Amplifiers operate over a frequency range that is normally between 20 and 20,000 hertz, according to Joe Roberts, a former U.S. Navy electronics engineer. Common power ratings for amplifiers range between 20 watts per output channel and 1000 watts per output channel, notes Audio Publishers Group.
Amplifiers are rated in terms of watts per channel at several different load impedances measured in ohms, according to Joe Roberts. The most common load impedances are 2, 4 and 8 ohms, although 4-, 8-, 16- and 32-ohm impedances are more likely with older vacuum tube amplifiers. Lower impedances create more difficult loads for amplifiers to drive. Some manufacturers include a specific amount of harmonic distortion in ratings.
Amplifiers of 250 watts or greater typically have a dynamic range of 110 to 120 decibels, notes ESR Acoustics. Car audio amplifiers may have from one to eight output channels as of 2015, according to Audio Publishers Group.