The first type is dynamic headphones, where the coil is directly glued to the diaphragm and fitted onto a circular magnet. This type is found in earphones, headphones, and speakers.
The second type is balanced armature headphones, unique to earphones. One end of the U-shaped armature is fixed to the driver unit wall, while the other end is movable, surrounded by magnets at the top and bottom. Sound is produced by connecting the diaphragm to the armature via a thin wire. These drivers can be made very small, have a narrow frequency response, and may consist of three or more drivers in a single headphone. I've seen up to 12 drivers on one side.
The third type is electrostatic headphones. Shure made an electrostatic earphone, but most others are headphones. These have no physical components on the diaphragm; sound is produced by electrostatic fields on the left and right sides, requiring a very high driving force.
