Audio Systems: noise cancelling headphones, noise cancelling headphones, piezo electric effect

Question
do all headphones have magnets in them?

Answer
No, only those that do!  I know that seems like a facetious reply, but most of them use a permanent magnet for which a voice coil is wound around it.  BUT, there are some that work on the Piezo Electric effect and there are electrostatics that have no magnet at all.

See this wiki site for a good summary:

http://en.wikipedia.org/wiki/Headphones

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