quadraphonic (adj.) Look up quadraphonic at Dictionary.com
1969, irregular formation from quadri- "four" + phonic, from Greek phone "sound, voice," from PIE root *bha- (2) "to speak, tell, say." The goal was to reproduce front-to-back sound distribution in addition to side-to-side stereo. The later term for the same idea, surround sound, is preferable to this.