Audio Power - Power Calculations

Power Calculations

Since the instantaneous power of an AC waveform varies over time, AC power, which includes audio power, is typically measured as an average over time. It is based on this formula:

$P_\mathrm{avg} = \frac{1}{T}\int_{0}^{T} v(t) \cdot i(t)\, dt \,$

For a purely resistive load, a simpler equation can be used, based on the root mean square (RMS) values of the voltage and current waveforms:

$P_\mathrm{avg} = V_\mathrm{rms} \cdot I_\mathrm{rms} \,$

In the case of a steady sinusoidal tone (not music) into a purely resistive load, this can be calculated from the peak amplitude of the voltage waveform (which is easier to measure with an oscilloscope) and the load's resistance:

$V_\mathrm{rms} \cdot I_\mathrm{rms} = \frac{V_\mathrm{rms}^2}{R} = \frac{V_\mathrm{peak}^2}{2R} \,$

Though a speaker is not purely resistive, these equations are often used to approximate power measurements for such a system.

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