Googleing for 2 coils doing something beside inducing.

[petemoore]

  Common place to get induction between two coils is transformers.
  Where else...I understand that transformers impart great force on the windings...seems like a pseudo speaker could be simple: hook a cone right to some loose windings ?
  Anyway looking for places where 2 coils do work of what a fixed magnet and a coil can do, ie push and/or pull using electromagnetic force.

[JKowalski]

Early speakers were made using two coils instead of a coil and a magnet - one coil was used as an electromagnet (ran DC voltage across it to create a fixed magnetic field). This was because back then they didn't have the ability to make strong permanent magnets. It was definitely a less efficient method of creating a speaker - which is why it is not seen anymore.

Google "field coil speaker"

[petemoore]

Early speakers were made using two coils instead of a coil and a magnet - one coil was used as an electromagnet (ran DC voltage across it to create a fixed magnetic field).
 10'' example of this sits right here, Stancor and basically premium amp, and the Jensen Field Coil speaker is one little gem of a find ! !
  This was because back then they didn't have the ability to make strong permanent magnets. It was definitely a less efficient method of creating a speaker - which is why it is not seen anymore.
 I see one and didn't even notice it's effeciency...granted it's more complicated and probably less effecient, but ineffeciency with woody tone like this is something I can work with.
 Google...yupp, rebuilt some of the caps on the Field Coil Speaker/amplifier...amazing tone.
 Anyway that's what I'm after and was thinkin' instead of a chokecoil/fixed magnet coil like field coil uses....fixed electromagnet and voice coil electromagnet, each recieveing signals from output amplifiers which cause them to move the cone.