The Meaning of PMPO?

[Shahriar]

Hi everybody,

Can anyone tell me what is the meaning of "3000 watt PMPO"
or some other things that are written on Casset players,
if you take a look on the Speaker: "4 watt, 8ohm", if we imagine the calculation of PMPO power is based on the pick of voltage, it won't go so much....

ThanX in advance...

[audioguru]

Hi Shahriar,
PMPO means Peak Music Power Output and is a way to advertise false power numbers that are much larger than they really are.

Audio power from an amplifier to a speaker is usually measured by feeding a sine-wave into the amplifier and measuring the power output into a resistor load that has the same value as a speaker. A sine-wave is used because its RMS value has the same heating effect in an electrical heater as the same value of Direct Current.
Power ratings should be measured in RMS Watts.

The peak of a sine wave measures 1.414 times higher than the RMS value. So if they use a peak voltage measurement then the current is also 1.414 times higher (Ohm's Law). Since Power = Voltage X Current, then the peak power number is 2 times the actual true RMS power. "Peak"power is also called "Maximum" power.

An amplifier's power supply voltage sags when operating continuously and is fully loaded. Amplifier power should be rated when operating continuously with its rated load, as a test of its power supply and its ability to dissipate its heat that is created.
So if they use just a short pulse of sine-wave when measuring, and the advertisers call that short pulse "music", then the power number again will be higher than the actual true continuous power. "Music" power is also called "Dynamic" power.

There are many other ways that advertisers claim false power output numbers, as follows:
1) They don't state what the distortion reading is for their measurement. So they turn the volume up and the output is very badly distorted, but the power number is much higher.
2) They don't state what load resistance they used for their measurement. So they use a resistor that is much lower in value than normal speakers, which increases the output current, then the power number again will be much higher than the actual true power into a normal speaker.
3) They don't state the frequency range (20Hz to 20,000Hz) (that you can hear) that they used for their measurement. So they measure only at a middle frequency that gives the most power output, and they don't tell you that the actual power output at 20Hz and 20,000Hz is much less.

So your 3000 Watt amplifier may truely be only 30 Watts RMS per channel continuously into 8 ohms, with both channels driven, from 20Hz to 20,000Hz, at no more than 0.1% total harmonic distortion. If all conditions of their power claim are not stated like this, then their power output claim is false.

Speaker power ratings are also falsely claimed, and if they don't say "RMS Watts", then you should assume that it is "Peak Watts", and that the actual power number is half.