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Ground loop on a microphone

  1. Aug 16, 2011 #1
    Noticed something interesting about my microphone today and cant stop thinking about it.
    So there's always been this humming noise with my microphone (I can clearly hear it since Im using headphones), but I've never really thought about it. Now suddenly today my foot touched the metal casing of another PC, and the humming stopped. I was confused, so I tried different things:

    Touching the metal case of that PC would minimize the humming.
    Touching an USB port on my PC (metal) would also minimize it.
    Touching a metal piece on a radiator in my room would amplify the humming sound.

    And then I noticed something even more strange - when the tip of the microphone (where you're supposed to speak in) was NOT pointed towards me, then me touching the USB port, the metal case of the PC or the radiator did NOT have as much effect as when it WAS pointed towards me.

    Apparently this is supposed to be ground looping sound, but I dont really understand whats going on here.

    Would someone care to explain?

    Thanks in advance,
    fawk3s
     
    Last edited: Aug 16, 2011
  2. jcsd
  3. Aug 16, 2011 #2
    It's 60 hertz hum. When you touch the case or USB port you're grounding yourself and the hum diminishes or goes away. When you touch the radiator the humming gets worse because the radiator is not grounded and it's acting like an antenna and picking up noise and conducting it to your body.

    When you say "radiator" do you mean the old style steam radiators because I would have thought that those were grounded.
     
  4. Aug 16, 2011 #3
    I don't want to discourage the field experimentors, but I recall a Colorado radio DJ that did essentially the same thing you did, but with the added complication of doing it in a spa tub.

    He died.

    So please be careful when researching electrical gizmos.


    And, grounding problems are notorious for being hard to diagnose and treat.
     
  5. Aug 17, 2011 #4
    No, Im talking about the http://upload.wikimedia.org/wikipedia/commons/c/c2/Radiator.png" [Broken], if you will. But I've always thought these were grounded, as in high school when the teacher was doing experiments with static, he always used the radiators for grounding, and these were practically the same I have in home.

    But why would I need to ground myself in the first place?

    Thanks in advance,
    fawk3s
     
    Last edited by a moderator: May 5, 2017
  6. Aug 17, 2011 #5

    sophiecentaur

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    Gold Member

    You can get both electric and magnetic hum pickup. Grounding equipment - or yourself - can reduce electric pickup but ground currents can sometimes increase it. There are many tales of people cutting ground connections, one by one, and eventually getting rid of an annoying hum because it eliminated one particular 'ground loop'.
    Experimenting can be useful - and dangerous, if you aren't careful. Touching with only one hand at a time is a good idea!
     
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