What characterizes a powerFET for audio use?

[Jeff Liebermann]

On Thu, 2 Jan 2014 12:22:44 +1100, "Phil Allison" <phil_a@tpg.com.au>
wrote:

"Jeff Liebermann"

Ok, I yield to a higher authority. Heating power is average power:
http://www.eznec.com/Amateur/RMS_Power.pdf
However that doesn't stop nearly everyone from specifying RMS power.

** There is no such quantity as " RMS power " if you are so stupid as to
interpret the term literally.

Which term should be interpreted non-literally? "RMS" or "power"?

Assuming a stable resistance load (i.e. no light bulbs), the RMS power
is simply the square of the RMS voltage divided by the resistance.
Seem literal enough for me.

So, why do people buy true-RMS voltmeters?

** To get " true RMS " volts of course.

Very good. But since there doesn't seem to be any correlation with
heating power (despite using a thermocouple to do the measuring) and
RMS volts or watts, what does the meter indication on a true RMS
voltmeter actually mean? Or is it just a mathematical abstraction?

If they don't measure anything useful,

** The RMS value of a voltage or current could hardly be more useful.

Useful for what? Obviously not heating value. Anything I missed?

> My god, you are SOOOOOO illiterate and SOOOOO retarded.

Very perceptive and partly true. I don't take you literally but the
timing on my car is not retarded.

<http://www.aqdi.com/rms.htm>
"You have read that there is no such thing as "RMS power."
Technically, you are right. However, over the years the term,
regarding audio gear, has come to be applied to the measurement
technique outlined above, so we use that language here, rather
than terminology with which the customer is unfamiliar. Yes,
the computation is mathematically an integral of the instantaneous
power."

<https://www.google.com/#q="RMS+power">
681,000 hits on "RMS power".

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Wond]

On Wed, 01 Jan 2014 18:49:17 -0800, Jeff Liebermann wrote:

http://www.eznec.com/Amateur/RMS_Power.pdf> On Pg 6 it says:
"The RMS value of power is not the equivalent heating power and, in
fact, it doesn't represent any useful physical quantity."
and:
"The RMS power is different than the average power, and therefore
isn’t the equivalent heating power. In fact, the RMS value of the
power doesn’t represent anything useful."

It would seem that the author finds average power different from, more
useful than, and closer to heating power. Perhaps we should change the
name from "true-RMS voltmeter" to "true heating average voltmeter"?

"So it is written, so it shall be."
(Ramses in the CB DeMille version of the 10 Commandments).

(snipped)
ISTR it used to be a DC equivalent thing, ie, you need 6Vrms ac to
operate a 6VDC light bulb at spec.
I think Leak confused the issue when he branded those wonderful
audio amplifiers "RMS", thus putting the term in the realm of marketting.

 

[William Sommerwerck]

"Jeff Liebermann" wrote in message
news:quc9c95b8el5pqevbftgm87mqs5cf8akrh@4ax.com...

OK, I yield to a higher authority. Heating power is average power:
http://www.eznec.com/Amateur/RMS_Power.pdf
However that doesn't stop nearly everyone from specifying
RMS power.

Unfortunately, no.

So, why do people buy true-RMS voltmeters? If they don't measure
anything useful, why bother?

A fair question. Apparently, there was a time when AC power had a significant
percentage of harmonics (perhaps it still does), and engineers wanted to know
its "true" heating effect.

 

[William Sommerwerck]

"Jeff Liebermann" wrote in message
news:nsj9c95bm2ec1giaju7tj0gc43ne25s007@4ax.com...

<http://www.eznec.com/Amateur/RMS_Power.pdf>
On Pg 6 it says:
"The RMS value of power is not the equivalent heating power and,
in fact, it doesn't represent any useful physical quantity."
and:
"The RMS power is different than the average power, and therefore
isn’t the equivalent heating power. In fact, the RMS value of the
power doesn’t represent anything useful."

It would seem that the author finds average power different from,
more useful than, and closer to heating power. Perhaps we should
change the name from "true-RMS voltmeter" to "true heating average
voltmeter"?

Jeff, you're misreading this. The author is saying //exactly// what I said.
(It's unfortunate he doesn't use a sine wave for his example, but the math
would then require integral calculus.)

Average power /is/ the heating power. (The rationale is that a resistor's
temperature is determined by the average power applied to it.) When we know
the RMS value of any repetitive waveform, we can compute its heating power by
squaring that voltage (current) and dividing (multiplying) by the resistor's
value.

Voltmeters (of all sorts) are usually calibrated to show the RMS value //of a
sine wave//. If the waveform differs, the value shown is wrong. One of the
advantages of a true-RMS meter is that all readings are "equivalent" in an
easily-comprehended way, regardless of the waveform -- even if that
"equivalency" has little practical usefulness. (If you want to know the
details of a waveform, you use a 'scope.)

I remember a Popular Electronics quiz with questions about how a voltmeter (at
that time, a moving-coil device) would read, depending on the waveform
supplied. A key point was that the deflection was proportional to the average
current flowing through the coil, but the meter was usually calibrated for the
RMS value of a sinewave.

 

[dave]

On 01/01/2014 05:22 PM, Phil Allison wrote:

"Jeff Liebermann"

Ok, I yield to a higher authority. Heating power is average power:
http://www.eznec.com/Amateur/RMS_Power.pdf
However that doesn't stop nearly everyone from specifying RMS power.


** There is no such quantity as " RMS power " if you are so stupid as to
interpret the term literally.

So, why do people buy true-RMS voltmeters?

** To get " true RMS " volts of course.


If they don't measure anything useful,


** The RMS value of a voltage or current could hardly be more useful.

My god, you are SOOOOOO illiterate and SOOOOO retarded.

The question was why is audio power spec is half that of DC on/off
capability. It is because the device stays on all the time and because
the audio waveform causes more heating. Worry about the labels and fight
all you want.

 

[dave]

On 01/02/2014 04:05 AM, William Sommerwerck wrote:

"Jeff Liebermann" wrote in message
news:nsj9c95bm2ec1giaju7tj0gc43ne25s007@4ax.com...

http://www.eznec.com/Amateur/RMS_Power.pdf
On Pg 6 it says:
"The RMS value of power is not the equivalent heating power and,
in fact, it doesn't represent any useful physical quantity."
and:
"The RMS power is different than the average power, and therefore
isn’t the equivalent heating power. In fact, the RMS value of the
power doesn’t represent anything useful."

I remember a Popular Electronics quiz with questions about how a
voltmeter (at that time, a moving-coil device) would read, depending on
the waveform supplied. A key point was that the deflection was
proportional to the average current flowing through the coil, but the
meter was usually calibrated for the RMS value of a sinewave.

Why do you keep quoting notes from Llewelen? He wrote a modeling program
for wire antennas. We are talking about FETs.

I think AVG = RMS only if waveform is pure sinewave. Otherwise you must
use calorimeter or thermocouple to find true RMS.

 

[Bob F]

Phil Allison wrote:

Leiberman - you are the stupidest, most retarded, constantly lying
fuckwit on the NG.

Get cancer and fucking DIE !

Plonk!

 

[William Sommerwerck]

"dave" wrote in message
news:B4GdnYZ19saY4VjPnZ2dnUVZ_tudnZ2d@earthlink.com...

I remember a Popular Electronics quiz with questions about how a
voltmeter (at that time, a moving-coil device) would read, depending on
the waveform supplied. A key point was that the deflection was
proportional to the average current flowing through the coil, but the
meter was usually calibrated for the RMS value of a sinewave.

Why do you keep quoting notes from Llewelen? He wrote a modeling
program for wire antennas. We are talking about FETs.

Who is Llewelen?

I think AVG = RMS only if waveform is pure sinewave. Otherwise,
you must use calorimeter or thermocouple to find true RMS.

RMS and average are the same only for square waves. True RMS can be computed
by analog circuits, one of which made its way in dbx devices.

 

[William Sommerwerck]

"dave" wrote in message
news:JIidnfhj6vc651jPnZ2dnUVZ_h2dnZ2d@earthlink.com...

The question was why is audio power spec is half that of DC on/off
capability. It is because the device stays on all the time and because the
audio waveform causes more heating. Worry about the labels
and fight all you want.

Exactly.

 

[Phil Allison]

"Bob Fuckwit ".


** Get cancer and fucking DIE !

Fuckwit plonker!

 

[Phil Allison]

"dave" <ricketzz@earthlink.net>


** FOAD - you autistic IDIOT !!!!!!

 

[Phil Allison]

"William Sommerwanker is a bullshitting ass."

So, why do people buy true-RMS voltmeters? If they don't measure
anything useful, why bother?

A fair question.

** Wrong - it's a fuckwit question.

Apparently, there was a time when AC power had a significant percentage of
harmonics (perhaps it still does), and engineers wanted to know its "true"
heating effect.

** Nonsense.

Any "moving iron" amp meter inherently reads "true RMS" values and they are
as old as the hills.

True RMS meters are mostly used to measure irregular signals like noise and
distorted current waveforms that exist with AC to DC supply conversion.

There is no way to compute these values ( from the peak or average rectified
value) as there is with sine or other regular waveforms.


..... Phil

 

[Phil Allison]

"Jeff Liebermann"


Leiberman - you are the stupidest, most retarded, constantly lying fuckwit
on the NG.

Get cancer and fucking DIE !

NOW !!!!!!!!!!!!

 

[Jeff Liebermann]

On Thu, 2 Jan 2014 11:21:15 -0800, "William Sommerwerck"
<grizzledgeezer@comcast.net> wrote:

Why do you keep quoting notes from Llewelen? He wrote a modeling
program for wire antennas. We are talking about FETs.

Who is Llewelen?

Author of Eznec antenna modeling software:
<http://www.eznec.com>



--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Maynard A. Philbrook Jr.]

In article <nsj9c95bm2ec1giaju7tj0gc43ne25s007@4ax.com>,
jeffl@cruzio.com says...

You are the stupidest, most retarded, constantly lying fuckwit on the NG.
Get cancer and fucking DIE !

You'll not get rid of me that easily. I've already had cancer and
Obamacare promises to keep me alive forever.

I'll be more than happy to put a Obama chia pet on your grave stone
for you.

I see Amazon has a deal for 28 bucks..

Jamie

 

[Maynard A. Philbrook Jr.]

In article <B4GdnYZ19saY4VjPnZ2dnUVZ_tudnZ2d@earthlink.com>,
ricketzz@earthlink.net says...

On 01/02/2014 04:05 AM, William Sommerwerck wrote:
"Jeff Liebermann" wrote in message
news:nsj9c95bm2ec1giaju7tj0gc43ne25s007@4ax.com...

http://www.eznec.com/Amateur/RMS_Power.pdf
On Pg 6 it says:
"The RMS value of power is not the equivalent heating power and,
in fact, it doesn't represent any useful physical quantity."
and:
"The RMS power is different than the average power, and therefore
isn?t the equivalent heating power. In fact, the RMS value of the
power doesn?t represent anything useful."

I remember a Popular Electronics quiz with questions about how a
voltmeter (at that time, a moving-coil device) would read, depending on
the waveform supplied. A key point was that the deflection was
proportional to the average current flowing through the coil, but the
meter was usually calibrated for the RMS value of a sinewave.

Why do you keep quoting notes from Llewelen? He wrote a modeling program
for wire antennas. We are talking about FETs.

I think AVG = RMS only if waveform is pure sinewave. Otherwise you must
use calorimeter or thermocouple to find true RMS.

AVG and RMS is not the same with sine waves..

Avg = 2/pi * peak Voltage.

And RMS is simply sqr( VP^2 / 2).
you'll notice the root his to look for the square not the
average of total voltage for example.

One can shorten that to say RMS = Vp * .707

Just think of a half round circle an draw and find the
area where you can evenly fit a square box in that half circle,
the value will be .707 times the Peak value of that circle.

Averaging ends up to be 2/pi = 0.637 * the peak voltage which
obviously gives you a different number..

And of course, no matter how you slice it, square waves at 50%
duty give you the same all around. AVG and RMS = peak.. cause there
is no slope in time for the avg and the nice square box I stated
fits perfectly in the already square wave for RMS. etc..

Jamie

 

[Phil Allison]

"Maynard A. Philbrook Jr."

And of course, no matter how you slice it, square waves at 50%
duty give you the same all around. AVG and RMS = peak.. cause there
is no slope in time ...

** Too complicated.

Q. When you ( full wave) rectify a square wave what do you get?

A. DC.

With DC, the average, peak and RMS value are the same.

Is any proof really needed ?




...... Phil

 

[Phil Allison]

"Maynard A. Philbrook Jr."

And of course, no matter how you slice it, square waves at 50%
duty give you the same all around. AVG and RMS = peak.. cause there
is no slope in time ...

** Too complicated.

Q. When you ( full wave) rectify a square wave what do you get?

A. DC.

With DC, the average, peak and RMS value are the same.

Is any proof really needed ?




And where was I disputing that?

** Yawnnnnnnnnn - wot a stupid straw man fallacy.

Read what I dam well wrote - fuckwit.



.... Phil

 

[Maynard A. Philbrook Jr.]

In article <bimdj1F69i3U1@mid.individual.net>, phil_a@tpg.com.au says...

"Maynard A. Philbrook Jr."

And of course, no matter how you slice it, square waves at 50%
duty give you the same all around. AVG and RMS = peak.. cause there
is no slope in time ...

** Too complicated.

Q. When you ( full wave) rectify a square wave what do you get?

A. DC.

With DC, the average, peak and RMS value are the same.

Is any proof really needed ?




..... Phil

And where was I disputing that?

Jamie

 

[Shaun]

"Phil Allison" wrote in message news:bik2r7FlgbdU1@mid.individual.net...

"Jeff Liebermann = retarded asshole "

Ok, I yield to a higher authority. Heating power is average power:
http://www.eznec.com/Amateur/RMS_Power.pdf
However that doesn't stop nearly everyone from specifying RMS power.

** There is no such quantity as " RMS power " if you are so stupid as
to
interpret the term literally.

Which term should be interpreted non-literally?

** The term " RMS power " of course -

I thought ...

** No you didn't - cos you are incapable of thought.

The quotation marks made my words quite *impossible* to misinterpret.

Very good. But since there doesn't seem to be any correlation with
heating power (despite using a thermocouple to do the measuring) and
RMS volts or watts,

** Quite wrong - there is a very close connection.

( snip more TOTALLY IRRELEVANT SHIT )

Leiberman - you are the stupidest, most retarded, constantly lying fuckwit
on the NG.

Get cancer and fucking DIE !


Hey Phil;

I used to work at an Industrial and Instrumentation repair and Calibration
shop that was licensed by Beckman to repair and calibrate there DMMs. In
the good ones, the RMS converted used a thermal method to determine RMS
Voltage and Current. That was 18 years ago and I don't remember any details
except that they used thermal measurement on a heated element. I have
compared the reading on the Beckman - Then Wavetek - now I don't know if
anyone is still making them, to a Fluke RMS DMM at 60 Hz and DC and the
readings matched.
I have always heard that if you really want to know the real value, you have
to buy an RMS meter.


Shaun