Read this article published in the May 2012 issue of « Ça m’intéresse » magazine.

The military and police are increasingly using acoustic tools to make prisoners talk, disperse demonstrators or weaken an enemy. But are the safeguards sufficient?

Gaza Strip, September 2005. A resounding bang echoes over the houses as a plane flies away. Windows shatter and walls tremble. A bomb? Yes, but with sound. An Israeli fighter jet has broken the sound barrier.

The immediate result was severe ear pain, nosebleeds and anxiety attacks. For four days, the aircraft flew overhead every hour, especially in the early hours of the morning. The aim? To sow fear and disrupt terrorist activity with an unprecedented weapon. An acoustic weapon, known as reduced lethality. It does not kill, but can neutralize or injure the enemy. According to the UN rapporteur, these operations, repeated at least until 2008, have in fact caused deafness in the Palestinians. Exploiting the destructive power of sound is nothing new.

Infrasound makes organs vibrate

Paradoxically, the military were first interested in the insidious power of infrasound (frequency not exceeding 20 Hz), which is inaudible to the human ear. It was French acoustician Vladimir Gavreau who discovered their impact by chance in the 60s. Frequently taken ill, he noticed that the symptoms were caused by a fan installed in a neighboring building. Enthusiastic, he set about developing weapons such as an acoustic laser, supposed to vibrate all organs. The U.S. Army was quick to jump on the bandwagon, but to date, these weapons have never made it beyond the prototype stage. Not least because low frequencies propagate in a circle. It is therefore difficult to direct them at a precise target…

Rock tunes at full volume

While research continues, the military prefers to concentrate on weapons that exploit the volume of sound. For example, in 2004, during the siege of Fallujah. At the time, following the murder of American civilians, the army decided to dislodge the rebel leaders. To do this, they broadcast AC/DC and Guns N’ Roses songs from trucks into the streets. The sound, bouncing off the walls, was all the more exhausting for the inhabitants, who were not used to this kind of music, considered Western, suggestive and shocking. This choice is no accident. The military have always relied on the psychological impact of sound, and have even enlisted the services of doctors to back up their scientific credentials. In 1957, for example, Dr. Donald Cameron forced female patients to listen to negative messages (you’ve never dared confront your mother), then positive ones (you’ll soon be free to be a wife like everyone else) for 16 hours a day. The impact is considerable: the guinea pigs lose their memory and autonomy.

The Guantanamo torture playlist

Armies then applied these sound-saturation techniques in military prisons, especially in Israel, China and the USA. The special torture playlist at the Guantanamo Bay detention center remains infamous: it mixes the acid notes of Britney Spears’ Baby One More Time and Eminem’s rage with anxiety-inducing sounds (infant screams, cat meows, sarcastic laughter). The tapes, played for weeks or even months on end to prisoners kept squatting or deprived of sleep, were designed to loosen tongues. Most often with success: not only does the sound prevent them from thinking and recovering from other forms of torture, but the cultural content of the songs offends the weakened prisoners.

While in prisons, music is broadcast via headphones held on the inmate, in conflict zones, sound saturation often relies on LRADs (long-range acoustic devices). This equipment, which combines several small loudspeakers, can propagate sound in a very targeted direction, up to 3km away… Originally developed to ward off pirates, it now also equips police officers, in charge of maintaining order. The LRAD emits a sound of 152 decibels – the equivalent of a plane taking off: at 100 meters, a person’s only desire is to flee, and at 5 meters, their hearing can be seriously impaired. The device has already been used in a number of demonstrations, including one against the G20 summit in Pittsburgh in 2009.

France: stun grenades

Does France have this type of equipment? It’s hard to say, as the French army has maintained a discreet silence on the subject. At most, it mentions loudspeakers continuously broadcasting unpleasant sounds, such as babies crying in reverse, crackling noises and the sound of helicopters in flight, at 140 dB. But without specifying where they have been deployed. On the other hand, the police have been equipped with stun grenades since 2004. Equipped with an explosive charge, they produce a blinding flash and a 160 db detonation 15 m away, while projecting rubber pads. Their use has resulted in a number of accidents on both sides of the Atlantic: a heart attack and tinnitus in the USA; loss of sight, smell and taste in a spectator at a demonstration in Grenoble in 2007 here. Injuries caused more by the shockwave induced by the grenade and bollards than by the sound itself.

Are the police abusing these weapons?

In the face of accidents, experts and associations are asking questions. Aren’t the police abusing less lethal weapons? The use of such weapons as sound grenades, tasers, irritant gas and high-pressure water jets has been on the increase since the 1990s. This was largely due to changes in warfare. Conflicts now often take place in densely populated urban areas, where the distinction between combatants and non-combatants has become blurred. « The aim is to provide an intermediate response to an intermediate threat, » explains an expert at the French defense procurement agency, Direction Générale de l’Armement (DGA). « These weapons create a gap between the moment when diplomacy fails and the moment when military forces decide to use lethal conventional force », confirms Luc Mampaey, Deputy Director of GRIP (Groupe de Recherche et d’Information sur la Paix et la Sécurité). They make it possible to control the progression towards violence. But in practice, they are often used to weaken the enemy in order to make conventional weapons more effective.

Are the safeguards sufficient?

Another concern: are these devices, which have taken over the civilian world, sufficiently controlled? The safeguards are colossal, and the use of these weapons is much more closely supervised by the Ministry of Defense than that of lethal weapons, » stresses the DGA expert. So much so that police officers no longer really dare to use them. It’s true that Tasers are equipped with a small camera that can be used to check the extent of the threat and the number of shots fired. But for the moment, nothing of the kind is fitted to stun grenades. What’s more, » adds Luc Mampaey, « it’s difficult to avoid any drift. In combat or tense situations, protocol becomes secondary. As a result, under the pretext that the shot won’t kill, the threshold at which it becomes acceptable to resort to violence is lowered. The same can be said of prisons, where these weapons trivialize torture and facilitate the act. Musical harassment does not leave any obvious traces, and seems less serious than other forms of abuse. In 2006, in the wake of controversy over the treatment inflicted on prisoners, the American authorities purged Field Manual 34-52, which describes authorized interrogation techniques. But the broadcasting of music remained…

Long-term effects still unknown

Yet the health consequences of incessant sonic blasting are still poorly understood. Just like the consequences of using sound as a weapon. « The DGA explains: « The devices are designed in collaboration with doctors to ensure that the effects remain reversible in healthy individuals. But what about fragile individuals or children? Doctors are all the more concerned as increasingly sophisticated inventions emerge: an American company, for example, has just developed a riot shield that propagates low-frequency sound, capable of causing breathing difficulties. Unfortunately, as is often the case, technology is advancing faster than the law. In the absence of clear regulations, certain systems – which are not considered to be weapons – risk being sold over the counter on the Internet. One example is sound repellents such as the Mosquito. This device, which emits shrill sounds at frequencies oscillating between 8,000 and 17,000 Hz, is designed to chase away unwanted squatters in front of buildings or supermarkets. Who are the most targeted? The under-25s, the only ones who can hear high-frequency sounds. In France, no law prohibits the device. But near Saint-Brieuc, following a complaint from local residents suffering from nausea and tinnitus against a neighbor who had installed an ultrasound transmitter, a court declared the device illegal on grounds of public order. A highly symbolic decision. Of course, the power of sound as a weapon or repellent lies in its ability to act without leaving any visible trace. But with the multiplication of applications, its effects will not be able to remain for long… under the radar.

How can sound hurt?

Even if you can’t hear it, a sound can cause severe pain. Infrasound (frequency below 20 Hz) is beyond the range of human hearing, but we can feel it. Low frequencies are processed by the vestibule of the inner ear (1), the organ responsible for our sense of balance. When the pressure of infrasound becomes too great, it over-stimulates the vestibular organ, leading to nausea, loss of balance and headaches (2). « What’s more, infrasound can resonate with the human body’s natural frequencies, creating unpleasant vibrations, » adds Xavier Perrot, a researcher in neurology-physiology, sensory neuroscience, behavior and cognition at the CNRS. Frequencies below 7Hz can even be lethal! As for ultrasound (frequency in excess of 20,000 Hz), if broadcast at very high intensity (120-140 decibels), the acoustic energy delivered can be transformed into heat to the point of causing heating of the exposed part of the body (3) and even a burn. High-intensity sound, on the other hand, over-stimulates the ossicular chain in the middle ear. The result is mechanical pain, « like that felt when someone twists your finger », says Xavier Perrot. Above 140 dB, the heart rate accelerates (4), at 160db, the eardrums tear, at 200, the lungs crack (5) and above 210, internal bleeding can lead to death. Of course, our ears protect themselves with the stapedial reflex. In the event of high-amplitude sound, the ossicle muscles contract to reduce the intensity of vibrations transmitted to the inner ear. But they are most active for low- and medium-frequency sounds lasting more than a second. Impulsive, high-pitched sounds, such as a detonation, are therefore particularly harmful. What’s more, as this reflex is fatiguable, it proves ineffective for intense sounds of long duration.

Our reference

Le son comme arme, les usages policiers et militaires du son, Juliette Volcler, éditions La découverte, 2011. A fascinating summary of the subject.