I was alternately fascinated and horrified by an article I read today
describing a new method of sound reproduction. Rather than use a
transducer to produce sounds in the audible range (20-20KHz), the
device transmits ultrasound that causes the air itself to produce new
sounds. The ultrasound can be narrowly focused, so only the target
individual can hear the resulting sounds.
Some possible applications of the technology include sending
different music to front and back seat passengers in a car; a
descriptive narration at a museum audible only when you're standing
directly in front of the exhibit; warning sirens for an ambulance
audible only by the cars in its path; home theater systems that can
play at loud volume without disturbing others outside the room; and
so on.
Here's how it works:
http://www.atcsd.com/tl_hss.html
"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 key phrase here is "with sufficient volume." I expect this will
cause a variety of unanticipated consequences in the natural world,
where sounds beyond 20KHz are perceived. Care to comment, Bernie
Krause?
________________________________________________________________________
________________________________________________________________________
|