Converting Average Power to "RMS Power"

Well, we drive on parkways and park on driveways. the macula in your eye us ed to be called the fovea. Double density floppy disks had half the capacit y or the high density disks.

Chalk it up to that.

Other than that "RMS power", no matter how nonexistant, is;

V * 0.707 ^ 2 / R

Might piss you off, but hey, what does a five pound can of coffee weigh the se days ? And they say you can use less, bullshit. Do that and you'll be dr inking dishwater. You are not supposed to see through coffee. And lowfat mi lk, no thanks, I got water. Go ahead "Oh they don't just add water", damn r ight, they are selling what they take out of it. Kinda like salt, they make more money from what they refine out of the salt than the salt itself.

This mythical RMS power is the result of the FTC trying to put a lid on rid iculous power claims back in the 1970s. It only has any real teeth when the power is stated in a certain way. Thye can rate a unit 2,000 watts on a 2 amp fuse, as long as they do not claim it as an actual, legal power rating. Note that the regulations do not apply to commercial or auto equipment, or to other than the front two main channels of a surround amp.

Now there are commercial amps lying their (_|_) off about power. Says 1,000 watts and I get into it and there is a little TO-220-15 package IC with a fan on it smaller than the one in my PC.

Same with cars. Do you really think they are 5,000 watts ? At 100 % efficie ncy it would have to pull over 400 amps. Even my 12 : 1 455 luxury racecar engine with a sloppy timing chain didn't pull that to start hot. For a car battery, 400 amps is a "cold cranking amps" rating. And alternators ? Chang e one lately ? They cannot handle anywhere near the current they used to, i t is right on the box "DO NOT ATTEMPT TO CHARGE A DEAD BATTERY AS PERMANENT DAMAGE WILL OCCUR, CHARGE BATTERY BEFORE USING ALTERNATOR. What ? Know wha t that means ? That means if you leave your light on and need a jumpstart, it might wreck your "new and improved" alternator. And that suits "them" ju st fine. (I think I prefer the old and shitty ones that worked reliably)

Now some of these guys DO have a second battery and alternator just for the amps, but still. Does anyone even know the gauge of wire needed to conduct 400 amps ? They got fat wires in them cars but not that fat.

So there is a formula for it though it does not exist. Well, neither does t he square root of -1.

[...]

Oh boy. Are you going to stir up a hornet's nest with that post! ;->

Don't get confused, RMS and AVG is not the same

While RMS is working in the 0.707 of the peak, AVG is in the 0.637 or there abouts.

Since Watts = 1 J(joule)/ Second we have this to look at;

Inject a 1 Hz tone into an amp from a clean sinewave source with

1 Volt Peak coming out going to a 1 ohm load. How do you measure Watts if Watts involves a J value over a 1 second period?

We know that the SINE wave isn't always at full level of 1 volt during that time period so that would indicate that we don't have 1 WATT of energy there, so what do you do ?

In retrospect that, you need to use voltage in your calculations to form a WATT value at some point. Wouldn't be logical to use RMS or AVG as the figure, one being a little different than the other?

Others will argue the fact that RMS power does not exist, I think they may have fallen off the cliff, turret, edge, mountain what ever it is they like to hang out on.

When I was schooled in electronics(Long time ago), starting at lower levels, through highschool, Post grade in a trade shop, college and adult lectures, there were never any discussion of RMS/AVG power ever not existing, because of the roots of how it is derived.

I just flip my eye brown when I hear otherwise and move on.

There are some twisted use of Peak, Peak To Peak power for sales only and they can get away with it. Only because in retrospect, it is valid, just the end user is getting fooled by the lack of reallity.

To add to this, doing power calculations in AC does bring in the phase angle but we get back to the power level of WATTS/second which then puts a fork into it, if you really think about it. So summing all the points of a sinewave when doing AC power, still comes out back to what we were talking about above.

P = I cos(V);do that for all 360 points or even closer if you wish and see where that leads to.

Just my opinion, really! :)

Jamie

Perhaps this might change your opinion:

-- Jeff Liebermann snipped-for-privacy@cruzio.com

150 Felker St #D Santa Cruz CA 95060 Skype: JeffLiebermann AE6KS 831-336-2558

Chalk it up to that.

Other than that "RMS power", no matter how nonexistant, is;

V * 0.707 ^ 2 / R

Might piss you off, but hey, what does a five pound can of coffee weigh these days ? And they say you can use less, bullshit. Do that and you'll be drinking dishwater. You are not supposed to see through coffee. And lowfat milk, no thanks, I got water. Go ahead "Oh they don't just add water", damn right, they are selling what they take out of it. Kinda like salt, they make more money from what they refine out of the salt than the salt itself.

This mythical RMS power is the result of the FTC trying to put a lid on ridiculous power claims back in the 1970s. It only has any real teeth when the power is stated in a certain way. Thye can rate a unit 2,000 watts on a

2 amp fuse, as long as they do not claim it as an actual, legal power rating. Note that the regulations do not apply to commercial or auto equipment, or to other than the front two main channels of a surround amp.

Now there are commercial amps lying their (_|_) off about power. Says 1,000 watts and I get into it and there is a little TO-220-15 package IC with a fan on >it smaller than the one in my PC.

There seems not to be any real standard for audio power.

Someone needs to define a standrd something like input a sine wave into the amp and get so much RMS volts (undistorted or a % distortion) across a resistive load for a period of time like 60 seconds. Do that at several frequencies across the audio range with one being the lowest and another the highest frequency the amp is rated for.

The 5 pound bag of sugar is now 4 pounds and the 2x4 boards seem to be srinking along with the thickness of plywood. A number of years ago I bought some "2x4"s and nails that just would not go all the way through them when the 2" sides were layed on top of each other. A while back I bought some new 2x4s and the same nalis went through by about 1/16 of an inch.

Mother had recipeas that called for a can of something. Now the size of the cans are smaller and difficult to convert so a cake comes out the same.

You are all wrong about those amps for cars. All you need to pull 400 amps from 60 watt 14 volt alternator is 4 gauge oxygen free gold plated Litz wire. Don't be fooled by claims that other than Litz wire can be used. And the gold must be 26 carat, that 24 carat stuff just won't pass the current without high losses. Airick

The reality of all this is, a clean sinewave at 1 Hz over a 1 second period to get WATTS is the average of the sinewave.

If you sum all values from the base line to the peak of a sinewave then divide by the number of samples you used, you'll get 63% or 0.634 which is really not too far from using RMS which is 0.707.

Although Technically, RMS is really not a proper measure in this case because it is not truely accurate for use of power but the average is. Like I said, if some one is using the RMS term for power over the average it really isn't that much more, even though its a little higher than it should be.

In Ac power measurements, you specify the phase angle, however, that is only a fraction and must be considered when calculating Watts. You need to consider the whole frame time which is why using the average is the apperent answer.

I prefer to blow it off and just accept the fact that I know the difference and that isn't enough to start a war over.

So when some one says RMS power, * that by 0.9

now to really thow you off, the RMS of a squarewave is the same as the Peak and also the average is the same.

And if you have triangles, the RMS = Pk*0.577 and AVG := 0.5 * PK.

You can see it's obvious there with the AVG how that works out.

Go figure :)

"RMS power" is a misnomer and doesn't represent anything useful (unlike RMS volts and RMS amps). It sounds to me like it's YOU who's fallen off the cliff of reality on this one. ;->

** The term "watts RMS" has been used in relation to audio amplifier specs for many decades, since the 1960s at least.

It is a shortened expression which indicates the long accepted method of au dio power measurement using a continuous sine wave into a resistive load. T he figure quoted is AVERAGE watts.

Other tests exist using either the peak value of the sine wave or short bur sts of sine wave, generally know as "peak power" or "music power" - the fig ures quotes are not average watts, but represent the maximum power availabl e on a short term basis for music and speech.

In nearly all cases,"RMS power" and "Watts RMS" have the same meaning.

Those who say otherwise must think that "Steak Sauce" contains actual steak .

... Phil

What a puts...

You don't get out much do you?

Jamie

There is a very good output measurement called voltage. Power is just a byproduct. Power more related to linear cost of product. Forget power.

Greg

You are correct on 'average' power but SO WHAT? Measure the average power a nd tell him it's RMS power. The method you're using is what all the reviewe rs use so where is the problem? You're being a 'purist' and it will get you NOTHING. Don't shoot yourself in the foot and then complain about the pain .

FWIW I have a little Technics receiver that the manual says is 40 Watts / c hannel. When I ran it up it sure SOUNDED like more than 40 Watts. When I me asured the power supply Voltage of +/- 42 I had my answer. It IS more than

40 Watts under 'music' conditions. Am I upset because the 'lied' about the power? Nope, I'm just fine with it.

/ channel. When I ran it up it sure SOUNDED like more than 40 >Watts. When I measured the power supply Voltage of +/- 42 I had my >answer."

Yup, 42 volt rails will give you a hair over 100 WPC, as long as they maint ain 42 volts. But you do have it for a matter of milliseconds. that is call ed dynamic headroom. Some manufacturers gave that rating and it was based a on a short term bust of a sine wave, specified in milliseconds. However the re is another factor about these "Old Marantz Watts" or OMWs as I like to c all them sometimes.

The older amp topologies and the devices available limited them somewhat be cause of non-linearities. These happened worst when you got near clipping. Bottom line, your 40 WPC Tecnics or whater really IS about 75 WPC, but at l ike 2 or 3 % THD.

Later, they made really good square waves. By that I mean they got the line arity closer to the rails and that is why the older stuff sounds better. A

40 WPC amp now might only really be 50 WPC, because they could keep it line ar though more of its high power range. That's why if I still had my old Ma rantz I could sell it for a grand, which I do believe is more than it cost new. (but not by all that much)

But yes, when you get older amps and receivers, don't be surprised if they even have double the power claimed. That would be 3 dB, that is all. The on es, maybe I can find some, that gave dynamic and clipping headroom specs co uld showya. If it has 1.8 dB clipping headroom and then on top of that 2 dB dynamic headroom, that amp is going to sound louder than its RMS power rat ing would allude to.

Only thing you can do is crank it up and enjoy, and hope your speakers can handle it. You really can't sue them for putting too much power in the amp.