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The question is purely academic, as normal sound dampening solutions seem to work fine.

I understand how electronic circuits make sound as per this answer:

How can "purely" electrical circuits emit sound?

My question is, a cheap 2 AA battery (3 volt) inverter makes as much sound as the cathode ray moving on an old tube television.

  1. What part in it is "moving" that creates that much noise?

  2. How much amplitude is created? and how? The sound can be heard from across quiet room.

  3. Normally high frequency sounds are very easy to locate the direction. However, in this instance, why does the sound appear directionless, like a low frequency sound?

  4. Is it possible to invert DC to AC without audible noise? Or is this a mechanical feature?

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I presume your inverter is operating at an audible frequency. If your transformer or inductor has multiple parts it could be one part moving relative to the other due to the magnetic forces or the magnetic materials changing shape due to magnetostriction. The usual solution is to increase the frequency to beyond the audible range, i.e. > 20 kHz. Regarding the perceived direction, could it be that the wavelength is short enough relative to the spacing of your ears for there to be ambiguity? ~23 mm at 15 kHz.

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  • \$\begingroup\$ Googled magnetostriction, it all makes sense now. I think your theory on the size makes total sense. Thank you!!!!! \$\endgroup\$ – Danielle Oct 21 '18 at 23:39

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