Buzz
Image courtesy of American Technology CorpIn November 2005, a group of pirates launched an attack on the Seabourn Spirit cruise ship off the coast of Somalia. Although they were in small boats, they were armed with machine guns and rocket-propelled grenades. On the other hand, the cruise ship was equipped with a Long Range Acoustic Device (LRAD).
Many news sources credited the LRAD with successfully driving away the pirates, leaving the Seabourn Spirit unharmed. The coverage was often dramatic, with reports portraying the LRAD as a powerful sonic weapon capable of emitting a focused sound beam that repelled the attackers.
But how exactly does sound become a weapon? In this article, we will break down the fundamentals of sound and explain how the LRAD creates its directed sound beam. We will also explore the LRAD's hailing and warning capabilities.
The louder the sound, the more it impacts the structures in your ear. The higher its frequency, the faster it causes these structures to move. Both loud and high-pitched sounds can exceed the pain threshold — the point at which a sound becomes physically painful. Here's a comparison between some common sounds and LRAD devices:
- Normal conversation: 60 dB
- Lawn mower: 90 dB
- Pain threshold: 130 dB, varying with individual tolerance
- Maximum continuous output of LRAD: 162 dB
A Comprehensive Look at Sound and Hearing
Wave Superposition. (This example uses transverse waves instead of longitudinal waves, as their differences are more visually noticeable.)Regardless of its origin, sound always consists of waves. These waves travel through various materials, such as air, water, or solid surfaces. As they move, they interact with the medium (and sometimes with each other). The following animation will demonstrate the fundamental behavior of sound waves and how they propagate.
Sound waves can overlap without causing significant changes or distortion. However, under certain conditions, sound waves can drastically alter one another. For instance, identical sound waves that are out of phase (with reversed compressions and rarefactions) can cancel each other out. Conversely, when identical waves are in phase, their compressions and rarefactions merge, amplifying their intensity.
As sound waves propagate, they expand outward in a curved wavefront, spreading in all directions. The further they travel from the source, the more they disperse, causing the sound to decrease in volume. However, higher-frequency waves do not spread as much as lower-frequency ones. Additionally, waves with longer wavelengths typically travel farther than those with shorter wavelengths.
While there's much more to explore about sound, this is the essential knowledge needed to grasp how LRAD systems work. Next, we’ll examine how the LRAD generates sound and utilizes these physical principles.
The LRAD System and its High-Volume Sound Capabilities
An LRAD device contains multiple transducers arranged in a staggered formation.The primary function of an LRAD system is to generate sound — a significant amount of sound. It creates extremely loud noises that can be heard over considerable distances. However, its purpose is not solely to produce painful sounds for use as a sonic weapon. It can also amplify speech or recordings to a level that is clear and loud, but not overwhelming or harmful.
Instead of relying on a single large, moving device to generate all the sound, the LRAD employs numerous smaller ones. A typical speaker uses a single diaphragm that moves rapidly to produce sound. In contrast, the LRAD uses an array of piezoelectric transducers. A transducer is a device that converts one form of energy into another — in this case, it transforms electrical impulses into sound.
A piezoelectric material is a substance that is permanently electrically polarized — it has one side that is positively charged and another that is negatively charged. When pressure is applied to a piezoelectric material, it generates an electrical impulse. Conversely, when an electrical charge is applied to it, the material's molecules shift and change shape.
By using electrical current from a battery, generator, or other power sources, the LRAD applies an electrical charge to a series of piezoelectric transducers. These transducers quickly alter their shape, producing sound waves. The application of an electrical charge causes the piezoelectric material to change its form.
Each of these transducers is mounted on a surface, with their arrangement staggered to maximize the number that can fit into a compact space. This design enables the LRAD to produce exceptionally loud sounds — identical waves emanate from the transducers, and their combined amplitudes result in louder sounds.
LRAD and Focused Sound
The back of the LRAD features handles that allow operators to direct the bulk of the sound it generates.
Image courtesy of American Technology CorpIn addition to producing substantial volume, LRADs are also quite directional. This means the sound from an LRAD doesn't spread out as much as sound from regular speakers. While people behind or beside the device can still hear the sound, it won't be as loud. Even outside the beam of sound, it can still be quite audible. Therefore, operators and nearby personnel often wear ear protection.
An LRAD device utilizes the phase of sound waves, the size of the device, and the characteristics of air to create a more directional sound:
- The outer transducers are slightly out of phase with the inner ones. This interaction between sound waves results in the cancellation of some of the outer waves, reducing the sound outside the focused beam.
- The device’s diameter exceeds that of most of the wavelengths it produces, allowing it to generate a flatter wavefront that prevents the sound from dispersing.
- As sound waves travel through the air, they are affected by the medium. The LRAD's sound waves interact with the air, generating additional frequencies within the wave. These are known as parametrically generated waves, which many traditional speakers attempt to avoid. The LRAD uses these waves to expand the range of pitches and increase the sound's volume.
The outcome is essentially a loudspeaker that can take input from a microphone or a recording device, amplifying it. This allows law enforcement officers and military personnel to issue commands, deliver warnings, clear buildings, and disperse crowds.
If verbal instructions fail to achieve the desired outcome, the LRAD can emit a piercing warning tone that approaches or exceeds the pain threshold. When used for pain or disorientation, the LRAD serves as a non-lethal weapon. Next, we will explore the advantages and disadvantages of utilizing the LRAD in this way.
Here are the key specifications for the most powerful LRAD model — the LRAD 2000x: It has a range of 8,900 meters and can output a maximum of 162 dB. Even the LRAD 100x, the basic model, is 20 to 30 dB louder than conventional bullhorns.
Crowd-Control Sound Cannon
Image courtesy of American Technology CorpThe LRAD Corporation developed the LRAD following the attack on the USS Cole in 2000. Initially, its purpose was to reinforce the safety zones surrounding U.S. military vessels. With the LRAD's default settings, the crew aboard a ship can alert an approaching vessel that it is nearing a military ship and must alter its course.
When used for communication, the LRAD delivers a loud and clear message, usually without causing pain. However, if the targeted craft fails to alter its course, the ship's crew can adjust the LRAD's settings. This causes the device to emit a loud, discomforting, potentially painful sound that serves as a deterrent. Ideally, this would encourage the vessel to leave the area without the need for lethal force.
Police forces and land-based military units have discovered various applications for Long Range Acoustic Devices. Authorities, such as police departments, can issue warnings and instructions audible to large crowds. They can even use these devices to command crowds to disperse.
Concerns About Hearing Damage and Hearing Loss
Both human rights organizations and hearing experts have voiced concerns regarding the LRAD. The National Institutes of Health (NIH) states that any sound above 75 dB can cause hearing damage. This means that the LRAD has the potential to harm the hearing of anyone within its range, even when it is used solely for communication, with no indication of wrongdoing.
Much like stun guns, tear gas, and less-lethal ammunition, the LRAD can be utilized in crowd control and other non-lethal situations. However, non-lethal weapons are a source of controversy. Human rights advocates emphasize that, despite their intended non-lethal nature, these weapons are still dangerous and have been linked to fatalities in certain situations.
The LRAD has sparked controversy due to its potential to cause permanent hearing damage, despite non-lethal weapons being intended for temporary effects. Additionally, doubts have been raised about its effectiveness, as simple ear protection can make the LRAD ineffective.
Sound serves many purposes beyond communication and music. In addition to LRAD technology, here are some examples:
- The Mosquito: Young people can hear higher-pitched sounds than older individuals. The Mosquito utilizes this by emitting a high-pitched tone that drives away teenagers, while most adults are unaffected.
- Ultrasound: Used for medical imaging, ultrasound waves allow doctors to examine internal organs and monitor the development of fetuses.
- SONAR: Sound waves reflect off objects, and SONAR uses this principle to locate underwater objects and aid in navigation.
- Extracorporeal Shock Wave Lithotripsy (ESWL): This medical procedure uses intense sound waves to break down kidney stones.
