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Definition of "variable-d":

Variable-D™ is the name of a technology developed by Electro-Voice in 1954 to reduce proximity effect of cardioid microphones.

Cardioid microphones achieve directionality by allowing sound from the front of the microphone to enter the space behind the transducer, usually via ports (holes) in the microphone case behind the capsule. Most microphone designs have their ports located at a single, fixed distance from the microphone capsule. E-V terms these “Single-D” designs, for “single distance.”

The “Varible-D” design uses multiple ports along the length of the microphone body. According to Electro-Voice, “high frequencies [enter] the port closest to the diaphragm, mid frequencies [enter] midway along the length of the microphone case, and low frequencies [enter] the port farthest from the diaphragm.”

The result is the “virtual elimination of proximity effect.”

Electro-Voice patented this development; see Patent 3,115,207.

See also Continuously Variable-D™, a refinement to the original design.

The term “Variable-D” is a registered trademark of Electro-Voice.

For more information, see this (PDF) excerpt from the 1980 Electro-Voice PA Bible.

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