A sound long-term investment, loudspeakers last for years.

The best array of audio or video components will let you down if matched with poor-quality speakers. Good speakers don’t have to cost a lot, though an audiophile might easily spend well into five figures. Speakers generally last a long time and are less likely to become outmoded than other home-theater gear.  For your system, you can start with two or three speakers and add others as need dictates and budget allows.

Among the hundreds of speaker brands available, the major names include Acoustic Research, Bose, Boston Acoustics, Infinity, JBL, KLH, and Polk Audio. Speakers are sold through mass merchandisers, audio/video stores, and “boutique” retailers. You can also buy speakers online, but shipping costs charges are often high-$100 or more-if the speakers are heavy.

Speakers are sold as pairs for traditional stereo setups, and singly or in sets of three to six for equipping a home theater. To keep a balanced system, buy left and right speakers in pairs rather than individually. The center-channel speaker should be sonically matched to the front (or main) speakers. For the best effect, rear speakers should also have a sound similar to front speakers.

Each type of speaker serves a different purpose. The front speakers are used for stereo music playback; in a home-theater setup, they provide front left and right sounds. The center (or center-channel) speaker chiefly delivers movie dialog and is usually placed on top of or beneath the TV in a home theater. Rear speakers, sometimes called surround or satellite speakers, deliver rear ambient effects such as crowd noise. A subwoofer carries the lowest tones, such as explosions in an action movie.

Bookshelf speakers. These are among the smaller speakers, but at 12 to 18 inches tall, many are still too big for most shelves, despite their name. A pair of bookshelf speakers can serve as the sole speakers in a stereo system or as the front or rear duo in a home theater. One can serve as the center-channel unit provided it’s magnetically shielded so it won’t interfere with the TV. Small speakers like these have made strides in their ability to handle deep bass without buzzing or distortion. Any bass-handling limitations would be less of a concern in a multispeaker system that uses a subwoofer to reproduce deep bass. Price: $50 to more than $800.

Floor-standing speakers. Typically about 3 to 4 feet tall, these large speakers can also serve as the sole speakers in a stereo system or as the front pair in a home-theater system. Their big cabinets have the potential to do more justice to deep bass than smaller speakers, but we think many listeners would be satisfied with smaller speakers that scored well for bass handling. Even if floor-standing models do a bit better, their size and cost may steer buyers toward smaller, cheaper bookshelf models. Price: $200 to more than $1,000.

Center-channel speaker. In a multichannel setup, the center-channel speaker sits on, above, or beneath the TV. Because it primarily handles dialog, its frequency range doesn’t have to be as full as that of the front pair, but its sound should be similar so that all three blend well. Most center- channel speakers are short and wide so they fit nicely atop a TV. Price: $100 to more than $500.

Rear-surround speakers. Rear speakers in a multichannel setup carry mostly background sound, such as crowd noise. Multichannel formats such as Dolby Digital, DTS, DVD-Audio, and SACD make fuller use of these speakers than earlier formats. You’ll get the best blend if the rear pair sounds similar to the front pair. Rear speakers tend to be small and light (often 5 to 10 inches high and 3 to 6 pounds) so they can be wall-mounted or placed on a shelf. Price: $50 to more than $500.

Three-piece sets. Designed to be used as a stand-alone system or integrated with other speakers, these sets combine two bookshelf or small satellite speakers for midrange and higher tones with either a center-channel speaker or a subwoofer for bass. Price: $100 to $800.

Six-piece sets. An easy route to a complete surround-sound system, these matched sets have small bookshelf or satellite speakers for both front and rear pairs, a center-channel speaker, and a subwoofer. Occasionally, the front pair consists of floor-standing speakers. Six-piece sets take the guesswork out of matching all the speakers, which can be a daunting task at home, and harder in a store without a listening room. Price: $400 to more than $1,000.

Lovers of loud sound should pay attention to a speaker's measured impedance. The speaker impedance should be matched with the receiver; check your receiver manual. Power range refers to the power-handling capability of the speaker, usually expressed in RMS (average power) and peak power (maximum surge power). Speakers placed near a TV set should have magnetic shielding so they won't distort the picture; check the literature before buying to make sure.

Consider size. Speakers come in all shapes and sizes, so see how they’ll fit in your room. Floor-standing speakers might overwhelm smaller spaces. Bookshelf speakers are often a better fit, but some are quite large, so make sure the model you choose will fit the shelf or niche you’ve earmarked for it. And don’t worry that you’re giving up quality for compactness. Many small speakers do a fine job. Style may factor into your decision as well. Some new speaker systems are thin and flat to complement flat-panel TVs; they can be wall-mounted or placed on a stand.

Focus on accuracy, not advertising. The most critical attribute of any speaker is accuracy --the ability to reproduce sound frequencies without over- or underemphasizing any part of the audio range. As our tests have shown time and again, some of the lowest-priced speakers are among the most accurate. Ads often tout two-way or three-way drivers and the size of the cone inside a speaker, but you can’t judge sound quality by those attributes.

Listen for the differences. Even speakers with comparable accuracy scores can sound quite different. One model may overemphasize treble, while another underemphasizes it. There’s no substitute for hearing speakers, so bring a CD with a familiar piece of music to the store. Pay special attention to the front pair of speakers because they do the most work.

Speakers will sound different at home because of your room size, shape, and furnishings, so see if the retailer will allow a home trial or ask about the return policy. If you’re torn between two choices, buy the cheaper. Stores may be more open to a return if you want to trade up to a pricier set.

Check impedance. If you like to play music loudly, make sure your receiver is rated to handle the impedance (generally from 4 to 8 ohms) of the front speaker pair. The lower the impedance, the more difficult it is for the amplifiers in the receiver to drive them, and the greater the chance that the receiver can be damaged.

Power range refers to the power-handling capability of a speaker, often expressed in RMS (average power) and peak power (maximum surge power). Speakers placed by a TV set should have magnetic shielding to avoid interfering with the picture. (This is not an issue with LCD and plasma sets.)