RMS Equation?

[JeffyZ33 10+ year member]

RMS equation? Go to your local shop and pay $10.

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[thch 10+ year member]

the formal equation is:

power, rms = (1/T) * integral( (over T) of (v(t)*i(t)) )

voltage, rms = (1/T) * integral( (over T) of (v(t)) )

this is typically overly complex for most cases. there is another equation as well, but its less useful.

typically you deal with sine waves. sine waves (into a resistive load) have an RMS value that is 0.707 * the peak value. in terms of power, that would be RMS power = 1/2 that of peak power.

square waves have an rms value that is the same as the peak value. not too hard of a wave.

RMS defines the "DC equivilent". basically the power to the speaker is constantly changing. the RMS value is the simplified value.

 

[Raven 10+ year member]

In car audio terms, power = volts ^ 2 / impedance.

If an amp maxes out at 20 volts (unclipped) and is on a 1 ohm load, you have 20^2/1, or 400 watts.

Clipping can seriously screw with the reading a DMM takes, so make sure you aren't clipping or you'll get some seriously freaky number. I pulled around 56 volts out of a 600 watt power acoustik amp before trying to do this. Needless to say, it was not possible for me to clip it any harder. =\