The Hafler diamond and DynaQuad are slightly different systems. The Hafler diamond was a system with F, L, R, and B speakers. DynaQuad has the traditional four corners LF RF LB and RB. They are real quadraphonic systems and encoders exist for them.
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I recorded a set of sound effects for a stage play held in 1971 using the Hafler diamond system. It worked very well. It is an encode/decode system.
I own a record encoded in DynaQuad.
There were no Hafler diamond systems in music stores because there was nothing to sell but speaker wire. But there were many DynaQuad decoders in stores. I have the original DynaQuad and several of the clones. Each company created their own name for their DynaQuad decoder. Here are some of them:
2-4 Enhance (Sony/Columbia)
Quadrant (H H Scott)
There were definitely DynaQuad systems in audio stores.
Occasionally a station published the circuit to let people get a taste of encoded quad in their broadcasts.
Any RM decoder (including Hafler diamond and DynaQuad can partially decode H. The front to back separation is lower.