>"What they are referring to is Continuous Average Power but calling it RMS
Power."
In 1974, the FTC regulated the use of power claims in audio amplifier
advertising. They required continuous sine wave testing if it was used in
an ad. For a while, audio amplifiers were described in terms of continuous
power, but as time went on, I noticed some manufactures were testing the
FTC's authority by re-invoking the "RMS Power" term.
Strictly speaking, "RMS Power" is a useless term. I learned the hard way
during a college physics course when I started quoting power in RMS terms.
During the classroom discussion the professor handed me the chalk and said:
"graph it."
So, I went to the blackboard and began drawing a sine wave and like most
sinewaves, equal amplitude was shown above and below a zero line. Then it
came: "stop." "What are you graphing?" My reply: "I'm graphing power -- I
am showing the difference between peak and RMS power." His reply: "Oh,
your audio amplifier at home produces negative power?" "Well no, but, I
mean..."
What I should have drawn was voltage and current, both described in terms of
peak and RMS then carefully take the root-mean-square in the proper order.
Since power is defined as energy divided by time, we can get awfully hung up
on these terms. If we reduce time toward a zero limit in the denominator,
what's the power?
Roy Lewallen, W7EL can explain it better than I:
http://eznec.com/Amateur/RMS_Power.pdf
Paul, W9AC
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