A car amplifier’s job is to convert power available from the battery into power sent to the speaker. A low-voltage signal, sent from the head unit, is converted into a high-voltage signal, which can deliver more current to the speaker. Ideally an amplifier should be a perfect voltage generator that maintains the output signal, regardless of connected load. A change in impedance should not affect the voltage-signal. Hence, decrease in impedance requires increase in output power. However, since a loudspeaker is not a simple resistor this is a complex task. The perfect amplifier should not care about the connected load, but always generate a constant undistorted output signal.
When determining the quality of an amplifier the two most essential questions to ask are how loud it can play and how good it sounds. This could be indicated through specify the output power, one of the most significant ratings included in the standard CEA 2006.