Dear Friend,

Can you tell me how to calculate RMS and PMPO of an audio system ? It is very much confusing for me !

Thank you,

Have a nice day !

 

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.

 

I can't understand what you say ,please tell me in details if you like !

 

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.

__________________
Uncle $crooge

 

RMS is the true judge of power for your stereo.

Peak (as joked about above) is a number plucked out of the air by the manufacturer to make their product look good

I've got a set of computer speakers which run at around 20W RMS but are advertised as 2000 watt peak

 

Have you any formula to calculate RMS of audio system ? If you have, It will be very helpful to me !

 

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.

__________________
Uncle $crooge

 

search these forums. iirc there is a looong thread on exactly this

long story short RMS is the only figure to look at, if you want to measure yr e-peen against PMPO well good for you. Real men don't need to measure

__________________
Nothing is impossible.
Once a problem is realised, the rest is just details

 

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!.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

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!.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

At least, RMS as a formulae, Root Mean Square...

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.



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...

 

...And also has no meaning unless you specify a standard function or signal, ie a sine wave...

 

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.

__________________
Uncle $crooge