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The Long Range Acoustic Device: pirate deterrent, crowd controller or soft drink seller?

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April 10, 2009

The Long Range Acoustic Device

The Long Range Acoustic Device

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April 9, 2009 When Somali pirates armed with RPGs attacked the luxury cruise ship Seaborn Spirit in November 2005 it wasn't armed troops or the threat of artillery that deterred the attack, it was sound waves. The ship was fitted with a clever bit of tech called the Long Range Acoustic Device (LRAD), a system which can emit painfully loud sound frequencies that are concentrated in a narrow beam and easily direct them at a target, not unlike using a spotlight.

The American Technology Corporation, led by its founder Woody Norris, developed the LRAD following the bombing of the USS Cole in October 2000. Designed to enforce safe zones around US military vessels, the device can be set at a frequency up to 120dB to first warn any craft approaching a military vessel to change course. If the craft doesn’t comply, then the frequency can be cranked up to 151dB, producing a loud, irritating and potentially painful noise. The idea is to act as a deterrent and avoid employing lethal force.

The technology also has been incorporated into another piece of military hardware – a nifty communication tool called the Phraselator. The implement is designed to give specific instructions and warnings in a range of languages. Again, if they aren’t followed, the Phraselator sounds a loud and, if necessary, painful warning.

The LRAD has found civilian uses, too, in controlling crowds and evacuating buildings. The New York Police Department City used the LRAD during protests at the 2004 Republican National Convention. Georgian police also used the technology on protesters in Tbilisi in November 2007. The LRAD is also being tested in areas of Iraq and prison camps, such as Camp Bucca.

In February, this year, Japanese whalers controversially used a sonic device against anti-whaling activists. Captain Paul Watson of the Sea Shepherd Conservation Society claimed that such a weapon was used against one of its helicopters, forcing it to back off and injuring an activist. Activists aboard the conservation ship, The Steve Irwin, supported these claims with photographs of the incident.

Police and US military are using the LRAD to provide warnings from up to 300m away and, in some cases, are using smaller versions, such as the MRAD and LRAD500. However, it is its use as a non-lethal weapon to quell civil disturbance and disobedience that has attracted criticism from human rights groups, who argue that sounds louder than 90dB potentially damage hearing.

The LRAD’s success in warding off attacks has also come under scrutiny. In November 2008, an LRAD failed to deter a pirate attack on the Liberian vessel MV Biscaglia. Additional concerns about its effectiveness have been raised with detractors arguing the device can be rendered harmless by simply wearing hearing protection.

On a more positive front, the technology may have some applications for consumers. By amplifying sound – whether it be voice, music or some other kind of recording – clearly over a long distance without causing pain or irritation, it’s possible for companies to target individuals. For example, a stream of sound can deliver a specifically tailored message to a person, based on some kind of sensory response. If a sensor, say, detects a person’s raised body temperature in a crowd, a message can be sent to that person pointing to a soft drink vending machine nearby.

LRAD technology may also be used to direct music, according to people’s preferences, to individual tables in a restaurant or bar, or perhaps pass messages directly to an individual without letting others know.

Talking tech: how the LRAD works

According to American Technology Corporation, the LRAD uses capacitive transducers requiring modest power requirements of less than 200 to 400 watts to achieve full output. The high directivity of the LRAD device reduces the risk of exposing bystanders or people in the vicinity to excessive audio levels. Sound behind the LRAD unit is more than 40dB, less than the on-axis forward output. The LRAD also incorporates multiple highly efficient switch-mode power conversion systems. The LRAD uses an array of piezoelectric transducers to produce sound. A transducer is simply a device that changes energy from one kind to another. In this case, it changes electrical impulses into sound. The transducers under charge rapidly change their shape and create sound waves. All of these transducers are attached to a mounting surface and staggered to allow more of them to fit into a smaller space. Identical waves emerge from the transducers and their amplitudes combine to help the LRAD create very loud sounds.

The LRAD uses the phase of the sound waves, the size of the device and the properties of air to create more directional sound. Essentially what you have is a loudspeaker that can receive input from a range of devices and amplify the signal, enabling the operator to send the target a clear message – painful or not. There's a good overview of the technology at “How Stuff Works” .

LRAD in brief:

  • The LRAD has a range of 984 feet (300m or about three city blocks) over land or 1640 feet (500m) over water
  • It has a beam width of about 30 degrees
  • The devices is 33 inches in diameter, five inches thick and weighs 45 lbs
  • Input signals can be anything from a microphone, laptop, MP3 player, CD player, Phraselator or translation device
  • The LRAD has maximum volume of 120dB at 1m in normal operation, 146 dB sustained or 151 dB burst at 1m with override.

David Greig

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