Typically, the output of the sound card
requires additional amplification if external speakers are used.
Figure 
shows a computer system with external speakers attached to the sound
card. Amplification circuitry is normally included in the external
speaker units. Power for these speakers is derived from batteries housed in
the speaker cabinets or from a small AC power converter. Most sound
cards do have the capability of directly driving low-power headphones.
The system internal speaker can also produce audio output, or it can
be amplified through external audio amplifier systems for applications
such as "Surround Sound".
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