A sound idea

Sound can be amplified using the power of wind

Published: Friday 31 October 1997

the Defence Research Technologies (drt) in Rockville, usa, has developed a method to amplify sound without using electricity. It would help crew members communicate amidst noisy atmosphere. The non-electrical sound-amplification technology is an upgraded version of a technology devised by Tadeusz Drzewiecki and others at the us Army's Harry Diamond Laboratories in 1960s. According to Drzewiecki, president of drt, the system worked on a principle that sound can travel farther if it is wind-borne (mit 's Technology Review , Vol 100, No 2).

The new technology dubbed as a wind microphone uses mechanical gain obtained by deflection of a high-energy jet of air. When a person speaks into an input horn, the voice generates pressure waves that hit a smooth jet of air released from compressed air and cause it to vibrate.

The jet stream is then split by a thin piece of laminated plastic into two channels, one carrying the upper range of sound waves and other carrying the lower range. The split sound waves are then routed through separate tubes so that they could bang from opposite sides into another faster-moving jet of compressed air. As waves from one channel push the jet stream with pressure, waves from other channel that are completely out of phase, pull on it from the other side with pressure, increasing the amplification effect.

The split jets of air that travel with more pace than the voice, cause smooth jets to vibrate at same frequency but with higher amplitude. This phenomenon can add enough kinetic energy to the pressure wave to raise its volume tenfold. The amplified sound, imprinted with the original voice travels along plastic pipe and emerges from speaker horns at the end of tubes.

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