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.
Re:Noise Cancelling a Fan
by lawlessone on Wednesday September 17, 2025 @05:48PM
(#45281790)
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?
Re:Noise Cancelling a Fan
by luke-stanley on Wednesday September 17, 2025 @06:38PM
(#45282269)
Perfectly? Surely that is not reasonable?
Even imperfectly, the problem remains - and is answered by the "the energy of the cancellation source counterbalances the noise energy."
That's an interesting question: what to do with the energy, ideally? Maybe convert it to very low frequency, so it only annoys elephants.
You are providing the energy by emitting the counter signal in the first place.
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.
Here's one: https://apenwarr.ca/beamlab -- as well as the author's writeup: 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.