http://www.turbulence.org/blog/archives/001274.html

Hypersonic Sound

LITERAL
«…Unlike traditional speakers, which scatter sound, Norris’ device streams it in a precise, laser-like beam for up to 150 yards with almost no degradation in quality or volume. (…) How does it work? The piezoelectric transducer emits sound at frequencies above the human ear’s 20,000-cycle threshold. Unlike low-frequency waves, the high-frequency signals don’t spread out as they travel through air. Yet they do interact with the air to induce a related set of ultrasonic waves. These waves combine with the original waves, interfering to create an audible signal, focused into a beam.

The applications are numerous, if not apparent: Thousands of soda machines in Tokyo will soon bombard passersby with the enticing sound of a Coke being poured, and several U.S. supermarkets will promote products to shoppers as they walk down corresponding aisles. Eventually HyperSonic Sound might enable a nightclub to play disco on one side of the dance floor and salsa on the other. Ambulances equipped with hypersonic sirens could clear the streets without waking the neighbors. Norris’ company, American Technology, sells the devices for $600.» From Woody Norris has a way of getting inside your head… by David Sparrow, Popular Science.
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