How microphones are made

A microphone is a loudspeaker in reverse, with moving air creating the current instead of current moving the air.

stations: 8
things upstream: 62
raw sources: 19
steps from the ground: 8

The short version

A dynamic model starts as a pressed aluminum or molded plastic case. Fine enameled copper wire is wound on a plastic bobbin and glued to a thin diaphragm, then the pair is lowered into a sintered neodymium magnet. A soldered cable, a foam spacer and a grille finish it. Condenser types swap the coil for two closely spaced metal plates.

Form the case

A hydraulic punch forces thin aluminum sheet into a die, and the excess is trimmed off. Plastic cases are injection molded instead. Any switch is then fixed in place with small screws or rivets.

Goes in
Aluminum Plastic
Wind the coil

Very fine enameled copper wire is wound many turns around a small plastic bobbin and glued so it stays put.

Goes in
Copper wire Adhesive
Sinter the magnet

Neodymium iron boron powder is squeezed and heated in a high-pressure die until it fuses solid. It can also be bonded with plastic binders.

Goes in
Neodymium magnet
Glue on the diaphragm

A pre-cut plastic diaphragm sits in a holding fixture while the bobbin is glued exactly in its center. The joint is left alone to cure.

about 24 hours

Goes in
Polyester Adhesive
Lower into the magnet

The cured diaphragm and coil are set down into the magnet assembly and glued. Sound will now push the coil along its axis and induce a current.
Measure the response

The coil assembly goes on a test station that plays white noise, which holds every audible frequency at once. Its response has to land within specification.
Solder in the cable

A coaxial cable is cut and stripped, and one end gets a soldered audio connector. The free end threads up through the bottom of the case and is soldered to the switch and coil.

Goes in
Solder Copper wire
Close with the grille

A foam rubber spacer wraps the coil assembly, which is lowered into the case and locked in place by a grille and cap.

End of the lineMicrophone

Worth repeating

RCA's ribbon microphone of 1931 weighed about 8 pounds and could be damaged just by blowing into it.
Alexander Graham Bell's first microphone of 1876, a telephone transmitter, relied on liquid and was far from practical.