Nobody interested? Really?
RMS Power?
I often see power specifications like "100W RMS". There is no such thing as RMS power. Of course, you can calculate RMS value from any curve, including power curve, but it won't represent anything. "Real" power representing heat dissipated in resistive load is "Average Power" Pavg=Vrms*Irms. In case of sinewaves Pavg=0.707Vpeak * 0.707Ipeak = 0.5Ppeak, or Ppeak = 2Pavg.
Term "RMS Power" or "watts RMS" is a mistake, very common in audio.
Term "RMS Power" or "watts RMS" is a mistake, very common in audio.
- ...
- 59 posts total
Post removed |
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. |
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 . |
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 ! |
- 59 posts total