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The coil is oriented coaxially inside the gap, a baby circular volume (a hole, slot, or groove) in the magnetic make within which it can move rear and forth |
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| The gap establishes a concentrated magnetic field between the two poles of a permanent magnet; the outside of the gap being one pole and the center post (a.k.a., the pole-piece) being the other |
| The center post and back-plate are sometimes a single piece called the yoke. |
Modern driver magnets are almost always permanent and imaginary of ceramic, ferrite, Alnico, or, besides recently, neodymium magnet. A hip trend in design, due to increases in transportation costs and a desire for smaller, allay devices (as in bountiful national theater multi-speaker installations), is the capitalization of neodymium magnet Wireless Speakers instead of ferrite types.