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 83 centimetres (33 in) in diameter. At maximum level, it can emit a warning tone that is 146 dB_SPL (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^[who?] 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 is 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 Corporation (and who now runs a company making a competing device), says that being within 90 metres (98 yd) of the device is extremely painful, but its use should be limited to 270 metres (300 yd) 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 on hand at protests of the 2004 Republican National Convention in New York City^[3] but not used; it was extensively used against opposition protesters in Tbilisi, Georgia, in 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, the Japanese whaling fleet operating in Antarctic waters near Australia installed LRADs on their vessels. The devices were later used to deter activists of the Sea Shepherd Conservation Society after they attacked the factory ship of the Japanese whaling fleet by throwing bottles filled with butyric acid.^[10]

The magazine Foreign Policy has revealed that LRADs have been sold to the government of the People's Republic of China. American companies have been banned from selling arms to China since the 1989 Tiananmen Square Massacre, but the LRAD is described by ATC as a “directed-sounds communications system".^[11]

Local residents of Dusit in Bangkok witnessed it in use during protests of Triumph factory employees against dismissals on August 28th, 2009.^[12] The LRAD was used for the first time in the USA in Pittsburgh during the time of G20 summit on September 24–25th, 2009.^[13][14]

That same week, the government of Honduras used it on at least two occasions, on September 22 and 25, against people inside the Brazilian embassy. In addition to embassy staff, these included the deposed president of Honduras, Manuel Zelaya, his family, and some supporters and journalists. Zelaya had been forcibly removed from the country by the military (after the Honduras supreme court unanimously ruled that he had violated the constitution) ^[15]) on June 28, 2009. After the military prevented two previous public efforts in July to return by air and road, Zelaya returned in secret to the capital on September 21 and was given diplomatic refuge by the Brazilian government.^[16][17]

[edit] See also

• Acoustic Hailing Device

[edit] References

[edit] External links

• American Technology Corporation Website
• LRAD Defense Updates' Summary
• Howstuffworks.com "How LRAD Works"
• Defense Update Non-lethal Directed Energy Weapons