a remarkable
new approach to the reproduction of sound.
How does it work?
The basic operating principle of HSS uses a property of air known as
"non-linearity". A normal sound wave (like someone talking) is a small
pressure wave that travels through the air. As the pressure goes up and
down, the "non-linear" nature of the air itself causes the sound wave to be
changed slightly. If you change a sound wave, new sounds (frequencies) are
formed within the wave. Therefore, if we know how the air affects the sound
waves, we can predict exactly what new frequencies (sounds) will be added
into the sound wave by the air itself. An ultrasonic (beyond the range of
human hearing) sound wave can be sent into the air with sufficient volume to
cause the air to create these new frequencies. Since we cannot hear the
ultrasonic sound, we only hear the new sounds that are formed by the
non-linear action of the air.
The HSS System
A HyperSonic Sound system consists of an audio program source such as a CD
player or microphone, an HSS signal processor, and an ultrasonic emitter or
transducer that is powered by an ultrasonic amplifier.
The music or voice from the audio source is converted to a highly complex
ultrasonic signal by the signal processor before being amplified and emitted
into the air by the transducer (emitter). Since the ultrasonic energy is
highly directional, it forms a virtual column of sound directly in front of
the emitter, much like the light from a flashlight. All along that column of
ultrasonic sound, the air is creating new sounds (the sound that we
originally converted to an ultrasonic wave). Since the sound that we hear is
created right in the column of ultrasonic energy, it does not spread in all
directions like the sound from a conventional loudspeaker, instead it stays
locked tightly inside the column of ultrasonic energy. In order to hear the
sound, your ears must be in line with the column of ultrasound, or, you can
hear the sound after it reflects off a hard surface. For example, if you
point the ultrasonic emitter toward a wall, you will only hear the audible
sound after it has reflected off the wall. This is similar to shining a
flashlight at a wall in a dark room. You do not see the light from the
flashlight, you only see the spot of light on the wall. HSS works the same
way, except instead of seeing the spot of light on the wall, you hear the
"spot" of sound reflected from the wall. For stereo, a separate ultrasonic
emitter is required for each channel of audio, one for the left channel and
one for the right channel.
Why HSS?
There are many reasons. The first and most important is the ability to
direct or focus sound into a tight beam, similar to the beam of light from
the flashlight described above. No other audio reproduction device available
today provides this unique ability. The opportunities for applying this
characteristic to the reproduction of sound are limitless. Think about the
ability in a museum to direct the narration about a specific display only to
the people standing directly in front of it. How about the potential to
reflect the rear channels of your surround TV from the rear wall of your
living room, by focusing HSS speakers mounted on the TV itself - no rear
speakers, no rear wiring. Think about the ability to focus sound into a
crowd of people on a football field and talk only to a selected few.
The following contains a brief list of other uses made possible by HSS:
Automobiles - HSS announcement device in the dash to "beam" alert signals
directly to the driver
Audio/Video Conferencing - project the audio from a conference in four
different languages, from a single central device, without the need for
headphones
Paging Systems - direct the announcement to the specific area of interest
Retail Sales - provide targeted advertising directly at the point of
purchase
Drive Through Ordering - intelligible communications directly with an
automobile driver without bothering the surrounding neighbors
Safety Officials - portable "bull horn" type device for communicating with a
specific person in a crowd of people
Military Applications - ship to ship communications, ship-board
announcements
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