4 ms·

> Probably somewhere on the internet is a fantastic interactive diagram that would clearly demonstrate this for you, but I couldn't google one up. Links solicit

> Probably somewhere on the internet is a fantastic interactive diagram that would clearly demonstrate this for you, but I couldn't google one up. Links solicited. Here's one: https://apenwarr.ca/beamlab https://apenwarr.ca/beamlab -- as well as the author's writeup: https://apenwarr.ca/log/20140801 https://apenwarr.ca/log/20140801 The author is focused on beamforming WiFi signals, but the principle is exactly the same whether it's a radio wave or a sound wave.

jerf 1y ago
Exactly what I was looking for, thank you. Interestingly, the wavelength of sound and the wavelength of wifi signals are in the same ballpark. 900MHz electromagnetic waves come out to ~30cm waves, which is about 1000Hz in sound-in-air.
- lawlessone 1y ago
  just my lay person thought here. But if you could cancel the noise/signal perfectly and everywhere wouldn't that sorta violate energy conservation? The sound energy has to go somewhere right?
  - luke-stanley 1y ago
    Perfectly? Surely that is not reasonable?
    - IAmBroom 1y ago
      Even imperfectly, the problem remains - and is answered by the "the energy of the cancellation source counterbalances the noise energy."
  - card_zero 1y ago
    That's an interesting question: what to do with the energy, ideally? Maybe convert it to very low frequency, so it only annoys elephants.
  - loa_in_ 1y ago
    You are providing the energy by emitting the counter signal in the first place.
jorvi 1y ago
My thought immediately jumped to beamforming / phased speaker array. What's more problematic is that its not the lower frequencies that are annoying (the 312Mhz drone), but the mid and high range. Think about it like this: fridge compressors suck to hear with their 2500Hz high-pitched electrical buzz, but once the compressor turns off, the gentle but deep slosh of the liquid being pumped around isn't annoying at all.

jerf 1y ago

Exactly what I was looking for, thank you. Interestingly, the wavelength of sound and the wavelength of wifi signals are in the same ballpark. 900MHz electromagnetic waves come out to ~30cm waves, which is about 1000Hz in sound-in-air.

lawlessone 1y ago
just my lay person thought here. But if you could cancel the noise/signal perfectly and everywhere wouldn't that sorta violate energy conservation? The sound energy has to go somewhere right?
- luke-stanley 1y ago
  Perfectly? Surely that is not reasonable?
  - IAmBroom 1y ago
    Even imperfectly, the problem remains - and is answered by the "the energy of the cancellation source counterbalances the noise energy."
- card_zero 1y ago
  That's an interesting question: what to do with the energy, ideally? Maybe convert it to very low frequency, so it only annoys elephants.
- loa_in_ 1y ago
  You are providing the energy by emitting the counter signal in the first place.

jorvi 1y ago

My thought immediately jumped to beamforming / phased speaker array. What's more problematic is that its not the lower frequencies that are annoying (the 312Mhz drone), but the mid and high range. Think about it like this: fridge compressors suck to hear with their 2500Hz high-pitched electrical buzz, but once the compressor turns off, the gentle but deep slosh of the liquid being pumped around isn't annoying at all.