> 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 -- 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.

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jerf 4 days ago | parent | next [-]

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.

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lawlessone 4 days ago | parent [-]

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?

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loa_in_ 4 days ago | parent | next [-]

You are providing the energy by emitting the counter signal in the first place.

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card_zero 4 days ago | parent | prev | next [-]

That's an interesting question: what to do with the energy, ideally? Maybe convert it to very low frequency, so it only annoys elephants.

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luke-stanley 4 days ago | parent | prev [-]

Perfectly? Surely that is not reasonable?

	▲	IAmBroom 3 days ago \| parent [-]
		Even imperfectly, the problem remains - and is answered by the "the energy of the cancellation source counterbalances the noise energy."

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jorvi 4 days ago | parent | prev [-]

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.