It involved hooking up the speakers in the rear out of phase, but pointing in towards the listener. It was interesting but nothing like as cool as Dolby Pro-Logic, and when I was taken on a press trip to hear stereo rears for what was then called Dolby AC-3, I nearly died of delight. Then of course came DTS and we now have fully lossless surround codecs from both Dolby and DTS, plus some fierce processing power available from our AVRs to interpolate seven surround channels.



Link: Techradar