Sound Bars can be separated into a few different groups:
Passive Sound Bars
These units allow a system approach to the sound by being able to use a nice 5.1 or higher rated Home Theater receiver such as a Sony, Yamaha, Onkyo, Pioneer, or Denon. This type of soundbar is the hardest to find and is sold primarily through higher end speakers builders like- Definitive Technology, KEF, Polk, Klipsch, and Pinnacle. Having all three front speakers directly under the TV is a compromise compared to 3 individual speakers with a greater distance between left and right.
This is not to say that the greater the distance the better it is. This is only true up to about 8-12 feet between left and right speakers. Greater distances than that will leave a large audible hole, in the next to center sound stage.
2.0 Sound Bar
This is the simplest style of self-amplified speaker which is left and right channel only. Usually hooks up with an optical cable on most new TV’s.
2.1 Sound Bar
Adds a subwoofer to the 2.0 unit for a much better bass sound.
3.1 Sound Bar
Adds a center channel speaker to the 2.1 unit.
5.1 All in one Sound Bar
Adds 2 speakers to the 3.1 unit which are supposed to mimic rear speakers, not very effectively however.
7.1 all in one Sound Bar
Adds 2 additional speakers to the 5.1 unit in a attempt to add surround plus surround back. Also not very effective.
5.1 Sound Bar with wireless Sub and rear speakers
These units only built by Vizio at this time have a 3 channel front speaker (left, center and right) with a wireless subwoofer which also has the built-in amps for the rear speakers.
These units for the price are very effective. You must however have a TV which allows for a surround output from the optical output or you must hook up the soundbar directly to the source (cable box, sat box, blu-ray or streaming device such as Roku or Apple TV.)