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RMS is very simple, just play a sine wave through a load and see when the waveform starts to clip. Back off a smidge, and calculate power based on voltage and load resistance.
For PMPO, take the above measurement, and multiply by an integer chosen so that is inversely related to the intelligence of your consumer.
heh... PMPO really has no meaning, basically ignore it. It's just a random marketing number. If you have a speaker rated in PMPO slowly back away from it and look elsewhere (unless you don't care what it sounds like...)
PMPO is Peak Music Power Output.
Peak power is double or more the real power.
Music Power is instantaneous power for a very short duration before the power supply voltage sags.
Marketers test their lousy products with a supply voltage that is higher than normal, using a load impedance that is lower than normal then turn up the volume so that a horrible-sounding 10% clipping distortion is produced.
Many car radios are advertised as "200W". They produce only 14 real Watts per channel.
The RMS power is the continuous power (not just for a moment) at a low distortion and with a normal supply voltage and load impedance.
Feed the amplifier a sine-wave in the audio frequency band and turn up the volume until clipping occurs, then reduce it a little. Measure the RMS voltage with an audio AC voltmeter (an ordinary voltmeter measures low frequencies only). Calculate the power by V squared divided by the load resistance.
Happened to notice an advert just the other day, it said "2000W audio system", I read on (while laughing!) and it said further down (2000W PMPO, 8W RMS).
The ONLY power output worth reading is RMS, anything else is completely useless and imaginary!.
RMS is difficult to calculate for real audio systems because frequency responce is never perfectly linear. If you want to accuratly represent the power of the system it should be done using either real audio samples or further averaging of the RMS power at all audio frequencies.
Remember, Wikipedia is your friend. The entries for RMS and PMPO contain all the information you need.
Hardly, RMS is good because it's so simple to measure, and so accurate to compare across systems - generally you would measure at a specific frequency and distortion, such as 100W at 1KHz and 0.01% distortion.Or a better method which gives a frequency range - like 100W at 0.01% distortion from 20Hz to 20KHz.
But really all you really need is the spot frequency at 1KHz, who's interested if the amp is 100W, 98.027W, or 104.76W - basically you would call them all 100W!.
Lets say the output is a time varying function F(t), then the RMS of that function Frms(t) is:
Frms(t) = Sqrt( Sqr( F(t) ) )
If you sum that, or integrate for an continuous signal (ie audio), over one period, you can use that to calculate power output. P = V^2/R. All that the squaring and rooting does, is to ensure that it's always a positive number. Mathematically Frms(t) = |F(t)| is the same, at least for a discreet functions.
**broken link removed**
Still, thought, as has been mentioned, it is BS without mentioning distortion. One such figure is THD - Total Harmonic Distortion, thought I have no idea what it's definition is...
If you turn up the volume way too high then the sine-wave becomes a square-wave due to clipping in the output stage.
Then the measured power output is double the RMS power that is at just below clipping. The harmonics have the same amount of power as the fundamental sine-wave.
Many speakers have a power rating only at a single frequency.
Many speaker power ratings are the false ones not with sine-waves and not measured in continuous RMS.
Look at the links. One 2000W speaker has a rating of only 4W RMS.
Are those car speakers? I guess the auto industry (though there is legislation pending) is not under the same rules as the rest of the consumer electronics industry is about power rateings. RMS power using a standard set of tones is required on home audio equipment.
Speakers have a mechanical power rating that is different from their thermal power rating.
At low frequencies a woofer can "bottom out" and destroy itself at a power that is much less than the power to burn it out at higher frequencies.
The thermal power rating for speakers has a time duration that frequently is not listed. It takes a few seconds for a woofer to burn out and milli-seconds for a tweeter to burn out.
The Jackhammer car sub-woofer speaker weighs 369 pounds. It is truthfully rated at 6000W RMS. In Google there are videos about it being installed and tested.
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