How loudspeakers are made

The magnet in a loudspeaker is not a magnet at all until the assembly reaches the end of the production line.

stations: 10
things upstream: 70
raw sources: 19
steps from the ground: 9

The short version

A speaker driver pairs a voice coil with a permanent magnet. The coil is wound on a steel mandrel and baked, metal plates are stamped and coated, and a magnet is sandwiched between them. The cone, spider and surround are glued in, the magnet is charged at the end of the line, and the driver is bolted into a cabinet.

Wind the voice coil

A former of paper, Kapton or fiberglass is wrapped around a steel mandrel that keeps it round. Copper wire is wound on, and the coil is baked to cure the adhesive coating the wire.

Goes in
Copper wire Adhesive
Stamp the metal parts

Top and back plates are stamped from rolls of steel, and baskets are stamped from steel or cast in aluminum. The plates are welded or staked to the basket and the core.

Goes in
Steel
E-coat the metal

The assembled metal parts go through an electro-coat paint line, which puts an even layer of cationic epoxy over the whole surface to stop corrosion.

Goes in
Epoxy
Form the cone

Paper pulp, polypropylene or another light material is pressed into a shallow cone. It has to be stiff enough not to flex and light enough to start and stop quickly.

Goes in
Paper Polypropylene
Assemble the motor

A ferrite or neodymium magnet, not yet magnetized, is sandwiched between the plates, which focus its field into a narrow gap around the core.

Goes in
Neodymium magnet Ferrite
Join cone and suspension

The voice coil goes into the gap without touching the sides, and the cone is glued to it. A flexible surround at the outer edge and a corrugated spider hold the coil centered.

Goes in
Vulcanized rubber Adhesive
Charge the magnet

At the end of the line the finished assembly passes through a magnetizer, and the magnet takes on its permanent field.
Build the cabinet

Fiberboard or plywood panels are cut, glued and sealed into a box. The cabinet is needed so that sound from the back of the driver does not cancel the sound from the front.

Goes in
MDF Plywood Adhesive
Wire the crossover

In multi-driver speakers, a small circuit of coils and capacitors splits the signal into frequency ranges for each driver. The drivers and crossover are screwed in and wired.

Goes in
Copper wire Screw
Test the response

Each speaker plays test tones in a measuring chamber, and the response is compared with a reference curve before it is packed.

End of the lineLoudspeaker

Worth repeating

Eminence, a Kentucky speaker maker, uses over 360,000 magnets each year.
In a powered speaker, the amplifier is built into the cabinet, which is common in computer and Bluetooth speakers.