I'm pretty sure Trifield was based on David Hafler's matrix approach. It was well documented in an article in Audio Amateur (AA) around 1984. Some libraries still have copies of this magazine.

That said, I'm pretty sure Meridian has significantly built on the original Trifield model (which I think [probably not remembering correctly] was based on Michael Gerzon's work on Hafler's matrix) so the channel matrixing info in the Audio Amateur article would probably just give a broad outline of the scheme.

I wish I could tell you the exact magazine issue number and month but I donated all my copies of AA to a library (different state) many years ago.

Sorry

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