A subwoofer is a type of loudspeaker designed specifically to reproduce low frequencies, specifically between 20-200 Hz. Conventional, full-range speakers try to cover as much of the frequency range as possible, up to (or beyond) 20kHz, but a subwoofer is intended to fill in the difficult-to-reproduce bass region up to around 80-150Hz. Subwoofers complement an audio system composed of mains and/or satellite speakers by doing the heavy lifting involved in extending the bass response down to the lowest register.
A subwoofer is crucial to a complete audio system because it delivers lower frequencies that traditional two-channel or surround sound setups cant produce on their own. These low frequencies come from instruments such as the kick drum, bass guitar, and pipe organ, as well as movie sound effects like explosions. A subwoofer enables the listener to feel the sound, not just hear it.
Subwoofers can be either active or passive. Passive subs need to be powered by an external amplifier or Audio/Video (A/V) receiver, while active or powered subs are self-contained speakers and amplifiers. The use of a subwoofer augments the bass capability of the main speakers, and allows them to be smaller without sacrificing low-frequency capability.
