An audio system consists of a number of components with the speaker cable serving as the major link in the system. A typical audio system contains a sound source, pre-amplifier, power amplifier, and speakers. The sound source is used to generate sound such as a microphone or CD player. A pre-amplifier is used to strengthen the small signals from the sound source while a power amplifier strengthens the signal to drive the speakers. The speakers act as an electrical transducer that transforms electrical energy into sound.