    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.

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