How much amplifier power do you really need?

[RebelMan]

@RebelMan - the Archimego link is interesting, although I am not sure about the merit of testing with test tones at specific frequencies.  For example, you might do the test with a 120Hz tone as suggested, and get a particular result.  However, with a specific speaker the result at 60Hz or 200Hz might be very different due to variations in the impedance curve.  So I think the proposed test might give you an indication of the power required, but only an approximation.  I guess you could try the test using real music, but then the results would depend on the response time of the voltmeter used.  I am not an expert with respect to voltmeters, but I suspect that the response time is typically somewhat less than would be ideal for this sort of test.

There are a few weaknesses with the testing as you noted but they can be overcome.  The static frequencies (120Hz or 220Hz) of the samples are intended to stabilize (maintain a constant) impedance for the given voltage reading so that an approximate power rating can be calculated.  This is why the step involving “some dynamic music that's not recorded loud nor unnaturally compressed” is required because it put’s your listening habits in the ball park of what voltage will actually be measured of the 120Hz or 220Hz samples in the following step.

It would be impractical to measure the entire frequency spectrum using static samples not to mention unnecessary.  Even though it’s true that other speakers may place greater demands at different frequencies, like 60Hz or 200Hz.  Despite the variations between speakers, the average power needed can still be reasonably determined using the 120Hz and 220Hz samples because it is typically around these lower frequencies where the greatest demands for power will occur.  As long as the listener factor’s in some additional headroom into the measured calculations (2dB-3dB) the amount of power for the job can be well determined.