Sound is an amazing force, and one that is often overlooked in terms of its powerful influence and destructive potential. The lucky ones among us get to hear sound every day, and what a privilege it is. There are times, however, when hearing may be a detriment to us. This is increasingly becoming the case with the development and application of sonic weapons by various military forces. Sound as a weapon is not a particularly new idea, but for years there has been much secrecy and misinformation shrouding the subject.
“Possibly the first mention of sonic warfare is the now much-cited ‘Walls of Jericho’ scenario — a biblical story which no doubt many of us are familiar with. The walls came tumbling down after the synchronised blast of trumpets and voices rendered it unstable. However, it is only recently that sound has seriously been considered as a valid medium for destruction. Human beings respond to certain categories of sound in a number of complex ways involving auditory perception and psycho-physiological response mechanisms rendered through the brain. Certain species of sound above (ultrasound) or below (infra-sound) the levels of human auditory perception would theoretically prove most effective within the crucible of warfare.” – Spannered
What can sound do that is so damaging? Well, this is a broad question and is best answered by saying that it depends on the frequency, amplitude and medium of the sound wave. For instance, have you ever heard of the opera singer, Caruso, who could shatter a crystal glass with the power of their voice alone? It is entirely possible to shatter glass with sound. It is simply a case of hitting a note that resonates sympathetically with the glass.
Along the same lines as the opera singer and the glass is another example of acoustic damage, a pretty extreme one actually. The human heart is, like everything, not indestructible. However, I bet you never thought you could stop a human heart with sound waves alone? Well, you can. Again, it wouldn’t be easy, but the science suggests it could be done. All that is required is a frequency that resonated with the heart significantly enough to actually stop it from beating. Imagine that…the potential to kill someone without touching them, poisoning them, shooting them or leaving a shred of evidence such as DNA on the crime scene. All that is essentially needed is a signal, an amp and a speaker, though this is a simplification!
“A variety of nonlethal acoustical weapons have been proposed and evaluated. Some of these are little more than fancy loud-speakers, while others involve more subtle or sophisticated processes and truely deserve the designation of acoustic weapon.” – Global Security
It is also possible to raze buildings with sound alone. Low frequency waves would be best ‘weapon of choice’ as they have a long wavelength and are able to vibrate a wall or structure quickly enough to cause degradation to the structural integrity of the building. The frequency of the tones would need to be very low, lower than can be heard by humans (below 20Hz). Sound below this threshold is known as infra-sound and it’s effects are felt but not heard. You would need a huge amount of amplification to achieve the destruction of a building in this way, but the fact that it is possible is amazing.
“Infra-sound would be a powerful ultra-low frequency (ULF) weapon that could be directional and tunable, penetrating buildings and vehicles. High Intensity infra-sound could induce disorientation and reduced sensory motor functions. At higher levels of intensity, experimental have shown that animals may cease breathing temporarily. But this has seemed to be not a very practical weapon, since large banks of speakers were required to provide directionality, and power demands were deemed excessive.” – Global Security
In other settings you may not wish to destroy a building, you may instead want to remove certain people from a building through relatively passive means, and sound can get the job done! An example of this was seen in 1990 when American forces attempted to drive Manual Norriega, military dictator of Panama from 1983-89, a from the Vatican Embassy in Panama in 1990 using sound. The US military played loud rock music such as Van Halen – Panama, and I fought the Law, by the Clash. Through continuous playback over many hours the US managed to psychologically wear-down the former dictator, resulting in his surrender. This method was preferable to brute force, as Norriega was holed up in the Vatican Embassy, and if US troops were to set foot in the Embassy they would anger many Catholics worldwide. In such a setting sound was the ideal solution to the problem at-hand.
Another example of the destructive capability of sound is feedback. This is a closed system where sound grows exponentially with every cycle of its loop. A classic, if not tired, example of this is the rock gig scenario. We’ve all heard the shrill shriek of feedback once or twice at least, and it’s not pleasant.
How is it caused? It’s really very simple. Sound waves from a vocalist, for example, are picked up by a microphone, which is connected to an amplifier. Amplification of the signal occurs and the sound is output through a speaker. If conditions are correct (or incorrect from a sound engineers point-of-view), sound will travel from the speaker and back into the microphone, this is the beginning of another loop. If sound repeats this loop too many times then audible feedback will arise, growing into a deafening howl. Literally. While the effects of a single exposure to feedback are likely to be minor to insignificant, if the exposure is significant enough then damage to the ear system could occur. Indeed, if you have ever suffered from ringing ears after exposure to high amplitude sounds then the chances are that you have suffered permanent hearing damage.
A diagram illustrating a feedback loop
If going to a rock gig with the intention of listening to the band – not being deafened by them – can cause permanent hearing loss to the majority of the audience, then imagine how damaging sound can be to us when we try to make it damaging!
LRAD, the Long Range Acoustic Device, is a new technology used to control crowds, deter pirates or insurgents from cruise or cargo ships. It has, allegedly, only been used a couple of times in a real-life setting, so accurate information on its effect is sparse. According to the manufacturers specification:
“The equipment weighs 45 pounds (20 kg) and can emit sound in a 30° beam (only at high frequency, 2.5 kHz) from a device 83 centimetres (33 in) in diameter. At maximum level, it can emit a warning tone that is 146 dB SPL (1,000 W/m2) at 1 metre, a level that is capable of permanently damaging hearing, and higher than the normal human threshold of pain (120–140 dB). The maximum usable design range extends to 300 metres. At 300 metres, the warning tone (measured) is less than 90 dB. The warning tone is a high-pitched shrill tone similar to that of a smoke detector.” – LRAD Corporation
The LRAD was first used on US citizens at the G20 protests. As you can see from the video it certainly gets people moving when it is switched on. If you are going to watch this video, turn your volume down first – it is very loud!
“In the early 1970’s, acoustic engineer Vladimir Gavreau was experimenting with infra-sound weaponry. Now the stuff of infra-sound legend, Gavreau was responsible for the construction of a giant 6ft whistle, powered by compressed air, which reputedly scrambled the inner organs of it’s unfortunate operator (a phenomenon known as ‘cavitation’, where the internal physiology was fatally resonated). Distraught, Gavreau ceased his experiments, but left behind plans and models for highly sophisticated, directional sound cannons, which were apparently seized by the French authorities. In a recent conference with Dr Guy Peter Manners, Professor of Cymatics (a form of sonic therapy)….he informed me of experiments which he had first hand experience of in wartime Germany, where sonic weapons were being developed under a highly classified strategy initiated and financed by Hitler’s government. …A separate source reveals the fact that the Germans were pioneering a sound-based weapon known as the ‘Luftkanone’, developed at Talstation Lofer. This was a parabolic device which, although untested on humans, was apparently… ‘capable of killing a man with sound pressure in about 30-40 seconds. At greater ranges, although not lethal it would be able to disable a man for an appreciable length of time. Vision would be affected, and low-level exposure would cause point sources of light to appear as lines.'” – Spannered
Acoustic devices being used as weapons doesn’t sound all that strange, not when you consider that the US military is behind it. They have a high military spending budget and view themselves as being the police force of the world. To me, an interesting question was “do acoustic weapons appear anywhere in nature? If so, why what, and what are the effects?”
After doing a small amount of research I discovered the amazing Pistol Shrimp. This little creature is capable of disrupting submarine communications with the sound of it’s pincers alone. They make a loud ‘chattering’ noise as they close the pincers, which carries a long way in water due to the density of the molecules (the speed of sound in wate is close to 1,500 metres per second, but it is temperature dependant). The really amazing part of the story about Pistol Shrimps is their ability to stun other sea creatures by snapping their pincers together extremely quickly. This creates a blast of bubbles which momentarily heats up to approximately 6,000 degrees Celsius (the same temperature as the surface of our Sun). The attacked creature is immediately stunned and is paralyzed, leaving the shrimp to clear up without a fight! It is incredible. You can really see why they have been given there name when you watch them using this incredible ability of theirs. Here is a video I found of the Pistol Shrimp in all its glory.
So, we have now seen acoustic weapons as used by Humans, and animals alike. Is there an application of sound that combines both animals and Humans? Yes, there is.
In Canada and North America the Bark Beetles population was growing rapidly and they little critters were destroying up to 33 million acres of forest in British Columbia and millions more in the United States. Scientists discovered that if they recorded the ‘song’ of the Bark Beetles, modified them slightly and played back the recording to the beetles they got instant and unexpected results. Hofstetter, one for the scientists involved in the research, explains.
“We could use a particular aggression call that would make the beetles move away from the sound as if they were avoiding another beetle. Or we could make our beetle sounds louder and stronger than that of a male beetle calling to a female, which would make the female beetle reject the male and go toward our speaker. We found we could disrupt mating, tunneling, and reproduction. We could even make the beetles turn on each other, which normally they would not do.” – Hofstetter
Using this technique they scientists were able to drive the beetles away from the trees and thus saving them from destruction.
As you can see, sound is very powerful and has many applications beyond the obvious ones such as listening to music and communicating ideas, etc.