The low frequency speaker of a multi-driver speaker system. Sometimes in very low frequency applications it is called a sub-woofer. Woofers are generally larger speakers (12″ – 18″), but the specific size is not a requirement or the defining feature. Rather the ability to accurately reproduce low frequencies of potentially high amplitude, which tends to require a large throw or excursion (the distance the speaker can move in and out). In any speaker system where multiple drivers are used the woofer is the one for producing the lowest frequencies.