Peak to Peak vs. RMS?

Question

Why does anyone care? Since RMS is computed off of peak-to-peak (p2p / 2 * .707 = RMS), why not just use peak-to-peak? Is RMS more accurate?

Answer 1

Well, when used in electrical engineering, RMS voltage can be used directly to calculate mean power consumption, if you know what the load is. That's why voltage stated for things such as the 120V in your wall outlet always means 120V RMS. It's much more useful in calculations.

In evaluating audio equipment like amplifiers and speakers, there isn't such an exact relationship, so manufacturers like to list both. In this case, when they say RMS power, they are referring to the average power capacity over a period of time. By peak power, they mean the power instantaneously attained in a spike, but which the system can't sustain for any duration.

Answer 2

The equation you give is only valid for a sine wave, not for all waveforms. A drum beat is a transient (impulse) and would have a different RMS if you calculated it (and that's a page of partial differential equations).

RMS is true power, not matter what the waveform is, so it is often considered more accurate for other calculations regarding audio loads.

Answer 3

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Answer 4

RMS is more honest, especially when you're talking about power.