Definitions for "Sub-woofer"
A dedicated low frequency Bass driver used as an addition to a hi-fi or home cinema speaker system to create deep, and possibly wall shaking, bass sounds. Subs can be the cheaper Passive type that requires external amplification, or an Active type that has its own built-in amplifier and requires only a Line Level signal.
a single speaker enclosure housing a bass driver, designed to reproduce only low frequency information
a speaker optimized