An LRAD is a long-range acoustic device, a powerful portable speaker designed to scare people away with sound, and it’s becoming increasingly popular among police departments. It is often described by critics as a sound cannon, offering a user “the ability to issue clear, authoritative verbal commands, followed with powerful deterrent tones.”
One popular device, the LRAD-100X, was used in Ferguson, and on two days last week, it was used to warn off demonstrators in New York City protesting the death of Eric Garner. According to its manufacturer, the LRAD offers police “near instantaneous escalation across the force protection spectrum” to “shape the behavior of potential threats.”
What would that sound like?
Unlike a conventional speaker, which uses electromagnetism vibrates a diaphragm to amplify sound, the LRAD uses piezoelectric transducers to concentrate and direct acoustic energy. Inner and outer transducers bend and vibrate to create sound waves that are not completely in phase with each other. This creates sound waves that cancel out those in the outermost edges of the beam. It also creates a sound that is “flatter” than usual, with minimal dispersion as it propagates.
The LRAD’s sound waves also interact with the air in ways that create additional frequencies within the wave, thus amplifying the sound and pitch. This allows for voice commands—pre-recorded and played off its built-in MP3 player, or spoken by an officer into a microphone—at a volume meant to be intelligible 600 meters away.
The machine’s “alert mode” is its deterrent feature. Imagine pressing your head against the hood of a car while its alarm is going off. Permanent hearing loss begins with a sustained sound that’s louder than 90 dB SPL—for example, a subway train 200 feet away—but you won’t start to feel immediate pain until 120 decibels, about the loudness of a shotgun blast. At 160 dB—a little less loud than a rocket launch—your eardrum will burst.
The tones of the LRAD can reach as high as 152 decibels—20 to 30 dB louder than a bullhorn—which can easily cause permanent can easily cause hearing damage. It’s a siren that makes the adjective “earsplitting” much less of a metaphor.
Read More: Here