November/December 2020 23a voice or recording across thousands of meters.
In the other, it emits a “deterrent tone” designed
to alert attention to that recording.
The first LR ADs were developed in response
to the bombing of the USS Cole off the coast of
Yemen in 2000. U.S. Navy officials asked the
LRAD Corporation (now Genasys) for a device
that could both communicate from a safe dis-
tance and disperse potential threats with an
unbearable sound. By 2009, police departments
had acquired LRADs for use in the United States.
“Humans are regularly exposed to noise that
can cause damage over time, but LRADs can
cause lasting hearing damage in a matter of sec-
onds,” says audio engineer and composer Marisa
Ewing. Any sounds above 85 decibels (dB) can
cause permanent damage to your hearing,
depending on how long you’re exposed to them,
she says. “Normal conversation is about 60 to 70
dB, concerts and sporting events can be about
94 to 110 dB, and a jet taking off can be between
120 and 140 dB. In contrast, some LRADs can
create sounds up to about 160 dB when used at
their full power.”
While LR ADs can cause migraines, dizzi-
ness, and hearing loss in the short term, people
exposed to them can re-experience those same
symptoms when they hear lesser loud noises, like
sirens, says Ewing.
LRAD’s maximum continuous audio output is
measured in decibels at a distance of one meter
in front of the system. The broadcasts follow the
inverse square law: For every doubling of the dis-
tance from the audio source, the sound pressure
level drops 50 percent. The National Institute of
Occupational Safety and Health guidelines says
that hearing loss could only occur at the decibel
levels that most law enforcement departments’
LR AD systems operate on based on repeated
exposure, while in extremely close proximity,
and over extended periods of time.
At a distance, an LRAD deterrent tone may
sound like any alarm. But while whistles and
sirens emit waves in all directions, like the light
from a naked lightbulb, LRADs produce a nar-
row cone of sound to be pointed at a target, like
the beam of a f lashlight. This packs the typically
diffuse kinetic energy into a tight space, bom-
barding anyone in its vicinity.
Publicly available marketing materials for
LR ADs rarely describe the deterrent tone. “We
don’t market LRAD as a weapon at all,” says
David Schnell, Vice President of U.S. sales at
Genasys. “It is a very loud, long-range speaker,
designed to allow people to communicate above
very loud noise and chaos.” The deterrent tone,
Schnell says, is “like anything else—there is
a risk, but if it’s operated correctly, you’re not
going to hurt anybody.”
The source of the LRAD’s power may be decid-
edly low-tech, says audio engineer Robert Auld.
After watching an LRAD-300X deconstructed
on video, Auld believes the LR AD contains a pair
of ordinary off-the-shelf drivers, much like the
ones that power stadium sound reinforcement
systems, mounted in a frame that encloses and
redirects the sound waves until they all head
in the same direction. This limited frequency
range—200 Hz to 10 kHz, roughly the same as
human speech—combines with the efficient
drivers to produce the destructive tone. “It is a
brute-force design dedicated to a single purpose:
playing really loud in the most sensitive part of
human hearing,” Auld says. “There is nothing
particularly sophisticated about it.”
Sound specialists and DIYers have scram-
bled—unsuccessfully—to find ways to protect
against the weapon’s effects. Cheap foam ear
plugs provide up to 30 dB of protection, while
covering your hands with your ears reduces
noise by around 20 dB. But the best protection
is to dodge the direct beam of the weapon, Auld
says. “Remember that the LRAD beams sound in
a narrow pattern, so move off to one side to get
out of the main pattern.”A JET TAKING OFF CAN
BE BETWEEN 120 AND^140
DECIBELS. IN CONTRAST,^ SOME^ LRADS
CAN CREATE SOUNDS^ UP^ TO^ ABOUT
160 DECIBELS^ WHEN^ USED^ AT^ THEIR
FULL POWER.