Starting with the monophonic sound, this had a single channel and directional sound with 1 amp speaker, the sound was channeled to a single point for all the audience.
Things changed with the stereophonic sound, in the 50’s movie theater started to use multi sound channels and the stereophonic tried to recreated at home, it had two channel sound, with a mixed sound going to left or right speaker which improved the sound greatly but created the ping pong or bounce effect.
In the 70’s the system changed to 4-channels, being 4 mono amps or 2 stereo amps, which made them a bit expensive for most home users. But then appeared the quad system, 4 channels within 2 channels recording and was less expensive than 4-channels.
Dolby surround became popular in the 80’s, encodes 4 channels within 2-channels signal decoding the sound to be sent to the right destination being multi-directional with a phantom center.
Which bring us to todays home theater systems more like an experience, being a complete surround sound atmosphere, most systems have a dolby tech support creating an amazing sound, can integrate with DVD, Blu-ray, Apple TV, Smart TV’s and many other devices, without mentioning that nowadays home theater can be set or designed based on the type and size of the room.