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In the Sound function section of the Turbo C Version 2.0 Reference Guide 1988, I found the following comment.

Emits a 7-Hz tone for 10 seconds.

True story: 7 Hz is the resonant frequency of a chicken's skull cavity. This was determined empirically in Australia, where a new factory generating 7-Hz tones was located too close to a chicken ranch: When the factory started up, all the chickens died.

Your PC may not be able to emit a 7-Hz tone.

Is this story true?

Wrzlprmft
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duongntbk
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  • [Welcome to Skeptics!](http://meta.skeptics.stackexchange.com/questions/1505/welcome-to-new-users) – Oddthinking Jan 30 '18 at 03:03
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    How loud? A 7-Hz tone that bangs you against a wall could kill a human. – Daniel R Hicks Jan 30 '18 at 03:31
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    Since the comment did not mention any human casualty, I think it is safe to assume that the sound is not that loud. – duongntbk Jan 30 '18 at 05:38
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    @tsukumogami The question brings up a good point though. The frequency is only a part of the situation here, and the amplitude will be a necessary consideration. Below a certain threshold, the resonance wouldn't really work quickly enough. – JMac Jan 30 '18 at 15:28
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    So it seems that it breaks down into two questions of fact. First, *is* the resonant frequency of the chicken skull 7 Hz (or close to it), and second, can that be exploited to kill chickens with 7 Hz tones at intensities that would not be meaningfully threatening at other frequencies. – Ben Barden Jan 30 '18 at 16:47
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    It's probably also safe to assume when researching that the claimed real-world incident was not precisely 7.00 Hz, that some rounding is involved in the retelling. – Riking Jan 31 '18 at 09:51
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    Do we have any photos of exploded chicken heads from before 1988, that would corroborate the story? – John Dvorak Jan 31 '18 at 15:19
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    Found this: https://www.quora.com/Will-a-7Hz-tone-really-kill-chickens - one of the two answers makes a good case for it not being plausible, but I don't think quora is a reliable enough source to base an answer on. It does help show the notoriety of the question, though. – Rob Watts Jan 31 '18 at 22:08
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    I think a better phrasing would be along the lines of "Is there a sound frequency in the neighborhood of 7 Hz to which chickens are extraordinarily sensitive to, in a manner that is injurious?" – Daniel R Hicks Jan 31 '18 at 22:32
  • Does a throwaway comment in a relatively obscure book on an unrelated subject count as a notable claim? – user2752467 Jan 31 '18 at 22:37
  • For a wavelength of, say, 10cm, 7 Hz would correspond to a speed of sound of 0.7m/s. How is sound traveling so slowly? – Acccumulation Feb 02 '18 at 19:27
  • @Acccumulation where do you get a 10cm wavelength from? –  Feb 04 '18 at 22:49
  • This is generally (not chicken related) a notable claim. I remember reading paper magazine articles on similar topic (resonance in human body to specific frequencies) back in 1980s pop science/technology magazines in USSR. – user5341 Feb 05 '18 at 15:45
  • @HorusKol It is, to within an order of magnitude, the size of a chicken's skull. – Acccumulation Feb 05 '18 at 18:26
  • With all the fluid and soft tissue in a chicken I'd expect it to be quite damped. Damped systems do not exhibit great amplification when excited at their natural frequency. It is possible that some less damped structure such as the ear drum might be damaged. – Eric S Feb 17 '23 at 21:53
  • Possibly worth noting that another explanation of it is that the chickens were killed by the stress of the one. After all, the comment doesn't state that the death was immediate. As one commenter [here](https://news.ycombinator.com/item?id=11190271) said, "Birds are weird, basically totally nuts when kept in groups indoors. A little stress could see them all stop eating or peck everyone to death. A less-than-lethal volume could do real damage. A strobelight cannot kill a horse. But set one up in a barn full of horses and they will probably kill themselves. Horses are also nuts." – Sean Duggan Feb 20 '23 at 14:54

2 Answers2

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Probably not.

I don't know about chickens, but I do know the resonance frequencies of a human head. If chicken heads can be exploded, presumably humans are in some sort of risk.

Multiscale Biomechanical Modeling of the [Human] Brain, Chapter 14 - Resonant frequencies of a human brain, skull, and head says...

...the first fundamental frequency for the whole head and the confined brain in the head was 22.3 Hz and 13.9 Hz, respectively. The second resonant frequency for the whole head and brain were 23.8 Hz and 14.2 Hz, respectively. The third resonant frequencies for the whole head and brain were 24.0 Hz and 14.3 Hz, respectively. Finally, the first three fundamental modes were in torsion.

A good subwoofer can produce sound in this range. But when the person in the car next to you is dropping beats so fat it vibrates the lamp posts, they don't explode.

However, they can effect you. This excerpt from The Universal Sense: How Hearing Shapes the Mind by Seth S. Horowitz, Ph.D says a good subwoofer can make you see lights.

If you sit in front of a very good-quality subwoofer and play a 19Hz sound (or have access to a sound programmer and get an audible sound to modulate at 19Hz), try taking off your glasses or removing your contacts. Your eyes will twitch. If you turn up the volume so you start approaching 110 dB, you may even start seeing colored lights at the periphery of your vision or ghostly gray regions in the center. This is because 19Hz is the resonant frequency of the human eyeball. The low-frequency pulsations start distorting the eyeball's shape and pushing on the retina, activating the rods and cones by pressure rather than light.

As for killing the person...

You would have to use a 240 dB source to get the head to resonate destructively. At that point it would be faster to just hit the person over the head.

The article explains the problem...

The problem is that while your skull may vibrate maximally at those frequencies, it is surrounded by soft wet muscular and connective tissue and filled with gloppy brains and blood that do not resonate at those frequencies and thus damp out the resonant vibration like a rug placed in front of your stereo speakers.

Chicken heads are also filled with gloppy brains and blood.

Schwern
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    "Chicken heads are also filled with gloppy brains and blood." [citation needed] :P – DenisS Feb 21 '23 at 04:16
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    Affect, not effect. Too few characters, too little reputation. – phoog Mar 17 '23 at 14:08
  • 240 dB doesn't sound like a big number, but this value is insanely high. The Tsar bomb, the largest nuclear bomb ever detonated, is estimated to be ["only" 224 dB](https://www.zmescience.com/science/the-loudest-sound-ever-in-mankinds-history/). I mean, at that point, the nuclear bomb is going to do a lot more damage than explode your head. – Nelson Mar 28 '23 at 04:41
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No. Resonance occurs when the frequency of the object is equal to the frequency of the sound. Resonance amplifies the sound, because the two vibrations are in sync and so are subject to constructive interference, which builds.

The increasing of amplitude (loudness/Db) is what kills, it is the increase in energy. The resonance simply amplifies the sound.

The sound in question is 7 Hz. Therefore, if the natural frequency of chickens is 7 Hz, then it will be subject to resonance. Keep in mind though that the natural frequency of every object is different.

https://sciencing.com/calculate-natural-frequency-5171316.html says

The natural frequency is the frequency of this oscillation, measured in hertz (Hz). This tells you how many oscillations happen per second, which depends on the properties of the spring and the mass of the ball attached to it.

Each chicken will have different mass.

However, on cambridge https://www.cambridge.org/core/journals/animal-science/article/abs/resonant-frequencies-of-broiler-chickens/5C2FD7CB6E0D2E13B19D4C85ECED9D00 which studied the natural frequency of broiler chickens, it says

...vibrating beam technique was used to measure the resonant frequencies of 22 birds which increased in weight from 0·75 to 4·5 kg over 32 days. For a 2-kg bird, the frequencies of 14·6 (s.e. 0·6) Hz when sitting and 3·7 (s.e. 0·8) Hz when standing lie...

This shows that the weight was from 0.75 kg to 4.5 kg, with a 2 kg bird having a frequency of 14.6 +- 0.6 Hz when sitting and 3.7+-0.8 when standing. Therefore, the frequency can even be affected by the position of the chicken.

The energy of sound is also partly dependent on the amplitude or intensity, also known as decibels. Less energy means less lethality; getting hit by an asteroid moving at 10,000 MPH is worse than getting hit by a tennis ball moving at 1,000 MPH because of the energy content (this is simplified, impact mechanics are too lengthy.)

In conclusion, it is possible for a chicken to have a resonance at 7Hz, but it varies so wildly with so many variables that it is unlikely that a frequency of exactly 7Hz would magically resonate with the chicken. The sound (if loud enough) could potentially kill the chicken, but it is not reliable and often times lengthy to calculate.

JRE
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David Hashem
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    The question notes that it’s supposedly the **skull cavity** of the chickens that has a resonant frequency of 7Hz rather than the whole bird, I *would* at least imagine less variance in skull size than overall weight. – fyrepenguin Feb 17 '23 at 23:37
  • I agree with @fyrepenguin, this doesn't really address the question. – Mark Feb 18 '23 at 02:35
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    Also, resonance won't work well if the vibrations are highly *damped*, which a chicken head is, being surrounded by soft tissue. – matt_black Feb 20 '23 at 11:08