Scott Dorsey wrote:

Bob Cain wrote:

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.

Right.


The doppler issues, though, don't have anything to do with amplitude
nonlinearities. The earlier reference made to Terman is a good one.

I'm still hoping someone with access to a source containing
the expression describing pressure/velocity in the wave as a
function of the velocity of the piston will transcribe it to
one of these threads. If it exists, it's just an equation.

If it doesn't, we simply _must_ consider why that is.


Bob
--

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

A. Einstein

William Sommerwerck wrote:

The behavior of the system is FULLY predicted by the Doppler formula, where THE
VELOCITY OF THE CONE MOTION (as produced by the lower tone) IS THE SOURCE
VELOCITY. That's all there is to it. It's no more complex than that.

All you have to do is plug and grind.

The expression Jim showed is only valid for the various
velocities being constant. Nowhere that I've seen that
expression has a dynamic situation been under discussion.
The dynmaics are included in the fs term.

There is a reason for that. Doppler shift only applies to
constant velocity components. The time varying ones are
incorporated correctly in the generated wave.


Bob
--

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

A. Einstein

so what wrote:

That's what I was saying, that any tone would warp its own waveshape due
to Doppler shift.

Under the flawed "analysis" that has been historically
presented, this is an inescapable conclusion.

No linear system is capable of producing frequency
components in its output that aren't in its input and no
non-linear system can produce exactly the input frequency
and no others for all sin waves. This is fundamental.

A system is either linear or it isn't. There is no
in-between to accomodate this hypothetical "Doppler distortion."


Bob
--

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

A. Einstein

The Ghost wrote:


The problem isn't that somebody left out an assumption somewhere. The
problem is that nobody involved in the discussion of this topic thus
far seems to have asked the question "upon what assumption is the
derivation of the formula based" Consequently those like Bob Cain,
who foolishly deny the existence of demonstrated reality, "assume"
that the equation that is cited for the constant-velocity case does
not also apply to the dynamic case. On the other hand, those with a
bit more common technical sense than Bob Cain similarly "assume" that
the equation applies to the dynamic case as well as to the constant
velocity case. The problem is that, for whatever reason, no one
debating the issue seems to actually know which of the two mutually
exclusive assumptions is correct. Those who are interested in knowing
can find the answer as well as the derivation from fundamental
principles of the formula for instantaneous Doppler shift in Allan
Pierce's book "Acoustics, An Introduction to Its Physical Principles
and Applications."

Why don't you consider actually contributing something of
substance to this conversation? I know you are capable.


Bob
--

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

A. Einstein

"Jim Carr" wrote in message news:LIzUc.9970$yh.371@fed1read05...

Bob can correct me here, but from where I sit, Bob does not deny the Doppler
shift. He completely accepts the formula fo = fs . (v - vo) / (v - vs). What
he does not accept is that you can insert the speaker diaphragm's movement
as vs. He accepts that you can put the speaker on the train and predict the
Doppler shift with the above formula as does everyone he's arguing with.

But here's the kicker: Either the above formula is wrong, there is no
Doppler Distortion, or somebody left out an assumption somewhere. Why?
Because the formula does not take into consideration the movement of the
diaphragm. If the source and observer are not moving, there is no Doppler
shift, right? But according to the proponents of Doppler Distortion, there
*is* a shift. Everything that creates sound moves in some way. So why hasn't
someone updated that formula?



The problem isn't that somebody left out an assumption somewhere. The
problem is that nobody involved in the discussion of this topic thus
far seems to have asked the question "upon what assumption is the
derivation of the formula based" Consequently those like Bob Cain,
who foolishly deny the existence of demonstrated reality, "assume"
that the equation that is cited for the constant-velocity case does
not also apply to the dynamic case. On the other hand, those with a
bit more common technical sense than Bob Cain similarly "assume" that
the equation applies to the dynamic case as well as to the constant
velocity case. The problem is that, for whatever reason, no one
debating the issue seems to actually know which of the two mutually
exclusive assumptions is correct. Those who are interested in knowing
can find the answer as well as the derivation from fundamental
principles of the formula for instantaneous Doppler shift in Allan
Pierce's book "Acoustics, An Introduction to Its Physical Principles
and Applications."

Scott Dorsey wrote:

Actually, to do it in the time domain, it takes a Bessel function. The
reference to Terman is an excellent one.

Scott, if you have that reference, would you _please_
transcribe here the expression that is the end result of
analyzing "Doppler distortion"?

I'll owe you a big one.


Bob
--

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

A. Einstein

Scott Dorsey wrote:

No, it should change it a little bit. Of course, the ratio between the
volume of the box behind the piston and the volume of the earth's atmosphere
is very small. But it's nonzero!

I'm afraid that's wrong, Scott. Anything producing Doppler
shift changes the global atmospheric pressure not a whit.
It's not asymptotically zero, it's zero, nuttin, nada. :-)


Bob
--

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

A. Einstein

The expression Jim showed is only valid for the various
velocities being constant. Nowhere that I've seen that
expression has a dynamic situation been under discussion.
The dynmaics are included in the fs term.

There is a reason for that. Doppler shift only applies to
constant velocity components. The time varying ones are
incorporated correctly in the generated wave.

No, no, no, no, no... If the train speeds up or slows down, you will the
magnitude of the Doppler shift change.

No, no, no, no, no... If the train speeds up or slows down, you will the
magnitude of the Doppler shift change.

God, I'm getting careless in my geezerhood...

No, no, no, no, no... If the train speeds up or slows down, the
Doppler shift will still be audible. Only its magnitude will change.

In alt.music.home-studio,rec.audio.tech,rec.audio.pro, Bob Cain
wrote:



so what wrote:

That's what I was saying, that any tone would warp its own waveshape due
to Doppler shift.

Under the flawed "analysis" that has been historically
presented, this is an inescapable conclusion.

No linear system is capable of producing frequency
components in its output that aren't in its input and no
non-linear system can produce exactly the input frequency
and no others for all sin waves. This is fundamental.

Let's pull the head of an engine to expose the piston, and spin
this thing fast enough that the piston exceeds the speed of sound at
its maximum speed. For a couple of inches stroke length, this will
probably be about 5kHz, and the crank will really be spinning at
30,000 RPM. But hey, the piston is tracing through a sine wave, isn't
it?

A system is either linear or it isn't. There is no
in-between to accomodate this hypothetical "Doppler distortion."

It's not in-between, it's a non-linear* system.


Bob


* A definition that works here is that there's at least one frequency
in the output that's not in the input. I was going to say that a
definition that doesn't work is that if a system has "amplitude
linearity" it's a linear system, but even in the doppler distortion
case, the FM'ed frequency has its fundamental frequency lowered as the
sidebands take power. So it's both a distortting and a non-linear
system no matter how you define those terms.

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

William Sommerwerck wrote:

The expression Jim showed is only valid for the various
velocities being constant. Nowhere that I've seen that
expression has a dynamic situation been under discussion.
The dynmaics are included in the fs term.


There is a reason for that. Doppler shift only applies to
constant velocity components. The time varying ones are
incorporated correctly in the generated wave.


No, no, no, no, no... If the train speeds up or slows down, you will the
magnitude of the Doppler shift change.

Here is where it goes from black and white to something
gray. In the free, far field, from a piston very small
relative to the wavelength, it isn't necessasary to get all
the way to DC for the system to lose the ability to generate
the lowest frequency components in any signifigant way
relative to the receiver. In that frequency region,
"Doppler distortion" should evidence itself.

This would only happen at DC in the closed, infinite tube
with a piston in it that I've been employing as a simplified
toy system.

Whenever the piston/air is able to well support the
bandwidth, however, I don't believe "Doppler distortion" can
be demonstrated. The motion will be incorporated in the
generated wave in a linear fashion.

BTW, I am in discussion right now with Art Ludwig about
this. At this point we are just settling on the correct
situation to analyze. Hopefully a definitive answer will
come out of our discussion.


Bob
--

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

A. Einstein

"Jonas P Eckerman"

** This man has mental disabilities.

"Bob Cain" wrote in message
...


Porky wrote:

thing and start from scratch, I think you'll see what Bob and I
see. Remember two things, an oscilloscope pattern is at best a two
dimensional representation of a three dimensional occurance and doesn't
necessarily represent what is actually happening, and the speaker cone
doesn't actually generate the sound wave (velocity too low and p-p cone
travel too short for the wavelength), the air it moves does.

No, the cone is actually moving with the right velocity for
the wave, and it is in the right position to impart that to
the air because its derivative gives the position in the
wave where that velocity applies and that's just where it
happens to be. Unless it's a constant component and then it
can't impart that to the air so it's position is in error.
That error is Doppler shift.

Well, the cone is oscillating at the same frequency as the wave it's
producing, but there's still the matter of the low velocity of the air
molecules it's moving being converted to the high velocity soundwave that we
hear. I think I see what you're saying though.

Ben Bradley wrote:


Let's pull the head of an engine to expose the piston, and spin
this thing fast enough that the piston exceeds the speed of sound at
its maximum speed. For a couple of inches stroke length, this will
probably be about 5kHz, and the crank will really be spinning at
30,000 RPM. But hey, the piston is tracing through a sine wave, isn't
it?

Uh, when did moving faster than the speed of sound enter the
discussion?



A system is either linear or it isn't. There is no
in-between to accomodate this hypothetical "Doppler distortion."


It's not in-between, it's a non-linear* system.

Then single frequency inputs are also distorted by the
phenomenon we are discussing, right?

* A definition that works here is that there's at least one frequency
in the output that's not in the input.

Ok. Close enough for horse shoes.


Bob
--

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

A. Einstein

"Phil Allison" wrote in message
...

"Porky"


Ignore Phil, he's just mad because he can't contribute anything
positive
to this discussion, he has neither the education nor the intelligence,


** You are well named - except pigs revelling in **** have more sense
and manners than you do.


FYI I studied physics at the University of Sydney at honours level.

My IQ is at least double yours.

Unlike you and Bob, I do not have mental disabilities.


Oh, wow! Your IQ would be something a bit over 280, in that case. You may
have studied physics, but you have yet to show that you benefitted in any
manner from your studying. You may or may not have a mental disability, but
you certainly have a major social disability.

On Sat, 7 Aug 2004 07:02:36 -0400, "Arny Krueger"
wrote:

.....stuff deleted........

I think that the triple tone test and modern spectrum analyzer technology
provides valuable insights into this area. I think that I've established
that when there are two upper-frequency probe tones, FM distortion will
produce sidebands with a higher amplitude with the highest frequency tone,
all other things being equal. This finding can be, and probably should be
applied to investigations relating to both Doppler distortion and jitter.


To get an idea of the magnitude of any Doppler (FM) artifacts, you
need to know the cone velocity. It is my understanding, that in the
area where a speaker has a flat response, the velocities are fairly
consistent as frequency changes. So within this area, you should be
able to analyze and predict the Doppler effects.
I don't have much data that represents typical cone velocities at
different power levels (or SPL level, at say, 1 meter). From some of
the data shown on the Linkwitz site, he has a woofer with about 1.5
Meters/sec at 86db @1meter (that's reasonably loud). Does anyone have
typical data for other loudspeakers, especially at higher frequencies
(tweeters, midrange)?

Using 1.5 M/s peak cone velocity, the speed of sound is about 340
M/sec, that should vary all the frequencies whose velocities were
supposed to be something else. Usually for the purpose of analysis, we
assume that all the other ones are pretty small. Anyhow, with those
numbers, you get about 0.44% change in frequency, higher or lower
depending which way the cone is moving. If the signal causing the 1.5
meter/sec was 50 Hz , and you had another signal of 4 KHz, then your
4khz note appears to be changing from 4khz to 4017 khz, then back then
to a low of 3983 khz, 50 times a second. In the frequency domain (your
ears, spectrum analyzer) things get weird. The result frequencies
(there are more than what you put in) depend on the ratio of the
change in frequency divided by the modulating frequency - this is the
modulation index - M. The total energy is unchanged, so that the
addition of extra stuff comes at the expense the main peak (unlike IM
distortion, where the modulating frequency has to add energy). If the
modulation index is less than 0.3, then there are 2 extra frequencies
(distortion), each one has an amplitude of 1/2 times M (modulation
index), or the total grunge is M . For low values of M, you get 2
extra freq., the sum and difference (just like IM distortion, but out
of phase with each other, and may sound QUITE different) . At higher M
the calculation is very complex, you can have almost all distortion
with almost no fundamental.
Using the above numbers, change in frequency is about 17 Hz,
modulation freq. is 50 Hz, so M=0.34 , or about 17% for each extra
frequency. These will be at 4050 and 3950. This is NOT IM distortion.
The thing to note is that theamount of distortion changes with
modulating frequency! At 10Hz modulating freq,. M is about 1.7 - that
will mess up the waveform badly. The worst case is when the
frequencies are very different. With high values of M, the note
spreads out in frequency - instead of a fundamental and two satellite
tones, there is an almost contiuous block of frequencies. With a 5 or
10 Hz modulation, instead of 4 KHz and 2 extra peaks, you get an
almost continuous band of frequencies around 4 KHz.
The sound? High M values are VERY noticeable, usually a warbling
sound, or noticeable extra frequencies. As M decreases to about 0.3,
the original pure tone sounds indistinct in pitch, or you might just
notice extra "stuff", and as M decreases to less than 0.1, it's very
hard to tell (for me). These were done at 4 KHz, with varying
amplitudes and frequency of the modulation frequency. This was not a
really good listening test, the real Golden Ears might be better at
finding the threshold. I used 2 signal generators, one modulating the
others frequency. I used a spectrum analyzer to determine M, and
adjusted the signal generators to vary M as I listened to the "tones".
My good signal generators are at work, so if you're interested, I can
compare IM and FM (Doppler) distortion with the same frequencies. I'm
sure Arny has the equipment more readily available - and may even have
..wav files for your listening pleasure, so you can hear for yourself
what the effects are. What would be really nice, is to frequency shift
a chunk of music with different delta-freq, and different modulation
frequencies, i.e., varying M with different conditions. Multi-tone and
real music should the preferred way to check this out.
The cure? Keep wide ranges of frequencies OUT of a loudspeaker,
i.e., use 2 or 3 way systems. Because the modulation index (M) is
calculated with the modulating frequency as DENOMINATOR, avoiding low
modulating frequencies reduces the distortion. That bears out in my
listening tests. As the modulating frequency increases, the less
noticeable things are. A 3 way system can have a 10 to 1 range of
frequencies for each driver, compared to almost a 1000 to 1 range for
a singe wide range speaker. That will make a big difference when you
calculate M, the modulation index.

-Paul
.................................................. .............
Paul Guy
Somewhere in the Nova Scotia fog

"Arny Krueger" wrote in message
...
"Ben Bradley" wrote in message


Arny, I can see a reluctance to even look, as the spectrum of an FM
signal is SO counterintuitive (at least to me) that it's actually hard
to believe (and thus the 'flattop' comment we saw earlier).

Really? It's fairly intuitive to me. However, not everybody spent three
years trying to grok Doppler radars that had LAYERS of AM & FM modulators
in
both the transmitter and receiver. That was a long time ago, but it seems
to
have stuck, at least a little.

Mine was Nike HiPAR and Nike missile and tracking radars, and it was many
years ago as well.

I do 'believe' the sidebands are as you say they are, but can't imagine
how
FM results in those sidebands.

The 50 Hz part I understand. The phase inversion of the upper sidebands I
understand. The multiple sidebands I take based on more-or-less faith,
based
on knowlege of Bessel functions and many hours spent with spectrum
analyzers.

Perhaps those with knowledge of higher
math (more than a couple quarters of calculus) can visualize it.

In the end, I think it is experience. The ultimate proof is when it works
as
predicted, theory and empirical knowlege tell the same story.

The experiment I suggested will give the results I gave, and if it is right
at under the circumstances I suggested, it should be right under all
circumstances with the same conditions, right? In other words, if it applies
with a LF of .1 Hz or 1 Hz, it will still apply at LF's 20Hz or 50Hz, is
that not correct? I'm not trying to say that there won't be other things
that happen under real world conditions, including what other folks have
observed and stated, I'm just saying they won't be because of Doppler
distortion.
Doppler shift is a special case, and it is certainly real, and it can
even be produced with a speaker (the Leslie speaker is a good case), but the
shift isn't produced by the cone motion, it is produced by moving the
speaker, or more accurately the mouth of the baffle (the HF horn and the LF
baffle rotating).

"Bob Cain" wrote in message
...


Porky wrote:

Bob, aren't they showing a 1KHz signal modulated with a 50 Hz signal?
That isn't what happens with Doppler shift, the modulation frequency
will
depend on the velocity of the source, not its frequency of oscillation,
and
it sure won't be sidebands at +-50Hz!, more like +-3 or 4Hz! If I'm
right,
this is an example of the fundamental mis-assumptions the pro-Doppler
group
is making, just like basing their logic on an analogy that doesn't meet
the
necessary criteria..

Something quite like that is what my inuition says too but
without a deeper analysis and a better understanding of
modulation theory I don't trust my intuition on this one.


The actual frequency modulation would be determined by the velocity of the
cone, wouldn't it? It would be a shift of X Hz varying back and forth at the
rate of the LF, and it would (and did, in my experiment) result in the HF
tone showing as a table top from HF-shift to HF+shift.
I found a wave of a train whistle on a train passing, at
http://weathersavvy.com/Doppler3.html, and recorded it, trimmed off the
conductor's voice and analyzed the entire wave in Cool Edit 96, the result
was multiple peaks due to the harmonic content of the whistle, but they were
all wide and of the roughly table top variety, and with no sidebands.

Bob Cain wrote in message ...

Why don't you consider actually contributing something of
substance to this conversation? I know you are capable.

I have, but you are too stupid to recognize it.

Bob Cain wrote in message ...

Why don't you consider actually contributing something of
substance to this conversation? I know you are capable.

I have, but you are too stupid to recognize it.

Bob Cain wrote in message ...

Why don't you consider actually contributing something of
substance to this conversation? I know you are capable.

I have, but you are too stupid to recognize it.

Bob Cain wrote in message ...

Why don't you consider actually contributing something of
substance to this conversation? I know you are capable.

I have, but you are too stupid to recognize it.

"Porky"


Well, the cone is oscillating at the same frequency as the wave it's
producing, but there's still the matter of the low velocity of the air
molecules it's moving being converted to the high velocity soundwave that
we
hear. I think I see what you're saying though.



** Air molecules are never slow moving - their average speed is some 46
% greater than the speed of a sound wave.




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

"Arny Krueger" wrote in message
...
However this is NOT what we are doing here, we
are dealing with a special case of frequency shift, Doppler shift,
and we most certainly are not modulating the carrier (HF tone) with
a LF tone.

Totally wrong. We are exactly modulating the HF tone with a LF tone,
but its a bit confusing becasue there is both AM and FM and you
clearly
don't get FM.

Once again, we are NOT modulating the Hf tone with a LF tone, we are
modulating the HF tone with the supposed Doppler shift caused by the
VELOCITY of the cone moving toward us and away from us!

But the toward/away motion is exactly due to the LF tone.

But the Doppler component is solely due to the velocity of the speaker cone,
and a fair model will be one P-P cycle, because the exact same thing occurs
every cycle, so the LF frequency has absolutely nothing to do with the
doppler shift.


Since Doppler
shift is supposed to occur any time the source is moving toward or
away from the listener, the rate of the cone's moving back and forth
doesn't matter, it's the velocity of the cone supposedly causing the
shift in frequency!

The velocity of the cone and the rate of the cone's motion are closely
tied
together.

The frequency is NOT relevant to Doppler, and in fact, the spectrum
analyzer's resolution when examining multiple cycles may be contributing to
the confusion. In our example, the cone's frequency remains constant, the
velocity varies with the amplitude of the cone's motion. Of course that only
applies directly as long as the cone doesn't exceed it's linear excursion
limits, but that's not Doppler. Again, what happens in any one p-p cycle is
exactly replicated in every other cycle, so a single cycle is sufficient for
predictive analysis.

We are supposedly Doppler shifting the carrier frequency by
some amount, depending on the cone velocity of the speaker.

Right, which produces discrete sidebands that differ from the
carrier by multiples of the modulating frequency.

Try my experiment and see what you get, you are still thinking in
terms of the LF tone modulating the HF tone and that ISN"T what's
happening with Doppler shift!

I've both done and debunked your experiment. Next!

In what way? If you did what I said, you got a roughly tabletop waveform
with no sidebands. Forget about multiple cycles, reduce it to a single cycle
which will give you all the info you need for the purpose of analyzing
Doppler shift, if you scan the entire cycle.

The Doppler shift is strictly a matter
of the velocity of a sound source in relation to a listener, that's
how Doppler is defined, it has nothing to do with how often the
source changes direction!!!

But it does. If the source doesn't change direction often enough, and the
peak velocity is high enough, the cone comes sailing out of the woofer
frame, destroying the woofer.

Which has absolutely nothing to do with Doppler shift!

The cyclic changing direction creates the sidebands we observe.


But what do they have to do with doppler shift? the answer is, "Nothing!"


If you go from 500 to 600Hz and then back to 500, then you are
simulating one cycle of the speaker cone. Whether the motion is
linear or sinusoid won't matter.

Oh but it does. A linear motion is characteristic of a sawtooth modulating
wave, and that gives a different collection of sidebands. You convolve the
spectrum of the carrier with the spectrum of the modulating signal....

But even if you apply a sinusiod frequency modulation to a single cycle, you
still get the roughly tabletop waveform.


What applies to one cycle will apply
to every other cycle.

Nope, the shape of the cycle matters.

I didn't say the shape didn't matter, the shape of the top of the wave will
vary depending on if the velocity is linear or in a sine pattern, but it
remains a rough tabletop regardless. Perhaps I should have said, what
happens in any one cycle will be repeated in every other identical cycle,
and will be similar in pattern even in non-identical cycles. You can take a
single cycle at any LF with any HF Tone and any real world possibility of
waveshape of the LF component (no squarewaves, that isn't possible with a
loud speaker), and the result will still be a roughly tabletop wave
extending from HF-shift to HF+shift. That is an accurate simulation of
Doppler shift.

If Doppler shift exists, the result will be a
table top, if not Wc will be represented as a spike. Try it!

Were talking about a speaker cone that moves in a periodic cycle, not a
train on a tabletop.

Go ahead, try it, go back and forth from one frequency to the other
as many times as you wish, the results will be the same!

Trust me, I've tried a ton of things.

Try this, generate a 20 second waveform of 500 Hz being modulated
by 100 hz at a modulation frequency of .1 hz. this represents a HF
tone of 500 Hz being moved on a giant speaker moving at a velocity
high enough to result in a Doppler shift of +-20% with a LF component
of .1 Hz. for two full p-p cycles.


OK, its on the screen before me in Audition/CE

Note that you will see the same
tabletop at higher frequencies if your resolution is fine enough.

Nope. I see a spike at whatever frequency the carrrier is at, where my
analysis intersects it.

I wish that people would do their own home work.

(I used an FFT of 65536 Blackman-Harris)

That is what I use.

BTW, Audition/CE does not animate the spectral display when you play a
file.

That is as far as I can take
this, but it seems adequate to me.

I don't think you understand the relevance of the time period over which
the
analysis is performed.

The issue of Doppler distortion is
related to the relative velocity of the listener and source,

So far so good.

nothing
in Doppler theory suggests that the frequency of change of direction
will have anything to do with the amount of frequency shift.

True, but the frequency of shift and the frequency of the sidebands are
two
vastly different things.

If the change of direction is such that the velocity graph forms a sine
wave, the amount of shift will vary with the changing velocity from
instant to instant, but the result will still be a varying amount of
shift directly related to the instantaneous velocity at the time of
measurement, and the result, assuming high enough resolution of the
analyzer will be some form of tabletop waveform that varies from Wc
minus shift to Wc plus shift.

OK, I think I follow this.

If you see this tabletop wave when
recording a speaker producing a complex waveform consisting of a HF
and a LF component, Doppler distortion exists in a speaker, if you
don't, it doesn't.

In fact, an ideal frequency domain analysis will show a moving spike. Your
tabletop is an artifact of the length of your sample, which is in turn
determined by the sample size. If you analyze a wave during a time period
when it has components at a range of frequencies (this time because the
frequency is slowly changing) then you get your tabletop.

A 65k point FFT is inappropriate for analyzing a wave with a modulation
frequency of 0.1 Hz. 0.1 Hz corresponds to 10 seconds of data. Normally,
we
would use a FFT that covered several times that much data to reveal the
sideband structure. A 44100 Hz you need a FFT that would be appropriate
would have like 4 million points or more.

I tried it with my speakers and I didn't see it
on the scan (no side bands either) or hear it on playback.

You picked a demonstration that is inapprorpiate for the data at hand.
Futhermore its not representaive of speakers, because it is based on a
1/10
th Hz modulating frequency.

As I said, that's as far as I can go with this, those with advanced
education
can debate further if they desire, but I've reached my limit and this
time I'm going to respect that.:-)

You've wasted both of our time with a very poorly-formed experiment. ;-(

"Porky"

"Phil Allison"


Ignore Phil, he's just mad because he can't contribute anything
positive to this discussion, he has neither the education nor the
intelligence,

** You are well named - except pigs revelling in **** have more
sense
and manners than you do.


FYI I studied physics at the University of Sydney at honours level.

My IQ is at least double yours.

Unlike you and Bob, I do not have mental disabilities.


Oh, wow! Your IQ would be something a bit over 280, in that case.



** Wrong direction Porker - yours is only about 85.

Plus you are autistic.

Learning to sing yet ???




.......... Phil

I think I'm closing in on the truth here and, as usual, we
are (mostly) all right in some regards and are all wrong in
some.

First, my analysis of what happens in an infinite tube
containing a piston is wrong in the case of a constant
velocity component.

If the piston contains no constant velocity component then
the propegating wave will be a reproduction of the velocity
of the piston because its position is always in proper
correspondence to the velocity it is imparting so as to
impart no error. The usual intuitive rationalization for
Doppler distortion is just wrong. The process is linear and
real in this case.

However, my belief that in the tube a piston of constant
velocity imparts no constant velocity to the wave was wrong
as shown he

http://www.silcom.com/~aludwig/Physi...collisions.htm

The upshot is that there is no Doppler distortion in an
infinite tube with a driving piston in it for any signal
(until the piston smacks into the receiver if moving toward
it. :-)

In all other configurations, no Doppler distortion will
occur among components within the portion of its passband
that is fairly flat. It is the difference in the coupling
between the piston and the air at different frequencies that
produces Doppler distortion in the far field. Yes, a
speaker swinging back and forth on a rope will evidence
Doppler distortion because the low frequence swing does not
couple to the air signifigantly. This means that the
piston's position is never appropriate to the superimposed
velocities and a Doppler shift that varies with the lower
frequency velocity will occur. (I still believe the
spectrum will have a flat top if it is emitting a single
tone but that's another story.)

A Doppler distortion will occur for any two frequencies that
couple differently to the air but in the region of fairly
flat transduction, there will be none.

This is a bit more elaborate and may well contain error but
I believe it is the case and accomodates all the cases of
whistles and trains or little speakers moving in big ways.
It does say, however, that the vernacular belief in Doppler
distortion from a speaker due to components within its flat
passband is simply wrong.

Whatcha think?


Bob
--

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

A. Einstein

On 18 Aug 2004 19:46:37 -0700, (The Ghost)
wrote:

Bob Cain wrote in message ...

Why don't you consider actually contributing something of
substance to this conversation? I know you are capable.

I have, but you are too stupid to recognize it.

You really want ...
-----
http://mindspring.com/~benbradley

On 18 Aug 2004 19:47:02 -0700, (The Ghost)
wrote:

Bob Cain wrote in message ...

Why don't you consider actually contributing something of
substance to this conversation? I know you are capable.

I have, but you are too stupid to recognize it.

... to hammer your ...
-----
http://mindspring.com/~benbradley

On 18 Aug 2004 19:47:14 -0700, (The Ghost)
wrote:

Bob Cain wrote in message ...

Why don't you consider actually contributing something of
substance to this conversation? I know you are capable.

I have, but you are too stupid to recognize it.

... point home tonight, ...
-----
http://mindspring.com/~benbradley

On 18 Aug 2004 19:47:15 -0700, (The Ghost)
wrote:

Bob Cain wrote in message ...

Why don't you consider actually contributing something of
substance to this conversation? I know you are capable.

I have, but you are too stupid to recognize it.

... don't you?

-----
Burma Shave, anyone?
http://mindspring.com/~benbradley

The Ghost wrote:

Bob Cain wrote in message ...


Why don't you consider actually contributing something of
substance to this conversation? I know you are capable.


I have, but you are too stupid to recognize it.

This must be Phil Allison using Gary Sokolich's handle.
Careful, Phil, Gary is one nasty, sociopathic SOB and if he
gets wind of this you are in real deap ****. He will stalk
you until the end of your days.


Bob
--

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

A. Einstein

"Arny Krueger" wrote in message
...

That's because the train is not moving back and forth in front of us, in a
periodic sine-shaped pattern.

You OBVIOUSLY have not seen the trains in America!

Bob Cain wrote in message ...


Why don't you consider actually contributing something of
substance to this conversation? I know you are capable.


I have. The problem is that you are too stupid to recognize it.

"Phil Allison" wrote in message
...

"Porky"


Well, the cone is oscillating at the same frequency as the wave it's
producing, but there's still the matter of the low velocity of the air
molecules it's moving being converted to the high velocity soundwave
that
we
hear. I think I see what you're saying though.



** Air molecules are never slow moving - their average speed is some
46
% greater than the speed of a sound wave.


Not the point, because they are all moving at random, and if you set your
thermostat to absolute zero, they don't move at all. General molecular
motion is a function of temperature, and other than a small variation of the
speed of sound with temperature it has little to do with this thread.
My point was that the cone's velocity is a very small compared to the
velocity of propagation of sound and the range of its excursion is very
small compared to the wavelength of the tone it is producing . Thus a low
velocity, small movement of the air in front of the cone is translated into
a high velocity, long acoustic wave by a mechanism I know I don't need to
explain to you because, with your IQ of 280, you grok it to the fullest
instantly.

Bob Cain wrote in message ...

Why don't you consider actually contributing something of
substance to this conversation? I know you are capable.

I have, but you are too stupid to recognize it.

"William Sommerwerck" wrote in message ...


In terms of the question Bob Cain initially asked, the formula doesn't matter,
because Doppler shift exists regardless of whether you're working in
constant-velocity medium ("the luminiferous ether") or a non-constant-velocity
medium (air).

The formulas are different, but that doesn't have anything to do with the nature of the argument.

Just to clarify my previous comments, I was referring to the velocity
of the source, not the medium...........ie a constant velocity source
such as a horn on a train vs a loudspeaker that is moving back and
forth at a low frequency and simultaneously radiating a high frequency
sound.

"Phil Allison" wrote in message
...

"Porky"

"Phil Allison"


Ignore Phil, he's just mad because he can't contribute anything
positive to this discussion, he has neither the education nor the
intelligence,

** You are well named - except pigs revelling in **** have more
sense
and manners than you do.


FYI I studied physics at the University of Sydney at honours
level.

My IQ is at least double yours.

Unlike you and Bob, I do not have mental disabilities.


Oh, wow! Your IQ would be something a bit over 280, in that case.



** Wrong direction Porker - yours is only about 85.

Plus you are autistic.

Learning to sing yet ???

Wrong, Phool, my IQ is a bit over 140 to a bit over 150, depending on the IQ
test used. Modest being that I am, I use the lower figure.
Yes, I am artistic, I am a musician and I paint on occasion, and I just love
your southern drawl.
Unlike you, I am always learning, period, and also unlike you, I have the
wisdom to learn and benefit from my mistakes.
BTW, I can sing, I just have a lousy voice and there is nothing I can do
about it.

"Jim Carr" wrote in message
news:1gVUc.10087$yh.1675@fed1read05...
"Arny Krueger" wrote in message
...

That's because the train is not moving back and forth in front of us, in
a
periodic sine-shaped pattern.

You OBVIOUSLY have not seen the trains in America!

Yeah, we have AMtrack, not FMtrack....

"Bob Cain" wrote in message
...

I think I'm closing in on the truth here and, as usual, we
are (mostly) all right in some regards and are all wrong in
some.

First, my analysis of what happens in an infinite tube
containing a piston is wrong in the case of a constant
velocity component.

If the piston contains no constant velocity component then
the propegating wave will be a reproduction of the velocity
of the piston because its position is always in proper
correspondence to the velocity it is imparting so as to
impart no error. The usual intuitive rationalization for
Doppler distortion is just wrong. The process is linear and
real in this case.

However, my belief that in the tube a piston of constant
velocity imparts no constant velocity to the wave was wrong
as shown he

http://www.silcom.com/~aludwig/Physi...collisions.htm

The upshot is that there is no Doppler distortion in an
infinite tube with a driving piston in it for any signal
(until the piston smacks into the receiver if moving toward
it. :-)

In all other configurations, no Doppler distortion will
occur among components within the portion of its passband
that is fairly flat. It is the difference in the coupling
between the piston and the air at different frequencies that
produces Doppler distortion in the far field. Yes, a
speaker swinging back and forth on a rope will evidence
Doppler distortion because the low frequence swing does not
couple to the air signifigantly. This means that the
piston's position is never appropriate to the superimposed
velocities and a Doppler shift that varies with the lower
frequency velocity will occur. (I still believe the
spectrum will have a flat top if it is emitting a single
tone but that's another story.)

A Doppler distortion will occur for any two frequencies that
couple differently to the air but in the region of fairly
flat transduction, there will be none.

This is a bit more elaborate and may well contain error but
I believe it is the case and accomodates all the cases of
whistles and trains or little speakers moving in big ways.
It does say, however, that the vernacular belief in Doppler
distortion from a speaker due to components within its flat
passband is simply wrong.

Whatcha think?


If you mean that a whistle riding on a moving train, or a speaker
swinging back and forth (or spinning round and round like in a Leslie
speaker system) in a repeating oscillation cycle will produce Doppler shift,
but a stationary speaker reproducing a complex waveform containing a mixed
LF and HF tone (or any multiple combination of tones, as would be the case
in a complex musical waveform) won't produce Doppler shift, then, by golly,
I think you're right!

"Porky"

"Phil Allison"


** Wrong direction Porker - yours is only about 85.

Plus you are autistic.

Learning to sing yet ???

Wrong, Phool, my IQ is a bit over 140 to a bit over 150, depending on the
IQ
test used. Modest being that I am, I use the lower figure.
Yes, I am artistic, I am a musician and I paint on occasion, and I just
love
your southern drawl.


** The word was "'autistic" - which proves my point.





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