Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization

First Edition

© 1975-1979, 2008 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization, First Edition, Xenology Research Institute, Sacramento, CA, 1979; http://www.xenology.info/Xeno.htm


18.3  Sonic Weapons

Sound, or acoustic radiation, might well be utilized by extraterrestrials against man and his artifacts. Although clearly limited in usefulness by the need for a transmitting medium (Figure 18.1), there are many jobs for which sonic weapons are uniquely suited.

The frequency spectrum for sound is chauvinistically, but conveniently, divided into three general regions -- the infrasonic, the sonic, and the ultrasonic. Infrasonic radiation ranges from about 0.001 Hz (cycles per second) for some seismic disturbances up to about 20 Hz. The sonic range, the bounds of human hearing, extends from 20 Hz on up to roughly 20 KHz. Then the ultrasonic takes over, reaching from 20 KHz up to 1 MHz (one million cycles per second) and beyond.


Figure 18.1 Range of Sound in Air and Water



A few general aspects of bioacoustics must first be appreciated. Figure 18.2 shows the two most important curves to our analysis. The first of these is called the threshold of hearing. This is the contour of zero loudness for normal human ears. It is the absolute lower limit of quietness below which we hear nothing.* Note that in the lower sonic range (20-200 Hz) and in the upper sonic range (above 10 KHz), sounds must be considerably more intense for them to become audible than in the middle regions of the spectrum.

The second important curve is called the threshold of pain. Sonic radiation of an intensity greater than this value at any frequency can cause permanent hearing impairment and excruciating physical pain, often described as an uncomfortable tickling sensation in the ears. Certainly, then, aliens could use focused sonic beams to quickly deafen their victims with an agonizingly painful blast of audible sound.


Figure 18.2 Sonic Intensity and the Thresholds of Hearing and Pain


But to leave it at this is to miss the most frightening aspect of sonic weapons. Compare the two threshold curves. The pain curve lies below the audibility curve for both infrasonic and ultrasonic frequencies. Beams of acoustic radiation of these kinds could be virtually undetectable by our ears, and yet carry an intensity well above our pain threshold. Here we have an "invisible" weapon, a force which can severely affect us physiologically -- yet we are unable to hear it. The specific effects of various frequencies differ, and we take this up next.

Although research in infrasonics is surprisingly scanty, one important conclusion has definitely emerged: Subsonics can affect humans adversely. Infrasound is felt rather than heard, and has the potential of shaking bodies and buildings to pieces at high intensities. But what are the usual symptoms of human exposure?2152

At relatively low power levels (about 120 dB) subjects report chest vibration, throat pressure and interference with respiration, and visual field vibration.431 Whole body mechanical vibration is very common.628 There are reports that emotional states may suffer some alteration under the influence of low intensity waves. It is entirely possible that fear may be induced,537 or psychological depression.432

At higher intensities, the effects are far more pronounced. Vladimir Gavreau, head of the Electroacoustics Laboratories of CNRS in Marseilles, France, relates that five minutes, exposure to 200 Hz at 160 dB caused painful and intense frictional rubbing of his internal organs, resonating with the sound. The accidental exposure was described as "almost lethal" by one researcher,448 and apparently the resulting pain took days to fully abate. Had they remained in the sonic fluence for another few minutes, there would almost certainly have been severe internal hemorrhaging, followed by death.

An Air Force study in the early 1960's tested subjects at power levels of 150 dB using frequencies of 50-100 Hz. The following symptoms were reported: coughing, choking respiration, pain on swallowing, headaches, loss of visual acuity and giddiness, severe substernal pressure, gagging, and tingling sensations.431

Lower frequencies seem to be most energy-efficient in eliciting disabling symptoms from the human organism (Table 18.1). Research in the subsonic range 2-20 Hz indicates the following: Intensities as low as 120 dB cause dizziness, feelings of lethargy and general lack of control.448 At 150 dB there is intense discomfort related to the organs of balance, causing nausea, a sensation of rotating, and involuntary movement of the eyeballs.622 General disequilibrium, disorientation, lassitude and weakness, and blurring of vision are also common.628 It would seem that high-intensity "subsonic stunners" postulated in various science fiction tales are a practical possibility.231


Table 18.1 Effects of Mechanical Vibration on Man628
Specific Vibrational Effect on Humans
Sound Frequency Range
Estimated Human
Tolerance Levels
Major body resonances
3 Hz – 300 Hz
140 -- 150 dB
Effects on postural control
0.1 Hz – 10 KHz
140 -- 155 dB
Motion sickness
0.1 Hz – 1 Hz
140 -- 145 dB
Blurring of vision
3 Hz – 1 KHz
140 -- 155 dB
Disturbance of breathing, speech
1 Hz – 100 Hz
140 -- 150 dB
Interference with task performance
3 Hz – 1 KHz
140 -- 155 dB


Infrasonic and low sonic radiation can also cause massive structural damage. The resonant modes of vibration for bridges, buildings and cars range from 10-100 Hz. Destruction occurs when a standing wave arises along one vibrational mode of the structure. At this resonant frequency the waves are virtually undamped and can build rapidly to a critical level -- as in the famous case of the Tacoma Narrows Bridge at Puget Sound, Washington, in 1940.

Infrasonic radiation surrounds us all the time. "Quiet" automobiles traveling at the speed limit commonly put out more than 100 dB in this range. Infrasound cannot be stopped by any normal building material, walls, or acoustic absorbers, since its wavelength is too long.

Gavreau has already constructed several alarmingly powerful "sonic guns." One such device is capable of emitting two kilowatts of power at 37 Hz. It has never been run at full power, since even at low levels the ceiling begins to crack and major body resonances are set up. Gavreau is reportedly now at work on the problem of building highly directional sonic projectors; for instance, an organ-pipe device 24 meters in length designed to operate at 3.5 Hz.628 He has estimated that large sonic cannon more than seven meters in diameter could now be constructed with power outputs close to the theoretical maximum for air -- roughly 200 dB.448 Can the aliens be far behind?

But let’s not ignore the opposite end of the sonic spectrum. Medical studies have shown that although ultrasonic radiation has more effect on the white matter in the brain than on the grey matter (the cerebral cortex), most neural components can be destroyed in a given region "without interrupting the blood vessels in the same region."623 Only a very detailed autopsy could reveal the true cause of death.

Other than effects on hearing acuity, however, the primary biological consequence of ultrasonic irradiation is vibrational heating. It is well-known that heat resulting from 20 KHz at 150-160 dB is quite sufficient to kill small animals. But apparently the presence of fur serves to absorb this radiation, and shaven animals fare much better. Men exposed to 150 dB were not significantly affected in one study,627 but it has been reliably estimated that 180 dB of airborne ultrasound would constitute a lethal dose for humans.

Would ETs select an ultrasonic weapon? It’s doubtful. Present human technology has been able to produce focused ultrasonic radiation, using a curved radiator, of more than 190 dB. That is, we‘ve already nearly attained the theoretical upper limit, and the effects are well known to us. And as we shall see in the next section, there are much more efficient ways to cause thermal destruction, techniques not nearly so range-restricted and medium-restricted as ultrasound.


* Intensity is measured in dB (decibels), a logarithmic scale of power pressure impinging on the ear. 30 dB is considered very quiet. Normal conversation takes place at about 60 dB. Driving diesel trucks or motorcycles exposes one to about 85-90 dB, and rock concerts may reach 110 dB or higher.


Last updated on 6 December 2008