Subwoofers
A subwoofer's job is to reproduce low-frequencies. In home theatre, there is a channel on the movie soundtrack just for the sub. A sub can also be incorporated into a music listening / 2-channel set-up, and is particularly beneficial where bookshelf speakers are being used in place of floorstanders. The sound produced by a subwoofer is somewhat less directional than that produced by full-range speakers; however, proper placement is still necessary to get the best results and avoid standing waves ('boomy' sound). More advanced subs will feature a comprehensive set of adjustable parameters for calibration to suit the acoustics of the room.
