Audio Spotlight

audio spotlight

Sound from ultrasound refers to ultrasound (sound pressure with a frequency greater than the upper limit of human hearing, approx. 20 kilohertz) that has been modulated and demodulated. Ultrasound has wavelengths much smaller than audible sound and thus can be aimed in a much tighter narrow beam than any traditional audible loudspeaker system. A narrow beam of modulated ultrasound changes the speed of sound in the air that it passes through. The air within the beam extracts the signal from the ultrasound, resulting in sound that can be heard only along the path of the beam, or that appears to radiate from any surface that the beam strikes.

The practical effect of this technology is that a beam of sound can be projected over a long distance to be heard only in a small well-defined area. A listener outside the beam hears nothing. Anyone or anything that disrupts the path of the beam will interrupt the progression of the beam, like interrupting the illumination of a spotlight. For this reason, most systems are mounted overhead, like lighting. This technology was originally developed by the US Navy and Soviet Navy for underwater sonar in the mid-1960s, and was briefly investigated by Japanese researchers in the early 1980s, but these efforts were abandoned due to extremely poor sound quality (high distortion) and substantial system cost.

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