We’ve previously shown ideas for homemade microphones, but unlike this one from75 years ago, none of them were made out of a walnut.

This one, from the October 1945 issue of Radio Craft is, indeed, housed inside a walnut. In addition to the large walnut shell, the required components are “a cord, a little cotton batting, a piece of tinfoil, and a few odds and ends.” The heart of the condenser mike is a diaphragm made of thin copper or tin foil, specifically, “the stiff kind, such as used to be used on cards of buttons.”

The foil is stretched carefully over one half of the shell. Through the other half of the shell a cork is inserted, and a brass screw passes through to a washer which is held in place just next to the foil. The article includes a circuit for a preamplifier. The author notes that the completed microphone “needs plenty of amplification, but the quality is as good as that of any commercial microphone I have ever heard.”