Can acoustic weapons be used to kill people?

The Secret of Hell’s Ladder

The Biomedical Building at Brown University has an elevator called the “Ladder to Hell”. Once the elevator door is closed, although no what abnormality will be heard, passengers can feel their ears vibrating about four times a second and their bodies vibrating without coats.

This is a typical old elevator, with an inner diameter of about 2 m × 2 m × 3 m, a buzzing fluorescent lamp and a curved blade of the fan on the ceiling. All these make it a perfect low frequency acoustic resonator.

Even if one takes the elevator to only two floors, one will feel sick and uncomfortable. The power of this fan is not large, but the broken fan blade changes the air flow in this confined space at a certain rate.

The influence of infrasound on human body is not in hearing, but in various parts of human body filled with liquid.

Inaudible infrasound waves are used in military research

In general, infrasound is not considered sound. If the frequency of the sound is slightly lower, but the loudness is above 88 ~ 100 dB (decibels, sound loudness units), one can still hear it.

However, when the sound wave frequency is lower than 20 Hz (Hertz, A unit of sound frequency), you can’t hear any sound-most of them just feel as if there is a beating pressure wave at this time. And, like other sound waves, if the loudness of infrasound waves exceeds 140 dB, it will cause pain. However, the main effect of infrasound waves is not in the human ear, but in other parts of the human body.

Since infrasound can affect various parts of the human body, Since the 1950s, military and scientific organizations (mainly the U.S. Navy and NASA) have been focusing on it, hoping to find out the impact of low-frequency vibrations on those workers who work in noisy ships equipped with giant engines or on space rocket launch bases.

Just as military research likes to make some [gimmicks], Infrasound is also a key word in news hype and vicious rumors. Among the developers of infrasound weapons, The most notorious is Vladimir Gavreau, a Russian-born French researcher. According to reports in the mass media at that time (and many websites that have not been censored at present), Gavreau had a disgusting reaction due to a malfunctioning ventilator in the laboratory and launched an investigation.

Later, he carried out a series of experiments on the effects of infrasound waves on various parts of the human body. According to the results of the experiments reported by the media at that time, infrasound waves are like a [envelope of death]. When people are wrapped in infrasound waves, their internal organs will become like jelly, so these subjects must be rescued at a critical moment.

When the infrasound loudness reached 166 dB, the subjects began to have breathing problems.

It is presumed that Gavreau applied for a patent at that time, and these experimental conclusions also became the basis for the government to develop confidential projects for infrasonic weapons.

If you easily believe these public web information, infrasound is indeed qualified to become an acoustic weapon.

However, when I went further, I found that although Gavreau did exist and did research on sound waves, in fact he only wrote a few short papers in the 1960s describing people’s exposure to low-frequency sound waves (not infrasound waves). What’s more, there are no speculated patents on infrasound waves.

Subsequent and current literature on infrasound research, The full citation of his research results is simply to make the media understand the problems behind this complicated work. His research results have survived so many years of gossip, probably because Vladimir Gavreau happens to be the [nickname] of a crazy scientist, and he himself has to bear the consequences.

A ghost in a ghost laboratory

Apart from conspiracy theories, the characteristics of infrasound do make it possible to become a weapon.

Infrasound has a low frequency and a correspondingly long wavelength, which makes it more capable of coiling around or penetrating into the human body, creating a vibration pressure system.

Different parts of the human body can resonate with different frequencies, resulting in some extremely abnormal non-auditory effects.

For example, one of the effects occurs at a relatively safe sound level of 19 Hz (< 100 dB). If the subject sits in front of a sound with good sound quality, the sound is playing a 19 Hz sound wave, and the glass glasses or contact lenses are removed, the subject’s eyes will feel convulsive.

Turning the volume up to nearly 110 dB, the subjects might even see colorful light around the field of vision or a ghostly gray area in the center of the vision. This is because 19 Hz is the resonant frequency of the human eye. Low frequency fluctuations can distort the shape of the eye, push the retina, and activate cone cells and rod cells through pressure rather than light.

Some people in the laboratory once said that they had seen dark gray [ghosts], but when they faced [ghosts], these [ghosts] disappeared again.

After examining this area, it was found that it was a fan in the room with a resonance frequency of 18.98 Hz, which is almost exactly the resonance frequency of human eyeballs. When the fan was turned off, the so-called “ghost” theory disappeared.

However, if you want to destroy a person’s head with resonance effect, I’m afraid you need a 240 dB sound source, otherwise you might as well hit the person’s head directly.

Depending on capacity and composition, Almost all parts of the human body can resonate at a specific frequency and with sufficient intensity. The human eyeball is an oval body filled with body fluid. The lung is a gas-filled membrane, while the abdomen contains various tissue structures filled with liquids, solids or gases. When subjected to external forces, these tissue structures have limited ability to stretch. Therefore, if the energy of external vibrations is sufficient, these tissue structures will stretch or contract with the low-frequency vibrations of gas molecules around them.

Since we cannot hear infrasound, we usually cannot realize exactly how loud this infrasound is.

When the sound wave reaches 130 dB, the inner ear will begin to produce directional pressure distortion unrelated to normal hearing, which can affect people’s language understanding ability.

At about 150 dB, people begin to complain about nausea and vibration of the whole body, usually in the chest and abdomen.

At 166 dB, people began to have some difficulty breathing, because low-frequency pulses began to act on the lungs.

At a critical loudness of about 177 dB, infrasound waves of 0.5 ~ 8 Hz can actually induce artificial respiration with abnormal frequency.

In addition, vibration waves propagated through media such as the ground can be transmitted to the human body through bones, which in turn can make the whole body resonate with longitudinal waves of 4-8 Hz and shear waves of 1-2 Hz.

This effect of whole body resonance will cause many problems, including bone and joint damage caused by short-term exposure, nausea and visual damage caused by long-term exposure.

Due to the prevalence of infrasound, especially in the field of heavy industry, in order to reduce the exposure of workers to this type of infrasound stimulation, the U.S. Federal and international health and safety organizations have formulated safety guidelines.

Killing with infrasonic weapons? It is better to hit it directly with the horn.

Since resonance occurs in all parts of the human body and resonance may be quite destructive, assuming that I am a crazy scientist and want to make an acoustic weapon to crack a person’s head, can I create a practical infrasonic weapon through a specific low-frequency resonance wave? In that way, there is no need to carry a heavy loudspeaker with you and there is no need to detain the victim in the elevator.

Some studies have calculated the resonance frequency of human skull by examining the bone conduction of certain types of hearing aids.

At about 9 or 12 kHz, a single experimental dry skull has significant acoustic resonance, slightly weaker at 14 and 17kHz, and even weaker at 32 and 38 kHz.

Sound waves of these frequencies are easy to obtain, so there is no need to carry a large sound transmitter. Most of these sound waves are not ultrasonic waves, and I don’t need to worry that the colloid in the skull will be damaged and the skull will burst.

If I only use one acoustic transmitter to output the two strongest resonant waves (9 kHz and 12kHz, 140dB), can this make people’s heads burst?

In fact, this method can only make a skull resonate on the bench, or make a living person turn his head to see where the annoying sound comes from. It has no effect on the human body.

The problem is that although the human skull may resonate very much at these acoustic frequencies, the resonance effect is weakened because the brain tissue and blood in the skull will not resonate at these frequencies, which is like covering a blanket on the sound.

In fact, in this same experiment, when the bare test skull was replaced by a living head, the resonance peak at 12 kHz was 70 dB lower than the maximum resonance wave of the skull. Even the current strongest resonance wave of about 200 kHz was 30 dB lower.

In order to make the human head produce destructive resonance, it may be necessary to use 240dB sound source. In this case, it is not as fast as hitting the human head directly with an acoustic transmitter.

Although we cannot use infrasound to fight against those dangerous people, infrasound can still cause potential harm to human body as long as there is a high-performance exhaust device or it is operated in a closed environment for a long time.

Although in the experimental base, I always fantasize about stringing up some loudspeakers and playing various sound waves to hunt down those murderers, I am sorry that I do not like infrasound weapons.

Most acoustic weapons are just hyped and exaggerated. Although there are long-distance loudspeaker devices, which can effectively intimidate, these devices still have obvious defects.

Hand-held acoustic weapons still need major breakthroughs in energy and sensing technology. However, in addition to destructiveness, sound waves are expected to play a more meaningful role in the future.

Responsible Editor: Fei Fei