Stereo-4

Stereo-4, also known as EV (from Electro-Voice) or EV-4, was a matrix 4-channel quadraphonic sound system developed in 1970 by Leonard Feldman and Jon Fixler.

The system was heavily promoted by RadioShack stores in the United States, and some record companies released LP albums encoded in this format. It was the first commercial quadraphonic sound system for LP records.