Forwarded by Negativland.
>
>http://www.nytimes.com/2001/05/15/science/15AUDI.html
>May 15, 2001
>An Audio Spotlight Creates a Personal Wall of Sound
>By JENNIFER 8. LEE
>
>A person hears a voice in her ear, turns around and sees nobody there. No
>one else has heard it. Or she hears footsteps in a room, the product of an
>invisible presence. Is her mind playing tricks on her?
>
>Or is it a jokester, F. Joseph Pompei? A 28-year-old graduate student who is
>part scientist and part showman, Mr. Pompei has invented a device that
>projects a discrete beam of sound in much the same way a spotlight projects
>a beam of light.
>
>The audio spotlight - as Mr. Pompei has dubbed it - emits a column of sound
>enveloped by silence, the way the glow of a spotlight is enveloped by
>darkness. Someone standing inside the beam emitted from his flat black disk
>hears the sound loud and clear. Outside the beam one hears silence or, if
>there are surfaces nearby, faint murmurs from the reflected sound waves. The
>beams can also bounce off walls to create an impression of the source of the
>sound.
>
>Companies are already dreaming up commercial applications for the beam.
>Supermarkets and retail stores may beam product enticements at customers.
>Vending machines may soon talk as people pass by. Dance clubs could divide
>up a single room into different music zones. DaimlerChrysler is looking into
>installing sound beams in a truck so that passengers can listen to their own
>music. The military could use it to confuse enemy troops.
>
>American Technology Corporation, a San Diego-based company that makes a
>similar product, has already sent out evaluations to military contractors,
>consumer electronic manufacturers and entertainment companies. It has signed
>a deal with the shipbuilder Bath Iron Works to install the sound beams on
>the deck of a new Aegis-class Navy destroyer as a optional substitute for
>radio operators' headsets. As for consumers, Terry Conrad, president of ATC,
>estimates they will start being hit by sound beams within two years.
>
>Mr. Pompei's audio spotlight, the engineering for which is awaiting patent
>approval, is the product of a childhood fascination for acoustics and his
>eight-year obsession with the idea that sound could "dance." He said he
>encountered resistance to the idea in his graduate school applications, but
>he found a warm reception at the M.I.T. Media Lab. "I had so many people
>tell me so many times that it wouldn't work," he said. "My response always
>was that this was too cool not to work."
>
>An audio spotlight is counterintuitive. Within the human range of hearing,
>sound tends to travel in all directions, as does a candle's light, and
>resists being focused in a beam.
>
>The smaller the sound waves, the less they spread out. But if the waves are
>too small, they lie outside the range of human hearing. For example, the
>tight waves of ultrasound are focused enough to use in medicine, but they
>cannot be heard by human ears.
>
>The magic combination is to merge the beamlike nature of ultrasound with the
>qualities of audible sound.
>
>Ultrasound frequencies are distorted by air in a way that can be captured by
>complex but well-defined mathematical equations. Mr. Pompei's insight was to
>use this air distortion to his advantage: start with the desired audible
>sound and work backward through the distortion to determine the original
>ultrasound source.
>
>Analogously, if someone with 20/20 vision put on a pair of prescription
>glasses, he would get a distorted view of the world. But for someone with
>the right level of bad eyesight, the eyeglasses will result in a clear view.
>The eyeglasses are similar to the distortion caused by the air, and the
>original bad eyesight is analogous to the inaudible ultrasound.
>
>Air distortion of sound waves happens all the time, but it is usually
>negligible, so it wasn't experimentally observed until the early 1970's when
>David Blackstock, a professor at the University of Texas, and one of his
>students, Mary Beth Bennett, were first able to create audible sounds by
>combining different frequencies of ultrasound. The resulting high-pitched
>chirps were significant, but not very practical.
>
>It wasn't until a decade later that a Japanese research team tried to adapt
>that breakthrough to produce music, speech and other sound. Masahide
>Yoneyama of Ricoh and colleagues at several other Japanese electronics firms
>in the early 1980's combined audible sound waves with ultrasound waves in a
>technique called amplitude modulation, or AM, often used in radio
>transmission.
>
>As the new hybrid wave traveled through the air, it self-demodulated - that
>is, the audible sound "unraveled" from the ultrasound. But their sound beam
>was grossly distorted. The high cost and the poor reliability caused the
>team to abandon the research.
>
>What eluded the Japanese team were the right equations to match the
>distortion. Mr. Pompei looked to sonar research from the 1960's for
>inspiration. Dr. Peter J. Westervelt, a Brown physicist, and Dr. Orhan
>Berktay, a British acoustician, had done seminal work in describing the
>distortion of ultrasound under water. Mr. Pompei took Dr. Berktay's
>equations, modified them for the air and engineered the design.
>
>The result is that the audio spotlight doesn't directly generate the audible
>sound. It generates a beam of ultrasound that acts like a long, thin
>loudspeaker and releases audible sound - a secondary effect. It's as though
>Pompei created a hologram of a lamp that then could be turned on to generate
>light. The ultrasound is the lamp, the audible sound is the light.
>
>Professor Blackstock, who has seen the American Technology Corporation
>product, still considers audio beams a novelty item since many of their uses
>could be accomplished through use of headphones. "It looks like a hard
>sell," he said. "Most of the uses of sound involve spreading it around."
>
>That's true, and that is the reason the audio spotlights may be the most
>radical technological development in acoustics since the coil loudspeaker
>was invented in 1925. The real revolution of the acoustic beams lies not in
>the circuit boards, but in the mind. The audio spotlight will force people
>to rethink their relationship with sound, as the arrivals of the phonograph,
>the telephone and the Walkman have done before. An occasional cathedral or
>dome delights us with acoustic tricks played by the architecture when sounds
>from far away seem to originate nearby. But those are isolated effects.
>
>With the exception of Walkmans and headsets, sound is public, a shared
>phenomenon. We are skeptical of those who claim to hear sounds and voices
>that we can't hear. Humans are immersed in a world of overlying spheres of
>sound. We can close our eyes, but can't shut off our ears. Darkness is
>common, but pure silence is difficult. A hum or a rustle breaks that purity.
>
>Now sound can be personal without any apparatus shielding our ears. Mr.
>Pompei gets letters and e-mail messages from around the world from people
>convinced that his audio spotlight is being used on them as a mind control
>device. "Absolutely not," he said, laughing. But Mr. Pompei is too
>fun-loving not to play a few mind tricks of his own. Among his favorites is
>to stand on the balcony near his fourth-floor office and emit sounds of
>breaking glass toward caterers below. The confused caterers nearly always
>stop to look at the floor. "Eventually they look up or they hear us
>laughing," he said. Now the caterers are used to it.
>
>People have written Mr. Pompei asking for devices to shield them from the
>audio spotlight's insidious mind control uses. He has toyed with the idea of
>selling audio-spotlight earplugs on his Web page to meet the demand. Of
>course, since the audible sounds generated by his device are normal sound
>waves, the product would simply be ordinary earplugs adorned with his logo.
>But if it gives people peace of mind, he says it may be worth it.
>
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