What’s inside an electret capsule? Took one apart.

This one is built in an aluminum can crimped shut. Uncrimp the edge of the can, unscrew the nut on the center screw, and spread the contents out front to back, left to right.

From left, a protective screen, the diaphragm made of mylar aluminized on the front side glued to a metal ring, a red plastic spacer which sets the distance between diaphragm and backplate, the backplate which appears to be stamped from tin plated brass and covered on the front side with the electret plastic film, a spacer and contact ring which creates the chamber behind the backplate and carries the screw which holds the delay line together, and a plastic piece which forms the body of the capsule. The backplate and spacer fit into a cavity in the front of the body piece.

In the back half of the body is the rest of the delay line. Three pieces of filter paper establish another chamber which is closed by another metal plate with six holes offset by 90 degrees from the holes through the body. A nut holds it in place, and the screw serves as a contact through to the backplate. A final tinned brass ring serves as contact for the shell and diaphragm, and the can holds everything.

A variation uses the same backplate and delay assembly with a gold-sputtered mylar diaphragm in a screw-together brass case. This one has an open front with no screen.

The aluminum capsules sound pretty good, are a bit bright, and are intended for voice pickup. For instrumental music, perhaps they can be improved. Experiments are underway. The brass version sounds more balanced, still has a bright sound, but is less peaky. It’s a pleasant surprise.