From bw@ashbysolutions.com Mon Jul 02 18:38:03 2012
Subject:Re: Alto amps - Peak Power and RMS

Hi Rock,

Yes and no. Peak is 1.414 x RMS *of a sine wave only*, and that's for
voltage, not power. So yes, if Amp A can produce 1V RMS of clean (<0.1%
HD) sine power, it can also produce 1.41V 'peak' and 2.83V
'peak-to-peak'. I did make a mistake: my earlier calculations should
be 2x for peak *watts* (1.414 *1.414), and 8x for peak-to-peak *watts*
(2.828 *2.828), because watts are proportional to the square of the
output voltage or current.

The term 'peak watts' when writings specs means different things to
different manufacturers, but generally tends to be 2-5x the RMS output.

The problem is, most musical sounds aren't composed of single,
continuous sine waves, so the ability to produce say, 100W of clean sine
power doesn't give much insight into the ability to produce typical
music. The simplistic approach would be to say that if an amp can
produce the 28.3V p-p of a 10V RMS sine wave, then it should also be
able to handle *any* transient that has a peak-to-peak measurement of
28.3V. This isn't always the case, though, because an amp might be able
to track the sine wave's comparatively slow changes, but not the punch
of a kick drum at the same magnitude; its ability to do so would depend
on other factors like the 'stiffness' of the power supply, the
amplifier's damping factor, etc.. This is what the IHF was trying to
convey with their music power ratings, but it turned out that it was
pretty easy to cheat on the math.

I think the pink noise spec used for wide-range speakers is on the right
track, although even that method has shortcomings for some musical
needs. A perfect example is the Hammond Organ, which is mostly midrange
in spectrum, and *does* tend to put out continuous tones (rather than
transients).

Regards,

-BW

Bruce Wahler
Ashby Solutions.com^(TM)
bw@ashbysolutions.com
http://music.ashbysolutions.com
877.55.ASHBY (877.552.7429)

On 7/2/2012 9:13 PM, rrockkey wrote:
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