I am off on holidays this week, but hope you will enjoy this top post from 2015.

 

 

 

 

Audiologists have long known that noise damages the auditory mechanism and that high level noise over 85-90 dBA for a long period of time can cause deafness. But what does it take in sound levels to produce a truly damaging weapon?   If you actually wanted to kill someone with a sonic weapon, there isn’t a whole lot of research on how you would go about doing it.  Anthony (2014) states that a loud enough sound, say 185-200 dB, “could cause an air embolism in your lungs, which then travels to your heart and kills you. Alternatively, your lungs might simply burst from the increased air pressure. There could also be a kind of underlying physical weakness where loud sounds might cause a seizure or heart attack, but there is very little research on what happens under the most intense sound.” I suspect that it is quite difficult to obtain subjects for that study!

The use of noise as a weapon might seem a like a 21st century tactic against terrorists, but this concept is part of a greater tactic known as Psychological Warfare(PSY OPS) that has been around since at least Alexander the Great and probably before.  The contemporary component of PSY OPS that uses sound actually had its beginnings during World War II. Albert Speer, Hitler’s Chief Architect, had set up research to explore sonic warfare.  His device, called anacoustic cannon, was intended to work by igniting a mixture of methane and oxygen in a resonant chamber that could create over 1000 explosions per second.  These explosions sent out a deafening and focused beam of sound that was magnified by parabolic reflector dishes.  While the weapon was never used,  the theory was that by compressing and releasing particular organs in the human body, the cannon could consistently kill someone standing within 100 yards of the device in 30 seconds. These days, some types of sonic and ultrasonic weapons are used by military and police forces; others are found only in science fiction.  They have been described as sonic bullets, sonic grenades, sonic mines or sonic cannons and often introduce some type of a focused beam of sound or ultrasonic energy into a particular sound field.  They are used to injure, incapacitate, or kill an enemy.

According to Goodman (2009), sonic warfare explores the uses of acoustic forces and how they affect various populations.  It looks at how sound can be deployed to produce discomfort, express a threat, or create an ambience of fear or dread–to produce a bad vibe. Goodman further states that “sonic weapons of this sort include the ‘psychoacoustic correction’ aimed at Panama strongman Manuel Noriega by the U.S. Army and at the Branch Davidians in Waco by the FBI, sonic booms (or “sound bombs”) over the Gaza Strip, and high-frequency rat repellents used against teenagers in malls.”  They are currently in use against pirates that try to hijack cruise ships.

How Does a Sonic Weapon Work?

In the case of Manuel Noriega who was holed up in the Vatican embassy in Panama City, it was the loud incessant rock music of Guns N Roses; for the Branch Dividians it was sleep deprivation of the inhabitants by means of all-night broadcasts of recordings of jet planes, pop music, chanting, and the screams of rabbits being slaughtered.  While  different types and levels of sonic warfare have been used with varying results, the characteristics of infrasound lend it certain possibilities to be used as a particularly effective weapon. The low frequency of infrasonic sound and its corresponding long wavelength make it much more capable of bending around or penetrating the human body, creating an oscillating pressure system. Depending on the frequency, different parts of the body will resonate, which can have very unusual non-auditory effects. For example, one occurs at 19 Hz at relatively safe sound levels (< 100 dB). If you sit in front of a very good subwoofer and play a 19-Hz sound (or have access to a sound programmer and get an audible sound to modulate at 19Hz), try taking off your glasses or removing your contacts. Your eyes will twitch. If you turn up the volume toward 110 dB, you may even start seeing colored lights at the periphery of your vision or ghostly gray regions in the center. This is because 19 Hz is the resonant frequency of the human eyeball. The low-frequency pulsations start distorting the eyeball’s shape and pushing on the retina, activating the rods and cones by pressure rather than light.

Studies have indicated that almost any part of the body, based on its volume and makeup, will vibrate at specific frequencies with enough power. Human eyeballs are fluid-filled ovoids, lungs are gas-filled membranes, and the human abdomen contains a variety of liquid-, solid-, and gas-filled pockets. All of these structures have limits to how much they can stretch when subjected to force, so if you provide enough power behind a vibration, they will stretch and shrink in time with the low-frequency vibrations of the air molecules around them.

Since we don’t hear infrasonic frequencies very well, we are often unaware of exactly how loud the sounds are. At 130 dB, the inner ear will start undergoing direct pressure distortions unrelated to normal hearing, which can affect one’s ability to understand speech. At about 150 dB, people start complaining about nausea and whole body vibrations, usually in the chest and abdomen. By the time 166 dB is reached, people start noticing problems breathing, as the low-frequency pulses start impacting the lungs, reaching a critical point at about 177 dB, when infrasound from 0.5 to 8 Hz can actually drive sonically induced artificial respiration at an abnormal rhythm.

References:

Antony, S. (2014).  Can a loud enough sound kill you?.  Extreme Tech.  Retrieved March 4, 2015: http://www.extremetech.com/extreme/175996-can-a-loud-enough-sound-kill-you

Goodman, S., (2009).  Sonic Warfare.  MIT Press.  Retrieved March 4, 2014: http://mitpress.mit.edu/books/sonic-warfare

Zadeh, J. (2014).  A history of using sound as a weapon.  Retrieved March 4, 2015: http://motherboard.vice.com/read/a-history-of-using-sound-as-a-weapon

Images:

Guns ‘N Roses album covers, (2014).  Retrieved March 4, 2015:

Horowitz, S. (2012).  Could a sonic weapon make your head explode?  Popular Science.  Retrieved March 4, 2015:  http://www.popsci.com/technology/article/2012-11/acoustic-weapons-book-excerpt

IMAKID (2014).  The imagekid has it.  Retrieved March 4, 2015:  http://imgkid.com/noise-level-chart.shtml

Video:

Disclose TV (2013). Sonic weapons bullets made of sound.  Retrieved March 5, 2015: https://www.youtube.com/watch?v=W8h4tV1fpDw