# Active speakers picking up cellular tower waves?

Since a week or so a constant high pitch sound (~4khz) emanates from my active monitor speakers. After eliminating any ground or power source issues I noticed, that the sound rises in volume whenever I open my window - which is exactly between my speakers and an array of cellular antennas on the opposite building. I recall there were new antennas added a few weeks ago. Our public database shows that there are over 20 transmitters on there, with 3 pointing exactly in my direction.

Question: Can HF-EMWs produce such a sound in an audio amplifier or through it's connectors (it's not the cables or whatever comes through them)?

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What exactly do you mean by "cellular antennas"? Are you talking about these kinds of signals? Signals that transmit to mobile phones? –  Kitchi Jan 29 '13 at 5:49
yes, cell-phone towers. these here: en.wikipedia.org/wiki/Cell_site –  reinhardt Jan 29 '13 at 12:21

Considering that cell phone towers broadcast at frequencies that start at ~ $100$ $MHz$ and go on all the way up to nearly $1$ $GHz$, I'd say that the interference you're hearing isn't due to the cell phone towers.

But to answer your other question - It is possible for electromagnetic radiation to induce a signal in an audio amplifier. An amplifier takes an electrical signal, sends it through some circuitry to boost the amplitude, which then drives a speaker of some manner.

An electromagnetic wave will induce oscillations in the amplifier circuit (exactly the same way as an antenna), which will presumably be amplified and that's the hum that you hear.

I doubt that it's the cell phone tower, because it will induce a frequency comparable to it's transmission frequency, and if you are hearing something at ~$4$ $KHz$, then it's way too low a frequency to be caused by the cell phone signal.

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That just means that the cellular transmissions (carrying messages to the phones) aren't affecting his amplifier. It doesn't mean that the cellular tower isn't also producing some other 4KHz noise that he's hearing. –  Peter Shor Jan 29 '13 at 13:44
Thanks for your answers! What would be most probable in a multi-condominium neighborhood? Is 4 khz at least narrowing the source down? –  reinhardt Jan 29 '13 at 14:11
For illustration, here is what it sounds like: mega.co.nz/… –  reinhardt Jan 29 '13 at 16:19

I can now safely say that it's LTE. For anyone interested: There are all sorts of lower frequency carrier waves that are then modulated with the actual HF. For UMTS, LTE or Bluetooth, perfectly distinctive sound signatures can be made audible with measurement-tools. Or a pair of KRK speakers that is, even with magnetic shielding. Although readings indicate a really unhealthy dose of radiation (6 μW/m2) in my room, it is still far below any judicial threshold.

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Same issue Here, I have a 4G tower 100m away in front of my windows and picking High pitched noise at frequencies of 4kHz, 6kHz and 8kHz. The noise appeared when the 3G cell towers were replaced by 4G towers.

The best solution I found was to wrap the active speakers in an emergency blanket (all the faces except the one containing the speaker). This drastically reduced the noise.

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