of, noting, or pertaining to the recording and reproduction of sound over four separate transmission or direct reproduction channels instead of the customary two of the stereo system: a quadraphonic recording.
(functioning as singular) a system of sound recording and reproduction that uses four independent loudspeakers to give directional sources of sound. The speakers are fed by four separate amplified signals
1969, irregular formation from quadri- "four" + phonic, from Gk. phone "sound, voice" (see fame). The goal was to reproduce front-to-back sound distribution in addition to side-to-side stereo.