Urban Warfare With Inaudible Infrasonic Sound
The human hearing range consists of certain boundaries outside of which our ears are not mechanically capable of detecting and realizing sound. Below the lower human hearing boundary of 20 Hz is infrasound, and above the upper human hearing boundary of 20 kHz is ultrasound. Each of the ranges has incredible uses in science. It is the ultrasound frequency waves of a prenatal sonogram that can give new parents a first look at their upcoming child. Medical ultrasonography can guide an anesthesiologist's needle as he delivers an important drug while avoiding a critical nerve juncture. On the lower end, infrasound can be used by monitoring stations to detect oceanic storms or nuclear test explosions. But like anything, more hazardous and promiscuous uses of sonic technology have led to the development of an arsenal of sonic weapons. Whether that be for better or for worse is debatable.
There are many theories as to how an infrasonic weapon might work, but there has not been much public information on how to create such a weapon. In fact, there has been quite a bit of disagreement from such physicists who argue that weaponizing is not feasible. It is now understood that infrasound frequencies can cause nausea, vomiting, uneasiness and a host of other related symptoms to those subjected to the invisible noise. Early investigators happened to discover that a fan in their building was emitting infrasonic waves and causing the workers there to become sick. It is known by the automobile industry that an open sunroof in a car can release infrasound and cause symptoms in the passengers. The primary dilemma is how exactly to weaponize the waves into a usable force. The advantage of infrasonic weapons is that the waves can travel incredible distances across the globe and propagate around objects unlike higher frequencies. Anecdotes exist of windows in homes being shattered by the infrasonic signature of a volcanic eruption that occurred thousands of miles away.
Hypersonic Sound Audiobeams and LRAD
Any even more nefarious sounding sonic warfare technology is "sound from ultrasound." Instead of using loudspeakers, the sound from ultrasound devices implement a heterodyning parametric array. It is the tiny wavelengths of ultrasound that allows a beam to be more narrowly focused than with conventional speakers and audible sound. The technology has gone by many names such as Audio Spotlight, Hypersonic Sound, or Audiobeam. Various manufacturers have dabbled in the game of ultranarrow sound encapsulation. ATC, LRAD Corporation, Parametric Sound Corporation, Mitsubishi and Sennheiser are some of the more well known companies. Nonlinear ultrasound acoustics is a pretty interesting field and despite many inherent drawbacks, researchers continue to look for military and government applications such as the sonic bullet.
The LRAD Corporation has developed what might be the most prominent of the audio weapons. Their long range acoustic device (LRAD) has been seen in prominent display as recent as the disbursement of the Occupy Wallstreet protests. That device operates at 2.5 kHz which is well within the human hearing range and can cause permanent damage and deafness to anyone too close within range. Hearing protection (along with gas masks and other protection) is just another necessity in the modern battlefield or urban warfare zone.