1) Quadraphonic system 2) Quadriphonic system 3) Stereo 4) Stereo system 5) Stereophonic system 1) Quadriphonics 
Four channel system used in audio to try and give the listener the effect of a 360 degree sound field.
[n] - a stereophonic sound recording or reproducing system system using four separate channels
quadraphonic system noun a stereophonic sound recording or reproducing system using four separate channels
high-fidelity sound reproduction involving signals transmitted through four different channels. Also called