How is quadraphonic sound different than sound produced by the usual two-speaker stereo system?

Quadraphonic systems used 4 speakers and reproduce music mixed with 4 independent channels. Unlike surround sound, Quadraphonic systems do not have a separate subwoofer channel, nor do they have a front center channel. They reproduced music from Quadraphonic 8-track cartridges, Reel-to-reel players and phonograph players which were made for the purpose.