Long range acoustic device

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The LRAD is the round black device on top of the New York City police Hummer.

The long range acoustic device (LRAD) is a crowd-control and hailing device developed by American Technology Corporation.

According to the manufacturer's specifications, the equipment weighs 45 pounds (20 kg) and can emit sound in a 30° beam (only at high frequency, 2.5 kHz) from a device 33 inches (83 cm) in diameter. At maximum level, it can emit a warning tone that is 146 dBSPL (1,000 W/m²) at 1 metre, a level that is capable of permanently damaging hearing, and higher than the normal human threshold of pain (120–140 dB). The maximum usable design range extends to 300 metres. At 300 metres, the warning tone (measured) is less than 90 dB. The warning tone is a high-pitched shrill tone similar to that of a smoke detector.

There appears to be some disagreement over these specifications, as some have reported measurements that differ from the manufacturer's specifications, and show reduced output with a less directive beam.

It's instructive to note that any loudspeaker of equal size will generate a beam of the same directivity as LRAD. 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 2.5kHz, and according to the LRAD data sheet, the beam angle of about 30 degrees total - precisely what is predicted for a regular loudspeaker.[1] Contrary to some beliefs, the device does not use ultrasound, nor is it a phased array; it uses an array of conventional acoustic tweeters, the same as those used in many professional audio applications, all driven together in parallel.[citation needed] The confusion spawns from a similar product marketed by the same company called the HyperSonic Sound.

Carl Gruenler, (former) vice president of military and government operations for American Technology Corp. (and who now runs a company making a competing device), says that being within 100 yards (90 m) of the device is extremely painful, but its use should be limited to 300 yards (270 m) to be effectively used. He concedes that the device is powerful enough to cause permanent auditory damage, but that it is only meant to be used for a few seconds at a time.

Countermeasures may include the use of passive hearing protection (earplugs, headsets), which may bring the sound down to ineffective levels. In addition, sound could be reflected from a solid surface, and redirected back to the originator.

Small spherical "point-source" acoustic devices follow the known inverse square law, which predicts the loss of 6 db per doubling of distance from the source. Large speakers (or large arrays), such as these mentioned above or those commonly used in concert halls, etc., produce less loss with distance in the nearfield, typically 3-4 db per doubling of distance from the source. The larger the speaker, and the higher the frequency, the longer the effective nearfield is (see Beranek). Devices like this generally have nearfields of only a few meters.

[edit] Usage

The LRAD in use on a U.S. Navy patrol ship.
LRAD on RMS Queen Mary 2

The device was originally intended to be used by American warships to warn incoming vessels approaching without permission, and some reports claim that this is now a "non-lethal weapon". Its output up to 155 db, focused at a distance, is sufficient to produce permanent ear damage and temporarily disrupt vision.[2] It may also be used simply as a very effective megaphone prior to any use as a weapon.

These devices are currently used at Camp Bucca Iraq and are being tested in regions of Baghdad, Fallujah, along with other regions of Iraq. The LRAD device was also used by police in New York City during protests of the 2004 Republican National Convention[3] and in Georgia against opposition protesters in Tbilisi on November 2007 [4][5].

The luxury cruise ship Seabourn Spirit employed an LRAD while repelling pirates who attacked the vessel with RPGs about 160 km off the coast of Somalia in early November 2005.[6] [7] The effectiveness of this device during the attack is not completely clear, but the pirates did not succeed in boarding the vessel and eventually fled.

The Liberian vessel MV Biscaglia was attacked on November 28, 2008. The security detachment aboard Biscaglia used an LRAD device in an effort to repel attackers armed with assault rifles and rocket-propelled grenades. Following a one-sided shootout, the ship was seized and the unarmed security contractors forced to abandon ship or be killed.[8] The incident caused the usefulness of LRADs to be called into question by Lloyd's List.[9]

In February 2009, Captain Paul Watson of the Sea Shepherd Conservation Society claimed that a Japanese whaling vessel used LRAD to deter the activists of the conservation ship the Steve Irwin backing these claims with photographic evidence. [10]

[edit] References

  1. ^ Beranek, Leo L. 1986. Acoustics, p.132, American Institute of Physics.
  2. ^ Sonic Canon Gives Pirates an Earful
  3. ^ ABC News. Technology & Science. August 25, 2004. Amanda Onion. RNC to Feature Unusual Forms of Sound: Unusual Forms of Sound to Emanate From RNC
  4. ^ RussiaToday : News : Georgian police accused of brutality
  5. ^ Georgia Police Turns Sonic Blaster on Demonstrators | Danger Room from Wired.com
  6. ^ Ship Blasted Pirates With Sonic Weapon
  7. ^ BBC NEWS | UK | 'I beat pirates with a hose and sonic cannon'
  8. ^ Sonic Device used to repel pirates
  9. ^ David Osler, Sonic solution may not be a sound investment, Lloyd's List, December 2, 2008.
  10. ^ [1]

[edit] External links

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