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I am creating a creature which uses infrasound to immobilize prey and I have done a little bit of research on the effects of Infrasound on animals, finding that 177 dB with a frequency between 0.5 to 8hz in infrasound can induce artificial ventilation in animals and cause respiration to cease.

I would like to know the frequency required to cause a human head to explode, and whether something like this could actually be achieved in real life.

(I do not care about the plausibility of such a creature's biology, how it would have evolved or any other such questions regarding its nature. Those are not the focus of this question.)

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This question asks for hard science. All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See the tag description for more information.

  • $\begingroup$ Are you limited to a specific decibel range? I suspect there is a level at which any frequency of sound could be applied that could cause almost anything to explode. It might be arbitrarily loud. Sound is energy, after all. $\endgroup$ – Wolfgang Aug 1 '17 at 20:31
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    $\begingroup$ No, there is not a specific decibel range that I am limited to. I only want to shatter human skulls through sound. $\endgroup$ – DevourerOfStars Aug 1 '17 at 20:41
  • $\begingroup$ Upvote for using the phrase, "I only want to shatter human skulls through sound." LOL. $\endgroup$ – ozone Aug 1 '17 at 21:22
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"Resonance frequencies of the human skull in vivo" by B. Håkansson, A. Brandt et al. (J. Acoust. Soc. Am., March 1994, vol. 95 (3) pp. 1474-1481), available on PubMed:

"Between 14 and 19 resonance frequencies were identified for each subject in the frequency range 500 Hz to 7.5 kHz. The two lowest resonance frequencies were found to be on the average 972 (range 828-1164) and 1230 (range 981-1417) Hz."

That is definitely not infrasound. And while it might shatter, it won't explode.

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  • $\begingroup$ So these frequencies would shatter a human skull, but would these frequencies be able to get through the soft tissue of the skull? Would the amount of decibels affect the effectiveness of the frequency between 500Hz -7.5kHz or no? $\endgroup$ – DevourerOfStars Aug 1 '17 at 19:52
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    $\begingroup$ @DevourerOfStars: I don't know whether they would shatter it under feasible conditions; the skull is pretty tough, that's why I said it might shatter. Sound pressure is of course important. Those are audible frequencies in the range of normal human voice, so I'd expect that nothing much will happen at reasonable sound pressures. How to convince a human not to flee from a sound source of more than 130 dB is left as an exercise. Sound pressure can never go above 1 atm for obvious reasons; that's about 191 dB. (You can have shock waves of more than 1 atm, but that's not sound.) $\endgroup$ – AlexP Aug 1 '17 at 19:57
  • $\begingroup$ Thank you for your help nonetheless, @AlexP . You helped me a great deal with this information. $\endgroup$ – DevourerOfStars Aug 1 '17 at 20:04
  • $\begingroup$ @DevourerOfStars: There is a reason why sonic weapons using infrasounds target the lungs and the belly... $\endgroup$ – AlexP Aug 1 '17 at 20:06
  • $\begingroup$ The creature I am making does primarily target the lungs (As I sort of mentioned in the question) in order to incapacitate prey, but I wanted to know whether or not I could have it shatter human skulls. $\endgroup$ – DevourerOfStars Aug 1 '17 at 20:10
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The human head can absorb a lot of energy, resonant frequencies or not.

According to here the threshold of death from decibels (loudness, you have to get to ultrasonic frequencies for the frequency to matter at all) is 185-200dBA. For comparison, a modern jet liner taking off is 120dBA and a flash-bang grenade produces 150-180dBA (the threshold of death, designed to stun and incapacitate). Remember that decibels are a logarithmic scale, so power increases exponentially.

I'm guess, but my sense of math with a logarithmic scale suggests you'd need 250-300dBA to pulpify the head — and that might be low.

Now, sound dissipates according to the inverse law (1/r). So, if you're 10 meters away the sound level is 10% of what you started with, or 20dBA. So the killing effect would be good for 1:1 combat.

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  • $\begingroup$ I found 200dB could kill a human by rupturing lungs and causing embolisms. So would 250-300dBA still cause the lethal effect between 180-200dB? And would 250-300dBA be enough to cause serious damage to the head? And if so, what kind of damage would it cause? $\endgroup$ – DevourerOfStars Aug 2 '17 at 1:32
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    $\begingroup$ The truth here is that no one knows. The sound is penetrating the body and, basically, doing nasty things with blood (pushing it through thin-walled capilaries, etc.) 250-300dB is whomping enormous. I'm willing to believe that it would crack bone. Please note that sound hasn't been used as an effective way to kill people for a reason. It's too hard to generate a leathal dose in a sensible manner. $\endgroup$ – JBH Aug 2 '17 at 2:17
  • $\begingroup$ 300 dB is a shock wave of unimaginable overpressure, about 10 billion atmospheres, stronger than, for example, the shock wave of an atomic bomb. It will certainly squish any human body, it will uproot forests, it will level walls etc. Be careful with decibels, they add up very quickly. $\endgroup$ – AlexP Aug 2 '17 at 11:08
  • $\begingroup$ @JBH So I found that 188dB is enough to destroy residential structures of brick and wood, 200db ruptures lungs, 210dB causes cavitation's in the brain, and at 260dB (roughly) you can match the 40,000 psi resistance of steel, so 300dB should be enough to knock down steel walls, at least that's what I think. $\endgroup$ – DevourerOfStars Aug 2 '17 at 20:29
  • $\begingroup$ :-) It sounds like we have a solution! Bear in mind that such a sound would be heard (metaphorically) a thousand miles away. Stealth is not us. $\endgroup$ – JBH Aug 2 '17 at 20:41

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