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Preamble: At 5 AM in the morning, if I sit quietly and listen attentively, I can hear many different noises, on a very high frequency. If I try to isolate the ones that are less noisy, I can clearly distinguish some "notes", which have a fixed frequency (pitch) but are also intermittent. Of course, this is no rigorous experiment, but I tried to get closer to electronic objects and the intensity of this sound increased. This made me think of a questions that I think many of us have thought about, at some point or another.

Question:

Do electromagnetic waves, like Wi-Fi and mobile phone signals, interact with air in such a way that could produce an hearable sound? If so, would this sound be at a determined frequency, and how would this be related to the frequency of the electromagnetic wave?

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  • $\begingroup$ Are any of those electronic objects designed to make sound? It's not unusual for cheaply-made devices to "leak" small amounts of electronic noise from their digital circuitry into their audio output. I have several devices in my own home which, If I hold my ear close to the speaker in a quiet room, I can hear faint electronic buzzings and chirpings. $\endgroup$ – Solomon Slow Dec 9 '15 at 14:16
  • $\begingroup$ Another possibility is, modern electronic "switching" power supplies often operate at high-ish audio frequencies, and even though they are not designed to make sound, they sometimes do, especially if they have any magnetic components: en.wikipedia.org/wiki/Magnetostriction $\endgroup$ – Solomon Slow Dec 9 '15 at 14:18
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The waves themselves don't usually produce sound, but their effect on other objects (particularly ferromagnetic ones) can be audible. This is similar to how speakers work (except they use magnetic fields, not waves). Maybe what you are hearing is the vibration caused when the radiation hits another object, but I would attribute it to small discharges within the wiring or possibly a fan in the device? I hope this helped answer your question.

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Don't forget that you ara actually "listening through your brain". The human perception is in this cases only the information given by your physiology, nervous system and your own psychology. It is not to be underestimated. I hope you don't have such a mess like tinnitus, but it is clear example of not really existing sound which is very well audible.

But the best chances are, as John Smith said, that you can hear an oscillation of some mechanical system driven by the changes of EM field. Usually, it is due to the higher energy EM prcesses and devices such as lightbulbs, starters of fluorescent lamps etc.

The signal processing part: It strongly depends on the device. The fundamental frequency could typically by the 50 Hz (the net frequency), but the driving could be pulse-like and therefore many frequencies can be driven and more oscillating system eigenfrequencies "hit". Usually the light fixtures etc. are vibrating at some higher frequencies.

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  • $\begingroup$ The operators of high energy radar units sometimes sense a clicking noise which is believed to be due to direct interaction of the intense EM field with their brain tissue. This might be termed induced tinnitus. $\endgroup$ – Lewis Miller Dec 9 '15 at 15:46

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