RMS Power?

Thank you roxy54.  Almarg is much better in explaining technical merits. I'm just trying to contribute something being grateful for all things I learn here.  

Nobody interested?  Really?

That’s true, but it is called average Power in every engineering textbook. Unit of watt already signifies power convertible to heat - a "real" power.

Pavg = 0.5Ppeak

Taking RMS of power curve would bring different, totally irrelevant result.

With sinewaves sin(x) for power would be squared sin^2(x)
|1. Square: (sin^2 (x))^2 = sin^4(x)
2. Mean: Integral of sin^4(x) over 0-pi is 3/8
3. Root: SQRT(3/8) = 0.61

Prms = 0.61Ppeak

This number does not represent anything useful.

Faulty term watts rms or rms power came most likely from around 1975 FTC standard for power rating. FTC realized, that they goofed up and 25 years later in 2000 they corrected it .

Wiliewonka - whoever wrote this doesn’t understand it. There is no such thing as rms power. There is only one power that produces heat and it is average power. He says that in his opinion it should be integral over time period of the v(t)*i(t) , instead of Irms*Vrms, but he doesn’t realize that it is exactly the same.

For sinusoids:
Pavg=0.707Vpeak*0.707Ipeak=0.5VpeakIpeak=0.5Ppeak

but integrating over period of time:

Pavg= Vpeak*sin(x) * Ipeak*sin(x)= Ppeak*sin^2(x)
Integral of sin^2(x) over 0-pi is 0.5 hence Pavg=0.5Ppeak

It is called Average Power since it is an average of all instantaneous V*I.

If I remember correctly there was a moment in time when some companies used Peak or Continuous power ratings, but it appears that things have reverted back to RMS

Again - there is no such thing as RMS Power. There is a momentary power, average power, real power, reactive power, total power but no RMS power.

Erik, They could say Average Power - power equivalent to power produced by DC voltage of 0.707Vp.
There are no two different power values - average and rms as it is with voltage. There is only one power - Average Power.

I’m pretty sure that when you visit websites of all major amp makers like Pass Labs, Jeff Rowland etc - you won’t find terms "rms power" or "watts rms".

I don’t have big hopes for changing anybody’s mind on this forum (even FTC stayed ignorant for 25 years).

Wliliewonka - It is "watt" and not "Watt" (units start with small letter - but I’m sure you don’t care). You can go back to sleep now.

imhififan, Thank you for posting.  Example of the wrong average power calculation in the second article is very interesting.  Using averaged values of voltage and current produced error of 50%.  It is very common error.  People who design test and measurement equipment (often big companies) make this mistake all the time.  For instance, when calculating mechanical power, they take average (filtered) values of speed and torque and multiply them, instead of taking instantaneous values of both, multiply and average (filter) the product - mechanical power.  For constant torque and speed it does not make a difference, but as soon as oscillatory component appears error becomes significant.  Even single percent error is very important for efficiency calculation.  Of course it has nothing to do with audio, but shows that "Power" is a muddy subject.

Output impedance term can be complex. Perhaps we should rate it in ohms RMS for clarity? :)

Williwonka, Peace!  I'm sorry for the tone of my comments toward you.  
Changing industry might not be possible, but we can start with our forum.

The kV rms varies greatly with the quality of the power supplied to the input of the transformer and even more with the form of rectification.

What is "quality of power"? Do you mean amount?
Is "form of rectification" - full wave or half wave?

Since the degree of rectification varies so greatly with various audio technologies from tubes to op amps to class D, maybe RMS is at least as meaningful as peak.

What is "degree of rectification" and how is it related to op-amps or class of the amplifier? RMS of power does not represent anything useful. Your kVrms * mArms is just power.

...or maybe radiography and audio have nothing in common and I’m full of s#!t.

You’re not. Asking questions is important.

Zavato, amp is rated 80watt and marked 80watt rms by mistake.  In watt rms it would be 97.6 watt.  Vrms*Irms=Pavg  NOT Prms.

From Wikipedia "Audio Power"

As described above, the term average power refers to the average value of the instantaneous power waveform over time. As this is typically derived from the root mean square (RMS) of the sine wave voltage,[6] it is often referred to as "RMS power" or "watts RMS", but this is incorrect: it is not the RMS value of the power waveform (which would be a larger, but meaningless, number).[7][8][9][10] (The erroneous term "watts RMS" is actually used in CE regulations.[11]) This is also referred to as the nominal value, there being a regulatory requirement to use it.

Al, leave it (he is not going to get it).

Ramtubes, - please read my post at "Running AHB2 in bridged mode..."

Al, I was right (he is not going to get it). RMS value of ANY sinusoidal waveform, having peak at 200 (of any unit) is 141 (of the same unit). 100W would be an average power value corresponding to VrmsxIrms and equal to half of peak power for sinewave (and equivalent to amount of DC power producing the same amount of heat). Guys, please, this is EE101.