Generally, the loudspeaker system comprises a woofer for reproducing low-frequencies, a squawker for reproducing midrange-frequencies, and a tweeter for reproducing high-frequencies. A common limitation of loudspeaker systems, particularly those intended for high quality stereo sound reproduction, is relatively inadequate low frequency performance. In response to the increased low frequency sound in recordings, a growing number of audio systems are adding an additional type of loudspeaker to their existing array of loudspeakers. This type of loudspeaker is known as a subwoofer. Subwoofers are specialized loudspeakers which reproduces the lowest bass frequencies in music and sound. Adding a subwoofer to an audio system relieves the full range loudspeaker from reproducing the lowest frequencies, thereby improving its performance. Subwoofers are designed to be either powered or passive. In the powered or active variety, the sub-woofer system has a built-in power amplifier to drive the sub-woofer speaker. Powered sub-woofers are used in applications where a local amplifier of a stereo or home entertainment system is limited in its output power and cannot drive the sub-woofer to its full efficiency. Passive subwoofers rely on the amplifier of the audio source to drive the sub-woofer audio driver. Passive sub-woofers are generally not able to produce the same sound level as powered sub-woofers due to the limited output power of most conventional stereo amplifiers. Powered or active sub-woofers include a class-AB audio power amplifier to drive the speaker.
