The range of human hearing is quite limited. This is not a revelation to most people, as it is common knowledge that animals, including our household pets, are able to perceive frequencies of sound beyond that of their human owners. In fact, dog whistles and certain types of “invisible fences” are practical applications of this knowledge. These devices operate at a higher frequency than humans can audibly perceive, however, there is also a bottom threshold to human hearing, which is about 15 cycles per second. The area below this frequency is known as infrasound. Although infrasonic frequencies cannot be heard by people, they can be felt. Perhaps you’ve experienced pressure or vibrating in your chest generated by powerful subwoofers blasting out bass lines at a concert.
At greater intensities, infrasound can make a person feel ill and disoriented. At even greater energies, infrasound can kill by causing the internal organs of a person to vibrate so violently that they rupture. Obviously any device that could generate infrasound at these energies would make a devious and lethal weapon.
The reason sound waves can kill is that they carry energy. The sound waves caused by a powerful thunderclap, though miles distant, can not only startle a person, but can rattle dishes in cabinets and knock knick-knacks off shelves. That is because the sound waves still carry enough energy to disturb physical objects despite traveling such a distance.
In 1957, while the Cold War was still quite heated, Dr. Vladimir Gavreau had assembled a team of researchers dedicated to developing robotic devices for a variety of military and industrial purposes. During work, the team would periodically fall victim to spells of nausea. Even those called upon to inspect the facility to determine the cause would experience the same ill feeling. Strangely, whenever the afflicted person or persons would step outside the building, the symptoms vanished. They found that opening the windows reduced the effect, but not did not eliminate it entirely. The mystery affliction persisted, causing a serious disruption of Gavreau’s work. Eventually, after other causes such as noxious vapors or compounds were ruled out, the culprit was determined to be a ventilation fan motor.
Gavreau’s team knew the fan motor was the culprit, as direct exposure to it caused its victim to be ill for hours afterward, but they did not know why.
The motor was causing vibrations of the air at 7 cycles per second, well into the infrasonic range. The sound from the fan motor could not be heard, but its effects were quite evident. Eventually they determined the infrasonic waves from the motor caused a resonance within the building. A resonance occurs when the frequency of sound is just right so that the peaks and troughs of the sound waves bouncing back and forth in a medium line up and reinforce each other. Thus, the peaks are higher and the troughs are deeper. The cavernous interior of the industrial building amplified the sound waves even more. When the thoughts of the group turned toward reproducing the effect through some type of self-contained, movable apparatus, the potential for weaponization became obvious. Experimentation produced a device utilizing large custom-built organ pipes, with the energy supplied first by a motor-driven piston, then by a pneumatic mechanism.
Dr. Gavreau’s team tested the infrasonic device on themselves. The effects were almost immediate. First came intense pressure on the eyes and eardrums. Soon after, intense pain racked the entire body. Then the entire building, a massive and stout concrete structure, was shaken. One of the team members managed to switch off the power, despite being in excruciating pain. The group experienced altered vision and painful spasms throughout the body for days following that one brief test. In retrospect, it seems that if the device had been left on any longer, Dr. Gavreau and his team would have died right there and then, victims of their impatience to have empirical data on the effect of their new endeavor on living human beings. The team had also seriously miscalculated the power that would be generated by their device.
Earlier I referred to infrasonic weapons as both lethal and devious. The devious nature is derived from the fact the weapon makes no audible sound. A soldier approaching a defense perimeter using infrasonic weaponry would have no advance warning that he or she was walking into a death trap. Additionally, sounds at such low frequencies pass easily through solid objects, such as concrete walls.
Given the rapid proliferation of atomic weapons following WWII, one might expect to have seen in the years following Gavreau’s discovery battlefield ready infrasonic weapons capable of slaughtering entire opposing armies, without warning and without the firing of a single bullet. It is surprising therefore, at least on some level, that infrasonic weapons of deadly capability have apparently never been used outside of an experimental setting.
Could it be that the superpowers of the East and West had conscientious objections to using such a stealthy but brutal weapon? Or were they afraid of tipping the balance of power that Mutually Assured Destruction maintained? These days we do not fear hydrogen bombs and ICBMs launched by the Soviets, rather we fear suitcase nukes and low-tech dirty bombs in the hands of terrorists and extremists. Considering a handful of scientists were able to build an effective infrasonic weapon out of oversized organ pipes and a simple air-compressor, would duplicating this really be outside the capability of a terrorist group or other rouge entity? Perhaps we should just be thankful that it appears there is little interest in weaponizing sound in such circles and Gavreau’s weapon is relegated to being another obscure historical curiosity.