Powered subwoofers have become integral to any complete audio/visual system, particularly home theater. Normal speakers leave the very lowest frequencies unheard. Powered subwoofers fill in those blanks. For years, AudioSource has been the leader in providing quality powered subs at affordable prices. All include level controls and both speaker and line inputs and outputs. All but the compact SW 300 feature a variable crossover from 40 Hz to 180 Hz, auto-on circuitry, and a phase reverse switch.