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Why is it that when you touch the a bare male end of a speaker feed that the speaker makes hissing noises? Is it just (eddy?) currents running through you?

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up vote 5 down vote accepted

First off, what you describe only happens for highly amplified speakers. The current change when you touch the wires is pretty tiny and you'll only hear a sound when that signal is being amplified significantly before being sent to the speakers.

There are many reasons why a tiny bit of electric current flows from your body to the speaker wire so I'll only list a few off the top of my head:

  • When you first touch the wire any static electricity can flow to the wire which could make a loud pop
  • Air moving over your body provides a constant source of static electrons which can flow into the wire
  • Sweat and salt can act as a tiny saltwater battery between your fingers and the wires
  • Your body produces tiny amounts of electrical current (this is how your neurons work)
  • Your body can act as a giant inductor for the $50$ or $60$ $\mathrm{Hz}$ electric current from the power grid (and therefore changing magnetic field) surrounding you
  • Your body is a (poor) antenna for the radio waves passing through you
  • The "ground" your body is making contact with may have a tiny varying potential which would allow current to flow from the wire through your body to this ground (and vice-versa)
  • The speaker wire is typically two wires right next to each other that act as an antenna. if you touch only one of the wires you act as a ground allowing induced current from radio waves to flow through you to the ground

Without a lot of experimentation it's hard to know which of these are the significant sources of electric noise and of course, there may be others I didn't list.

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