RMS Power?

kijanki,
Even though I am completely ignorant on the subject, I can fully understand why the incorrect term bugs you. I'm glad that there are people like you around to make us aware of these things.
I'm expecting Almarg to jump into this any minute...

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.

The reason for introducing Wrms has more to do with distortion measurements. At some point at least in the US, requirements for producting THD+N along with power and pre-heating requirements occured and this settled down. The Wrms came out of that.

For a while amplifier manufacturers could measure watts any damn way they wanted to, so some used the Vpk-pk as the source for the wattage measurements, and never mind the distortion at all.

So Wrms is more of a commercial standards thing than a purely electrical one, and implies that it is a sine wave with THD+n below rated.

Have fun arguing it though.

Best,

E

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.

Here’s what Wiki thinks (it’s very long)
https://en.wikipedia.org/wiki/Talk%3AAudio_power

One line in the text ...

For most, just comparing the RMS power number is useful

I guess to some - But it’s been a while since I paid any attention to the RMS numbers on amps or speakers - I go to the store and audition. You can quickly tell if the amp has enough oooomph (or not)

I really think there are a lot more "pressing things" to get this worked up about - world peace, climate change, famine, disease, etc......

After all it’s just a number!
- It’s used by many in the audio business as " the norm"

And y’ain’t gonna change that any time soon!

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

But I would like to thank Kijanki for letting us know "watts" what
- or is that whats "Watt" :-)

Hmmm - I think I’ll elect to - NOT loose any sleep over it.

Just sayin !

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 .

The term refers to the fact that if you are to calculate the output power, then the AC voltage used in the calculation must be RMS volts.

To do this, first find the peak to peak AC voltage that is the output of the amplifier into a known load such as 8 ohms (usually non-inductive).

Then divide by 2 to get the peak voltage. Then multiply by 0.707 to obtain the RMS voltage. Then perform the power formula on the result.

Nobody interested?  Really?