western United States.

Problem / Question

The bad power in my house is somehow producing EMI in my audio equipment. Will a simple Faraday cage help? (Using an aluminum metal screen) If not that, then what would be the best, most practical, cost-effective solution to blocking this interference.

  • As is usual on S.E., if you think I'm wrong about something, please tell me why.

  • I'm not inexperienced with engineering / physics, although not a professional. Technical explanations are welcome but not required.


I recently moved into a new rental house. It has old wiring (pre-60s) which is mostly un-grounded and quite degraded. The landlord offered to ground a few of the outlets, but not replace all the wiring. For now, I'm going to have to live with the wiring as-is.

Why I think this is EMI

  • Using an amp with a cord as an antenna, the noise behaves exactly like radio wave reception in a TV or a radio. It changes depending on angle, and dissipating somewhat when I block it with my body.
  • I'm using a new power conditioner with ground noise eliminating circutry.
  • There was no noise at all, even without the power conditioner, at my last place.
  • Several other non-audio electrical appliances around the house hum, and sound quite a bit like the noise I hear in the amps.
  • The produced audio frequencies from the noise are all above 500hz or so. It's my understanding that ground loops are usually low-frequency.
  • Using other outlets, grounded or not, all have the same issue.

Things I already tried that didn't work

  • Plugging in to the grounded outlets around the house using an extension cord.
  • Turning off as many things as possible to find the source of the noise.
  • Using different circuit breakers, turning off as many as possible.
  • Using different combination of audio equipment to reduce noise. Using shielded, balanced audio cables greatly reduces the hum. However, that's not possible with everything I own.
  • Standing in such a way as to reduce the noise. This works somewhat, but is untenable. (this lead me to the Faraday cage idea).
  • $\begingroup$ Couldn't edit first line, should read: "Greetings from the mid-western United States" $\endgroup$
    – user14088
    Dec 6, 2017 at 19:23
  • $\begingroup$ As you're probably aware, AC current in the U.S. is 60 Hz. If your interference is, in fact, above 500 Hz, then your household AC would not be the source. Would some sort of mesh Faraday Cage reduce it regardless? Probably. But I'd be concerned with heat dissipation. I'd experiment with grounding the amp's chassis first, assuming you have a normal two-prong power cord. You'd also want to check and make sure the power outlet is properly polarized before grounding the chassis. $\endgroup$
    – BillDOe
    Dec 6, 2017 at 20:40
  • $\begingroup$ Hmm, good thoughts. Any way I can easily check for grounding of something? Can I use a multimeter on the ground and one of the plug prongs? I get this even with newer equipment with three pronged cords, so I expect that they're already grounded (at least they should be). Will check out the polarization next time I get a chance. $\endgroup$
    – user14088
    Dec 6, 2017 at 22:01
  • $\begingroup$ there are multipurpose AC plug testers you can buy at hardware stores which will tell you whether or not your outlets are wired up correctly. Also note that you may have two different sources of electrical noise in your environment: radiated EMI (radio waves) or conducted EMI (comes into your audio system as trashy waveforms on top of the 60Hz AC from the wall). you need to know which is the problem in order to know what to fix. $\endgroup$ Dec 6, 2017 at 22:18
  • $\begingroup$ I'm almost positive it's RMI, at least the majority of it. You're probably right, the grounding can't be good, but for now, I'm not as worried about that. $\endgroup$
    – user14088
    Dec 8, 2017 at 4:06

1 Answer 1


After having the power company fix my mains connection, most of the noise dissapeared

I finally got around to calling my power company, and had them come out and test my mains connection. They told me that the grounding on it was bad. After a repair team fixed it, I found about 75% of the noise was gone.

Still more noise than past places, (again, I suspect the old wiring) but at least now the noise is at a manageable level.


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