Everyone spelled "Quadraphonic" differently back then - one magazine, I think Popular Electronics, had a little blurb about it stating that the term "quadra" in
"quadraphonic" was not latin or greek but garbage and that "quadriphonic" was correct. Quadrophonic was used often too. I like "QUADRAphonic" best and that seems to be the term that's the 'correct' spelling nowadays. In reality, "Tetraphonic" is what it really should be. So we'd go from monophonic to stereophonic to tetraphonic then quintaphonic.