A Sound Bar (sometimes also referred to as a Surround Bar) is a product which utilizes speaker design that creates a wider sound field from a single speaker cabinet. Sound Bars are designed to complement flat panel LCD and Plasma TVs. A sound bar can be mounted on a shelf or table just below the TV, and many units are also able to be wall mounted (sometimes the wall mounting hardware is provided).
Sound Bars come in two types of configurations: Self-Powered and Passive. Although both provide a similar listening result, the way they integrate into the audio portion of your home theater or home entertainment setup is slightly different.
Self-Powered or Self-Amplified Sound Bars
Self-powered Sound Bars are designed to be used as an independent audio system. This makes them very convenient as you can simply connect the audio outputs of your TV to the Sound Bar and the Sound Bar will both amplify and reproduce the sound without the need for added connection to an external amplifier or home theater receiver. In addition, most self-powered Sound Bars have provisions (such analog and digital audio inputs) for connecting one or two additional devices, such as DVD/Blu-ray Disc Player, or Cable/Satellite Box. Some Self-powered sound bars even incorporate Wireless Bluetooth to access audio content from compatible portable devices.
Non-Powered (Passive) Sound Bars
On the other hand, a passive Sound Bar does not house its own amplifiers, and still needs to be connected to an amplifier or home theater receiver in order to produce sound. Passive sound bars are often referred to as 2-in-1 or 3-in-1 (LCR) speaker systems in which the left, center, and right channel speakers are simply enclosed in a single cabinet with speaker terminals the only provided connections. Although not as "self-contained" as self-powered Sound Bar, this option is still desirable for some in that it decreases "speaker clutter" by combining the three main speakers into one cabinet that can be placed above or below a flat panel television set. Quality of these systems vary, but the concept is very appealing, in terms of style and saving space.
Sound Bars and Surround Sound
Also, Sound Bars, depending on design, may, or may not, have surround sound properties. In a self-powered Sound Bar, a surround sound effect may be produced by one or more audio processing modes, usually labeled "Virtual Surround Sound". The surround effect is not quite as good as a dedicated multi-speaker home theater system, but is still a viable, cost effective, and space-saving option for many consumers, especially in a smaller room or if all you desire is better sound quality for your TV without a going the full home theater system route. In a non-self-powered Sound Bar, the actual design a placement of speakers in the cabinet may provide a modest surround sound effect.
Digital Sound Projectors
Another type of product that is similar to a Sound Bar is a Digital Sound Projector, which is a product category marketed by Yamaha. A Digital Sound Projector employs technology that utilizes a series of small speakers that can be assigned to various channels and project sound to different points in a room, all within a single cabinet. A Digital Sound Projector houses all needed amplifiers and audio processors, and some also include built-in AM/FM radios, iPod connectivity, and inputs for multiple audio and video components. Higher end units may even include features such as video upscaling. In essence, a Digital Sound Projector combines the functions of a home theater receiver, amplifier, and speakers all in one cabinet.
For more details on Digital Sound Projector technology, check out the Yamaha Digital Sound Projection Page.
The Under-TV Sound System Option
In addition to the sound bar, or digital sound projector, concept that can be placed above or below a TV in a shelf or wall mount configuration, another variation of the sound bar concept that includes all of the elements normally associated with sound bars, and places them in an "Under TV" unit. These are referred to by several names (depending on the manufacturer), including: "sound base", "audio console", "sound platform", "pedestal", "sound plate", and "TV speaker base", What make this a convenient option is that these "Under TV" systems perform double duty as an audio system for your TV, as well as providing a platform or stand to set you TV on top of.
Sound Bars and Home Theater Receivers
A self-amplified sound bar (or digital sound projector, or under TV sound system) is a standalone audio system that is not designed to connect to a home theater receiver, while a passive sound bar actually requires that it be connected to an amplifier or home theater receiver.
So when looking for a sound bar, first determine whether you are considering it for use a way to get better sound for TV viewing, without the need for a separate home theater receiver setup with lots of speakers vs a desire to decrease the number of speakers connected to an existing home theater receiver setup. If you are looking for the former, go with a self-amplified sound bar or digital sound projector. If you desire the latter, go with a passive sound bar, such as those labeled as an LCR or 3-in-1 speaker system.
You May Still Need a Subwoofer
One of the drawbacks of Sound Bars and Digital Sound Projectors is that while they may provide good mid-range and high frequency response, they are usually lacking in good bass response. In other words, you may need to add a subwoofer in order to get the desired deep bass found in DVD and Blu-ray Disc soundtracks. In some cases, the subwoofer may actually come with the Sound Bar. In fact, some Sound Bar systems utilize a wireless subwoofer, which makes placement easier and eliminates the need for a cable connection between the Sound Bar or external amplifier/receiver and the subwoofer.
A Sound Bar, or Digital Sound Projector, is not a replacement for a true 5.1/7.1 multi-channel speaker system in a large room, but it can be a great option for a basic, uncluttered, audio and speaker system that can enhance your TV viewing enjoyment. Sound Bars and Digital Sound Projectors can also be a great speaker solution in a second system, such as in a bedroom, office, or secondary family room.
If you are considering a Sound Bar purchase, the most important thing to do, in addition to reading reviews, is to actually go a dealer and listen to several and see what looks and sounds good to you and what fits your setup. If you already have a TV and home theater receiver, consider a non-powered Sound Bar. On the other hand, if you just have a TV, then consider a self-powered Sound Bar or Digital Sound Projector.
For some suggestions, check out my current list of Sound Bars and Digital Sound Projectors.
For another perspective on options that can provide a good alternative to poor TV sound quality, without adding a lot of clutter, also check out an article from About.com Stereos, About 2.1 Channel Home Theater Systems.