As members of the AEC community , we feel it is our responsibility to speak out on subjects we are knowledgeable and passionate about. We are becoming increasingly aware and active in taking steps to end systemic inequality and racism in the United States. An issue that has come into mainstream public discourse recently is the use of force against protesters in recent marches in support of the Black Lives Matter movement across the country. LRAD systems produce much higher sound levels volume than normal loudspeakers or megaphones.
Over shorter distances, LRAD signals are loud enough to cause pain in the ears of people in their path. At first blush, the use of noise rather than physical force might seem like a safe, non-lethal way to move and direct crowds, but if used improperly they can cause permanent hearing damage.
This is not only an issue for the intended targets; it also poses a significant threat to public safety officers working nearby. An LRAD is a loudspeaker-like device that emits a focused beam of sound.
What makes these systems unique is that rather than transmitting sound like a loudspeaker in many directions similar to the way a lightbulb emits light , LRAD systems transmit sound in a narrow beam much like a flashlight. Smaller LRAD models are simple acoustic horns similar to those you see in megaphones or air-horns.
Larger LRAD models employ a series of small loudspeakers to create a much more powerful, and narrower, beam of sound. Their military function is to alert and communicate with approaching ships, and to repel potential attackers attempting to sabotage or pirate US Navy vessels. LRAD military-grade systems were remodeled and remarketed as Acoustic Hailing Devices for civilian environments in the early s.
LRAD use at this time did not come under public scrutiny because the devices were used in voice command mode at safe distances. Using LRAD systems to communicate from safe standoff distances provides more time for mutual assessment, interaction and de-escalation.
In practice, rather than simply communicating with protesters, LRAD systems can also be used to generate ear-splitting tones designed to cause pain and disperse crowds. In this way, the weaponized use of LRAD alarm mode poses safety issues for both users and receivers.
LRAD systems can produce maximum continuous sound pressure levels that vary, depending on model size, from dBA to dBA measured 3 feet from the device. For context, this is much louder than electronic dance music concerts, or a commercial jet take off at feet.
The chart below shows typical sound pressure levels that people experience in their daily lives compared to the sound pressure levels various LRAD models are capable of producing.
There are a few reasons why LRAD systems can be harmful beyond their innate ability to generate extremely loud sound pressure levels. One, they are not meant to be heard from up close. Sound pressure levels attenuate with distance, and like many other sound sources the farther you stand from an LRAD system, the less loud the device will sound.
LRAD systems can be used to safely communicate from safe standoff distances. Unfortunately, safe operating distances for LRAD systems are not readily available in product specifications and data sheets accessible to the public. LRAD systems are of particular concern when they operate in alarm mode aka the alert or tone mode.
In order to generate very high sound levels, these loudspeakers produce tones that occupy part of the most sensitive portion of the human hearing range: from 2, to 3, Hz, which can damage long-term hearing health see Sensorineural Hearing Loss here. The concern is elevated for LRAD systems because of the narrow beam width these devices produce.
LRAD systems are highly directional, emitting most of their acoustic energy forward in a degree beam. The LRAD sound field is innocuous until you are in the midst of it.
Sound levels can go from hardly noticeable to intensely loud within a few footsteps, leaving targets without proper ability to distance themselves or prepare for a potentially dangerous noise exposure. LRAD speakers are also extremely portable. They are are designed to be handheld, or mounted on vehicles, allowing for quick deployment and orientation changes.
This means the danger zone where hearing damage is likely to occur can change quickly, leaving targets unprepared for a sudden escalation to very intense sound levels.
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A transducer is simply a device that changes one kind of energy into another kind of energy. In this case, it changes electrical impulses into sound. A piezoelectric material is a substance that is permanently electrically polarized -- it has a positively charged side and a negatively charged side. If you apply pressure to a piezoelectric material, it creates an electrical impulse.
On the other hand, if you apply an electrical charge to it, its molecules move and it changes shape. Using electrical current from a battery, generator or other source, the LRAD applies electrical charge to lots of piezoelectric transducers.
The transducers rapidly change their shape and create sound waves. All of these transducers are attached to a mounting surface. They're staggered to allow more of them to fit into a smaller space. This helps the LRAD create very loud sounds -- identical waves emerge from the transducers, and their amplitudes combine to create louder sounds. On the previous page, we looked at how the LRAD creates lots of volume. So that's how the LRAD creates lots of volume.
But the sound coming from the LRAD is also relatively directional. It doesn't disperse as much as sounds from typical speakers. People behind or next to the device still hear the sound, it isn't as loud. Even outside the beam, the sound can still be loud, so operators and nearby personnel often wear ear protection.
The LRAD uses the phase of the sound waves, the size of the device and the properties of air to create more directional sound:. The result is essentially a loudspeaker that can receive input from a microphone, a recording device or a Phraselator translation device. It can then amplify that input, allowing law enforcement, security and military personnel to give instructions and warnings or to clear buildings and disperse crowds.
If those verbal instructions don't produce a result, the LRAD can produce a loud warning tone that approaches or passes the threshold of pain. When used to cause pain or disorientation, the LRAD is a non-lethal weapon. Next, we'll look at the pros and cons of using LRAD in this manner. Basic specs for the LRAD x :.
Its original purpose was to help enforce the safe zones around United States military vessels. Using the LRAD's default settings, a ship's crew can warn a craft that it is approaching a military ship and must change course. When used for communication, it's loud and clear but not usually painful. But if the craft doesn't change course, the ship's crew can override the LRAD's default settings.
It can then produce a loud, irritating, potentially painful noise that acts as a deterrent. Ideally, the craft would then leave the area without the ship having to use lethal force. Police and land-based military units have found uses for the LRAD. Using the same principles, authorities can give warnings and instructions that are audible to a large group of people.
Law enforcement officials can use the devices to give instructions to large groups of people or order them to disperse, or to use loud sound levels to deter people from entering an area or warn them away. However, human rights groups and hearing specialists alike have raised concerns about the LRAD. According to the National Institute on Deafness and Other Communication Disorders, any sound over 90 dB can damage a person's hearing [ref].
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