Quoted from mbwalker:
Resurrecting a slightly old post about subwoofers. I printed the amp manual, but one thing that's not clear...I assume the sub needs to be powered, not just a speaker?
Powered stand alone units are available that plug into the wall for power and into the source/amp for signal.
Powered speakers of any type (regular or sub) are punchier and have more clarity. The increased power to the speaker magnets make them more responsive.
However it's good to mix unpowered speakers in the setup to add warmth also.