Active Speakers vs. Passive Speakers
All speakers in a home theater system fall into one of two categories: active or passive. How active and passive speakers are classified depends on their relationship to the amplifier driving them.
Here are the primary differences between active and passive speakers:
Passive speakers: A passive speaker doesn’t have a built-in amplifier; it needs to be connected to your amplifier through normal speaker wire. This speaker-level signal has been amplified enough to drive the speakers sufficiently. The vast majority of speakers are passive.
Active speakers: Active speakers have a built-in amplifier and are fed by a low-level (line-level) signal passed along an interconnect cable originating at a preamplifier or controller. Because the amplifier is an active electronic device, it needs power, so you have to put any active speakers near power outlets.
For most home theaters, the subwoofer is probably going to be your only active speaker (though you can also find passive subwoofers; some high-end home theater systems use these). There’s no practical reason for any of your other speakers to be active.
Active speakers limit your ability to choose amplifiers tailored to your home theater and are generally expensive. They are also much harder to find. Most active speakers are in either the low price/low-end category (designed for hooking into PCs or portable CD/MP3 players) or the really high end (where the speakers cost $5,000 to $10,000 each).