Word: echoless
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Dates: during 1960-1969
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Pulsed Beam. Working in an all but echoless 10-ft. by 13-ft. room lined with sound-absorbing wedges of glass fiber, Lockheed's scientists have set up a sort of searchlight with a sound generator in its throat. The researcher sits in a chair, covers his eyes with a blindfold and presses a button with his right hand. Out of the searchlight comes a beam of noise, 50 pulses per second, which sounds like a distant chorus of crickets and spring peepers. The mixed frequencies are higher than human ears normally hear, but the researchers have found that...