Work in Progress
EV-4 (originally called ‘Stereo-4’) was developed by ********* & ******* and taken up by Electro-Voice as a way of producing a four channel compatible stereo LP. With record labels like Project 3, Ovation & Quad-Spectrum backing the system and Radio Shack selling EV-4 equipped amplifiers and systems, it is fair to say that this is where LP based quad as we know it really started.
Unfortunately EV-4 turned out to be very closely related to DY, even to the point the decoder was not designed to attempt an accurate decode but to create an impression of space. It was possible to play either systems LP’s th the other system’s decoder and get the same results, that being a restricted front channel stage and a maximum of 2db rear separation.
When CBS released SQ, Electro-Voice released a modified decoder that was able to decode both systems, but in reality it decoded neither system at all well and it quickly died out.
With the improved matrix systems SQ & QS rapidly gaining ground, Ovation and Quad-Spectrum moved over to QS while Project 3 released albums in all the available systems, including CD-4, until they finally settled on SQ.
The comments regarding QS compatibility with DY obviously relate to Stereo-4/EV-4