page_title: Long Range Acoustic Device
section_title: Function
hierarchical_section_title: Long Range Acoustic Device / Function
caption_attribution_description: English: US Navy Ship with LRAD system aboard.
context_page_description: The Long Range Acoustic Device is an acoustic hailing device and sonic weapon developed by LRAD Corporation to send messages and warning tones over longer distances or at higher volume than normal loudspeakers. LRAD systems are used for long-range communications in a variety of applications including as a means of non-lethal, non-kinetic crowd control.
  According to the manufacturer's specifications, the systems weigh from 15 to 320 pounds and can emit sound in a 30–60° beam at 2.5 kHz. The manufacturer also produces systems for public address and mass notification use that broadcast 360°.
  LRAD systems are used by law enforcement, government and defense agencies, as well as maritime and commercial security companies to broadcast audible notifications and warnings over distance. LRAD systems are also used to deter wildlife from airport runways, wind and solar farms, nuclear power facilities, gas and oil platforms, mining and agricultural operations, and industrial plants.
context_section_description: The parameter "ka", which is the wave number multiplied by the speaker radius, is often used to characterize sound source directivity. For this source, ka=19 at 2.5 kHz, and according to the LRAD data sheet, the beam angle of about 30 degrees total is what is predicted for a regular loudspeaker.
  Small spherical "point-source" acoustic devices follow the known inverse square law, which predicts the loss of 6 decibels (dB) per doubling of distance from the source, solely due to geometric spreading. Large speakers (or large arrays), such as these, have an interference pattern in the nearfield which produces peaks 6 dB higher than the output pressure and nulls where the pressure is essentially zero. The larger the speaker, and the higher the frequency, the longer the effective nearfield. The nearfield for this device is approximately 8 metres (26 ft).
  LRAD Corporation was formerly named American Technology Corporation.
caption: LRAD on a U.S. Navy ship
exif: {"Image Orientation": "Horizontal (normal)", "Image XResolution": "150", "Image YResolution": "150", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop CS3 Macintosh", "Image DateTime": "2010:03:03 15:53:47", "Image ExifOffset": "164", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "302", "Thumbnail JPEGInterchangeFormatLength": "5895", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "1500", "EXIF ExifImageLength": "1125"}