Recently a customer sent in an EV 666 for restoration, which isn't unusual. What is unusual is that when I'd opened it up, I found that the EV 666 has three diaphragms: one active and two passive. The passive diaphragms sit a little inside the capsule assembly, and measure about 1/2" in diameter. They appear to guard one entrance to the acoustic labyrinth that results in the mic's cardioid pickup pattern.
I couldn't find any photos of the internals of this mic online, so they're presented below.