Connecting a subwoofer (or more than one if you love the bass) to your home theater is an essential part of providing the sound for your movies and TV. The majority of subwoofers are active (they have their own built-in amplifiers). So you need an output on your A/V receiver to connect a standard analog audio cable to the subwoofer. On most receivers, this output is labeled the LFE (Low Frequency Effects) channel -- the ".1" of the 5.1/6.1/7.1 channel surround-sound formats.

The other subwoofer-related thing to look for is an adjustable crossover, which lets you select which audio frequencies go to the subwoofer and which go to the main front speakers. Different speaker systems sound better with the crossover set at different frequencies. If you have small bookshelf speakers in the front, you might set the crossover to a higher frequency. If you have a set of huge tower speakers with giant woofers (bass speakers) of their own, you might set the crossover to a lower frequency and let the subwoofer concentrate on only the really deep sounds.