Computer speakers, or multimedia speakers, are speakers marketed for use with computers, although usually capable of other audio uses, e.g. for a shelf stereo or television. Most such speakers have an internal amplifier and consequently require a power source, which may be by a mains power supply often via an AC adapter, batteries, or a USB port. The signal input connector is often an analog 3.5 mm jack plug ; RCA connectors are sometimes used, and a USB port or Bluetooth antenna may supply a digital signal to an onboard DAC. Battery-powered wireless speakers require no cables at all. Most computers have speakers of low power and quality built in; when external speakers are connected they disable the built-in speakers by default. Altec Lansing claims to have created the computer speaker market in 1990.