I am often asked what impedance speaker a client will need, or how much output power a design will produce. Channel output power is dependent upon several factors. The dominant factors are power supply voltage, and speaker impedance. The following table shows the expected output power for a variety of supply voltages & speaker impedances.
To use the chart, find your operating voltage in the left column, and your speaker impedance in the second row. The intersection will give you the ideal output power. Secondary effects such as your amplifier and speaker efficiencies will reduce the actual power that is delivered, but this number gives you a pretty good idea. You also need to be sure that the signal levels & gains in a system allow you to actually reach these levels (and don’t push you into clipping).