RMS Power?

@kijanki @almarg

Like to make it hard done you. I looked at all the references listed in the Wicki article. They can easily be clicked on above.

Half of them are referring to average power as a speaker sees it so as not to overheat the voice coil. That is indeed time averaged and all is well there.

However a speaker is not an amplifier. If you are betting on reference #8 being valid I will take $100 on that bet. Its pure fiction. http://www.hifi-writer.com/he/misc/rmspower.htm

Besides the admission at the top Most of what follows is an edited version of an email sent to me in April 2003 by the editor of Australian HI-FI. It was so well expressed I want to see it published, somewhere. So here it is.

Unfortunately the precise authorship has been lost due to rigorous cleaning of computer archives and trashed hard disks. I am told that much of it was probably from ’an electronics professor at Uni of NSW’, originally written as a letter to The Guide, an insert into The Age newspaper. Should the lost electronics professor seek to claim authorship (or even banish his words from this site), I would plead with him or her to email me at scdawson (at) hifi-writer.com.

Do you agree with this statement... By contrast, RMS (root mean square) power, would have to be defined as the square root of the time average of the square of the instantaneous power, since this is what ’RMS’ means.

FIrst thing wrong with that sentence is that if you take the square root of something you squared you get the same thing back. And what is the square of the instantenous power anyway.

Could a math major please come help us out. This is getting no where.

Though I love and contribute often to Wickipedia this article needs a lot of help. Did you not read the banner at the top of the article..

This article has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these template messages)This article may require cleanup to meet Wikipedia’s quality standards. (June 2011)This article possibly contains original research. (October 2008)

Please read this also. https://en.wikipedia.org/wiki/Talk:Audio_power

This is a "start class" article, please read the following https://en.wikipedia.org/wiki/Wikipedia:Content_assessment

Evidently you guys have not vetted this article at all. Heres another complaint I found on the talk page..   

 One thing this article does poorly is differentiate between speaker and amp ratings. Both are given "RMS" and "PMPO" ratings, but the conditions are different. The peak power of an amps is directly limited by their voltage rails and the minimum impedance of the loudspeaker. It is impossible to have a higher peak instantaneous power than this (unless due to reactance?) But for loudspeakers, the peak instantaneous power is not as clearly defined, and has to do with destruction of the speaker. — Omegatron04:48, 25 October 2007 (UTC)

Hi Roger,

I haven't read any of the Wikipedia article besides the paragraph Kijanki quoted in his post, and I don't consider whatever flaws the article may have to be relevant to Kijanki's point about terminology, especially given the further explanations of his point that I have provided.

I provided a link to the article simply because you requested it, and I was able to find it quickly.

Regards,
-- Al 

@almarg 

To be sure it’s clear, I absolutely did not say that "RMS power" varies as a function of time, although I can see how my statement might have been misread. I said that...

... what the words "RMS power" literally mean is the RMS value of a waveform that defines how power varies as a function of time.

(The "waveform defines how power varies as a function of time"; the RMS value of that waveform of course does not define how power varies as a function of time).

The paragraph above appears to me contradictory. First you say the waveform defines how power varies as a function of time. That would be instaneous power or instaneous heating, agreed? The RMS also defines how power varies as a function of time and defines its DC heating value. We needed that when Tesla won the "war of the currents" over Edison. How else were we to specify the voltage of the required sine wave.

As to the WIckipedia article i did find it and its many flaws. If you have the time, rather than defend kijanki do some reading yourself. There are 18 complaints about this article on the talk page of which 13 and 14 pretty much kill the whole thing. If kijanki learned this from articles like this then he is in the same mistaken camp. Shall we leave him there?

Would you care to tell me why an amplifier producing 100 watts RMS is any different than an AC generator producing 100 watts RMS. We are talking about sine waves here, that is all. 
 
And then please where 141 watts comes from. What kind of inbetween power is that to be called?

@kijanki . FWIW some respected manufacturers quote power output as for example 200 watts RMS. I am with atmosphere - the term is used,usefully, in the trade, for amplifiers. This is not hard for you to verify. Interesting post thanks. 

That would be instaneous power or instaneous heating, agreed?

Yes.

The RMS ... defines its DC heating value.

Yes.

The RMS also defines how power varies as a function of time ...

Well, if the waveshape is known, for example if it is known to be a sine wave, then of course one can determine the amplitude of that waveform from the RMS value. But I don’t see how my statement that you were referring to is contradictory, as you claimed. My statement, once again, being as follows:

... what the words "RMS power" literally mean is the RMS value of a waveform that defines how power varies as a function of time.

Honestly, I think you may be misreading my statement.

Would you care to tell me why an amplifier producing 100 watts RMS is any different than an AC generator producing 100 watts RMS.

The 100 watts is the same in both cases, of course. I have never said anything that is in any way to the contrary, and as far as I can recall neither has Kijanki.

And then please where 141 watts comes from. What kind of inbetween power is that to be called?

As I have said, it is the RMS value of a sinusoidal power waveform having a peak value of 200 watts.

There are 18 complaints about this article on the talk page of which 13 and 14 pretty much kill the whole thing. If kijanki learned this from articles like this then he is in the same mistaken camp. Shall we leave him there?

The fact that the article has numerous flaws has nothing to do with the subject matter of this thread. And Kijanki is a very experienced engineer who doesn’t need any such help.


I have nothing further to say on this matter.


Regards,
-- Al