RMS Power Question

[stormin]

I don't believe people buy high powered amps for volume(you know how loud the darn thing will play). It's the weight and authority at any volume thats a turn on!

And without a doubt amps aren't built the same. Just because she says shes got big watts doesn't mean she can play like it.

[ELA]

My pet peeve is saying,

"This is defined as the time integral of the instantaneous power over the measured time, divided by that time "

when you really mean average power or "RMS as it is commonly referred to whether or not it really exists.

[garyrc]

I think RMS served a purpose, and still does.

If some other, better, standard replaces it, so be it, but a vague nickname like "average" without adjectives, or without an always stated operational definition, will be misleading and exploited.

I remember the history of RMS, at least in advertising, differently:

In the late '50s, when I was in High School, ads would just state "power" with no adjectives attached. A good amp company, like McIntosh, might list "30 wts power at less that .5% distortion (60 wts peak)," but with no other measurement standards or techniques listed.

Sometime in the '60s, the field of audio advertising lost what little conscience it had, and started to say that what had been a 30 wt per channel amplifier was now a 60 wt amplifier (summing the power of the two channels, and advertising that), and then it got totally ridiculous: An amp a relatively honest company might rate at 30 wt per channel could be listed at anywhere from 75 wts to over 100 wts, by the average (i.e., dishonest) company depending on the kind of Hocus Pocus performed on the specs. The >100 wt figure might be @ 4 ohms (not the usual 8), Peak power, far beyond rated distortion, only at 1 KHz, with only one channel operating, therefore not taxing the power supply.

So, some kind of standard was called for! In the late 60s/ early 70s, the better companies could have settled on the continuous power of a sine wave, just below the point it began to show clipping, but they didn't. Perhaps they felt this would overestimate the usable amplifier -- who knows? They decided on the more conservative RMS power, which, my sources state, turns out to be .707 times continuous sine wave power, or 70.7%, naturally. It seems to me that this would be O.K., if everybody used it, but everybody doesn't.

My NAD C 272 power amps measure 171 w/ch continuous, are "rated" at 150 w/ch, and would be about (.707 X 171) 120 w/ch RMS. 120 wts into a single Kilpschorn (conservative sensitivity of 103 dB @ 1w @ 1M), by the way, would produce the equivalent sound pressure level of about 2400 w into a single speaker of typical sensitivity (90 dB @ 1w @ 1M).

[JohnA]

One of my pet peeves is the use (or misuse) of the term "RMS power". There is no such quantity as "RMS power".

Here's a good article which addresses the fallacy of using this over used expression.

http://www.hifi-writer.com/he/misc/rmspower.htm

He's just arguing symantecs...

Exactly!

RMS power IS and accurate description of RMS voltage x RMS

current. We all understand it that way. The arguement is

flat and is probably made because of a deficiency in his test

gear. It's also like arguing that "Kleenex" cannot be a

generic term for tissue. The public has defined as such.

My Harmon Kardon 430 reciever with just 24 watts

going to Klipschorns or RB35s is darn loud believe me even at 9AM

position on the volume dial.Just to add this the HK with 24 watts beats

my Yammy reciever with 8o watts.So not everything is as it seems.

Rick

That's

an invalid comparison, Rick. The preamp gain could easily be

different enough to cause the behaviour you describe.