Computer speakers range widely in quality and in price. The computer speakers typically packaged with computer systems are small, plastic,and have mediocre sound quality. Some computer speakers have equalization features such as bass and treble controls.The internal amplifiers require an external power source, usually an AC Adapter. More sophisticated computer speakers can have a 'subwoofer' unit, to enhance bass output, and these units usually include the power amplifiers both for the bass speaker, and the small 'satellite' speakers.