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How to Measure Wattage

From rfrie–(at)–etcom.com Sat Dec 28 17:39:19 CST 1996
Newsgroups: alt.guitar.amps
From: rfrie–(at)–etcom.com (Robert Fries)
Subject: Re: Mark Garvins SF-BF suggestions.
Sender: rfrie–(at)–etcom13.netcom.com
Date: Sat, 28 Dec 1996 23:15:10 GMT

cmiy56–(at)–pcf.cc.utexas.edu (Thomas C. Clancy) wrote:

>>For the expected voltage at the speaker, the following formula will
>>be of assistance:
>>P =(Vp-p)^2 / (8*R)
>>which means: Power equals the peak-to-peak voltage squared, divided by eight
>>times the resistance.

>Well, they usually list watts as RMS, root mean squared.
>I don’t think this is the same as peak to peak voltage.

RMS IS root mean squared; anyway, this is the correct formula for deriving the
RMS power of a sine wave from a peak-to-peak voltage measurement through a
known resistance. It includes the conversion between a peak-to-peak
measurement and the RMS voltage.


Robert Fries