At its most basic, a sound bar consists of a pair of speakers at each end so as to do stereo. Of course there's no such thing today as a "basic" sound bar; many have wireless subwoofers and added features like Bluetooth for audio streaming capabilities (example: SONY HTCT260H Soundbar Wireless Subwoofer). Some even present their menus on the TV screen, which makes for an easy setup or access to "Smart TV" features like downloadable apps or video streaming (i.e., Netflix).
But the best part of getting a sound bar is to have a surround sound system that doesn't require all kinds of speakers throughout the room — filling it up with wires you can trip over and speaker stands that ruin the decor and end up scratching the floor. But not all sound bar surround sound systems are the same — in fact, there are two different kinds to choose from.
#1 Audio That Doesn't Stay In One PlaceA basic stereo system employs two speakers set at the front left and right. Sound comes out of each and your ears take care of noting what sound is coming from what speaker. In a surround sound system, sound has to come from more positions than just the front left and right — there also has to be sound coming from the left and right sides of the person. If the sound bar has multiple speakers and the right "tech," then the sound from certain speakers can bounce around (off the walls, etc.) and end up "striking" the person's ear at the appropriate left and right side. That's a simplified way to explain how this kind of sound bar works because you know there's all kinds of tech working on the inside to make it happen.
The Sony HTST7 HD Soundbar is an example that goes even better than the 5.1 system of front L/R speakers, a Center and a pair of side surrounds: it’s a 7.1 system that can envelop (the “1” refers to the 100 watt wireless subwoofer) with 9 magnetic fluid speakers that are each able to crank out sound 1.6X that of conventional speakers. The speakers are each individually powered by a 50-watt amplifier, making this a 450-watt audio system in all. Sony creates the surround sound effect by decoding high-resolution audio formats like Dolby TrueHD and dts-HD Master audio, and then using intense signal processing to accurately reproduce the sound characteristics of a movie theater for home use through the speakers. Plenty of “bells and whistles” to accompany what you’ll be hearing too, but it’s the surround effect that ties in all of the high-end components of this Sony sound bar.
#2 Fooling Your EarsOptical illusions fool the eye into thinking it sees something that isn't really there and the same can be done to a person's ears. It's called "psycho-acoustics" and once you get past the fancy name, all it means is that the audio is enhanced in such a way that it appears to the person seated that there's sound coming from different positions around him. This simulated surround is very picky because it doesn't work with everyone, nor does everyone "hear" the simulated effect in the same way. That's why many simulated surround systems on sound bars will give you variable control over the effect, along with pre-selected choices for the effects. For a good example here, check out the Harman Karon SB16 Soundbar. The subwoofer is wireless and adds 100 watts of deep bass to the 25 watts driving the left and right speakers (two cone midrange speakers and a dome tweeter X 2 channels). All that layers behind the 3D virtual surround sound, powered by digital signal processing, which creates the effect that there are speakers aimed at you from all around. And yes this model does include switches for "tweaking" the sound to be more precise to your preferences.
And if simplification is what's desired (as well as low-cost), then the LG NB2030A Sound Bar might be attractive — thanks to its 40 watts 2-channel, Sontia Sound enhanced virtual surround sound setting.
But I should have said that there's even a #3 to choose from — sound bars that eschews all the "bells and whistles" to just give you clarity of sound and plenty of volume. That fits the no-frills, inexpensive Sony All-In-One Sound Bar (SA-40SE1) to a T: it has 8 built-in speakers powered by 40 watts (20 per channel) and is designed for HDTVs 40" and up. If what you're looking for is a better stereo "sound field" than the tiny speakers in the TV can provide, then this is how you'll get it.