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Old 20th Jun 2021, 10:09 pm   #2380
Synchrodyne
Nonode
 
Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
Posts: 2,943
Default Re: The Audiophoolery Thread.

Quote:
Originally Posted by merlinmaxwell View Post
And I do agree a bit that watts RMS is a silly thing to do but doesn't change the value and can be a clarifying feature of a specification for the layman.
Would not the “RMS power” number be different to the “average power” number for a given situation?

For a sine wave voltage driving a resistive load, the resultant power curve is a sine wave of twice the frequency, displaced in the positive direction so that whilst it periodically touches zero, it never goes negative. Let’s say for a specific example the curve oscillates between zero and 10 watts, for an average of 5 watts. But the points on the curve above 5 watts have a bigger effect on the RMS value than those below 5 watts. One may do a very rough approximation using just the (nine) pi/4 points of a cycle, namely 5, 8.5, 10, 8.5, 5, 2.5, 0, 2.5, 5 watts. The sum of the squares is 332, the mean of that is 36.89, and its square root is 6.07. That indicates that the RMS power number will be a little larger than the average power number.

One could say that amplifier makers who quote RMS power but use the average power number are in fact missing an opportunity to inflate their published power outputs.


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