In the early 1980's, several Japanese companies, such as
Nippon Columbia, Ricoh, and Matsushita, attempted to develop
the parametric array for the reproduction of broadband audible
sound.  They typically deployed large arrays containing
hundreds of piezoelectric transducers, such as the one to the
right [3], to transmit simple AM modulated audible signals.
While successful in reproducing sound, tremendous problems
with cost, robustness, and extremely poor sound quality (up to
50% total harmonic distortion) caused them to abandon the
technology as unfeasible.

More recently in mid 1996, an American company produced their
own version of this device and proclaimed it 'a revolution' in
audio. In fact, this device, contrary to their claims and
unbeknownst to the popular press, was very similar to those
described in audio journals a decade earlier (shown to the
left), and of course suffered from the very same problems of
poor sound quality and lack of robustness that plagued the
earlier researchers [4].  Since then, there has been no
published evidence of progress towards a practical device.

Background

Since his days as a part-time musician and young acoustics
engineer at Bose in the early 1990's, Mr. Pompei recognized
that a key ingredient missing from audio reproduction was the
ability to reliably spatialize sound.  While in a natural
environment, sound occurs all around us, giving us a
tremendously strong impression of our environment, the
reproduction of sound over loudspeakers, at best, provides a
very vague and limited spatial impression.  Similarly, what
was missing from music, he decided, was the ability to
choreograph musical instruments in space, just as you would
dancers.

While pursuing as a Master's student techniques related to '3D
Audio' technologies, he realized that this method would simply
not work in an uncontrolled acoustic environment - if the
listener moved out of the small 'sweet spot', the illusion
would vanish, and there were no practical remedies to this
problem, so long as traditional loudspeakers were used.  The
solution, then, was to not rely on psychoacoustic illusions,
but instead to create sound independently of the loudspeaker.
One of several ideas he had at the time was the use of
interacting ultrasound beams to produce audible sound.

                              -96-