MOST INTENSE MANMADE SOUND . The production of sound waves with 1600 times more energy per unit volume than previously achieved has been announced by researchers at this week's meeting of the Acoustical Society of America in San Diego, opening up possible new uses for sound in science and technology. Sound waves, patterns of compression and expansion in a gas such as air, are often created and studied in closed or semi-closed containers called cavities. In the past, attempts to make such sound waves louder (by adding more sound energy into the cavity) would fail beyond a certain point because additional energy would merely lead to the formation of a shock wave which would quickly dissipate the energy as heat. Until the late 1980s, researchers thought shock-wave formation was inevitable. In a new technique called "resonant macrosonic synthesis," Tim Lucas and colleagues at MacroSonix Corporation in Virginia have built cavities with special shapes (horns, bulbs, cones) each tailored to promote certain distinct modes of sound vibration which combine in such a way as to inhibit the creation of shock waves, allowing sound waves of unprecedented energy density to build up. Filling the containers with gas, and vibrating them to generate sound waves inside, the researchers produced sound waves with oscillating pressures up to 500 pounds per square inch. The first technological application for these powerful sound waves will be in an "acoustic compressor" which uses sound rather than moving parts to compress gas inside refrigerators and air conditioners. (Images at Physics News Graphics.)