9

ACOUSTICS

With a great shout, the walls fell down flat.

—Joshua 6:20

The best known use of acoustic weapons dates to the time of Joshua and the battle for the seemingly impenetrable walled city of Jericho. To break the siege, Joshua was commanded to have seven priests, each bearing a ram’s horn, circle the city on six consecutive days. Each time they traveled around the walls, they were to blow loudly on their trumpets, but the accompanying soldiers were to remain silent. On the seventh day, the priests circled the city seven times, continuously making noise from the rams’ horns. Upon completion of the seventh circumnavigation, the soldiers of Israel let forth a great shout. At that point, the Bible states, the heavy stone wall collapsed, and Joshua’s men entered Jericho and killed the inhabitants.¹

The cause of the structural failure of the stone walls has long been debated. The commonly accepted version infers that divine intervention led to the collapse. Another interpretation suggests that the acoustic vibrations set up by the rams’ horns actually weakened the internal structure of the walls to the point that they became incapable of supporting their own weight. As we shall discuss, there may be some scientific support for that claim. Whichever is correct, the incident remains one of the most well-known tales of Biblical warfare.

A more recent, and very crude, attempt at acoustic warfare took place during Just Cause, the U.S. invasion of Panama. One of the primary missions was to capture Manuel Noriega and return him to face trial in the United States on drug charges. During the early days of the invasion, with help from his many loyal supporters, Noriega managed to elude capture. As the U.S. forces tightened the noose on him, Noriega surreptitiously slipped into the papal Nuncio of the Catholic Church and requested asylum. Honoring the age-old tradition of religious sanctuary, our soldiers were ordered to stay out of the grounds. Arresting Noriega under such conditions would set extremely poor precedence, not to mention making very bad press.

General Maxwell Thurman, the newly appointed Commander in Chief of U.S. Southern Command, ordered another tactic employed. He had high-powered loudspeakers set up outside the Nuncio and directed that heavy metal rock music blare around the clock. The attempt was insufficient to drive Noriega out, but it did anger many of the adjacent residents. However, the troops generally enjoyed the music, thus demonstrating the cultural gap between General Thurman and the young soldiers.² While the music did receive a lot of press at the time, these actions are probably more in line with a poorly designed psychological operations project than a true acoustic weapon.

An important adjunct in non-lethal weapons development, acoustic technology has made some major advances in the past few years. Both matériel, as in the walls of Jericho, and personnel, such as Noriega, can be attacked by acoustic weapons. In general, these capabilities have been overlooked. However, at the end of this chapter, a recent breakthrough that could revolutionize the importance of acoustic weapons will be revealed.

There are many military law enforcement applications for acoustic weapons. In civil disturbances and peace support operations, there is a need to gain control of violent situations with minimal force. These weapons can be used to drive people away from a selected area or to enforce a safety zone between troops or police and potential attackers. By keeping people at a distance greater than they can throw rocks or other missiles, they provide a margin of safety currently not offered by other non-lethal systems. Unlike chemical agents, an acoustic field does not contaminate the area; thus, no cleanup is necessary. An incremental application can be envisioned. Tunable systems can be employed initially at low levels. Should violators not respond, intensity can be increased until compliance, voluntary or otherwise, is obtained. This can be accomplished either by increasing power or by moving the source closer to the target. Another advantage is that acoustic waves are efficiently transmitted through smoke, fog, and dust. That is not true for electromagnetic weapons.

Acoustic beams might be used as point-defense tools. Consider a situation similar to the takeover of the U.S. embassy in Tehran in 1979. Embassies are outposts, and external security is the responsibility of the host nation. When that fails, the guard force on duty is usually insufficient to hold off an adversary, except for a brief period of time. However, that may be a very important period during which cipher machines and other sensitive equipment are destroyed and, if possible, key people evacuated. It is understood that without external support, the physical compound will be lost. Therefore, lethal force, while possibly authorized, is very unwise. The guards and other embassy personnel will undoubtedly become prisoners. The crowd is already hostile, and killing some of them as they break in is likely to lead to exceptionally harsh treatment. Acoustic weapons offer an ideal non-lethal alternative for this scenario. With international trade expanding, businesses may be faced with similar situations.

The objective of antipersonnel acoustic weapons is not to create untenable sound, but, rather, to vibrate the targeted people physically. In order to establish barriers or to cause people to move from a restricted area, it is necessary to do more than make loud noises. The countermeasure for that is simply to cover one’s ears.

By way of comparison, the effects of acoustic weapons are not unlike long-term exposure to rock music. Some rock concerts are so loud, often exceeding 110 decibels (dB) that pronounced hearing loss has occurred in people of relatively young age who attend frequently or participate in a band. Most rock concerts may peak for very brief periods of time—measured in milliseconds—up to 130 dB. Note that aircraft engines at a distance of about 100 meters will register only 100 dB. Acoustic weapons will range from about 120 dB to as high as 170 dB. At levels above 150 dB, internal injury can occur.

There are three levels of acoustic frequencies that might be applied as weapons: infrasound, audible sound, and ultrasound. Infrasound is at the low end of the spectrum. Some believe there is little practical use for infrasound but in the natural environment, it can cause illness and even damage to buildings.³ Exposure to low-energy infrasound for long periods has been listed as the attributable cause for “sick buildings” or “sick cities.” Due to the low frequency, it is very difficult to screen out and can easily penetrate inside buildings. Higher intensities can cause nausea and disorientation.

Audible sound, in frequencies from 20 to 20,000 hertz, can be applied to influence behavior, as most people are sensitive to very loud noises. Further, sound plays a major role in our psychological makeup and behavior. The entertainment industry figured that out long ago. Movies use music and other sounds to manipulate the audience. Remember the heartbeat sound used so effectively in the landmark movie Jaws? It was not accidental that the sound used when the great white shark was about to strike would evoke a visceral response in those watching. The impact of the sound alone was sufficient to keep many people out of the water that summer. Similarly, there is a reason that fingernails scraping across a blackboard will send shivers through almost everyone. Even thinking about it now might elicit that same response. Through physical and psychological maneuvering, there is a role for audible sound in non-lethal weapons.

Ultrasound, frequencies above 20 kilohertz, are well known to the medical community. It was first used by an Austrian psychiatrist, Karl Dussik, in 1942 to locate tumors in the brain visually. Since then, ultrasound has been used in both diagnostic and healing procedures. Although no hazard has been identified with diagnostic ultrasound, people exposed to high dosages report noticeable heating effects that could lead to injury.⁴ However, the high frequencies involved do not propagate as well as the lower frequencies and can easily be externally blocked. I am not aware of any attempt to develop weapons in the ultrasonic range.

Given the advantages of better propagation, most work on acoustic weapons has been done at the lower end of the spectrum. At low frequencies, it is possible to cause internal vibrations that generate a number of effects, depending on the frequency and power levels employed. The effects cannot be overcome through hearing protection, personal perseverance, or being impervious to pain. Of course, care must be taken in the use of low-frequency sound so as to prevent permanent injury, or in extreme cases, death. There are persistent rumors about a French researcher, Professor Vladimir Gavreau of Marseilles, who was developing high-power infrasound weapons. Gavreau began his work after an unanticipated exposure to infrasound from a defective ventilator. When he discovered a method to direct acoustic energy, he turned to weapons development. He reported that his tests, which caused internal vibrations of internal body organs, brought “unanimous and vociferous protests from members of nearby laboratories.” The available information suggests that a colleague, Dr. Levavasseur, accidentally was subjected to a blast from the weapon and died as his internal organs turned to jelly.⁵ However, no matter how persistent the rumors, others who have researched the field have failed to confirm this story. It is recanted as one of the enduring myths of acoustic weapons. But acoustic weapons have been explored for a long time.

The first developmental obstacle that had to be overcome was size. Early attempts at introducing acoustic weaponry were limited by the enormous size requirement for speakers. Those dimensions were determined by the wavelength of the low-frequency sounds desired. The physics problem was that, simply, the lower the frequency, the larger the speaker had to be. The low frequencies were needed to produce the physical effects.

During World War II, German and Austrian scientists were employed in the development of powerful acoustic weapons. Reichsminister Speer became convinced that an acoustic-beam weapon could be developed that could incapacitate troops at ranges up to twenty kilometers. Hochtal Laboratory at Lofer, Austria, was assigned the research and development task. The director, Dr. Wallanschek, formerly of Telefunken, believed the range objective was absurd. However, he was able to produce intense sound that could incapacitate people at distances of sixty meters. His technique, controlled intermittent combustion, was the forerunner of today’s technology. They probably were able to produce in the order of 100 kilowatts of power. A military utility problem was that the reflectors for the sound generators were greater than ten feet in diameter.⁶ There is some evidence that the Germans attempted to develop acoustic antiaircraft weapons. Conventional antiaircraft weapons could not reliably strike bombers flying above 15,000 feet, and as saturation bombing of German industry was increased dramatically, new weapons were needed to hit the high-flying aircraft. Any and all possibilities were considered. One such weapon involved the detonation of gases that produced pulses designed to break off the wings of bombers. It was too late in the war, however, to be fully implemented. Present-day aircraft fly far too high to be at risk from acoustic weapons.

However, following World War II, others, including some American inventors, did follow up on the German experiments. Acoustics was one of many areas of science explored by Guy Obolensky. An innovative and entrepreneurial researcher, Obolensky explored several unique areas from which others shied away. Learning of the prior German work, he conducted several experiments demonstrating that acoustic weapons could project sufficient force to make a viable weapon. The work led to the fundamental patent in the field of physical and chemical effects from sound waves, which is held by another inventor, Robert P. Shawl ⁷

Obolensky noted an interesting physiological effect that could be induced by high-power infrasound. He found that, frequently, exposure to critical frequency would cause the bowels to release involuntarily. The concept was considered interesting as a riot control measure. A formal proposal was submitted to the Navy with the title of SuperPooper. The idea was reportedly rejected by a Marine general who felt the potential weapon to be too undignified.⁸

The current leader in development of acoustic weapons in the United States is Scientific Applications and Research Associates (SARA), a small company located in Huntington Beach, California. The president, Parvis Parmani, enticed several innovative scientists, including Tim Rynne and John Dering, away from a major aerospace company. Each was searching for a challenging work environment, one in which they could explore emerging technologies in ways not appreciated by corporate giants.

Among Dering’s past excursions was a study of ancient applications of acoustics. During his studies, Dering located the work done by the Germans and others, years before. Based on this knowledge, he convinced his colleagues that acoustic weapons could play an important role in the emerging non-lethal weapons field. Jointly, they developed a proposal that was subsequently funded by the Army’s ARDEC and ARPA to research and develop prototype acoustic weapons. By 1993, SARA conducted the proof-of-principle demonstrations of an infrasound weapon system.⁹

Similar to the German approach, SARA employed repetitive detonation to create intense toroidal vortices. The fuel is a simple mixture of methane and oxygen. This combustion-driven acoustic source emits pressure waves at greater than 130 dB, sufficient to incapacitate anyone within a targeted area.¹⁰ In fact, most attempts at developing intense sound devices have used the repetitive-explosion technique.

At Los Alamos, Ricky Faehl and George Nichols also developed a prototype acoustic system using propane. In their experiments, they were able to add another innovation that is important for making compact acoustic sources. Using multiple tubes, they cut small holes in each tube so that the sound resonated between them. This phased-array system allowed devices to be reduced in size at least an order of magnitude.¹¹

In Europe, Bengt Wigbrant, of the Swedish National Defence Research Establishment, was the project manager for the development of their Vortex-Generator. ¹² Their system, which also has been demonstrated, was fueled by propane that was detonated in a combustion chamber. A tube placed in front of the chamber formed the pulses of energy into a whirl that was projected toward the target. It could easily be thought of in terms of invisible smoke rings projected one after another. The gas whirls are energy packages that move through the air at speeds of forty to sixty meters per second and pack a significant wallop. The name applied to this system was High-Energy Whirls, or HEW. In August 1997, SARA, applying the same principles, was able to generate ring vortices two feet in diameter that traveled more than the length of a football field at 70 meters per second.¹³

During development of the Swedish system, they noted the early German experimentation and urged that caution be taken when testing the elementary devices. According to their sources, a 1945-era generator had been tested against some large pine trees. The records indicated that when the whirls hit the top of the tree, “limbs as thick as an arm were cracked and fell to the ground.”¹⁴ A friend of mine in the German Air Force observed a demonstration and confided in me his concern that the current Swedish system might cause more physical damage to humans than would be acceptable. However, that is an engineering problem that can be overcome.

Before the end of the Cold War, the Soviet Union experimented with acoustic weapons. U.S. intelligence reports indicated that Soviet scientists had been experimenting with a wide range of sounds in efforts to determine the physiological and psychological effects. In the infrasound zone, they discovered that exposure for extended periods of time brought on impairment in tracking ability, choice-reaction time, and peripheral vision. At seven hertz they reported difficulty in mental activities and precision work. High-intensity infrasound induced sensations of panic in some subjects.

When they tested the audible frequencies, they found that certain sounds could also disrupt thinking and frequently produced drowsiness. At times, with prolonged exposure, the effects were strong enough to have test subjects falling asleep on their feet. In addition, ultrasound was reported to create fatigue and general weakness.¹⁵

The Soviets then took this fundamental research and converted it to weapons design. There were later reports that they had an external acoustic system that was mounted on some tanks. The system was designed to keep dismounted infantry soldiers from approaching from blind spots and climbing up on the tanks. In cities with limited maneuvering space and when operating against civilians, the threat from primitive weapons can be considerable. The Molotov cocktail, a simple bottle filled with gasoline and capped with a rag fuse, is now known around the world as a poor-man’s antitank weapon. Acoustic devices could keep people with primitive devices far enough away to prevent them from striking the tank with such a weapon.

Both the Soviet Union and Sweden have also experimented with beam convergence. The process involves generating two different frequencies and pointing them toward the target. It is at the point of convergence that the effects are noticed. In the acoustic range, it allows for line-of-sight, covert communication without the hindrance of any electronic device. This would be advantageous, for example, to an agent buying drugs. He or she could undergo a thorough inspection for “wires” and found to be “clean.” Although they could not transmit, the agent could be warned of danger or when the bust was about to go down. From a weapons perspective, the psychophysiological effects would only be present at that precise location. It was reported that the Soviets tested this approach as a means for clearing buildings or underground structures. The concept entailed creation of synchronous, rhythmic vibrations approximating an earthquake. It was believed that there is a natural aversion to those frequencies, causing continued habitation to be untenable.

Developing directionality for acoustic weapons is very important. One problem with early attempts was that everyone in the area could be adversely affected by the weapons. In fact, some of the infrasound effects were discovered through accidental exposure. These omnidirectional adverse effects limited the potential usefulness of the early acoustic systems. In the United States, SARA has demonstrated advanced beam steering techniques that are necessary for weaponizing acoustics. Based on the concept of multi-element RF antenna engineering, SARA developed an end-fire system that provides the user with a wide variety of acoustic capabilities.¹⁶ They can tune the antenna from narrow to wide angles, depending upon the size and location of the threat.

Additionally, SARA engineers have adapted several of their acoustic systems for mounting on aircraft. These are designed for crowd control and area-denial missions in which other technologies are not available or sufficient. For airborne applications, it is imperative that the acoustic output can be carefully controlled.

While most acoustic work has focused on antipersonnel applications, some work has been done on antimatériel weapons. The mythology of acoustic interactions with materials is not limited to the battle for Jericho. Ancient Tibetan applications of sound for levitation of heavy objects have been documented in recent years. A famed Swedish aircraft designer, Henry Kjellson, observed and recorded heavy stones, each about a 1.5-meter cube, being lifted to a position 400 meters above them by monks using musical instruments.¹⁷ The technique required thirteen drums and six trumpets, complemented by about 200 priests, all placed in a specific pattern. When the trumpets were blown at about two blasts per minute, the stones reportedly would rise and follow a prescribed trajectory to the top of the cliff. Other, poorly documented, stories have suggested that a similar procedure may have been used to move stones at the pyramids in Egypt. On a more scientific note, recent advances in ultrasound have been used to levitate lightweight items close to the source.

In addition to levitation of objects, it is known that materials can be destabilized with acoustic energy. Other indications of the interaction of sound on stone objects include complaints that have been lodged by the U.S. Parks and Recreation Service about damage to the bridges of red rock at Arches National Monument in Utah. The damage has been caused by U.S. Air Force fighters that frequently overfly the area on combat maneuvers.

Dean Barker, an Old Crow from the World War II era, has continued to explore military applications of acoustic technology. He stated that, in experiments he conducted for the Army twenty years ago, they were able to move concrete walls a slight distance. Barker also reported that they had successfully destabilized critical metal elements. He claimed to have an acoustic device that could be placed next to railroad tracks that would cause them to weaken. The structural fatigue was not visible to the naked eye, but the track would disintegrate when a train ran over it.¹⁸ Clearly, there is a military mission for acoustic technology that can prevent enemy material from being used effectively.

One area that was explored by Soviet researchers but received little attention in the West was the use of acoustic systems in conjunction with chemicals to enhance their effects. While some of the reported effects were intentionally fatal by initiation of anaphylactic shock in test animals, non-lethal approaches could also be considered. As an example it may be feasible to apply subcritical doses of a substance to one or more people, then later induce hypersensitivity with an infrasound device.¹⁹ While this technique would surely come under extensive criticism, its application by those not constrained by international treaties makes the possibility worth exploring from a defensive posture.

Probably the most important breakthrough in acoustic weapons was accomplished by the engineers at SARA, with the support of Richard Dickhaut, until recently the president of Spectra. Dickhaut has extensive experience in studies employing electroneurophysiology. Specifically, he had designed a mechanism for using an electroencephalograph (EEG) to monitor the brain’s processing of specific thoughts. Using that knowledge, he could then determine when a designated thought had been processed. Working with SARA, Dickhaut and his colleagues were able to design a system that can create neuropsychological distress in the central nervous system through use of modulated pulse. The technique is called Pulsed Periodic Stimuli (PPS). The technique can be applied in situations where it is desirable to cause perceptual disorientation in targeted individuals. This is important, as it is the first acoustic weapon that does not rely on high intensity to cause the desired effects. Rather, low-intensity, pulsed, acoustic energy can induce fairly strong effects in humans.²⁰