A high quality speaker for use with a personal computer is used in two modes, first as a conventional, multi-function speaker for conventional computer audio output and second as a sub-woofer for use in combination with auxiliary speakers. The input of the speaker circuitry is adjusted according to the desired use. In a third mode, the speaker is deactivated entirely. Automatic switching between modes avoids having to manually reconfigure the mode of speaker operation when activating or deactivating an auxiliary speaker system. The speaker can be integrated with the computer enclosure. For example, a separate speaker enclosure can be designed to occupy some portion of space internal to a computer enclosure at least some of which would otherwise have been merely empty space.