Long-range acoustic device
A long-range acoustic device, acoustic hailing device, or sound cannon is a specialized loudspeaker and sound weapon that produces sound at high power for communicating at a distance. It has been used as a method of crowd control, which has caused permanent hearing damage, having an extremely high decibel capacity. Other uses have included for negotiations in siege situations; to deal with piracy at sea; for mass notification during natural disasters or other emergencies; and by the military, including several navies.
Overview
Acoustic hailing devices are acoustic devices capable of outputting intelligible sound at very high volumes. The distance at which acoustic hailing can be effective varies based on several factors including the sound level, directionality, and frequency of the acoustic source, the sensitivity and directionality of the receiver, and the transmission channel environment. The sound level diminishes or attenuates with distance. Consequently, as a general rule, higher source levels have greater range.Acoustic hailing devices can come in two forms;
- Directional models: These AHDs are characterized by their ability to create long-range, directional voice communications and warning tones. Their directionality is typically 5° to 60° radius conical at a 2 kHz tone.
- Omnidirectional models: These acoustic hailing devices are capable of creating 360° voice communications and warning tones. These devices are capable of being heard over away from the emitter head.
Origin
Present
Since their inception in 2002, acoustic hailing devices have grown into a variety of applications. AHD uses include checkpoints, crowd control, maritime shipping, mass notification, early warning systems, critical infrastructure protection, military applications and wildlife protection and control. Acoustic hailing devices are now fielded all over the world by various commercial, law enforcement, and military groups.History
In October 2000 the, an American guided missile destroyer, was bombed in an attack by al-Qaeda operatives, using a small boat packed with explosives. The naval personnel on Cole were unable to be sure that their messages could be heard by the approaching boat at a sufficient distance to possibly avert the attack. The ship was badly damaged, with 17 U.S. Navy sailors killed and 37 injured.Following this attack, navies around the world made several policy changes, while the American Technology Corporation created and developed the AHD market, which included the launch of its proprietary Long Range Acoustic Device, a type of acoustic hailing device, in 2003. Using this new technology, it became possible for naval personnel to contact approaching vessels which did not respond to radio calls from a distance of over, enabling them to respond appropriately in a timely manner and avert danger.
Since then the technology has developed and expanded. Genasys launched its voice-based mass notification systems in 2012, and in 2019 its unified multichannel Critical Communications and Enterprise Safety system.
LRAD devices have become widely used for communications, and increasingly for crowd control in a range of settings, including civil disturbances and protests.
Characteristics and measurements
Acoustic hailing devices differ from conventional speaker systems in three key ways: volume, clarity, and directionality. AHD manufacturers use different methods to measure their products, but a common standard has emerged.Volume
Since sound attenuates with distance, extremely high outputs are required to achieve the required range. Acoustic hailing devices have an output of 135 decibels or greater. The acoustic level of the source is commonly expressed in terms of sound pressure level or SPL. SPL is a logarithmic measure of the rms sound pressure of a sound relative to a reference value. It is measured in decibels above a standard reference level. For reference, at a distance of 1 meter, a normal talking voice is approximately 50 dB and a jet engine at 30 meters is 150 dB.Clarity
A principal weakness of common speaker systems and bullhorns is their clarity. Their horns and cones create sound that is distorted or out of phase. This results in the common "Charlie Brown" effect, where the message is muffled and misunderstood, analogous to the muted brass squawks representing the unintelligible voices of adults in animated Peanuts specials. AHDs create sound that is in phase. Because of this, sound emitted from acoustic hailing devices is intelligible at distance. Clarity is difficult to measure, since it is a subjective reference. However, different scales have been created to compare devices. A common measurement is the speech transmission index. STI ratings range from 0–1.0, with 1.0 being perfect clarity.Focus
AHDs are lastly characterized by directionality. To ensure messages are broadcast to the target, AHDs shape sound into a 30–60° audio beam. This shaping is accomplished through the design of the transducers as well as various reflective horns.The focus of an AHD is typically measured at the frequency of peak directionality. This is typically in the 1–2 kHz range. Not all frequencies of sound are able to be directed equally. Lower frequencies in the bass range are difficult to form. As such, their directionality may be a 40 degree radius or more depending on the design of the AHD.
Specifications and functionality
LRAD devices are made by Genasys., the company claims its LRAD products meet the following specifications:- 30° audible transmission ranges out to 5,000 meters
- 60º–360° audible mass notification coverage over areas up to
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 per doubling of distance from the source, solely due to geometric spreading. Large speakers, 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. An LRAD can thus emit a targeted "beam" of sound at very high volume, up to 160 dB at one meter from the device. This is louder than standing behind a jet engine taking off, or a nearby gunshot.
Use
Following the impetus for its initial development, 25 navies have adopted the use of LRADs as of 2022, to provide protection for their vessels. Navy personnel can contact approaching vessels from over and respond defensively if necessary. They are also used by coast guards, naval bases, commercial vessels, and in ports.Genasys offers its products for the following categories of use on its U.S. website: defense, law enforcement, fire and rescue services, border security, protection of critical infrastructure, and maritime safety. its products are in use in 100 countries. The Asia-Pacific website is focused on emergency management during natural disasters such as bushfires. It is not categorized as a defense item, and does not require an export license.
The technology can also be used to deter wildlife from airport runways, as at Changi Airport in Singapore, and to protect gas and oil platforms from fishing boats, birds and security threats.
There are two basic ways of using LRAD devices: for voice amplification and as an alert. The technology used in "siren mode", primarily for usage in emergency situations, has also been used for crowd control. In this mode, it allows sound transmission at around 2,000–4,000 Hertz, which causes maximum discomfort for the people targeted, as this is the frequency range at human hearing is most sensitive. Although sometimes referred to as an Active Denial System, the latter is based on a different technology, in which millimetre-wave radiation causes nerve receptors in the skin to feel heat, via dielectric heating.
Risks
Acoustic hailing devices are being used as weapons. The human ear can typically stand a sound pressure level of 120 dB before feeling pain. AHDs are capable of 135 dB or more of acoustic energy. OSHA states that any sound pressure level over 90 dB requires hearing protection. As volume increases so does the chance of hearing loss. The effective non-lethal range of an AHD depends on the total acoustic output of the unit. Typically, this range is or less.In addition to its "voice" feature, which acts as a loudspeaker, the LRAD has an "alert" feature, which emits loud chirping or beeping sounds, which can be used at the top of the decibel range of the device. These sounds have been reported to cause pain and hearing damage. The use of the alert function for crowd control has been described as a "sound cannon" or sonic weapon, although this has been denied by the manufacturer.
The sound can be targeted within a narrow and specific range that does not impact those operating the device or standing next to it. Civil liberties organizations are concerned about its use by police forces, and its use has been contested in law courts in the United States. One concern is that police officers are not receiving enough training in its use. Due to potential risks and a lack of studies on the health impact of sonic weapons, the American Civil Liberties Union recommended in a fact sheet that their use in protests be suspended.
Law enforcement organizations and the manufacturer claim that LRAD systems are primarily designed for long-range communications; however, the device has an extremely high decibel capacity and has been controversially used as a less-lethal weapon for crowd control. Police usually use models that are not quite as powerful as the military-grade version; however, generating levels ranging from 137 dB to 154 dB, they are capable of causing pain, disorientation, nausea, migraines, and permanent hearing damage.
The New York City Police Department's LRAD use was to be challenged in US federal court in 2020. In the lawsuit, five protestors and photographers sued the city, alleging that they'd experienced migraines, sinus pain, dizziness, facial pressure and ear ringing after they were exposed to the LRAD's alert tone. The city settled the lawsuit in 2021, with an agreement that the police would be banned from using the alert feature and that rules would be created on how and when the police could use LRADs. The city also agreed to pay $98,000 in damages to the plaintiffs, as well as $650,000 in legal fees.