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Posted by deepti (202.9.131.235) on March 02, 2003 at 12:25:53:
In Reply to: Re: pmpo vs rms posted by KC on December 28, 2002 at 23:31:17:
: : : Time and time again I see people referring to r.m.s. power, and time and time again I see people correcting, as I am about to do yet again, the confusion.
: : : The product of r.m.s. voltage and r.m.s. current, (i.e. Vrms x Irms), is equal to AVERAGE power, NOT r.m.s. power. There is NO SUCH THING as r.m.s. power.
: : :
: : : Yet people doggedly cling to their misconceptions and propogate the myth. Part of the trouble is that no-one likes to have their cherished beliefs challenged and most of them refuse to accept that they could, even possibly, be wrong.
: : RE: Boy that really is bad news to those of us that have spent years in the indusry using RMS power meters made by such pervayers of misinformation as Hewlett-Packard for example. Which reference material are you quoting that indicates there is no such thing as R.M.S. power?
: Try using E2/R instead of ExI to get power. A typical example is an amplifier providing 20 vrms into an 8 ohm load. That will give you 20x20 (400) / 8 = 50 watts RMS into 8 ohms. This is a federally mandated standard as outlined:
: Back in the 1960's, audio equipment manufacturers and dealers were having a hey-day with power specifications, rating their little 20-watt-per-channel amplifiers as having 80 watts. Here's what they would do. Rather than using the RMS voltage of the amplifier output which might be 12.6 volts driving the 8 ohm speaker, they would use the peak voltage (17.9 volts) and figure power that way: (17.9)(17.9)/8 = 40 watts. And then they'd add both channels together: 80 watts. Sounds high-power in the advertizing, but in actual practice was misleading.
: The Feds finally got into their faces and made everyone rate their equipment in RMS power into 8 ohms for each channel.
: Ok, now I feel better.