A few individuals have pioneered the field of ultra-directional audio, usually utilizing the “sound from ultrasound” concept. Among them, Woody Norris, founder of the LRAD Corporation, has been particularly influential. While my device is designed to evoke connotations of sonic weaponry, the low powered operation (by design) makes it unsuitable for offensive use, and functions more as a technology demonstrator.
Diagram illustrating the principles of “sound from ultrasound,” and a simple circuit diagram that uses a pulse-width methodology for audible sound generation.
Rather than utilizing conventional audio shaping technologies like cone design, sound dampening, or line arrays, the Man-Portable Long Range Acoustic Device uses ultrasonic transducers to send out a modulated frequency that, upon collision with an object, demodulates from ultrasound into sound that is within human hearing. The highly directional nature of ultrasound (especially compared to lower frequencies) gives the device the apparent effect of “throwing” sound (where human listener will be fooled by the sound source).
ABOVE: Proof of concept build with ultrasonic transducer array. Note that the ability to carry low frequencies is limited. The ultrasonic transducer array & audio driver were sourced from a Japanese manufacturer.
Ultrasonic transducer array. The nature of ultrasound creates an ultrasonic beam with low spread. The acrylic cone is largely for aesthetics as the audio “beam” is already highly directional, and does not require additional sound dampening.
Final build. Powered by two 18560 batteries, an adjustable DC voltage regulator controlled power & volume (without affecting spread). The audio interface utilized a DR-05X Tascam audio recorder for playback, with slightly modifications to map the recorder functions to buttons in the grip. The entire device is housed in a plastic airsoft rifle.
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