Boom Box; February 1998; Scientific American Magazine; by Yam; 2 Page(s)
Blowing across the lip of a bottle to produce that satisfying hum would not seem to be the basis for new discoveries. But that is essentially what Timothy S. Lucas claims he has made. Reporting at the Acoustical Society of America meeting last December, the founder and president of Macro- Sonix Corporation in Richmond, Va., says his torpedo-shaped "bottles," when shaken back and forth hundreds of times a second, can create standing sound waves within them that pack energy densities 1,600 times greater than that previously achieved in acoustics. The process, which Lucas calls "resonant macrosonic synthesis," can produce pressures exceeding 3.5 million pascals (500 pounds per square inch), more than enough for industrial applications such as compressing and pumping.
The key is the shape of the bottle, or resonator. In the past, resonators were often cylindrical, and shock waves formed inside them if they vibrated too quickly. A shock wave--a compression wave that delineates a sharp boundary between high and low pressures--dissipated energy, preventing the internal pressure from getting too high. As a result, driving the resonator faster--the equivalent of blowing harder across the top of a bottle--would no longer boost the volume of the internal sound.