PMPO - The term again

Anyway here is one of the best explanations of PMPO (from one of the websites)

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**Power Ratings In The New Millennium (and Beyond)**

Much has been said - and will no doubt continue to be said - about amplifier power ratings. There has been a disturbing tendency over the last few years to revisit the bad old days where terms such as PMP (Peak Music Power) and PMPO (Peak Music Power Output) have once again raised their ugly heads.

Admittedly, these 'new' power rating are not used by hi-fi manufacturers, other than in the low-end equipment. These new terms are soundly (no pun intended) based on the science of marketing, having nothing to do with actual science or physics. PMPO is mathematically expressed as

PMPO = PREAL * k

where PREAL is the real power as calculated by the formula below, and k is a constant whose value is approximately equal to one's grandmother's age, divided by the square root of the distance from the office to the advertisement writer's normal place of abode - measured in millimetres, inches, furlongs, statute miles or pounds per square inch (as appropriate) to provide the number you first thought of.

In the unlikely event that the value of k cannot be calculated from the above formulae to provide a totally meaningless (but plausible-looking) final result, a randomly selected value of between 20 and 75 should be used.

An alternative (and equally useless) way to measure PMPO is to multiply the supply voltage by the instantaneous short-circuit current from the amplifier - the amplifier does not have to survive this test, and the current only has to exist for around 1us to obtain a satisfactory rating ...

PMPO = Vsupply * Ipeak

where Vsupply is the total supply voltage and Ipeak is the instantaneous (and possibly destructive) short-circuit current. Given that a 12V plugpack (wall wart) supply may be capable of perhaps 30A for a microsecond or two, this is perfectly acceptable, and gives a PMPO of ...

PMPO = 12 * 30 = 360W

This is a perfectly acceptable figure, and may be used with gay abandon (in the hope that someone will actually believe it).

Thus (using the first equation) we can now compute the power of an amplifier which manages to impress a voltage (which need not be sinusoidal - an harmonic distortion of up to 400% is considered perfectly acceptable - albeit mathematically impossible) of 8V across a speaker of 8 ohms. Actual (real) power may be calculated by

Preal = VRMS * IRMS

Since 8V across an 8 ohm load provides 1 Ampere of current, we obtain

Preal = 8 * 1 = 8 Watts

or, using the power formula

Preal = V / R (Voltage squared, divided by impedance in ohms)

thus

Preal = 8 / 8 = 64 / 8 = 8 Watts

PMPO may now readily be calculated, using a median value of 45 which results in a totally satisfactory advertising power (Pa) of

Pa = 8 * 45 = 360W PMPO

You will notice that by fiddling with the figures to suit my goal, I have been able to make the PMPO figure the same, using two completely different 'test methods' and 'formulae'. Therefore, the figures must be correct, and the result must therefore be genuine .

What ? You think I'm lying ? Well spotted gentle reader - the whole process is unadulterated horse-feathers.'