On Fri, 07 Jan 2005 19:18:57 GMT, "Leo Lichtman"
wrote:


"Vaughn" wrote: I disagree. In my experience, Watts RMS is the ONLY
meaningful measurement of the power output capability of an amplifier.
^^^^^^^^^^^^^
Vaughn, lets look at this one step at a time. RMS stands for "root mean
square." If you look at the equation for power, it is I^2 R, or E^2/R. For
DC that is very simple, but for AC, it is necessary to use an average figure
for E or I that gives the correct power. The way to get that average is to
square the instantaneous voltage or current at every instant, take an
average of the squared values, and take the square root of the
average--hence: root (meaning square root) mean (same as average) square.

The wattage rating or operating point of an amplifier is already in power
units. It is perfectly OK to talk about "average power," or "peak power,"
but RMS power suggests doing something to the numbers that has already been
done. To square, average, and take the square root again would produce a
figure that has no meaning. That's my gripe.


Agreed that average power is more useful and descriptive than RMS
power. For unvarying power output they're the same. Peak output
is also a useful measure, though. Two amps with identical average
power ratings may differ in the peak power they can deliver without
clipping on transients like rim shots on a snare drum. Average
power rating is determined by the amp's efficiency and ability to
dissipate heat. Peak power would be governed by available supply
voltage and the output devices used. The length of time that it can
deliver peak power without overheating is determined by the thermal
mass of the heatsink.