The Electro-Voice 664 was designed as a public-address microphone in the 1950s. The mic is commonly used today in both amateur radio and studio applications.

The mic was a cardioid dynamic, designed to maintain a consistent cardioid pickup pattern over a wide frequency range, regardless of proximity. This feat was achieved through an innovation that E-V named “Variable-D™.”

US Patent 3115207, filed in January 1954 and granted in December 1963, is for “a unidirectional microphone having a substantially constant response for all frequencies within a predetermined range.” A second goal and benefit of the design covered by this patent is to reduce the proximity effect that is common to pressure-gradient transducers.

The mic’s “Acoustalloy” diaphragm was said to withstand high humidity, temperature extremes, mechanical shocks, and salt air. The Engineering datasheet claims “it is practically indestructible with normal use.”

Electro-Voice Model Cardioid Dynamic Mic 1950's