The Universal Sense (29 page)

Some in the intelligence community saw opportunities for acoustic weapons that took a much more personal approach. In the 1970s, there were several interesting patents issued that described using modulated microwave energy to act as a carrier to beam sounds directly into a listener’s head at a distance. The few direct sources that describe this technique describe it as a potential communication device that would prevent eavesdropping by any outside source, communicating directly from the source to the listener’s brain without any external acoustic energy. However, given the proclivities of the intelligence community in this era, it’s been suggested that it was more likely that this would be used as a psychological disrupter, making someone think they were hearing voices or sounds in an attempt to drive them mad.

Could such a system work? In a way, yes. You can perceive microwave energy, but not really in a useful manner. The first indication that people could hear electromagnetic energy arose
during the early days of radar, when operators claimed that if they walked in front of radar emitters, they would hear distinctive clicking sounds. Subsequent studies by Ken Foster in 1974 showed that subjects actually could detect microwave energy. Unfortunately, it wasn’t some odd neural receptor tuned to the electromagnetic spectrum. It’s just that sufficiently powerful microwaves do what you think of microwave ovens doing—they heat different parts of the ear at different rates. So the listener is hearing the sound of his inner ear cooking.

But the idea that you could control the amount of thermal damage while modulating the microwave beam at an acoustically appropriate level lives on, not as a super-secret communication channel or a psyops device to make you think you’re hearing voices, but rather as a purported crowd control device. The Sierra Nevada Corporation is planning on building what they describe as a non-lethal microwave ray gun, the Mob Excess Deterrent Using Silent Audio (MEDUSA). Initially developed with a military innovation grant, the idea is that the device could be used to deliver loud enough clicking sounds to drive people away from an area. The problem is that to create sounds that are even barely audible above background, you’d have to deliver about 40 watts of microwave energy per square centimeter. Considering that the safe limit for microwave exposure is about 1/1,000 watt per square centimeter, this sounds a lot more like a recipe for cooked humans than it does an effective means of crowd control.

There are much better ways to get sounds delivered in a tight radius at long distances, and that’s by using piezoelectric speakers. Directional piezoelectric speakers work on a different principle than the diaphragm-based speakers we’re more familiar with. Rather than using an electrical signal to induce changes in the
strength of a magnet to vibrate a cone, piezoelectrics use special materials that vibrate directly in response to an electrical charge. A major advantage to them is that they can vibrate much faster than a mechanical speaker, allowing them to emit sounds far up in the ultrasonic range. Sounds with shorter wavelengths are less prone to diffraction, meaning they tend not to spread out as easily as sounds with longer wavelengths. So as long as you pour enough power into them, you can end up with a very long and relatively narrow acoustic “spotlight” (bearing in mind that the higher the frequency, the shorter the range at a given power level).

These piezo directional speakers typically use frequencies from 60 kHz to 200 kHz, far above the range of human hearing. In order to embed an audible signal into such a high-frequency carrier, you actually play two separate signals through the speakers, one a steady reference tone at the carrier frequency (say, 60 kHz) and a second one that is amplitude-modulated (AM) by an audible signal, varying between 60 kHz and 80 kHz. When the two signals strike your ear, they interfere with each other constructively and destructively, leaving only the difference between the two, at frequencies audible to your ear. You can experience this kind of ultrasonic modulation in many museums—these type of speakers let you walk in front of a painting or sculpture and hear a description of it that only projects in a very narrow area, using very high-frequency carriers to limit its travel so that it doesn’t interfere with sound in the rest of the area and you don’t get overlap from descriptions of other exhibits.

So could these be used as an acoustic psychological weapon? Maybe. Years ago I purchased one of the commercially available units, the Holosonics Audio Spotlight, with the idea of
using it in field work. One of the issues you face in trying to study animal calling behavior is the difficulty of sending a signal to just one animal as opposed to an entire group. My idea was to use it to try to send signals to flying bats or calling frogs. Problems arose almost immediately. For the bats, 60 kHz is right in the middle of the echolocation range, so a half-meter-wide beam of 60 kHz sound was the bat equivalent of shining a strong spotlight right into your eyes. They all avoided it.
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On the other hand, while the frogs didn’t care about the carrier signal, the amplitude modulation technique used to get the audible signal mixed into the carrier doesn’t really work on signals below 300 Hz, where much of the frogs’ acoustic energy lies, so they just sat there and ignored it.

This left me with an expensive acoustic toy, time on my hands, and something of a mad-scientist bent, so I of course brought it down to my wife’s loft in Williamsburg and hung it out the window, attached a microphone to the input, and waited for people we knew to walk down the street. The first time I tried it on a friend about halfway down the block, I used it to whisper that he owed me $50; his reaction was to immediately turn around and look for me, then to scan the street to see where the voice came from. I waited until he’d calmed down a bit and come closer, at which point I said, “Or was it $100?” His reaction was totally worth the money I never got back from him. He rapidly scanned the area again and then ran for the door and started pounding on it. When I let him in, I asked if he was okay, because he seemed a bit on edge. (I lose more friends that way.)

And that’s the problem with using these types of acoustic tools for psychological manipulation—my friend knew that anything weird that happened to his ears was likely my fault, especially if there was new equipment around. In the same way, people who have experienced this type of constrained sound—in museums, airports, casinos, and hotels—are not too likely to think they are hearing voices from a supernatural source or even inside their own heads; they are going to think that they are experiencing some technological effect. Several companies are even exploring tying video cameras with facial recognition software into use with directional speakers to play individually targeted ads to people walking by stores. The scenarios of science fiction movies are beginning to be played out, targeting not your sanity but your wallet.

Still, long-distance directional speakers have played a role in acoustic weapons technology—not for putting voices into people’s heads but for using our own fearful reaction to loud, irritating sounds against us. Stories about acoustic weapons began emerging after 9/11, when almost every online and print news source began talking about unusual weaponry that played horrifying sounds, including those of fingernails on a blackboard or a baby’s scream played backward at high levels, meant to drive anyone in its range away. While anyone who has been stuck in an airplane or other enclosed space while a baby screams knows how irritating this sound is, few people actually open the door in midflight to get away from it.

These types of stories kept cropping up for the next few years, less and less in legitimate news outlets and more and more on conspiracy web pages, until in 2004 when police on duty for the Republican National Convention in New York City were observed carrying a large flat black disk on a vehicle. This gadget
matched descriptions of high-powered piezoelectric speakers that were just becoming commercially available. While the device was not used at the time, the Long Range Acoustic Device (LRAD) was first used in the United States in Pittsburgh in 2009, on protestors at the G20 summit. The LRAD is different from audio spotlights in that while it uses a phase array of piezoelectric speakers to create a tight cone of sound that can project for a long distance, it uses not ultrasonics but rather sounds around 2 kHz, just about in the center of humans’ best auditory range. It creates an extremely powerful and piercing sound that is likely to activate just about every fight-or-flight circuit in the human brain.

People who have been close to the units describe an intense desire to get away, with some describing extreme nausea and panic, both responses modulated by elements of their sympathetic nervous system. Anyone within about 100 meters of an active LRAD is also in danger of suffering temporary and possibly permanent hearing damage. The LRAD has been credited by some as having a role in helping stave off attacks from pirates at sea; however, the distances between the two ships involved suggests that it was more useful as a warning signal than as a direct factor in getting the pirates to surrender. Unfortunately, its role has more often been to clear protestors away from an area; most recently it was used against Occupy Oakland protestors in 2011, with little regard for the long-term hearing damage or emotional trauma suffered by those subjected to deafening sounds directed against them. So acoustic weapons that work at a psychological level are here and in the hands of police and military units, but their long-term utility is yet to be determined. As Stephen Colbert pointed out, while these devices are useful against naive targets, what happens when people stop
panicking in the face of a new device and start wearing noise-suppressing headphones to protests, or just putting their fingers in their ears? Will the acoustic arms race amp up into finding ways to actually injure targets without killing them all, allowing those weapons to wear the fundable label “non-lethal?”

Sound can certainly affect people at a physiological level, and not all of these effects are secondary biochemical ones, such as flooding people’s brains and bodies with panic-induced biochemicals such as adrenaline and cortisol. The right kind of sound can actually cause physical damage to the ears and other parts of the body. Sound at 120 dB is at about the threshold for pain. Your ears are full of free nerve endings that act as pain receptors to warn you of potentially damaging events, ranging from noise above a certain level to the fact that a Q-tip is way too far in your ear canal. At 120 dB, the amplitude of the vibration of the air molecules is creating pressure changes extreme enough that your eardrum is stretching out of control and inner hair cells, particularly the high-frequency ones nearest the eardrum, are in danger of being ripped free of their moorings.

Your ear has a pressure relief system, called the round window, that flexes outward and inward as the fluids in the inner ear are pushed back and forth; however, even this system only has so much give to it. At sounds above this level, you start getting damage to the hair cells that causes your hearing to start losing sensitivity, starting at the high frequencies and slowly moving downward as the sounds get louder. If the duration of the loud sounds is relatively short or not too much above 120 dB, the loss of hearing is temporary and usually limited to certain frequencies. You can identify this damage by a loud hissing sound you’d hear for varying lengths of time, depending on how long you were exposed to a given sound (something I
experienced after being too close to a few speakers at rock concerts). But if the sound goes above 160 dB, as when you’re too close to an explosion or working in demolition or with heavy equipment without hearing protection, you get serious damage with permanent results, including ruptured eardrums, tinnitus (ringing in the ears), or even complete or partial permanent hearing loss. This is one reason why most consumer and professional amplifiers have a cutoff circuit, to make sure that you can’t get sound above this level. And this is why the LRAD, which is supposed to be a psychological deterrent, can be put in the category of a physiologically damaging device: it puts out a whopping 167 dB at 1 meter, but because of the restricted nature of its beam shape, the dangerous level of sound extends for tens of meters in front of the device.

The type of sound that gets tagged as futuristically dangerous is usually ultrasound. I think there’s something about the “ultra-” prefix that gets people cognitively and culturally excited and makes writers of science fiction feel a need to stick ultrasound weapons into futuristic scenarios ranging from the original
Star Trek
’s “Whom Gods Destroy” and “Way to Eden” through
Warehouse 13
’s supersonic zills in “Nevermore.” It’s probably helped along by ultrasound’s association with high-tech medical imaging applications and numerous stories on conspiracy web sites about how ultrasound is used as a driver for psychological manipulation, as in the audio spotlight technology. But the uncool truth is that ultrasound has severe limitations as a weapon because of its limited range.

Ultrasound is defined as sound above the human upper auditory limit, around 20 kHz. While these high-frequency sounds are not as prone to diffraction as lower-frequency ones, their short wavelengths make them lose energy much faster. Getting
ultrasound to work at any distance requires a lot of power. Bat echolocation uses ultrasonic frequencies up to 100 kHz blasted at 120 dB, giving it a range of about 30 feet. Some deep-sea dolphins use frequencies up to about 200 kHz emitted at about 130 dB, which might give them a range of 50–90 feet. But in both these cases, the ultrasonic signals are just being used to detect objects in the environment. For ultrasound to have any physical or physiological effect, it has to be very high-powered, very high-frequency, and very, very close. Under these conditions, ultrasound does pack a lot of energy into a very tight beam, not only capable of creating echoes for medical imaging but also capable of creating shock waves to blast apart kidney stones. This makes medical ultrasound sound like a small-scale sonic weapon. But the key is that medical ultrasound is using sound waves at millions of cycles per seconds, not thousands, and is close to the tissue being treated, helped by a gel that forms a liquid seal between the transducer head and the overlying skin. So what happens if you move the source further away? Could you use an ultrasonic blaster to blow something apart? I’m afraid not. Ultrasonic energy at a distance, even at very high power, will mostly just bounce off your skin. Even if you waved your blaster directly at someone’s ear, it wouldn’t even have enough power to move any of the hair cells, let alone rupture anything. So unless someone comes up with a power cell capable of emitting ultrasound at several million Hz and hundreds of decibels, you are safe from ultrasonic weapons.