Item — HN Reader

https://everything2.com/title/7+hertz+-+the+resonant+frequen...

Example (for both functions):

    /* 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. */

 #include 

   int main(void)
   {
     sound(7);
     delay(10000);
     nosound();
     return 0;
   }

from the comments over there (2002)

3 comments

Not very likely

https://skeptics.stackexchange.com/a/54400

I don't see how even an entire chicken is going to meaningfully respond to a wavelength of almost 50 meters. Their coop could though.

> I don't see how even an entire chicken is going to meaningfully respond to a wavelength of almost 50 meters.

Without disputing the conclusion, is the wavelength the right measurement, or should that be half the wavelength?

That's a more natural way to consider the resonance, certainly. What I was getting at is that if we were using a 7hz tone to explore a big room, we couldn't tell if there was a chicken in there or not. We'd have a hard time sensing an elephant. Let alone exert enough of a force to harm. Because the wave is so much larger that they barely interact.

You're not generating a 7 hz tone on any sort of conventional audio gear, and definitely not a pc speaker.

The SVS PB-17 Ultra advertises a range of 12-220Hz at -3dB. I imagine it could play a pure 7Hz tone if you turn it up.

And most speakers can play infrasound for many non-sinusoidal waveforms [0]. They'll drop the fundamental and some lower-end harmonics but can still give a sense of what it sounds like

[0] https://szynalski.com/tone#7,saw,v0.5

> I imagine it could play a pure 7Hz tone if you turn it up.

You're misunderstanding the numbers here. Going from 12 to 7 Hz is most of an octave, nearly doubling wavelengths.

Also SVS's numbers are gonna be the usual marketing stuff, so they're assuming a fat room gain curve, and just looking at their website they have a disclaimer on their graphs that it doesn't represent actual total output capability. Which is a way of hiding that if you actually try to drive it that hard that low with ~3kw electrical in those voice coils are going to torch.

The non lying way to prove that claim is to show large signal Kipple results including the heat soak. They ain't doin' that here.

Basically stuff going this low is really exotic and more in the realm of servos that simulate earthquakes than traditional transducers.

Tom Danley is the world expert on this sort of thing. He used to build stuff like ultrasonic levitation ovens and full scale sonic boom simulators for JPL/NASA.

In the audio world he was first famous as the tech lead behind ServoDrive. This now defunct company made special effects subwoofers using DC rotary servo motors to drive the diaphragm. They were used as special effects subs in that era by big acts like Garth Brooks. But they didn't catch on outside that niche because very little music has significant content below 40 hz as it just turns into a muddy rumble that harms sound quality as a whole. So to use these sorts of things you have to mix for it specifically. Cinema goes lower with the rumbles down to 15hz, but that's basically it.

Getting anything that's like a clean tone at 7hz is not gonna happen without a purpose built device.

FWIW Tom Danley started his own company[1] after Servo Drive failed on the business side, where he focuses on large scale horn speakers using novel topologies. They're among the best in the business at what they. Again, they don't have anything that even remotely tries to go down to 7hz.

[1]: https://www.danleysoundlabs.com/

Tom's a nice guy, I've traded emails with him a few times over the years. He used to be pretty active on the DIY speaker building mailing lists sharing his very in depth knowledge freely.

For context, the lowest notes on most pipe organs are typically about 33 or 16 Hz (from a pipe that is 8', 16', or 32' long).

If I feed a 7hz input to some cheap hand-made thing like https://www.youtube.com/watch?v=liSEwqdq7aA , will it not vibrate at 7hz and thus produce a 7hz "tone" (disregarding that humans won't perceive that as sound, at least not the fundamental)?

No, because reproducing the fundamental is the thing. Saying otherwise is kinda like me saying I'm gonna take a voice call, run it through a filter that generates a ton of distortion harmonics, then seperate out those distortion harmonics, and then call it a "tone" of your voice.

But also the original post was about a 7hz tone somehow resonating with a chicken's skull cavity, which if you know the basic wave equation relating wavelength with frequency is an absurdity. The waves involved are multiple orders of magnitude too big to couple to a volume that small. They'll just diffract around like nothing.

Who said the source has to stationary? Doppler shift for the win.

You can with your hands, just shake them

An easier way to generate a 7 Hz tone is to just move your hands back and forth 7 times a second. Either way you won't be able to hear because we can't hear 7 Hz anyway