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I disagree with that

"The electrons moving back and forth in the speaker voice coil on the + and minus wires produce an alternating magnetic field that interacts with the speaker permanent magnet"

That isn't completely explanatory either in my opinion.

There is a direct force on the moving electron in a combined EM field:

F = q(E + v x B)

making a force perpendicular to the net current flow and the external magnetic field. The "E" is the electric field producing the primary current flow axially down the wire (the consequent 'v' of electrons), but then the v x B term comes into play (assuming the B is large and externally generated as a voice coil in a permanent magnet).

In a physical wire with a conduction band (which has low resistance for some electrons) these electrons are then pushed to one boundary of the wire on the side.

At this point the electrons are somewhat bunched up but the nuclei and bound electrons, net positively charged, are displaced from the electrons by a slight amount. Now the electrostatic attraction pulls them together, moving the physical bulk of the wire (whose mass is dominated in the stationary nuclei in the crystal). This is then experienced as a physical force in the wire in the v X B direction. This is the speaker.

The magnetic field produced by the motion of the conduction electrons itself is a secondary effect, which produces a force back onto the permanent magnets to satisfy Newton's 3rd law. But it's not necessary to explain the force on the wire that is the purpose of the speaker.


Edits: 02/11/22 02/11/22 02/11/22
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