What is inside a sound bar?

Unsound - maybe it's a substitute for a 5.1 system for those people who don't have room or interest, and have other things to do like read a book, play with their kids, help someone out, build something or whatever, rather than obsess about which cable to buy, what power chord(sic)is the best, what speaker will "blow away" another, the nuances of image depth or some other audio neurosis that appears to take so much time for so many people (that maybe could be used to play with their kids, or build something......)

To the OP - it's a bunch of (usually) cheap speakers in a box with some set up to achieve a (usually) poor psychoacoustic effort of having a 5.1 system. Some are alleged to be OK at their purpose (I haven't heard them), but they typically have a very small sweet spot

I've never opened one up, but by the sound (I've heard several), I'd say a bunch of crap - they all gave me a headache.

There are a couple different threads here in the responses, and I think they sort of intertwine two different lines of thought, with two very different conclusions.

First, a well-designed soundbar (and there are a number -- the responses mention Polk, Definitive Technology and Yamaha) will offer stereo sound that is far superior to the sound provided by most internal speakers in flat screen TVs. In particular, they will often offer far superior reproduction of dialog. Generally they use pretty decent, but not outstanding, "cone and dome" speakers, and often have an associated subwoofer you stick in a corner. So if your TV speakers leave something to be desired, a good sound bar can be a very worthwhile investment.

Second, a number of them also claim to offer a simple alternative to producing surround sound -- and for someone with different priorities, as Snofun3 suggests, they probably offer a decent experience at a reasonable price --I have one in my family room, and it provides some "surround" ambience. But for someone seriously into Home Theater (I'm not) -- a sound bar is not going to fill the bill.

Snofun3, so we agree.

Do try before you buy. I bought a used Yamaha 1000 soundbar and can't get a realistic sound in our room. Maybe the Audioengine A5 powered speakers might be worth a try.