Amplifier output power is one of the most important considerations in choosing a stereo receiver. Power is measured in watts per channel and the decision about how much power you need should be based on your selection of loudspeakers, the size and acoustic characteristics of your listening room, and how loud you like to listen.
It is always best to match the power requirements of the speakers with the output power of the receiver. Some speakers require more or less power, expressed as loudspeaker sensitivity (in decibels , dB), which is a measure of how much sound output is produced with a specified amount of amplifier power. A speaker with lower sensitivity of 88dB-93dB (also known as speaker efficiency) will require more amplifier power than a speaker with a higher sensitivity (94dB to 100dB or more) to play at the same volume level.
Power output and speaker volume is not a linear relationship.For example, a receiver with 100 watts per channel will not play twice as loud as a receiver with 50 watts per channel using the same speakers – the difference in maximum loudness would be barely discernable, only 3 decibels (dB). Rather, more amplifier power will allow the system to more easily handle musical peaks without straining, which results in better sound clarity.
When comparing the power output of different amplifiers, it is important to know how the power is measured. The most accurate measure of power is RMS (Root Mean Square, a mathematical formula), as opposed to peak amplifier power, a less accurate specification. Some manufacturers inflate specifications by measuring power at a single frequency, say 1kHz, instead of the frequency entire range, 20Hz-20kHz. When comparing receivers with different power outputs, always make sure they are measured the same way.