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

"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

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).

"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

"William Sommerwerck" wrote in message
...
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).

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.

William Sommerwerck wrote:
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.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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.

"William Sommerwerck" wrote in message
...
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.

"William Sommerwerck" wrote in message
...
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.



** Try modulating a 2000 Hz tone so the frequency shifts up and down by 5
Hz - see how wrong you are.


BTW ES speakers have large diaphragm areas and small excursions so they
have less Doppler than cone
speakers.



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

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

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

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.

"Carey Carlan" wrote in message
. 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.

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

On or about Wed, 11 Aug 2004 13:10:23 GMT, Carey Carlan allegedly 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.

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.

Thanks. That helps me get a handle on this.

If they are real sounds, and were captured by a single microphone, then a
similar doppler shifting would be encoded by the microphone, so the
speaker would simply be decoding that, and effectively restoring the HF
tone to it's original timing. Of course the mic would typically have less
excursion than the speaker, but if frequency response was flat for both,
everything should be in the same balance.

If such a doppler encoded signal from a single mic is then reproduced on a
typical two way speaker system, then the hf component would have doppler
shifting that does not get decoded. But as others have mentioned,
multiway speakers would reduce that modulating effect, so perhaps are more
suited to reproducing material that has been mixed from widely different
sources so would not have the natural doppler encoding.

Sounds like a good argument for minimalist recording (one of many), and
don't touch that eq. at all, or you'll ruin everything.


Noel Bachelor noelbachelorAT(From:_domain)
Language Recordings Inc (Darwin Australia)

"Noel Bachelor" wrote in message

On or about Wed, 11 Aug 2004 13:10:23 GMT, Carey Carlan allegedly
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.

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.

Thanks. That helps me get a handle on this.

If they are real sounds, and were captured by a single microphone,
then a similar doppler shifting would be encoded by the microphone,
so the speaker would simply be decoding that, and effectively
restoring the HF tone to it's original timing.

The cause of Doppler distortion is large amounts of diaphragm displacement.
Because the diaphragm in microphones is so small, they cause very little
Doppler distortion. Therefore, it is highly unlikely that a microphone would
be able to compensate for Doppler distortion in a loudspeaker.

(Noel Bachelor) wrote in
:

If they are real sounds, and were captured by a single microphone,
then a similar doppler shifting would be encoded by the microphone, so
the speaker would simply be decoding that, and effectively restoring
the HF tone to it's original timing. Of course the mic would
typically have less excursion than the speaker, but if frequency
response was flat for both, everything should be in the same balance.

Your argument assumes that the microphone diaphragm moves the same extent
during recording as the speaker does during playback.

Carey Carlan wrote:

Your argument assumes that the microphone diaphragm moves the same extent
during recording as the speaker does during playback.

Another way of pointing out that it wouldn't be a linear
phenomenon. If it were it would scale with everything else.


Bob
--

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

A. Einstein

Carey Carlan wrote:

Your argument assumes that the microphone diaphragm moves the same extent
during recording as the speaker does during playback.

Another way of pointing out that it wouldn't be a linear
phenomenon. If it were it would scale with everything else.


Bob
--

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

A. Einstein

On or about Fri, 13 Aug 2004 13:12:50 GMT, Carey Carlan allegedly wrote:

(Noel Bachelor) wrote in
:

If they are real sounds, and were captured by a single microphone,
then a similar doppler shifting would be encoded by the microphone, so
the speaker would simply be decoding that, and effectively restoring
the HF tone to it's original timing. Of course the mic would
typically have less excursion than the speaker, but if frequency
response was flat for both, everything should be in the same balance.

Your argument assumes that the microphone diaphragm moves the same extent
during recording as the speaker does during playback.

Yes I suppose I was thinking that the ratio of movement at the two
frequencies would be similar, but it's the actual length of displacement
that determines the timing change.


Noel Bachelor noelbachelorAT(From:_domain)
Language Recordings Inc (Darwin Australia)

"Noel Bachelor" wrote in message

On or about Wed, 11 Aug 2004 13:10:23 GMT, Carey Carlan allegedly
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.

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.

Thanks. That helps me get a handle on this.

If they are real sounds, and were captured by a single microphone,
then a similar doppler shifting would be encoded by the microphone,
so the speaker would simply be decoding that, and effectively
restoring the HF tone to it's original timing.

The cause of Doppler distortion is large amounts of diaphragm displacement.
Because the diaphragm in microphones is so small, they cause very little
Doppler distortion. Therefore, it is highly unlikely that a microphone would
be able to compensate for Doppler distortion in a loudspeaker.

(Noel Bachelor) wrote in
:

If they are real sounds, and were captured by a single microphone,
then a similar doppler shifting would be encoded by the microphone, so
the speaker would simply be decoding that, and effectively restoring
the HF tone to it's original timing. Of course the mic would
typically have less excursion than the speaker, but if frequency
response was flat for both, everything should be in the same balance.

Your argument assumes that the microphone diaphragm moves the same extent
during recording as the speaker does during playback.

"Bob Cain" 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.

A couple of us have been pursuing the measurement route, and as often the
case the results are practically speaking, not all that startling.

First off, we've found that actually measuring Doppler distortion is not all
that easy. This is complexified by the fact that speakers have lots of
distortion of many kinds, and at most loudspeaker Doppler distortion is
relatively small. BTW, along the way, I've found reason to doubt a lot of
published jitter measurements. They don't seem to distinguish AM from FM.

But bottom line, we think we are measuring some Doppler distortion.
However, there's so many other kinds of distortion of a similar nature
happening at the same time, that it's practically a non-issue.

People who like looking at raw evidence can visit:
http://www.pcavtech.com/techtalk/doppler/ .

It might be most informative to compare these two sets of graphs and data:

"Triple Tone Lab Measurements - 316 millivolts RMS" and "Triple Tone Lab
Measurements - 10 Volts RMS"

Triple Tone Lab Measurements - 316 millivolts RMS shows a speaker operating
at a 1 meter SPL of about 78 dB. The background noise in the room actually
masks harmonics generated by the 50 Hz fundamental. Most visible distortion
products are 60 dB or more down (0.1%). Of course 0.1% is an absolutely
rediculously huge amount of distortion compared to the 0.003% THD that some
on RAP seem to want to worry about.

Triple Tone Lab Measurements - 10 Volts RMS shows a speaker operating at a
1 meter SPL of about 105 dB SPL. Don't be confused by the 1 meter SPL of 105
dB, out in the room the SPL is loud enough, but fairly modest (under 100 dB)
by modern standards.

Frankly, with 10 volts applied to its voice coil, this speaker has been
turned just about every which way but loose. 50 Hz THD is some place around
10%. IM is around 3%. It sounds pretty badly stressed, in real life.

The driver under test is a Peerless 6.5" speaker that is similar to what you
might find in one of the better near-field monitors. I would imagine that a
speaker like this would be rated for a maximum 1 meter SPL in excess of 110
dB. You can imagine how distorted it is under those conditions!

Arny Krueger wrote:
"Bob Cain" 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."

"Scott Dorsey" wrote in message

Arny Krueger wrote:

"Bob Cain" 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.

Arny Krueger wrote:
"Scott Dorsey" 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.

A better one would be one of the Radian drivers, which are really bad about
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."

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

"Bob Cain" 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?

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

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
know the answer.


Bob
--

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

A. Einstein

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

On Wed, 11 Aug 2004 10:56:27 -0700, Bob Cain
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

"Bob Cain" wrote in message


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.

On Wed, 11 Aug 2004 10:56:27 -0700, Bob Cain
wrote:

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

No amplitude non-linearity is needed to generate phase or
frequency modulation.

I'm not following this discussion at all. Are you asking
if a train whistle's pitch changes as it passes by?

Or that a recorded train whistle played through a speaker
doesn't change pitch as it passes by?


Chris Hornbeck

On Wed, 11 Aug 2004 01:31:04 -0700, Bob Cain
wrote:


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

I think I understand what you're getting at, so let me restate it
non-mathermatically, for those of us who are sound techs rather than
audio engineers.

Example 1:

I take a tiny 2" speaker, and mount in on the center of an 18"
high-excursion driver. The tiny speaker has tiny wires leading to a
tiny amplifier. I drive it with 4KHz; it reproduces the tone.

Now I drive the 18" driver with 50Hz at maximum excursion. I hear a
50Hz vibrato on the 4KHz tone. This is Doppler distortion.

Example 2:

I generate a 4 KHz tone and a 50Hz tone. I sum them, and feed them to
a full-range speaker through an amplifier with low IM distortion. From
the speaker, I hear 4KHz and 50Hz. No vibrato, because the speaker is
accurately reproducing the waveform that is the sum of the two tones.
No Doppler distortion.

Example 3:

I take the full range speaker which is accurately reproducing the
two-tone waveform, and shake it rapidly back and forth, toward and
away from the listener. The listener hears variations in pitch.
Dopppler distortion.

Mike T.

Example 2:

I generate a 4 KHz tone and a 50Hz tone. I sum them, and feed them to
a full-range speaker through an amplifier with low IM distortion. From
the speaker, I hear 4KHz and 50Hz. No vibrato, because the speaker is
accurately reproducing the waveform that is the sum of the two tones.
No Doppler distortion.

Well... No. The 4kHz signal is being reproduced from a source that is moving
with respect to the listener.

On Wed, 11 Aug 2004 16:21:24 -0700, William Sommerwerck wrote:

Example 2:

I generate a 4 KHz tone and a 50Hz tone. I sum them, and feed them to
a full-range speaker through an amplifier with low IM distortion. From
the speaker, I hear 4KHz and 50Hz. No vibrato, because the speaker is
accurately reproducing the waveform that is the sum of the two tones.
No Doppler distortion.

Well... No. The 4kHz signal is being reproduced from a source that is moving
with respect to the listener.

Say I have a diaphram like a bass drum, and hit it, surely the same thing
is going on (tones at higher multiple frquencies+the skin moving slowly at
the fundamental pitch).

So, would a speaker cone not have to do the same thing to reproduce it?
Is there 'doppler distortion' on acoustic instruments?
Could the same thing be said about microphone diaphrams? By picking up a
low frequency and high frequency sound at the same time, would the same
effect not apply?

Sorry for all the questions.

"philicorda" wrote in message
news
On Wed, 11 Aug 2004 16:21:24 -0700, William Sommerwerck wrote:

Example 2:

I generate a 4 KHz tone and a 50Hz tone. I sum them, and feed them
to a full-range speaker through an amplifier with low IM
distortion. From the speaker, I hear 4KHz and 50Hz. No vibrato,
because the speaker is accurately reproducing the waveform that is
the sum of the two tones. No Doppler distortion.

Well... No. The 4kHz signal is being reproduced from a source that
is moving with respect to the listener.

Say I have a diaphram like a bass drum, and hit it, surely the same
thing is going on (tones at higher multiple frquencies+the skin
moving slowly at the fundamental pitch).

I believe so.

So, would a speaker cone not have to do the same thing to reproduce it?

Remember, that a speaker does not reproduce the motion of a drum diaphragm,
it reproduces that which was picked up by a microphone that was in the
sound field of the drum. Your example would be more valid if we were in the
habit of putting transducers on bass drum diaphragms.

Is there 'doppler distortion' on acoustic instruments?

So it would seem.

Could the same thing be said about microphone diaphrams? By picking
up a low frequency and high frequency sound at the same time, would
the same effect not apply?

So it would seem. However, in the case of mics the motion of the diaphragm
is so small that its Doppler distoriton is really small.

Sorry for all the questions.

Well, the big lesson is that in the current context, Doppler FM distortion
is submerged by the large amounts of AM distortion in speakers.

Mike Tulley wrote:


I think I understand what you're getting at, so let me restate it
non-mathermatically, for those of us who are sound techs rather than
audio engineers.

Disqualified. :-)


Example 1:

I take a tiny 2" speaker, and mount in on the center of an 18"
high-excursion driver. The tiny speaker has tiny wires leading to a
tiny amplifier. I drive it with 4KHz; it reproduces the tone.

Now I drive the 18" driver with 50Hz at maximum excursion. I hear a
50Hz vibrato on the 4KHz tone. This is Doppler distortion.

No you won't and I'm going to explain why in a response to
my original post since this argument in various forms has
come up frequently and was in fact the original motivation
for thinking there was such a thing.

The flaw in this and the traditional reasoning finally came
to me just now with a response to you in progress and
pending while I watched the news. Stay tuned to this
thread. :-)


Bob
--

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

A. Einstein