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RMS



Original poster: "Albert Hassick by way of Terry Fritz <twftesla-at-uswest-dot-net>" <uncadoc-at-juno-dot-com>

Hi, Terry, Members.   I am still trying to figure out why many list
members say that RMS ratings have no value.  But if RMS ratings have no
significance, then why are they used so widely in audio equipment and
transducers? I always considered the RMS to be the safe 'clean' output
rating of power amps.  Any more power output than RMS will result in
excess heat/clipping/and distortion in the waveform that the human ear
can readily discern. And you know that you cannot run audio equipment (or
any thing else for that matter)at 'continuous ratings'  for long because
the equipment invariably begins break up at some point in time.  A case
in point,  I have several big old Electrovoice 15" SRO loudspeakers in my
"Leslie" twins, which are nothing more than a real big voice coil and
magnet that can more efficiently pump air volume.  They are rated at RMS,
which to a keyboard musician like myself would be the "clean" power
output of the transducer rated at about .6.  Then there is another rating
for the same transducer that rates continuous power at about .707. Then
last but not least we have the ultimate peak power output of the
transducer which in this case is 300 watts or a rating at peak of 1.0. 
Then they give a 600 watt 'peak to peak' rating. This also encompasses
the entire begining and end of one complete cycle of the 'sine waveform'
.  And I seem to remember vaguely from tech school about the values of
Sine,Cosine etc. tangents on the slide rule that were applied as
constants to a given electrical component at a true value as to the
amount of work that the component could give at varying levels of 
torque, load and failure rate that as a model could be calculated.  I can
try to scan and post some interesting scope readings that Electrovoice
made available showing the graphs that delineate the effect of the
different power levels and their effect on the copper voice coil at RMS,
continuous, and peak ratings.  I still think RMS ratings have relevance. 
If not, then why do all manufacturers of audio output amps and
transducers even bother to use the RMS value when rating their equipment?
Is it just a moot selling point?   Anyways, I think these ratings could
be similarly applied to say, neon transformers and Tesla secondary coils.
 AL.
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