Doppler Distortion - Fact or Fiction

Tags:
Last response: in Home Audio
Share
Anonymous

I've got an argument that so far has withstood some scrutiny
which shows that Doppler distortion in a myth.

What would refute it and point out any flaw in the reasoning
would be the dynamical expression for the time varying
function of the pressure wave in an infinite tube with an
ideal piston as a function of an arbitrary, time varying
function of the force applied to that piston. I've asked
numerous places for that, including alt.sci.acoustics,
sci.physics and sci.physics.research and have looked hard
for a solution in the literature. Nothing to date. I think
there is a good reason for that; the force and pressure in
the wave are simply proportional and thus there is no such
thing as Doppler distortion. At least that is what my
reasoning from first principles says.

So I'm issuing a challenge to anyone here that thinks they
might be able to analyze it and produce an equation that
isn't a simple proportionality and is non-linear, as it must
be for the frequency modulation required of this so called
Doppler distortion. If you do it and it withstands peer
scrutiny, you get the pleasure of knowing that I have a
leather hat meal awaiting me (and the strong possiblity that
you've gone where no one else has gone before.) :-)

No heuristic arguments involving two tones, please, but a
real (or complex) equation that applies to any signal.

Bob
--

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

A. Einstein
Anonymous

I think there are two simple refutations, one theoretical, the other practical.

Theoretical -- If the output of a driver accurately follows its input waveform,
how can there be Doppler distortion?

Practical -- It should be trivial to compute the sidebands produced by combining
(say) a 60Hz signal and 6000 Hz signal. By looking at the phase of the
sidebands, it should be possible to determine what part of them is IM distortion
(AM components) and what part is Doppler (FM components).
Anonymous

Arny Krueger <arnyk@hotpop.com> wrote:
>"Bob Cain" <arcane@arcanemethods.com> wrote in message
>
>> I've got an argument that so far has withstood some scrutiny
>> which shows that Doppler distortion in a myth.
>
>> What would refute it and point out any flaw in the reasoning
>> would be the dynamical expression for the time varying
>> function of the pressure wave in an infinite tube with an
>> ideal piston as a function of an arbitrary, time varying
>> function of the force applied to that piston.
>
>Fool that I am, I'm kinda stuck down here in the real world. Forget the
>math, forget the long-winded discussions, the question that interests me
>most is whether or not there's Doppler distortion where it really matters -
>in the sound field in front of the speaker.

Well, surprisingly enough, Phil actually made the good point that the woofer
position does not directly follow the input signal, but that the excursion
at lower frequencies is exaggerated. This is indeed the reason that we get
Doppler distortion. But, how do we compensate for this? And can we, even?

Of course, reducing the bandwidth to each driver and reducing the driver
excursion as much as possible are crude ways around the problem.

A more exaggerated example of the distortion, though, is found in coaxial
speakers where the moving woofer cone is used as the horn for the tweeter.
Here, though, I am not sure the math model is quite so easy, and it would
be interesting to see if anyone can model the boundary effects near the
moving woofer cone.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Related resources
Anonymous

"Scott Dorsey" <kludge@panix.com> wrote in message
news:cfd8cj\$neb\$1@panix2.panix.com
> Arny Krueger <arnyk@hotpop.com> wrote:

>> "Bob Cain" <arcane@arcanemethods.com> wrote in message

>>> I've got an argument that so far has withstood some scrutiny
>>> which shows that Doppler distortion in a myth.

>>> What would refute it and point out any flaw in the reasoning
>>> would be the dynamical expression for the time varying
>>> function of the pressure wave in an infinite tube with an
>>> ideal piston as a function of an arbitrary, time varying
>>> function of the force applied to that piston.

>> Fool that I am, I'm kinda stuck down here in the real world. Forget
>> the math, forget the long-winded discussions, the question that
>> interests me most is whether or not there's Doppler distortion where
>> it really matters - in the sound field in front of the speaker.

> Well, surprisingly enough, Phil actually made the good point that the
> woofer position does not directly follow the input signal, but that
> the excursion at lower frequencies is exaggerated. This is indeed
> the reason that we get Doppler distortion.

I would say that the exaggerated excursion at low frequencies is a
contributing cause for Doppler distortion, but not the only cause.

> But, how do we compensate for this? And can we, even?

> Of course, reducing the bandwidth to each driver and reducing the
> driver excursion as much as possible are crude ways around the problem.

Crude but effective! ;-)

Doppler is exactly proportional to the upper frequency being modulated. Drop
the upper crossover frequency on that woofer by a factor of two, and you
drop the Doppler distortion by 2. Double the diaphragm area, and you get the
same benefit. Subwoofers make even more sense!

BTW, this effect is the justification for the triple-tone tests posted at
http://www.pcavtech.com/techtalk/doppler/ . The FM-related sidebands on the
uppermost tone (4.25 KHz) will be about 4 times larger, compared to the
carrier, as those on the middle tone (1.0 KHz). The two tones are not even
multiples of each other so that the sidebands from each tone will not be
unlikely to land on top the sidebands of the other.

> A more exaggerated example of the distortion, though, is found in
> coaxial speakers where the moving woofer cone is used as the horn for
> the tweeter.

Yes, and I even have a KEF Q-15 to test that with.

However, our preliminary results show that even with a reasonable worst case
(small woofer, relatively high upper frequency) the Doppler tends to get
lost in the AM distortion. Claiming it isn't there is wrong, but getting
worked up about it seems a little foolish.

>Here, though, I am not sure the math model is quite so
> easy, and it would be interesting to see if anyone can model the
> boundary effects near the moving woofer cone.

It's tough enough to work with the case we're working with, which seems to
be far simpler.
Anonymous

Arny Krueger <arnyk@hotpop.com> wrote:
>"Scott Dorsey" <kludge@panix.com> wrote in message
>
>> Well, surprisingly enough, Phil actually made the good point that the
>> woofer position does not directly follow the input signal, but that
>> the excursion at lower frequencies is exaggerated. This is indeed
>> the reason that we get Doppler distortion.
>
>I would say that the exaggerated excursion at low frequencies is a
>contributing cause for Doppler distortion, but not the only cause.

On a typical full-range speaker _not_ breaking up, what other good
causes are there? With coaxials and with speakers in breakup, there
are all kinds of wacky things going on.

The only other cause I can think of has to do with compressibility of
air and it would seem to be a comparatively small issue.

>> But, how do we compensate for this? And can we, even?
>
>> Of course, reducing the bandwidth to each driver and reducing the
>> driver excursion as much as possible are crude ways around the problem.
>
>Crude but effective! ;-)
>
>Doppler is exactly proportional to the upper frequency being modulated. Drop
>the upper crossover frequency on that woofer by a factor of two, and you
>drop the Doppler distortion by 2.

That's reducing the bandwidth.

>Double the diaphragm area, and you get the
>same benefit.

That's reducing the driver excursion.

>Subwoofers make even more sense!

Yes, but they bring another whole set of issues along with them.

>> A more exaggerated example of the distortion, though, is found in
>> coaxial speakers where the moving woofer cone is used as the horn for
>> the tweeter.
>
>Yes, and I even have a KEF Q-15 to test that with.

it.

It would be interesting to see if the Urei horn assemblies on the Altec
coaxial drivers really do minimize doppler modulation compared with the
original Altec horn assemblies. That was one of the arguments the Urei
guys used for the extended horns they employed.

>However, our preliminary results show that even with a reasonable worst case
>(small woofer, relatively high upper frequency) the Doppler tends to get
>lost in the AM distortion. Claiming it isn't there is wrong, but getting
>worked up about it seems a little foolish.

Yes, but how audible is it? You can treat the doppler modulation sort of
like spurious sidebands, BUT they are sidebands that are modulated by
the signal. Does it make it mode or less audible than a fixed sideband?

>>Here, though, I am not sure the math model is quite so
>> easy, and it would be interesting to see if anyone can model the
>> boundary effects near the moving woofer cone.
>
>It's tough enough to work with the case we're working with, which seems to
>be far simpler.

Right, because you have pretty much one dominant distortion source, and it
is an easy one to model. You should be able to plug and chug and get a
simple value for doppler distortion due to increased excursion at low
frequencies, knowing little more than the tone frequencies and the driver
excursion for a given cabinet. How does that compare with the measured
doppler modulation on that cabinet? That will tell you if there are any
other hidden effects to worry about.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous

William Sommerwerck wrote:

> I think there are two simple refutations, one theoretical, the other practical.
>
> Theoretical -- If the output of a driver accurately follows its input waveform,
> how can there be Doppler distortion?

Precisely, and an argument by reciprocity shows that to be
the case. If you measure the particle (voxel if you don't
like discrete) velocity and then make the reproducing system
follow that velocity function then what goes out as a wave
will be the same as what was measured.

>
> Practical -- It should be trivial to compute the sidebands produced by combining
> (say) a 60Hz signal and 6000 Hz signal. By looking at the phase of the
> sidebands, it should be possible to determine what part of them is IM distortion
> (AM components) and what part is Doppler (FM components).
>

Non-linearities mix in very wierd ways. The only real
experimental test would require a super-linear driver and
those are hard to find.

Bob
--

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

A. Einstein
Anonymous

"Scott Dorsey" <kludge@panix.com> wrote in message
news:cfdaf6\$41b\$1@panix2.panix.com

> Arny Krueger <arnyk@hotpop.com> wrote:
>> "Scott Dorsey" <kludge@panix.com> wrote in message

>>> Well, surprisingly enough, Phil actually made the good point that
>>> the woofer position does not directly follow the input signal, but
>>> that the excursion at lower frequencies is exaggerated. This is
>>> indeed the reason that we get Doppler distortion.

>> I would say that the exaggerated excursion at low frequencies is a
>> contributing cause for Doppler distortion, but not the only cause.

> On a typical full-range speaker _not_ breaking up, what other good
> causes are there?

My point is that you don't need exaggerated excursion, just any substantial
excursion at all.

> With coaxials and with speakers in breakup, there
> are all kinds of wacky things going on.

Agreed.

> The only other cause I can think of has to do with compressibility of
> air and it would seem to be a comparatively small issue.

>>> But, how do we compensate for this? And can we, even?

>>> Of course, reducing the bandwidth to each driver and reducing the
>>> driver excursion as much as possible are crude ways around the
>>> problem.

>> Crude but effective! ;-)

>> Doppler is exactly proportional to the upper frequency being
>> modulated. Drop the upper crossover frequency on that woofer by a
>> factor of two, and you drop the Doppler distortion by 2.

> That's reducing the bandwidth.

Agreed. I just added some quantification.

>> Double the diaphragm area, and you get the
>> same benefit.

> That's reducing the driver excursion.

Agreed. I just added some quantification.

>> Subwoofers make even more sense!

> Yes, but they bring another whole set of issues along with them.

Again, agreed.

>>> A more exaggerated example of the distortion, though, is found in
>>> coaxial speakers where the moving woofer cone is used as the horn
>>> for the tweeter.

>> Yes, and I even have a KEF Q-15 to test that with.

> A better one would be one of the Radian drivers, which are really bad

I really don't see a lot of difference. Compression driver tweeter versus
woofers. OTOH, they are probably more likely to be driven very hard.

> It would be interesting to see if the Urei horn assemblies on the
> Altec coaxial drivers really do minimize Doppler modulation compared
> with the original Altec horn assemblies. That was one of the
> arguments the Urei guys used for the extended horns they employed.

Underlying this all is how much Doppler is there, and how audible is it?
Right now we've got a fairly extreme case, and we're scratching pretty hard
to find the Doppler FM in and among all of the AM distortion.

>> However, our preliminary results show that even with a reasonable
>> worst case (small woofer, relatively high upper frequency) the
>> Doppler tends to get lost in the AM distortion. Claiming it isn't
>> there is wrong, but getting worked up about it seems a little
>> foolish.

> Yes, but how audible is it? You can treat the Doppler modulation
> sort of like spurious sidebands, BUT they are sidebands that are
> modulated by the signal. Does it make it mode or less audible than a
> fixed sideband?

For small modulation indices, the sidebands related to AM and FM follow
similar rules. One difference is the fact that the modulation index for FM
rises with carrier frequency. AM sidebands maintain a constant relative
amplitude as the carrier frequency rises, all other things being equal.

>>> Here, though, I am not sure the math model is quite so
>>> easy, and it would be interesting to see if anyone can model the
>>> boundary effects near the moving woofer cone.

>> It's tough enough to work with the case we're working with, which
>> seems to be far simpler.

> Right, because you have pretty much one dominant distortion source,
> and it is an easy one to model.

But, that dominant modulation source seems to want to be AM, not FM.

>You should be able to plug and chug
> and get a simple value for Doppler distortion due to increased
> excursion at low frequencies, knowing little more than the tone
> frequencies and the driver excursion for a given cabinet.

There's quite a bit about that in the technical literature. I cited some of
the JAES papers about a week ago in another forum.

> How does
> that compare with the measured Doppler modulation on that cabinet?
> That will tell you if there are any other hidden effects to worry

Theory and practice seem to correspond pretty well.
Anonymous

Arny Krueger wrote:

> Fool that I am, I'm kinda stuck down here in the real world. Forget the
> math,

Then we are whistling in the dark. I admire your
experimentalist approach. Experiment trumps theory, always.

I just ask that you draw no conclusions from a system that
contains measurable non-linearity in the transducer itself.

Bob
--

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

A. Einstein
Anonymous

Arny Krueger <arnyk@hotpop.com> wrote:
>"Scott Dorsey" <kludge@panix.com> wrote in message
>news:cfdaf6\$41b\$1@panix2.panix.com
>
>> Arny Krueger <arnyk@hotpop.com> wrote:
>>> "Scott Dorsey" <kludge@panix.com> wrote in message
>
>>>> Well, surprisingly enough, Phil actually made the good point that
>>>> the woofer position does not directly follow the input signal, but
>>>> that the excursion at lower frequencies is exaggerated. This is
>>>> indeed the reason that we get Doppler distortion.
>
>>> I would say that the exaggerated excursion at low frequencies is a
>>> contributing cause for Doppler distortion, but not the only cause.
>
>> On a typical full-range speaker _not_ breaking up, what other good
>> causes are there?
>
>My point is that you don't need exaggerated excursion, just any substantial
>excursion at all.

No. If the motion of the cone perfectly follows the waveform, and the air
is not compressable, the pressure waveform that results in the air will be
a perfect representation of the original wave. If you can somehow arrange
for perfect coupling so that the woofer excursion perfectly matches the
input signal, doppler effects should be a non-issue. Unfortunately this
does not go along well with accurate frequency response in the real world.

>For small modulation indices, the sidebands related to AM and FM follow
>similar rules. One difference is the fact that the modulation index for FM
>rises with carrier frequency. AM sidebands maintain a constant relative
>amplitude as the carrier frequency rises, all other things being equal.

Right, but what you are seeing are not just fixed sidebands, but sidebands
that are modulated by another signal. If you've got a fixed sideband caused
by constant modulation, the audibility of it is predictable and there are
some good studies on audibility. If it's not caused by constant modulation,
all that becomes meaningless.

>> Right, because you have pretty much one dominant distortion source,
>> and it is an easy one to model.
>
>But, that dominant modulation source seems to want to be AM, not FM.

So?

>>You should be able to plug and chug
>> and get a simple value for Doppler distortion due to increased
>> excursion at low frequencies, knowing little more than the tone
>> frequencies and the driver excursion for a given cabinet.
>
>There's quite a bit about that in the technical literature. I cited some of
>the JAES papers about a week ago in another forum.

Right. It's very easy to model that effect. The questions are how audible
it is, and whether there are any other effects involved. The latter is easier
to answer than it seems, the former is probably more difficult.

>> How does
>> that compare with the measured Doppler modulation on that cabinet?
>> That will tell you if there are any other hidden effects to worry
>
>Theory and practice seem to correspond pretty well.

If that is the case, then there should really be no other doppler sources
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous

Scott Dorsey wrote:

> No. If the motion of the cone perfectly follows the waveform, and the air
> is not compressable, the pressure waveform that results in the air will be
> a perfect representation of the original wave. If you can somehow arrange
> for perfect coupling so that the woofer excursion perfectly matches the
> input signal, doppler effects should be a non-issue. Unfortunately this
> does not go along well with accurate frequency response in the real world.

However, for it to be a real, non-linear effect it must be
demonstrable in a hyperlinear transducer. All linear
imperfections in the system can be cancelled by a suitable
linear function block between the input and the transducer
such that the cone follows the waveform. If there are
non-linearities in the transducer all bets are off because
we don't really know what is the cause of the resulting
non-linear output.

The reason that it must be a non-linear effect is that any
linear system has sinusoids as eigenfunctions.
Eigenfunctions are those functions which when presented to
the system as input, in any summation, result in an output
that contains only complex scalings of the magnitudes of the
input eigenfunctions, which are called the eigenvalues.
Scaling zero results in zero which means that no non-zero
eigenvalues can result in the output which were zero in the
input. The hypothetical Doppler distortion fails this test.

> Right. It's very easy to model that effect.

Actually, for an arbitrary input it has not been done.
There is no model even that will quantitatively predict the
measured result of experiments with two tones.

Bob
--

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

A. Einstein
Anonymous

"William Sommerwerck" <williams@nwlink.com> wrote in message
news:10hjsuu23dlsqfe@corp.supernews.com...
> I think there are two simple refutations, one theoretical, the other
practical.
>
> Theoretical -- If the output of a driver accurately follows its input
waveform,
> how can there be Doppler distortion?

If the driver converted voltage to air pressure, there could be no Doppler
distortion.
However, the driver, even under the best of circumstances, does not do that.
It converts, approximately, to displacement.

Displacement is not equivalent to air pressure.
>
> Practical -- It should be trivial to compute the sidebands produced by
combining
> (say) a 60Hz signal and 6000 Hz signal. By looking at the phase of the
> sidebands, it should be possible to determine what part of them is IM
distortion
> (AM components) and what part is Doppler (FM components).
>
Anonymous

Doppler distortion obviously exists. The question is one of how audible it is.

My feelings are "not very." You don't hear people who own full-range

Consider the following. Suppose an electrostatic speaker is reproducting 60Hz at
a peak-to-peak excursion of 0.25". That means its maximum velocity would be
around 30 inches per second. That's less than 1/4 of 1% of the speed of sound!

I really, really doubt that's audible.
Anonymous

Robert Morein wrote:

> If the driver converted voltage to air pressure, there could be no Doppler
> distortion.
> However, the driver, even under the best of circumstances, does not do that.
> It converts, approximately, to displacement.

I'm afraid this is incorrect. The heuristics usually used
to describe this effect apply equally well to an ideal
system where a massless, infinitely compliant and lossless
piston is driven by a force function.

Bob
--

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

A. Einstein
Anonymous

"Scott Dorsey" <kludge@panix.com> wrote in message
news:cfde31\$2nj\$1@panix2.panix.com
> Arny Krueger <arnyk@hotpop.com> wrote:
>> "Scott Dorsey" <kludge@panix.com> wrote in message
>> news:cfdaf6\$41b\$1@panix2.panix.com
>>
>>> Arny Krueger <arnyk@hotpop.com> wrote:
>>>> "Scott Dorsey" <kludge@panix.com> wrote in message
>>
>>>>> Well, surprisingly enough, Phil actually made the good point that
>>>>> the woofer position does not directly follow the input signal, but
>>>>> that the excursion at lower frequencies is exaggerated. This is
>>>>> indeed the reason that we get Doppler distortion.
>>
>>>> I would say that the exaggerated excursion at low frequencies is a
>>>> contributing cause for Doppler distortion, but not the only cause.
>>
>>> On a typical full-range speaker _not_ breaking up, what other good
>>> causes are there?
>>
>> My point is that you don't need exaggerated excursion, just any
>> substantial excursion at all.

> No.

Yes.

>If the motion of the cone perfectly follows the waveform, and
> the air is not compressable, the pressure waveform that results in
> the air will be a perfect representation of the original wave.

Scott, I think you've missed a critical point. A speaker is a transducer,
and that means that in the process of following the waveform ideally, the
results in the air can be a little different than what was intended.

> If you can somehow arrange for perfect coupling so that the woofer
> excursion perfectly matches the input signal, doppler effects should
> be a non-issue.

No. Imperfect woofer excursion is more along the line of AM effects.

> Unfortunately this does not go along well with
> accurate frequency response in the real world.

I think that this issue of imperfect cone motion has some light shed on it
by contemplating a system with a tweeter, versus a system that lacks one. In
both cases the respective signals are transduced into the air with ideal
waveforms. The Doppler comes from the fact that the HF gets transduced into
the air from a platform with large-scale motion due to some other signal.
The tweeter does not have this situation.

It's like the train whistle. The whistle itself need not be affected by its
motion through the air. The fact that the whistle is moving w/r/t the
listener is the root cause of the Doppler effect.

>> For small modulation indices, the sidebands related to AM and FM
>> follow similar rules. One difference is the fact that the modulation
>> index for FM rises with carrier frequency. AM sidebands maintain a
>> constant relative amplitude as the carrier frequency rises, all
>> other things being equal.

> Right, but what you are seeing are not just fixed sidebands, but
> sidebands that are modulated by another signal.

Well, if there was no modulation, there would be no sidebands. So, the
presence of sidebands are *always* due to that other signal that is
modulating the carrier. When you FM modulate with a continuous wave, the
sidebands are fixed in the frequency spectrum just like the ones for AM. The
FM effect comes from the vector sum of the sidebands and the carrier. In AM,
the AM effect comes from a similar vector sum.

> If you've got a fixed sideband caused by constant modulation, the
audibility of it is
> predictable and there are some good studies on audibility. If it's
> not caused by constant modulation, all that becomes meaningless.

I wouldn't call it meaningless, I'd call it potentially very nasty to
analyze and characterize.

>>> Right, because you have pretty much one dominant distortion source,
>>> and it is an easy one to model.

>> But, that dominant modulation source seems to want to be AM, not FM.

> So?

Which means that while we can't deny that the FM is there, we assign it a
lower importance until we fix the AM distortion a whole lot more.

>>> You should be able to plug and chug
>>> and get a simple value for Doppler distortion due to increased
>>> excursion at low frequencies, knowing little more than the tone
>>> frequencies and the driver excursion for a given cabinet.

>> There's quite a bit about that in the technical literature. I cited
>> some of the JAES papers about a week ago in another forum.

> Right. It's very easy to model that effect. The questions are how
> audible it is, and whether there are any other effects involved. The
> latter is easier to answer than it seems, the former is probably more
> difficult.

The BIG other effect is AM.

The audibility of AM and FM is similar. The sidebands are heard as a varying
carrier when they are very close to the carrrier. They are heard as
*roughness* for sidebands that are moderately close to the carrier. When the
sidebands get widely dispersed they eventually crawl out from under the
masking curve and are heard as separate tones.

>>> How does
>>> that compare with the measured Doppler modulation on that cabinet?
>>> That will tell you if there are any other hidden effects to worry
>
>> Theory and practice seem to correspond pretty well.

> If that is the case, then there should really be no other doppler
> sources you need to worry about.

Frankly, I'm not all that worried about the sources we know about. The other
sources are known to be even smaller.
Anonymous

"William Sommerwerck" <williams@nwlink.com> wrote in message
news:10hki31tolf6o38@corp.supernews.com

> Doppler distortion obviously exists. The question is one of how
> audible it is.

Agreed.

> My feelings are "not very." You don't hear people who own full-range
> electrostatics complaining about Doppler distortion.

AFAIK, I can't think of a reasonable case where anybody should complain
about Doppler (FM) distortion in loudspeakers.

> Consider the following. Suppose an electrostatic speaker is
> reproducing 60Hz at a peak-to-peak excursion of 0.25".

I did a little rummaging around. It appears that a practical inter-electrode
gap for an electrostatic speaker might be 2 mm or about 0.05". I believe
that bad things might happen if the diaphragm traversed a great deal of that
gap.

In the +20 example posted at http://www.pcavtech.com/techtalk/doppler/ , the
cone excursion was very roughly on the order of 1/8" . There was a ton of
distortion, almost all of which was AM distortion, not FM.

>That means its maximum velocity would be around 30 inches per second.
That's
> less than 1/4 of 1% of the speed of sound!

With suitable adjustments, the probable maximum excursion is far, far less,
making the resulting FM distortion far, far less.

> I really, really doubt that's audible.

Agreed.

I admit it, my interest in Doppler distortion was peaked by someone who had
doubts about high-Xmax woofers because of the exposure to Doppler
distortion.
Anonymous

>> Consider the following. Suppose an electrostatic speaker is
>> reproducing 60Hz at a peak-to-peak excursion of 0.25".

>> That means its maximum velocity would be around 30 inches
>> per second. That's less than 1/4 of 1% of the speed of sound!

> It appears that a practical inter-electrode gap for an electrostatic
> speaker might be 2 mm or about 0.05". I believe that bad things
> might happen if the diaphragm traversed a great deal of that gap.

> In the +20 example posted at http://www.pcavtech.com/techtalk/doppler,
> the cone excursion was very roughly on the order of 1/8". There was
> a ton of distortion, almost all of which was AM distortion, not FM.

I deliberately chose an obviously extreme (!!!) situation to make the point.

> I admit it, my interest in Doppler distortion was peaked by someone
> to Doppler distortion.

piqued
Anonymous

As a non-mathematical type I understood Doppler distortion to be caused
when a high frequency was generated by a driver already in motion with a
low frequency.

The example was a woofer moving full excursion on a very low tone while
generating a higher tone. Let's do an extreme case of a 10 Hz excursion
and a 1000 Hz tone. Every 20th of a second (change in direction at 10 Hz)
the pitch of the 1000 Hz tone would change as its vibrating medium (the
woofer cone) changed from moving toward the listener to moving away.
Anonymous

"Carey Carlan" <gulfjoe@hotmail.com> wrote in message
news:Xns95425D5ACF8BBgulfjoehotmailcom@207.69.154.203

> As a non-mathematical type I understood Doppler distortion to be
> caused when a high frequency was generated by a driver already in
> motion with a low frequency.

That's it.

> The example was a woofer moving full excursion on a very low tone
> while generating a higher tone. Let's do an extreme case of a 10 Hz
> excursion and a 1000 Hz tone. Every 20th of a second (change in
> direction at 10 Hz) the pitch of the 1000 Hz tone would change as its
> vibrating medium (the woofer cone) changed from moving toward the
> listener to moving away.

Yes, that's it. Just like the whistle on a busy train engine in a switch
yard. No amplitude modulation distortion required.

I probably have an easier time than most with this sort of thing because of
my long-ago tour with Uncle Sam as a Doppler Radar technican.

If some of the arguments presented were taken to their logical conclusion,
the whole missle system I worked on would have never worked.

While high tech military toys of that era tended to be dodgy, the one I
worked on could at least partially work, and did I see the most important
parts of it work from incoming bogey to big bang in the sky.
Anonymous

Carey Carlan wrote:

> As a non-mathematical type I understood Doppler distortion to be caused
> when a high frequency was generated by a driver already in motion with a
> low frequency.

That's the definition. What is needed to put the question
to bed is a general dynamical equation for what happens at a
piston-air interface which will yield that result when
applied to a sum of such sinusiods. No such equation has
been forthcoming in places where it should be a trivial
exercise for those in attendance.

Bob
--

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

A. Einstein
Anonymous

>Doppler distortion obviously exists. The question is one of how audible it is.
>
>My feelings are "not very." You don't hear people who own full-range
>
>Consider the following. Suppose an electrostatic speaker is reproducting 60Hz at
>a peak-to-peak excursion of 0.25". That means its maximum velocity would be
>around 30 inches per second. That's less than 1/4 of 1% of the speed of sound!

Right, but this is a speaker that has a huge surface area and therefore has
a very low total excursion. This is a _good_ thing. When your woofer
excursion starts getting to be an order of magnitude larger, the numbers
change. But the large surface area of an electrostatic panel means you can
get considerable bass without substantial excursion... which is good because
nonlinearities in the field become a big issue when there is substantial
excursion.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous

>> Doppler distortion obviously exists. The question is one of how audible it
is.
>> My feelings are "not very." You don't hear people who own full-range
>> electrostatics complaining about Doppler distortion.

>> Consider the following. Suppose an electrostatic speaker is reproducting 60Hz
at
>> a peak-to-peak excursion of 0.25". That means its maximum velocity would be
>> around 30 inches per second. That's less than 1/4 of 1% of the speed of
sound!

> Right, but this is a speaker that has a huge surface area and therefore has
> a very low total excursion. This is a _good_ thing. When your woofer
> excursion starts getting to be an order of magnitude larger, the numbers
> change. But the large surface area of an electrostatic panel means you can
> get considerable bass without substantial excursion... which is good because
> nonlinearities in the field become a big issue when there is substantial
> excursion.

All correct, but multi-way dynamic systems with such large excursions eliminate
much of the potential for Doppler distortion, simply because the higher
frequencies are reproduced through a separate driver.

Note, also, that such a large excursion would usually occur on a bass transient,
not during "normal" (???) music.
Anonymous

"William Sommerwerck" <williams@nwlink.com> wrote in message
news:10hki31tolf6o38@corp.supernews.com...
> Doppler distortion obviously exists. The question is one of how audible it
is.
>
> My feelings are "not very." You don't hear people who own full-range
> electrostatics complaining about Doppler distortion.
>
> Consider the following. Suppose an electrostatic speaker is reproducting
60Hz at
> a peak-to-peak excursion of 0.25". That means its maximum velocity would
be
> around 30 inches per second. That's less than 1/4 of 1% of the speed of
sound!
>
> I really, really doubt that's audible.
>
Electrostatics should be less prone to doppler than many other speakers,
because of the large diaphram size.
1/4" is an impossible excursion for an electrostatic, because electric force
is much weaker than magnetic force.
The diaphrams of these speakers move minutely, inversely proportional to the
size of the diaphram for a given SPL.

The most serious examples would be:
1. a two-way, with a bass/mid driver that's really pumping
2. A three-way with a small driver optimized for dispersion, in which case
both the bass and mid drivers might be stressed.

I'm not commenting on the audibility of Doppler, only that an electrostat is
not a good example.

I do own Acoustat 2+2's, and I do not complain about Doppler distortion
Unless it were introduced to me in a laboratory setting, I would have no way
of recognizing it.
Anonymous

"Bob Cain" <arcane@arcanemethods.com> wrote in message
news:cfdm3u018rv@enews4.newsguy.com

> Arny Krueger wrote:

>> Fool that I am, I'm kinda stuck down here in the real world. Forget
>> the math,

> Then we are whistling in the dark. I admire your
> experimentalist approach. Experiment trumps theory, always.

> I just ask that you draw no conclusions from a system that
> contains measurable non-linearity in the transducer itself.

I think that's being too restrictive. We have at least two ways to
distinguish AM from FM. The fact that we're finding so much AM is probably a
guide to the most practical answer.
Anonymous

Arny Krueger wrote:

>>I just ask that you draw no conclusions from a system that
>>contains measurable non-linearity in the transducer itself.
>
>
> I think that's being too restrictive. We have at least two ways to
> distinguish AM from FM. The fact that we're finding so much AM is probably a
> guide to the most practical answer.

Arny, when you start mixing distributed non-linearities such
as that in the surround, that of cone distortion, that of
the magnetic circuit, etc. It is not generally possible to
describe the resulting form of distortion. It most likely
involves recursion and thus results in chaotic effects. I
can see no reason why FM cannot occur as a consequence of
these mixed factors. Just about any form of non-linearity
can result from them.

In fact, when I simulated a simple model of the described
effect, the distortion produced was chaotic and broadband,
not isolated spectral lines.

The only way to experimentally learn about the effect we are
discussing is to isolate it.

Until that can be done the effect described remains
hypothetical from an experimental standpoint.

Bob

--

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

A. Einstein
Anonymous

"Bob Cain" <arcane@arcanemethods.com> wrote in message
news:cfdljp018ck@enews4.newsguy.com...
>
>
> Robert Morein wrote:
>
>
> > If the driver converted voltage to air pressure, there could be no
Doppler
> > distortion.
> > However, the driver, even under the best of circumstances, does not do
that.
> > It converts, approximately, to displacement.
>
> I'm afraid this is incorrect. The heuristics usually used
> to describe this effect apply equally well to an ideal
> system where a massless, infinitely compliant and lossless
> piston is driven by a force function.
>
1. You can't contradict what I said with a heuristic. See
http://www.hyperdictionary.com/dictionary/heuristic

2. The "heuristic", by which you probably mean approximation, is exactly
that and no more, a very useful approximation.

3. The subject under discussion is whether the "heuristic" breaks down in a
meaningful fashion. This is the very core of the discussion. If Doppler
effect influences the sound output, then, to the extent which it does, the
"heuristic" is invalid.

4. I do not imply by the above that Doppler is important, or is not. But
please understand that the following is an equivalence relationship:

a. If Doppler is unimportant, then the heuristic you mention is, for all
practical purposes, a very good one.
b. If Doppler is in some situation important, then the heuristic cannot
be used in that situation.

Because the two are equivalent, we need to be wary of saying things like:
"Doppler is unimportant because the approximation we use that excluded
Doppler says Doppler is unimportant."

That would be circular reasoning.
>
> Bob
> --
>
> "Things should be described as simply as possible, but no
> simpler."
>
> A. Einstein
Anonymous

Robert Morein wrote:

>>I'm afraid this is incorrect. The heuristics usually used
>>to describe this effect apply equally well to an ideal
>>system where a massless, infinitely compliant and lossless
>>piston is driven by a force function.
>>
>
> 1. You can't contradict what I said with a heuristic. See
> http://www.hyperdictionary.com/dictionary/heuristic

I'm not trying to; I'm trying to cast doubt on the heuristic
description. All too often when this is attempted, the
result is a failure of intuition.

>
> 2. The "heuristic", by which you probably mean approximation, is exactly
> that and no more, a very useful approximation.

Can you state an expression for it? That, if it is
justifiable from first principles, eliminates heuristics.

>
> 3. The subject under discussion is whether the "heuristic" breaks down in a
> meaningful fashion. This is the very core of the discussion. If Doppler
> effect influences the sound output, then, to the extent which it does, the
> "heuristic" is invalid.

No, it is whether it has any validity at all.

>
> 4. I do not imply by the above that Doppler is important, or is not. But
> please understand that the following is an equivalence relationship:
>
> a. If Doppler is unimportant, then the heuristic you mention is, for all
> practical purposes, a very good one.

It is just hand waving to this point.

Bob
--

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

A. Einstein
Anonymous

>>> Consider the following. Suppose an electrostatic speaker is reproducting 60Hz
>at
>>> a peak-to-peak excursion of 0.25". That means its maximum velocity would be
>>> around 30 inches per second. That's less than 1/4 of 1% of the speed of
>sound!
>
>> Right, but this is a speaker that has a huge surface area and therefore has
>> a very low total excursion. This is a _good_ thing. When your woofer
>> excursion starts getting to be an order of magnitude larger, the numbers
>> change. But the large surface area of an electrostatic panel means you can
>> get considerable bass without substantial excursion... which is good because
>> nonlinearities in the field become a big issue when there is substantial
>> excursion.
>
>All correct, but multi-way dynamic systems with such large excursions eliminate
>much of the potential for Doppler distortion, simply because the higher
>frequencies are reproduced through a separate driver.

In most cases, yes. When Doppler distortion becomes a big problem is in
systems like the Lowther when you have both large excursions and wide
bandwidth through a driver. Or, in coaxial systems, where the seperate
driver is still using the bass driver cone. In typical multi-way systems,
the issue is much smaller.

>Note, also, that such a large excursion would usually occur on a bass transient,
>not during "normal" (???) music.

Right. But what if if the string section is playing a nice long note that
is held for a while, and there is a hit on the tympani? Can you hear the
strings being modulated? The "Ondekoza" track I submitted to one of the RAP
CDS should be a real torture test since it has some clean flute notes combined
with heavy low end . I can't hear any modulation at all on the Magnepans,
but I can hear lots on my father's old Wharfdales (which have 6 dB/octave
crossovers on the top and bottom and run the midrange full range).
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous

"Bob Cain" <arcane@arcanemethods.com> wrote in message
>
> I've got an argument that so far has withstood some scrutiny
> which shows that Doppler distortion in a myth.
>
> What would refute it and point out any flaw in the reasoning
> would be the dynamical expression for the time varying
> function of the pressure wave in an infinite tube with an
> ideal piston as a function of an arbitrary, time varying
> function of the force applied to that piston.
>

I would be willing to wager that it's damn near unmeasurable and
impossible to hear, compared to the other types of distortion
loudspeakers introduce.

Of course "It can be shown" that it exists for any mechanical
transducer--effectively a moving sound source, and be relatively easy to
calculate--it's a fairly straightforward manipulation of the wave
function for velocity, then make the velocity a function of the input
signal . . .

"Easy" to set up . . . but the algebra and trig gets a smidgeon knotty.

Anyone have Maple or Mathematica handy?
Anonymous

U-CDK_CHARLES\Charles wrote:

>
> Of course "It can be shown" that it exists for any mechanical
> transducer--effectively a moving sound source, and be relatively easy to
> calculate--it's a fairly straightforward manipulation of the wave
> function for velocity, then make the velocity a function of the input
> signal . . .
>
> "Easy" to set up . . . but the algebra and trig gets a smidgeon knotty.
>
> Anyone have Maple or Mathematica handy?

Nope, or I'd lend it to you. If it can be "shown" in a
fully general way that withstands scrutiny I really want to

Bob
--

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

A. Einstein
Anonymous

On Wed, 11 Aug 2004 11:47:23 -0400, "Arny Krueger" <arnyk@hotpop.com>
wrote:

>"Scott Dorsey" <kludge@panix.com> wrote in message
>news:cfde31\$2nj\$1@panix2.panix.com

>>If the motion of the cone perfectly follows the waveform, and
>> the air is not compressable,

Air is compressible, even water is compressible, and that's why the
speed of sound in air and water are finite.

>> the pressure waveform that results in
>> the air will be a perfect representation of the original wave.
>
>Scott, I think you've missed a critical point. A speaker is a transducer,
>and that means that in the process of following the waveform ideally, the
>results in the air can be a little different than what was intended.
>
>> If you can somehow arrange for perfect coupling so that the woofer
>> excursion perfectly matches the input signal, doppler effects should
>> be a non-issue.

If you made a transducer that increases and decreases the air
pressure without using physical movement, there would be no doppler
distortion. You could have two valves that alternately open and close,
connected to a source of compressed air and the other to a vacuum,
which would cause increase and decrease in air pressure without
movement, but this doesn't seem practical for good audio reproduction.
The problem is that the cone moves, and its movement is significant
in relation to the speed of sound in air.

>No. Imperfect woofer excursion is more along the line of AM effects.
>
>> Unfortunately this does not go along well with
>> accurate frequency response in the real world.
>
>I think that this issue of imperfect cone motion has some light shed on it
>by contemplating a system with a tweeter, versus a system that lacks one. In
>both cases the respective signals are transduced into the air with ideal
>waveforms. The Doppler comes from the fact that the HF gets transduced into
>the air from a platform with large-scale motion due to some other signal.
>The tweeter does not have this situation.
>
>It's like the train whistle. The whistle itself need not be affected by its
>motion through the air. The fact that the whistle is moving w/r/t the
>listener

AND that the speed of sound is finite, and that the speed of the
train is a significant percentage of the speed of sound...

>is the root cause of the Doppler effect.

A lot of stuff has already been covered (and uncovered and
discovered and recovered...) on "another forum." If anyone wants to
read some "background info" before posting further (I suggest it just
and "Doppler Distoriton?" on alt.music.home-studio:

or

or

And a heads up, "Porky" over there is quite similar in demeanor to
"Phil Allison" here on RAP.

-----
Anonymous

>
> If you made a transducer that increases and decreases the air
> pressure without using physical movement, there would be no doppler
> distortion.

Impossible on first principles of acoustics. Increasing and
decreasing the air pressure results in totally predictable
changes in the velocity of the air. The are simply
proportional through the (real) characteristic impedence of air.

If the SPL is high enough, yes, nonlinearities occur in the
air and the above isn't true but you have to get pretty
darned high for that to have any signifigance. At the
levels we listen to, air is highly linear.

My argument is simply that if you can reproduce velocity of
air then by the above, the pressure has no choice but to
remain in phase and proportional if it remains in the linear
regime. If you can measure it you can reproduce it by
moving a piston with the measured velocity. Exactly. The
resulting pressure wave contains no distortion.

The above argument stands whether we are talking about
reproducing pressure or velocity because in air they are in
phase and proportional in a plane wave and deviations from
planarity only have linear consequences.

> And a heads up, "Porky" over there is quite similar in demeanor to
> "Phil Allison" here on RAP.

Actually, Porky has been nothing but congenial and careful
of late. It was on that tentative basis that I chose to

Bob
--

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

A. Einstein
Anonymous

<< It would be interesting to see if the Urei horn assemblies on the Altec
coaxial drivers really do minimize doppler modulation compared with the
original Altec horn assemblies. That was one of the arguments the Urei
guys used for the extended horns they employed. >>

I think they traded one problem for another. By building the horn flare out
they may have avoided modulating the HF by the 15" cone, but in so doing they
also placed a substantial acoustic mask in front of the woofer. Still, the UREI
implementation was more successful than the Altec device it replaced, with its
hard edges, sectoral dividers, & straight sides.

Scott Fraser
Anonymous

I recorded some violins, viola & cello through a nice speaker last week, a
lovely lacquered maple cabinet made by somebody named Leslie. I'll be damned if
there wasn't a ton of distortion AND doppler shifting. Just couldn't get rid of
it. It kind of made everybody seasick, but they all loved it anyway.

Scott Fraser
Anonymous

so, anybody see where bob went...?
Anonymous

"Bob Cain" <arcane@arcanemethods.com> wrote in message
news:cfe0nk0261j@enews2.newsguy.com
> Arny Krueger wrote:
>
>>> I just ask that you draw no conclusions from a system that
>>> contains measurable non-linearity in the transducer itself.
>>
>>
>> I think that's being too restrictive. We have at least two ways to
>> distinguish AM from FM. The fact that we're finding so much AM is
>> probably a guide to the most practical answer.
>
> Arny, when you start mixing distributed non-linearities such
> as that in the surround, that of cone distortion, that of
> the magnetic circuit, etc. It is not generally possible to
> describe the resulting form of distortion.

What, whether it is AM or FM or what proportion of which?

Sources don't matter, all that matter is a clean enough signal to analyze.

> It most likely
> involves recursion and thus results in chaotic effects. I
> can see no reason why FM cannot occur as a consequence of
> these mixed factors. Just about any form of non-linearity
> can result from them.

(1) that in the surround - doesn't matter where the Doppler comes from,
just that it is.
(2) that of cone distortion - doesn't matter where the Doppler comes from,
just that it is.
(3) the magnetic circuit - not moving, so it can't cause Doppler

> In fact, when I simulated a simple model of the described
> effect, the distortion produced was chaotic and broadband,
> not isolated spectral lines.

We get pretty clean isolated spectral lines from real-world measurements.
Guess what that says about the simulation?

>Until that can be done the effect described remains hypothetical from an
experimental standpoint.

We don't need a working theory to have believable experimental results.
Anonymous

> What, whether it is AM or FM or what proportion of which?

> Sources don't matter, all that matter is a clean enough signal to analyze.

Point... My memory of modulation theory is that the only difference between AM
and weak FM is the phase of the sidebands. (This is how modern high-powered AM
transmitters are built -- the carrier is weakly FM modulated, then amplified,
then goes through a phase shifter. Or something like that.)

So... If you analyze the sideband frequencies into their AM (in-phase) and FM
(quadrature) components, you have the relative amounts of IM and Doppler
distortion.

The FM component is, by definition, Doppler distortion. (Right? ???) So its
source or cause doesn't matter.
Anonymous

Arny Krueger wrote:

>>Arny, when you start mixing distributed non-linearities such
>>as that in the surround, that of cone distortion, that of
>>the magnetic circuit, etc. It is not generally possible to
>>describe the resulting form of distortion.
>
>
> What, whether it is AM or FM or what proportion of which?

Whether it is even formally describable.

>
> Sources don't matter, all that matter is a clean enough signal to analyze.

The hell they don't. If what is generating the data to be
measured cannot be characterized then neither can the data.

> Lets go down your list:
>
> (1) that in the surround - doesn't matter where the Doppler comes from,
> just that it is.

> (2) that of cone distortion - doesn't matter where the Doppler comes from,
> just that it is.'

This either.

> (3) the magnetic circuit - not moving, so it can't cause Doppler

I understand this one. The question remains whether FM can
be ruled out of an active system that has these forms of
distortion in a distributed and interacting fashion. Can it?

>>In fact, when I simulated a simple model of the described
>>effect, the distortion produced was chaotic and broadband,
>>not isolated spectral lines.
>
>
> We get pretty clean isolated spectral lines from real-world measurements.
> Guess what that says about the simulation?

What's it say about the system under test? What does it

> We don't need a working theory to have believable experimental results.

Absolutely agreed, but to have a believable experimental
result all factors that can contribute to the data in the
same way that the phenomenon being investigated can must
either be completely characterized or eliminated. This is
fundamental.

Bob
--

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

A. Einstein
Anonymous

""Granma" Dave Schein II, CSO" <granmadave@yahoo.com> wrote in message

> In layman's terms, what, exactly, is Doppler Distortion?

http://www.sweetwater.com/insync/word.php?find=Doppler

The Doppler effect, named after a German physicist (how come things are
always named after a German physicist?), is the apparent change in pitch of
the sound that occurs when the source of the sound is moving relative to the
listener. For example: A car horn will sound higher in pitch as it
approaches, and lower in pitch after it passes us. This is one principle
that is employed in a rotating speaker system like a Leslie. The rapid
movement of the horn to and away from the listener creates a sort of vibrato
effect. There are many modern effects units that simulate the Leslie sound,
and also offer other types of Doppler effects.

If a loudspeaker is producing both low and high frequencies, the low
frequencies will cause the cone to move alternatingly toward and away from
the listener (obviously high frequencies do this too, but the lows are much
more pronounced). As this is happening the perceived pitch of the higher
frequency sounds rise and fall at a rate (or rates) equal to the low
frequencies moving the cone. This is actually Frequency Modulation of the
high frequency by the low frequency, and is called "Doppler Distortion." It
manifests itself as a sort of "muddiness" (subjective audio term #108) of
the sound.
Anonymous

> The Doppler effect, named after a German physicist (how come
> things are always named after a German physicist?)...

They aren't. I own lots of Land cameras, and they're named after a
Russian/American physicist.
Anonymous

"Bob Cain" <arcane@arcanemethods.com> wrote in message
news:cfe100026b8@enews2.newsguy.com...
>
>
> Robert Morein wrote:
>
>
> >>I'm afraid this is incorrect. The heuristics usually used
> >>to describe this effect apply equally well to an ideal
> >>system where a massless, infinitely compliant and lossless
> >>piston is driven by a force function.
> >>
> >
> > 1. You can't contradict what I said with a heuristic. See
> > http://www.hyperdictionary.com/dictionary/heuristic
>
> I'm not trying to; I'm trying to cast doubt on the heuristic
> description. All too often when this is attempted, the
> result is a failure of intuition.
>
Well, then, no argument on that account!
> >
> > 2. The "heuristic", by which you probably mean approximation, is exactly
> > that and no more, a very useful approximation.
>
> Can you state an expression for it? That, if it is
> justifiable from first principles, eliminates heuristics.
>
No, I can't, and I don't think it's been done.
The heuristic you mention is a linear approximation, which is useful because
it allows the "transfer function" methodology.
The Doppler effect is, like most things considered distortions, nonlinear.
The transfer function methodology is not extensible to nonlinear processes.
Hence, if the Doppler effect is considered important in a particular
instance, the machinery of linear systems cannot be used.

An additional way it breaks down is thus:
We usually consider a particular distortion in terms of percentages of the
total signal strength.
But the Doppler effect shifts ALL signals coming out of the driver, to some
degree.
Usually, one mentally organizes the problem in terms of a low frequency
signal, and a high frequency signal, and the peturbation in frequency caused
by the low frequency signal on the high frequency signal. However, this is
artificial. Two signals, one at 50 Hz and another at 51 Hz, theoretically
intermodulate due to the Doppler effect.

Unless some arbitrary standard is used, there's nothing left of the original
signal at all! Ridiculous, of course, but this shows the weakness of
thinking in linear terms about a nonlinear system. A percentage of Doppler
distortion cannot be recognized unless arbitrary criteria are used to define
it.

Consequently, I wave my hand at you (in a friendly gesture  .

> >
> > 3. The subject under discussion is whether the "heuristic" breaks down
in a
> > meaningful fashion. This is the very core of the discussion. If Doppler
> > effect influences the sound output, then, to the extent which it does,
the
> > "heuristic" is invalid.
>
> No, it is whether it has any validity at all.
>
> >
> > 4. I do not imply by the above that Doppler is important, or is not.
But
> > please understand that the following is an equivalence relationship:
> >
> > a. If Doppler is unimportant, then the heuristic you mention is, for
all
> > practical purposes, a very good one.
>
> It is just hand waving to this point.
>
>
> Bob
> --
>
> "Things should be described as simply as possible, but no
> simpler."
>
> A. Einstein
Anonymous

I've been really stuck finding the flaw in the traditional
arguement for Doppler distortion and in some of the
scenarios that have been presented here in argument for it.
It finally just came to me.

It's really simple and even easy to understand. Doppler
shift is a phenomenon that occurs when a source is moving
with respect to the medium or _through_ the medium in which
it is generating a wave. In the case of a loudspeaker, or a
little one mounted on a big one, or whatever, it is not
moving with respect to the medium, it is moving the medium.
There is a fundamental difference.

In the situation presented of a little speaker mounted on a
big one, you will get Doppler distortion only if the big one
is acoustically transparent. When it is acoustically rigid
you have an entirely different situation and no Doppler
distortion will occur.

Doppler distortion in loudspeakers is a dead issue. It does
not exist. I cannot explain the posted data other than to
wonder if the effect was accidently in the input data.

Bob
--

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

A. Einstein
Anonymous

On Wed, 11 Aug 2004 10:56:27 -0700, Bob Cain
<arcane@arcanemethods.com> wrote:

>
>
>Arny Krueger wrote:
>
>> Fool that I am, I'm kinda stuck down here in the real world. Forget the
>> math,
>
>Then we are whistling in the dark. I admire your
>experimentalist approach. Experiment trumps theory, always.
>
>I just ask that you draw no conclusions from a system that
>contains measurable non-linearity in the transducer itself.
>
>

That does not seem fair. . .

>Bob
>--
>
>"Things should be described as simply as possible, but no
>simpler."
>
> A. Einstein
Anonymous

Goofball_star_dot_etal wrote:

> On Wed, 11 Aug 2004 10:56:27 -0700, Bob Cain
> <arcane@arcanemethods.com> wrote:
>
>
>>
>>Arny Krueger wrote:
>>
>>
>>>Fool that I am, I'm kinda stuck down here in the real world. Forget the
>>>math,
>>
>>Then we are whistling in the dark. I admire your
>>experimentalist approach. Experiment trumps theory, always.
>>
>>I just ask that you draw no conclusions from a system that
>>contains measurable non-linearity in the transducer itself.
>>
>>
>
>
> That does not seem fair. . .

Why? Separation of variables is essential to an experiment
attempting to measure the consequences of one effect.

Bob
--

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

A. Einstein
Anonymous

"Bob Cain" <arcane@arcanemethods.com> wrote in message
news:cfe0371243e@enews2.newsguy.com
> Goofball_star_dot_etal wrote:
>
>> On Wed, 11 Aug 2004 10:56:27 -0700, Bob Cain
>> <arcane@arcanemethods.com> wrote:
>>
>>
>>>
>>> Arny Krueger wrote:
>>>
>>>
>>>> Fool that I am, I'm kinda stuck down here in the real world.
>>>> Forget the math,
>>>
>>> Then we are whistling in the dark. I admire your
>>> experimentalist approach. Experiment trumps theory, always.
>>>
>>> I just ask that you draw no conclusions from a system that
>>> contains measurable non-linearity in the transducer itself.
>>>
>>>
>>
>>
>> That does not seem fair. . .
>
> Why? Separation of variables is essential to an experiment
> attempting to measure the consequences of one effect.

The reason is quite clear. The question at hand is about loudspeaker
Doppler distortion. All known loudspeakers have copious amounts of
measurable nonlinearity.. If we disallow experimental results from
loudspeakers that have measurable non-linearity, we disallow all experiments
with loudspeakers.
Anonymous

Arny Krueger wrote:

>>Why? Separation of variables is essential to an experiment
>>attempting to measure the consequences of one effect.
>
>
> The reason is quite clear. The question at hand is about loudspeaker
> Doppler distortion. All known loudspeakers have copious amounts of
> measurable nonlinearity.. If we disallow experimental results from
> loudspeakers that have measurable non-linearity, we disallow all experiments
> with loudspeakers.

And rightfully so.

Please believe that I'm not trying to be right here but just
correct. I will be just as happy if someone can come up
with the formal theoretical underpinning of this
hypothetical phenomenon as I will if it is found that there
isn't one.

So far no physicist or acoustician that reads usenet has
even tried in public. What's up with that? It's not like
it's an uninteresting problem.

Bob
--

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

A. Einstein
Anonymous

> It's really simple and even easy to understand. Doppler
> shift is a phenomenon that occurs when a source is moving
> with respect to the medium or _through_ the medium in which
> it is generating a wave. In the case of a loudspeaker, or a
> little one mounted on a big one, or whatever, it is not
> moving with respect to the medium, it is moving the medium.
> There is a fundamental difference.

Interesting. (Sounds like one of my own posts.)

Question: How does the air in front of the speaker "distinguish" between the
cone moving back and forth, and the driver as a whole being moved back and forth
(without any signal applied to the voice coil) at the same rate and amplitude?
Anonymous

"Bob Cain"
>
> I've got an argument that so far has withstood some scrutiny
> which shows that Doppler distortion in a myth.

** Doppler distortion from what cause ???????

The air ?

Some moving cone driver ????

........... Phil
Anonymous

"William Sommerwerck" <williams@nwlink.com> wrote in message
news:10hl8gppngp9tca@corp.supernews.com
>> What, whether it is AM or FM or what proportion of which?
>
>> Sources don't matter, all that matter is a clean enough signal to
>> analyze.

> Point... My memory of modulation theory is that the only difference
> between AM and weak FM is the phase of the sidebands. (This is how
> modern high-powered AM transmitters are built -- the carrier is
> weakly FM modulated, then amplified, then goes through a phase
> shifter. Or something like that.)

Agreed.

> So... If you analyze the sideband frequencies into their AM
> (in-phase) and FM (quadrature) components, you have the relative
> amounts of IM and Doppler distortion.

Agreed.

And what we find is a mixture of AM distortion and FM distortion.

A number of other tests pass, as well.

> The FM component is, by definition, Doppler distortion. (Right? ???)

Agreed.

> So its source or cause doesn't matter.
Anonymous

William Sommerwerck wrote:

>>It's really simple and even easy to understand. Doppler
>>shift is a phenomenon that occurs when a source is moving
>>with respect to the medium or _through_ the medium in which
>>it is generating a wave. In the case of a loudspeaker, or a
>>little one mounted on a big one, or whatever, it is not
>>moving with respect to the medium, it is moving the medium.
>> There is a fundamental difference.
>
>
> Interesting. (Sounds like one of my own posts.)
>
> Question: How does the air in front of the speaker "distinguish" between the
> cone moving back and forth, and the driver as a whole being moved back and forth
> (without any signal applied to the voice coil) at the same rate and amplitude?

I don't think a question of how it distinguishes is
meaninful. The physics is simply different if the generator
is moving within the medium or moving it.

Notice the difference I alluded to between a speaker just
moving back and forth in a medium by itself and mounted to
the face of a plane that is moving the same way and itself
generating a plane wave. Does it not seem logical that
there would be a difference?

I say that the difference is that when it is mounted on a
plane that is moving it just adds to the velocity/pressure
of the wave that is generated in a linear fashion and when
it is moving the same way by itself, without being part of a
larger generator, the result is "Doppler distortion" of
whatever it is generating. Thing is, though, that the
latter doesn't describe the physics of loudspeakers we use.

Bob
--

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

A. Einstein
Anonymous

"William Sommerwerck"

> I think there are two simple refutations, one theoretical, the other
practical.
>
> Theoretical -- If the output of a driver accurately follows its input
waveform,
> how can there be Doppler distortion?

** No driver ever does that - the excursion quadruples every octave
lower you go for the same voltage input.

> Practical -- It should be trivial to compute the sidebands produced by
combining
> (say) a 60Hz signal and 6000 Hz signal. By looking at the phase of the
> sidebands, it should be possible to determine what part of them is IM
distortion
> (AM components) and what part is Doppler (FM components).
>

** Bob Cain never mentioned drivers at all.

He may well be referring to Doppler in the air itself.

.............. Phil
Related resources :
!