True if what you mean in both cases is
Vrms^2/R
or 1/T*Integral from 0 to T of V(t)^2/R dt
But that's kind of tautological, it comes from the definition of RMS voltage.
But if by RMS power you mean
sqrt( 1/T*Integral from 0 to T of V^4/R^2 dt ),
ie the square root of the mean of the square of the instantaneous power,
then they're not the same.
And that last expression is what I'd say has little if any meaning.
is the horse dead yet?
"Since we spend all out time talking about power in terms
of sine waves at the output of amplifiers, and for an undistorted
sine wave rms and average watts are the same, it is moot."
Nelson,
Not true 🙁 . Do the maths. 😉 Even if the voltage/current is a pure sinewave into a resistive load, the RMS value of the power is NOT the same as the average power calculated using the RMS value of voltage/current.
I reckon the RMS term was invented as a mathematical short-cut for engineers dealing with mains electricity. It is a way of working out power by finding the "dc equivalent heating value" of an ac current or voltage sinusoid into a resistive load. I think the misnomer "RMS power" came from a shortening of some phrase like "the average power calculated by using RMS voltage/current".
I did notice your advice about measuring clipping using a pair of headphones by the way. 🙂 Speaking of distortion, have you ever noticed that an amp that sounds poor into a loudspeaker also sounds poor into a pair of hig Z headphones? Just curious if you've noticed this.
"Since we spend all out time talking about power in terms
of sine waves at the output of amplifiers, and for an undistorted
sine wave rms and average watts are the same, it is moot."
Nelson,
Not true 🙁 . Do the maths. 😉 Even if the voltage/current is a pure sinewave into a resistive load, the RMS value of the power is NOT the same as the average power calculated using the RMS value of voltage/current.
I reckon the RMS term was invented as a mathematical short-cut for engineers dealing with mains electricity. It is a way of working out power by finding the "dc equivalent heating value" of an ac current or voltage sinusoid into a resistive load. I think the misnomer "RMS power" came from a shortening of some phrase like "the average power calculated by using RMS voltage/current".
I did notice your advice about measuring clipping using a pair of headphones by the way. 🙂 Speaking of distortion, have you ever noticed that an amp that sounds poor into a loudspeaker also sounds poor into a pair of hig Z headphones? Just curious if you've noticed this.
Yes and so it is...
We have RMS Current, RMS Voltage and Average Power. Just another fork in the road to confuse those that dont know or have not done the theory.
We have RMS Current, RMS Voltage and Average Power. Just another fork in the road to confuse those that dont know or have not done the theory.
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