Subwoofer
Alternatively
known as a sub or woofer, a subwoofer
is a speaker that is designed to only reproduce low frequencies, also known as the bass. Subwoofers are what produce the rumble you may experience in a movie theater or the thumping noise you hear in a passing car.
In the picture to the right, is an example of the Altec Lansing VS2221 speakers and subwoofer. Not all speakers include a subwoofer; however, if you want more out of an experience from your speakers, you should only consider getting speakers that come with a subwoofer.
Also see: Sound definitions, Speakers