"Bob Cain" wrote in message

Randy Yates wrote:

Not. Get a clue, people. Doppler is a *PHYSICAL PHENOMENOM* that
WILL happen whether or not you decide it can WHENEVER a sound wave
source and observer are moving relative to each other. Period. This
isn't open for debate.

Randy has spoken. Without one shread of a predictive
theory. Odd, that.

GMAB. He cited Halliday and Resnick. I cited the JAES. Someone else cited
the JAES.

BTW Halliday and Resnick ride on:

http://jws-edcv.wiley.com/college/bc...74____,00.html

"Bob Cain" wrote in message

Arny Krueger wrote:


If you do the math, nonlinearities can't produce FM distoriton. You
need something that operates in the time domain, not the amplitude
domain.

If you do the math, FM distortion and linearity are mutually exclusive.

In many senses, I totally agree. However, Doppler distortion, while clearly
agreeing with the formal definition of nonlinear distortion, is not related
to any of the manifold other causes of nonlinear distortion in speakers.
Those other forms of nonlinear distoriton are due to changes of speaker
parameters, such as suspension compliance, as a function of the position of
the cone.

This is not debatable. Find a rigorous definition of linearity.

I think I just posted one.

I cheated, I picked it up from my www.pcavtech.com web site, I'm the author
of record. But, its pretty orthodox and I can find a dozen others online
that are about the same.

For example:

http://www.prosoundweb.com/install/s...rtion/dist.php

"I was mistaken this afternoon in defining distortion broadly instead of
nonlinear distortion. This latter gives rise to new frequencies not
originally present and which cannot be restored."

http://my.starstream.net/mk/Webpages...on_testing.htm

"Non-linear distortion refers to the generation of different frequencies
measured in a loudspeaker response that are not present in the original
stimulus."

http://www.daqarta.com/0diidist.htm

"This results when two or more different frequency components interact
within a nonlinear system. The output will then contain not only harmonics
of the original frequencies, but also components at sum and difference
frequencies that typically aren't harmonics of either input."


I've presented it but it doesn't
seem to have taken hold despite it being the bedrock of
linear systems theory.

There are in fact several different definitions of nonlinear distortion,
some that focus on the cause (transfer function curvature) and some that
focus on the effect (production of sounds not present in the input). In
general they are very closely related. Either is fine with me, even though
they don't mean identically the same.

"Jim Carr" wrote in message
news:iygUc.9870$yh.2511@fed1read05
"Phil Allison" wrote in message
...

** The words of an ass.

Can't you do any better than calling people names?

Agreed.

"Arny Krueger"
"Jim Carr"
"Phil Allison"



** The words of an ass.

Can't you do any better than calling people names?

Agreed.



** What happened to the context ????????????????????????

The remark was about the words posted.

Arny is another ass.



............. Phil

"Bob Cain" wrote in message

Randy Yates wrote:

"*IF* a system is linear, then it will not exhibit the Doppler
effect" is a true statement. However, get this:

T H E S Y S T E M I S N 'T L I N E A R !!!!!!!!!!!!!!!

Well, Randy, many people are saying that it is and produces
FM distortion anyway.

That could be both true and confusing, no?

Note carefully, (for thine ist a beanhead): the "system" here is
defined to be the entire electro-mechanical path from the speaker's
electrical input to the acoustic receiver's input.

This is a critcal point.

**** you, and I say that with all due respect. The system
here is everything from the face of the piston on out.

Out how far? Until we get to the receiver, there is no Doppler distortion
from that piston. Once we get to the receiver, there is Doppler distortion.
But judged all by itself fixed in space, the receiver can be
distortion-free.

Nothing that occurs before that can be contributory and must
be eliminated in some way from any experiment designed to
catch Doppler at work.

It would be nice to eliminate that, but in the real world of acoustic
measurements...

Again, give me a mathematical expression which describes in
a quantitative way what should be measured at a distance
from that speaker as a function of the motion of that speaker.

Asked and answered, but it takes a little reading in standard references.

Until that is done, "Doppler distortion" is not supported in
theory.

But it was all done 30 or more years ago, in the JAES.

I sincerely hope no one will say that it isn't
required because you see evidence of frequency modulation.

Where else might that FM come from?

According to a recent post, even that evidence may not
really indicate frequency modulation but can be accounted
for by non-linearity in the driver.

Except, that the driver does not evidence that nonlinearity unless the
distance between the diaphragm and the receiver is varying.

I don't know the
intricasies of modulation theory but it was said by someone
who does that the data shown does not carry the signature of
this supposed effect.

At this point all sorts of things have been said. Me, I trust my
experimental data, Halliday and Resnick, and the JAES.

Until "Doppler distortion" is supported in theory, and I
hope all know by now what qualifies as a theory, there is no
basis for it and no basis for correct interpretation of any
measurement data.

So get thee to the library and study up!

This is just basic science, folks.

Sometimes you just got to do your reading.

"Bob Cain" wrote in message

Arny Krueger wrote:

If all the explanations for Doppler distortion are wrong, where does
all of the FM we measure come from? Why does it correlate well with
the *incorrect* theoretical predictions?

What theoretical prediction might that be? I've yet to see
a theory for "Doppler distortion" that predicts. Odd, that.

Inability to obtain well-known, even classic references that have been
formally cited, noted.

This whole argument is based on the wrong assumption that the high
frequency source is "riding on" the low frequency source like a whistle
on a train. It is NOT!

Sorry, but it is. See my previous postings.


Both sounds are being produced simultaneously by the
complex electrical waveform driving the speaker cone which moves in
accordance. Assuming that the speaker is being driven within its linear
limits, the cone's motion accurately follows the driving signal, and it is a
linear system.

Doppler "distortion" is not the result of non-linear distortion.

"Porky" wrote in message


I think you're right, Bob, that certainly seems logical to me. If it
is Doppler distortion, the tone should be vary in a continuous warble
from -50Hz to +50Hz because the woofer's velocity is continuously
changing.

The FFT plots are snapshots of a kind, but they are also time-exposures. 1
million points at 96 KHz is about 11 seconds worth of data. It is all
averaged together in those pictures.

If one uses a low enough modulating frequency, and a small enough sample
set, snapshots with a faster effective exposure times result.

One can then actually can see the carrier warbling. It will show up at
different frequencies at different times in a sucession of snapshots.

However, with a long exposure you see the results averaging of about 550
cycles of the 50 Hz tone.

It is hard for me to believe that you don't know that a
predictive theory is one for which there is a mathematical
model which can predict, with accuracy, the results of the
kind of hypothetical situations that are being bandied about
in order to compare measurement to theory. Where is it?

Any book on physics has a section on Doppler effects. There are two basic
formulas -- one for which the velocity of the signal varies with the velocity of
the observer (eg, sound) and one for which the velocity of the signal does not
vary with the velocity of the observer (eg, light).

It's a trivial matter to compute the velocity of a driver cone moving at a
particular frequency and excursion. You can then easily compute the frequency
shift of a HF signal being reproduced by the cone.

I'm bothered by all this arguing, because I've repeatedly given clear, simple,
non-mathematical explanations of what's going on. Yet there has been neither a
consensus that they were correct, or a clear refutation of them.

The purpose of "argument" is to arrive at the truth, not to stubbornly defend
your present point of view.

I can't believe I'm the only "intelligent" person in this group with any real
insight into this issue.

"William Sommerwerck" wrote in message


I can't believe I'm the only "intelligent" person in this group with
any real insight into this issue.

Thanks a lot, Bill.

Not!

The problem here is whether the sound source is actually moving relative
to the listener, when the source is a speaker being driven by a complex
waveform. There are models that show that the actual source of the sound is
a point or plane that lies approximately at the center of the motion
described by the cone (I say approximately because the inertia of the cone
and of the air it is acting on may move the source a bit). If these models
are correct, then the source of the sound is not in motion relative to the
listener and therefore Doppler distortion does not and cannot exist in a
speaker. Certainly, this model, exact or not, is more accurate than the
train/whistle model.

The model you describe is a linear approximation of a nonlinear
system. It works because the center is the *average* sound source
position for a signal with no DC component. Once you start thinking
about adding a DC bias, the model breaks down.

As you've agreed, if the sound source is in motion, the system is no
longer linear due to the speed at which sound travels in air, and can
produce doppler distortion (for example, if I were to hold a speaker
in my hands and run back and forth towards and away from you, there
would be doppler, right?).

Ok, so to show that the sound source is moving, we have to show two
things:
1) that the sound source can change position.
2) that the sound source actually does change position while playing a
sound.

for #1, picture an ideal speaker surface. It has perfect frequency
response all the way down to DC. If you put any waveform on its
inputs, it follows it exactly, even if it's just a pure voltage.

So if I put 3 volts on the speaker, say the surface moves forwards 3
feet. If I put -3 volts on the speaker, it moves backwards 6 feed to
an absolute position (relative to its center position) of -3 feet.

Now, while it's at -3 feet bias, I add a small sine wave to the
signal. The voltage vibrates between -3.1 and -2.9 volts, and the
speaker position, relatively to its neutral 0, vibrates around -3.1
and -2.9 feet.

Would you still argue, in this case, that the sound is coming from the
0 foot position? If no, then you will agree that I have demonstrated
that #1 is possible. If yes, then please explain how (make the speaker
excursion 30 miles instead of 3 feet if you like).

Now I will go for #2:

Since I can set the speaker's position however I like by setting the
DC bias, it follows that I can change that position while the high
frequency sound is playing back on top of it. I could move it at say,
1 ft per second -- this speed is far too slow to produce a sound, and
is practically DC. If you agree that I can set the position of the
sound source by adjusting the DC bias, then it follows that I can
*change* the position of the sound source by *changing* the DC bias.
Any change in the position of the sound source is movement of the
sound source (by the definitions of "movement" and "position"), and
any movement of the sound source creates doppler distortion. QED.

Furthermore, if moving the plate at 1ft per second creates doppler
distortion, then moving at, say, 50 hz or whatever would also create
it -- unless you can think of some arbitrary dividing line above which
doppler distortion no longer occurs.


Now, if you fall back on the "but the speaker is linear!" argument
that you haven't let go of yet, then why don't *you* show the source,
experiement, or mathematical derivation that proves that a speaker-air
system is linear? This seems to be an assumption you're holding with
absolutely *no* justification.

Now, as for evidence that shows this occurs, I believe someone in this
thread mentioned an article with measurements of doppler distortion.
Of course, you've already dismissed any possible empirical evidence
ahead of time by saying it's due to some non-linearity in the speaker
itself and not doppler distortion. This shows a grave misunderstanding
of how science works -- we can *never* proove 100% that something
happens. We can only prove that things *don't* happen in certain ways.
If the distortion measured fits the doppler model perfectly (and I'm
pretty sure it does), then we're right to say that by current
scientific knowledge, it's doppler distortion. If you'd like to
hypothesize a new model for that measured distortion, or come up with
an experiment to show that doppler distortion doesn't exist with a
purely linear speaker, then go right ahead.

Ken

Nothing stupid about it. If both systems are linear then they will work
in an identical manner.

The system by which a single ideal speaker surface transduces an
electrical waveform my moving and producing a series of travelling
pressure changes in the air is *not* a linear system.

Ken

I can't believe I'm the only "intelligent" person in this group with
any real insight into this issue.

Thanks a lot, Bill.

Not!

I don't remember you posting any elegant thought experiments, Arny. (If you did,
and I overlooked them, I apologize.)

Since I can set the speaker's position however I like by setting the
DC bias, it follows that I can change that position while the high
frequency sound is playing back on top of it. I could move it at say,
1 ft per second -- this speed is far too slow to produce a sound, and
is practically DC. If you agree that I can set the position of the
sound source by adjusting the DC bias, then it follows that I can
*change* the position of the sound source by *changing* the DC bias.
Any change in the position of the sound source is movement of the
sound source (by the definitions of "movement" and "position"), and
any movement of the sound source creates doppler distortion. QED.

This is basically correct reasoning.

"William Sommerwerck" wrote in message

I can't believe I'm the only "intelligent" person in this group with
any real insight into this issue.

Thanks a lot, Bill.

Not!

I don't remember you posting any elegant thought experiments, Arny.
(If you did, and I overlooked them, I apologize.)

OK.

BTW your thought experiments are generally just fine. I've posted my support
for them at times, right?

I find the whole situation quite instructive. Formal cites have been given,
which can be resolved with a trip to any number of libraries. People argue
on, regardless.

In short, people seem to be a lot more enthusiastic about writing than
reading. That seems to have the same effect as speaking instead of
listening.

I haven't seen anything correct that has posted on the audio groups of
Usenet for days if not weeks, that the well-known scientific literature
doesn't cover in spades. We're talking papers and books that are 30+ years
old.

It seems like I'm the only one in this group with ready access to the JAES
which may be understandable. But Halliday and Resnick should be in a jillion
different libraries. There don't seem to be a lot of people here who have
actually taken first year college physics, it seems.

On Tue, 17 Aug 2004 04:56:40 GMT, Randy Yates wrote:

Bob Cain writes:

Randy Yates wrote:

Proof by assertion?

Sorry, Randy. I see nothing but proof by assertion from the
supporters of "Doppler distortion." It shouldn't be incumbent on
those that observe that no predictive theory exists to prove why it
doesn't, although I've been trying, it should be incumbent on those
claiming that it exists to produce the predictive theory. Have at it.
This isn't string theory. If it's there, a precise model should
almost fall out by inspection.

If by "predictive theory" you mean a theory by which this phenomenom
can be predicted, then I must ask if you are blind.

That's not the problem here. Bob "believes in" Doppler theory when
it's a whistle on a train.
Bob refuses to see that the source of soud is the speaker cone,
moved back and forth by the voice coil, thus the "source of sound" in
a loudspeaker driver is moving.
Bob claims and believes the sound source is a 'fixed source'
relative to the driver's frame. I imagine this comes from multi-way
loudspeaker system design, so that driver positions can be set
relative to each other so that they are "phase coherent" or
"time-aligned." (Off topic, both of these are probably registered
trademarks of speaker makers from the '70's) This model is a good one
and certainly works for this purpose, but like many models, it doesn't
work for all situations. Specifically, it doesn't predict doppler
distortion caused by cone excursion.

I have stated it
several times in several different ways. I have cited a reference for
it (Halliday and Resnick). I am assuming you are familiar with the
theory. Is that assumption invalid? Do you want a rehashing of the
theory of the Doppler effect? Do you want me to transcribe my Physics
text into a usenet news article for you so you don't have to go to the
library and check one out?

I suspect Bob knows it as well as you do, but he's just missing it
and has some other idea in mind when it comes to a speaker cone.

-----
http://mindspring.com/~benbradley

"Ben Bradley"

I suspect Bob knows it as well as you do, but he's just missing it
and has some other idea in mind when it comes to a speaker cone.



** We are all the victims of a pathetic NG troll's wet dream and a hoax.

Bob Cain has no interest in the facts - he is having a giant hoot at our
expense.

Only complete fools keep going when they are being conned.




............. Phil

"ruffrecords"


To produce FM there needs to be a non-linearity.


Not really. A nonlinearity produces AM.

Yes really. It is exactly how a mixer works in a receiver. The non
linearity produces sum and difference frequencies.



** Which is characteristic of AM - you jerk.




.......... Phil

Arny Krueger wrote:
"ruffrecords" wrote in message


Arny Krueger wrote:

"ruffrecords" wrote in message




PenguiN wrote:


As far as our


super-excursion speaker is concerned, the location that's
generating the high pitched sound is moving forward and backward
several feet.


No it isn't. This is the flaw in all the doppler distortion
arguments.


If all the explanations for Doppler distortion are wrong, where does
all of the FM we measure come from? Why does it correlate well with
the *incorrect* theoretical predictions?



To produce FM there needs to be a non-linearity.


Not really. A nonlinearity produces AM.

Yes really. It is exactly how a mixer works in a receiver. The non
linearity produces sum and difference frequencies.

Ian

BTW your thought experiments are generally just fine.
I've posted my support for them at times, right?

Right. And I saw them. I appreciate your support. (Though it was for the truth,
as you saw it, and not for me. Which is as it should be.)


I find the whole situation quite instructive. Formal cites have
been given, which can be resolved with a trip to any number
of libraries. People argue on, regardless.

That's what I was griping about.

The pro-Doppler explanations are almost certainly correct. But no one seems to
be paying them much attention, or incisively refuting them. It's like explaining
that something is impossible because it violates the law of energy conservation,
but people keep arguing.


In short, people seem to be a lot more enthusiastic about writing than
reading. That seems to have the same effect as speaking instead of
listening.

Absatively.


It seems like I'm the only one in this group with ready access to the JAES
which may be understandable. But Halliday and Resnick should be in a jillion
different libraries.

Mine's somewhere in my library.


There don't seem to be a lot of people here who have
actually taken first year college physics, it seems.

Or understood it. I have an above-Mensa IQ, but I had to take physics several
times (ar, ar) before I really started "understanding" it. (Maybe.)

Randy Yates wrote:
ruffrecords writes:

If both systems are linear then they will
work in an identical manner.


That statement is absolutely correct, just as "If I am pregnant,
then I am a female." is absolutely correct.

And your point is what?

Ian

Bob Cain has no interest in the facts -- he is having a giant hoot
at our expense.

I don't think so. It's rather that Bob is open-mined enough to ask for other
people's opinions -- but when he gets a response that doesn't fit with his
opinion, he doesn't want to accept it. We're all like that at one time or
another.

Porky wrote:
"Randy Yates" wrote in message
...

Bob Cain writes:


ruffrecords wrote:


To produce FM there needs to be a non-linearity. If you detect FM
there is a good chance a non-linearity exists. But it is not due to
the doppler effect.

Exactly,

Not. Get a clue, people. Doppler is a *PHYSICAL PHENOMENOM* that
WILL happen whether or not you decide it can WHENEVER a sound wave
source and observer are moving relative to each other. Period. This
isn't open for debate.


This whole argument is based on the wrong assumption that the high
frequency source is "riding on" the low frequency source like a whistle on a
train. It is NOT! Both sounds are being produced simultaneously by the
complex electrical waveform driving the speaker cone which moves in
accordance. Assuming that the speaker is being driven within its linear
limits, the cone's motion accurately follows the driving signal, and it is a
linear system.
Forget the train/whistle anology, it is not an accurate representation for
what goes on with a speaker, period!




Precisely.

Ian

Randy Yates wrote:
Bob Cain writes:


If you do the math, FM distortion and linearity are mutually
exclusive. This is not debatable. Find a rigorous definition of
linearity. I've presented it but it doesn't seem to have taken hold
despite it being the bedrock of linear systems theory.


You need remedial work in logic, Bob. Even though the
statement "A - B" may be true, there is nothing you can
conclude if A is not true.

"*IF* a system is linear, then it will not exhibit the Doppler
effect" is a true statement. However, get this:

T H E S Y S T E M I S N 'T L I N E A R !!!!!!!!!!!!!!!

Note carefully, (for thine ist a beanhead): the "system" here is
defined to be the entire electro-mechanical path from the speaker's
electrical input to the acoustic receiver's input.

No problem with that. The problem is which non-linearity in which bit
of the system causes the sidebands the doppler boys have measured?

Ian

Phil Allison wrote:
"Porky"

"Phil Allison"

** This little piggy cannot trot and chew gum at the same time.


Are you kidding?



** Not one bit - you are clearly an utter imbecile.


And you are clearly a mental midget who must cover his ignorance with
flippant comments and smart-alecky remarks which have nothing to do with

the

topic at hand.



** When I saw YOU doing EXACTLY that I gave up trying to correct you.

I repeat : YOU are clearly an utter imbecile.




............ Phil




Looks to me like Porky has moved up a few grades and phil is the new
class idiot. (and I don't know if I can walk and chew gum because I hate
the stuff).

Ian

Jim Carr wrote:
Here's a link that you tech folks can argue about:

http://www.pcavtech.com/techtalk/doppler/




Looks good to me. Plenty of evidence of harmonic distortion (casued by
non-linearites and no evidence of 50Hz sidebands arounf the 4KHz signal.
Doppler distortion is dead.

Ian

"Picture the largest loudspeaker in the universe sitting outside"
"Now add to that signal a small, high pitched, low amplitude waveform"

I couldn't of put it better myself. I was watching the argument and
watching it turn into a slanging match. I wish that wouldn't happen.
The only problem as far as I could see is that Porky was thinking of
just a singular frequency, rather than a high frequency "riding" a low
frequency.

When that occurs, the train and whistle analogy indeed seems to make
sense. With a singular frequency, IMHO, it does not.

Cheers,

Mark.
--

PenguiN wrote:
Picture the largest loudspeaker in the universe sitting outside
somewhere. It's so big that it has a maximal excursion of several
feet. Now picture a very low bass signal played on that speaker at
almost maximal volume. The speaker cone is vibrating
in-out-in-out-in-out.

Now add to that signal a small, high pitched, low amplitude waveform.
The two waveforms are added together so that it seems like the higher
pitched wave is "riding on top of" the bass wave. As far as our
super-excursion speaker is concerned, the location that's generating
the high pitched sound is moving forward and backward several feet.

"Porky" wrote in message ...
"Bob Cain" wrote in message
...


Jim Carr wrote:
Here's a link that you tech folks can argue about:

http://www.pcavtech.com/techtalk/doppler/

What's to argue? What it all means?

Here's an observation based on intuition that I'd like
someone to dispell. Since the high frequency component is
supposed to be continuously oscilating in frequency between
two extrema, why is the spectrum at its location in the FFT
composed of peaks instead of a tabletop. Seems to me that
all values of the frequencies between those extrema should
show up and show up in equal amounts if the model everyone
talks about is valid.

I think you're right, Bob, that certainly seems logical to me. If it is
Doppler distortion, the tone should be vary in a continuous warble
from -50Hz to +50Hz because the woofer's velocity is continuously changing.

Uhm, no. Frequency modulation does *not* produce a flat tabletop.

http://www2.sfu.ca/sonic-studio/hand...odulation.html

Perhaps you both should review your basic signals & systems course
before continuing this discussion?

Ken

PenguiN wrote:
for #1, picture an ideal speaker surface. It has perfect frequency
response all the way down to DC. If you put any waveform on its
inputs, it follows it exactly, even if it's just a pure voltage.

So if I put 3 volts on the speaker, say the surface moves forwards 3
feet. If I put -3 volts on the speaker, it moves backwards 6 feed to
an absolute position (relative to its center position) of -3 feet.

Now, while it's at -3 feet bias, I add a small sine wave to the
signal. The voltage vibrates between -3.1 and -2.9 volts, and the
speaker position, relatively to its neutral 0, vibrates around -3.1
and -2.9 feet.

Again, I can't think of a better way of describing what is happening,
nice one Ken. If you cannot picture what is happening in your head,
then this description should help a lot IMHO.

Mark.
--

Bob Cain wrote in message ...
Ben Bradley wrote:


Okay, Bob, I'm going to add a DC component, but I'm not going to
tell you that this DC component is really a millihertz-frequency sine
wave. How will you know the difference? Just what IS the difference
over a time period of one second?

Enough. :-)


Bob

Woah, wait a second, you're hand-waving your way out of this one
without actually addressing it.

Please explain how, exactly, a DC component changes the "source" of
the signal, but when there's an infinitesimally small frequency, so
small that one can't detect it, but that technically is not DC, the
"source" of the signal suddenly "snaps back" to be the center, or zero
excursion point, of the driver?

Ken

OK here is some math.

The first pair of sidebands are about -40dBc. Assuming this is caused
by FM for the moment and as stated before, using the standard FM
sideband calculations, this corresponds to a frequency deviation of
about +/- 1 Hz at 4000 Hz. (The 4000 Hz tone is raised and lowered by
1 Hz at a 50 Hz rate.)

Using 344.3 m/sec for the speed of sound and the Doppler equations
found he

http://www.mathpages.com/rr/s2-04/2-04.htm

The relative speed needed to shift 4kHz by 1 HZ is about 0.2 MPH or
0.3 feet/ sec or about 3.5 inches per second.

If I make the simplifying assumption that the loudspeaker cone is
moving back and forth at 50 Hz with a triangular wave rather than
sinusoidal (just to make the math a bit easier). At 50Hz the cycle is
0.02 seconds and the speaker cone would move about 0.07 inches in that
time. Since it is moving back and forth that is +/-0.035 inches. This
seems perfectly reasonable to me.

Working it the other way round, if you assume a loudspeaker is
reproducing a 50 Hz tone, and the cone is moving +/-0.035 inches at 50
Hz, that is about 3.5 inches per second or 0.2 miles per hour. This
speed produces a Doppler shift (frequency deviation) of about 1 Hz to
a 4 kHz tone which corresponds to -40 dBc first sidebands.

So this is an inherent non-linear distortion but it can be reduced by
using a separate woofer and tweeter or making the speaker cone larger
so it does not have to move as far and therefore as fast. But I don't
think it sounds any different than any other form of non-linear
distortion such as intermodulation. But also the magnitude if this
distortion is much larger than produced by any reasonable electronics
it points out that we should stop worrying about the electronics so
much. The electronics are much better than the speakers.

Interesting question, how does the VELOCITY of the cone change as the
50 Hz is increased in frequency at a fixed amplitude. I know from
looking at a speaker that the excursion reduces as the frequency goes
up, but in this case it is the velocity (not the excursion) of the
cone that it key.

Mark

OK here is some math.

The first pair of sidebands are about -40dBc. Assuming this is caused
by FM for the moment and as stated before, using the standard FM
sideband calculations, this corresponds to a frequency deviation of
about +/- 1 Hz at 4000 Hz. (The 4000 Hz tone is raised and lowered by
1 Hz at a 50 Hz rate.)

Using 344.3 m/sec for the speed of sound and the Doppler equations
found he

http://www.mathpages.com/rr/s2-04/2-04.htm

The relative speed needed to shift 4kHz by 1 HZ is about 0.2 MPH or
0.3 feet/ sec or about 3.5 inches per second.

If I make the simplifying assumption that the loudspeaker cone is
moving back and forth at 50 Hz with a triangular wave rather than
sinusoidal (just to make the math a bit easier). At 50Hz the cycle is
0.02 seconds and the speaker cone would move about 0.07 inches in that
time. Since it is moving back and forth that is +/-0.035 inches. This
seems perfectly reasonable to me.

Working it the other way round, if you assume a loudspeaker is
reproducing a 50 Hz tone, and the cone is moving +/-0.035 inches at 50
Hz, that is about 3.5 inches per second or 0.2 miles per hour. This
speed produces a Doppler shift (frequency deviation) of about 1 Hz to
a 4 kHz tone which corresponds to -40 dBc first sidebands.

So this is an inherent non-linear distortion but it can be reduced by
using a separate woofer and tweeter or making the speaker cone larger
so it does not have to move as far and therefore as fast. But I don't
think it sounds any different than any other form of non-linear
distortion such as intermodulation. But also the magnitude if this
distortion is much larger than produced by any reasonable electronics
it points out that we should stop worrying about the electronics so
much. The electronics are much better than the speakers.

Interesting question, how does the VELOCITY of the cone change as the
50 Hz is increased in frequency at a fixed amplitude. I know from
looking at a speaker that the excursion reduces as the frequency goes
up, but in this case it is the velocity (not the excursion) of the
cone that it key.

Mark

PenguiN wrote:
Nothing stupid about it. If both systems are linear then they will work
in an identical manner.


The system by which a single ideal speaker surface transduces an
electrical waveform my moving and producing a series of travelling
pressure changes in the air is *not* a linear system.

Ken

Excellent. So what is its transfer function then?

Ian

ruffrecords writes:

Randy Yates wrote:
ruffrecords writes:

If both systems are linear then they will
work in an identical manner.
That statement is absolutely correct, just as "If I am pregnant,
then I am a female." is absolutely correct.

And your point is what?

Are you REALLY this clueless and/or stupid? I give up. You apparently
do not have the facilities to reason rationally.
--
% Randy Yates % "Watching all the days go by...
%% Fuquay-Varina, NC % Who are you and who am I?"
%%% 919-577-9882 % 'Mission (A World Record)',
%%%% % *A New World Record*, ELO
http://home.earthlink.net/~yatescr

(Mark) writes:
[...]
Interesting question, how does the VELOCITY of the cone change as the
50 Hz is increased in frequency at a fixed amplitude.

Simple. v(t) = dx(t) / dt. Since x(t) = A*sin(w*t), the dx(t) /dt = A*w*cos(w*t).
--
% Randy Yates % "The dreamer, the unwoken fool -
%% Fuquay-Varina, NC % in dreams, no pain will kiss the brow..."
%%% 919-577-9882 %
%%%% % 'Eldorado Overture', *Eldorado*, ELO
http://home.earthlink.net/~yatescr

Phil Allison wrote:
"ruffrecords"


To produce FM there needs to be a non-linearity.


Not really. A nonlinearity produces AM.

Yes really. It is exactly how a mixer works in a receiver. The non
linearity produces sum and difference frequencies.




** Which is characteristic of AM - you jerk.

......... Phil


Both FM and AM have sidebands (sum and difference frequencies). A
non-linearity can produce a number of effects, like harmonics for
example, not just AM.

And if you continue to reply with personal remarks I'll simply ignore you.

Ian

"Bob Cain" wrote in message
...


Jim Carr wrote:
Here's a link that you tech folks can argue about:

http://www.pcavtech.com/techtalk/doppler/

What's to argue? What it all means?

Hell if I know! I was hoping you would tell me!

PenguiN wrote:


Okay, Bob, I'm going to add a DC component, but I'm not going to
tell you that this DC component is really a millihertz-frequency sine
wave. How will you know the difference? Just what IS the difference
over a time period of one second?

Enough. :-)


Bob


Woah, wait a second, you're hand-waving your way out of this one
without actually addressing it.

Please explain how, exactly, a DC component changes the "source" of
the signal, but when there's an infinitesimally small frequency, so
small that one can't detect it, but that technically is not DC, the
"source" of the signal suddenly "snaps back" to be the center, or zero
excursion point, of the driver?

Because there is a real difference. Air can't carry the DC
component of velocity but it can carry any time varying
component.

It appears to me that Doppler shift is a consequence of that
difference.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

PenguiN wrote:

Nothing stupid about it. If both systems are linear then they will work
in an identical manner.


The system by which a single ideal speaker surface transduces an
electrical waveform my moving and producing a series of travelling
pressure changes in the air is *not* a linear system.

Please prove that. It has yet to be done.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein

Bob Cain wrote:
PenguiN wrote:

Nothing stupid about it. If both systems are linear then they will work
in an identical manner.


The system by which a single ideal speaker surface transduces an
electrical waveform my moving and producing a series of travelling
pressure changes in the air is *not* a linear system.

Please prove that. It has yet to be done.

I can prove that easily, but not in any way that has anything to do with
doppler effect. There are plenty of amplitude nonlinearities, from a
dead band due to spider friction, to break-up modes at high levels. But
none of them have anything to do with the doppler issues.

The doppler issues, though, don't have anything to do with amplitude
nonlinearities. The earlier reference made to Terman is a good one.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."