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.

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

A question about the Leslie, though: I thought the Leslie had two
speakers,

Yes.

one high and one low, rotating at user-defined rates.

There are two speeds, slow & fast, controllable from the organ console. You can
trim these speeds somewhat within the unit, although it isn't a realtime
performance control. And, there are two motors, so some customization is
possible by offsetting the low & high frequency slow & fast speeds. BTW, they
rotate in opposite directions.

Would that cause
Doppler, or simply a tremolo effect based around the directionality of the
speaker? I.e., if the speaker is pointed away from the microphone (or ear),
the volume would be softer, and vice-versa?


It's complex. There is amplitude modulation, frequency modulation, phase
modulation, timbre modulation, varying amounts of overdive distortion from the
tube amps, & a whole lot of reflections inside the cabinet. In a word, they
sound fantastic.


Scott Fraser

On 11 Aug 2004 18:14:09 -0400, (Scott Dorsey) wrote:

\"Granma\" Dave Schein II, CSO wrote:
wow! NEAT!

A question about the Leslie, though: I thought the Leslie had two speakers,
one high and one low, rotating at user-defined rates. Would that cause
Doppler, or simply a tremolo effect based around the directionality of the
speaker? I.e., if the speaker is pointed away from the microphone (or ear),
the volume would be softer, and vice-versa?

This is true, but the pitch also changes as the thing rotates. Play a
note, and you not only hear tremolo caused by changing amplitude, you
also hear vibrato caused by changing frequency. This is part of why the
Leslie is so hard to model accurately and why most of the Leslie simulators
don't sound like the real thing.
--scott

Actually in a leslie the horn in front of the driver rotates, the
speaker driver remains stationary. Which creates a much more complex
phenomena than mere doppler. Doppler is supposedly in there but there
a lot of complex wavefronts being combed at once as that baby turns
insude a hard-walled cabinet, which is why simulators are too clean in
comparison. I personally hear more phasing than doppler. Someday I'll
pump a sine wave through it

Also - only one of the sides of the spinning horn is open, the other
is closed off. Unless some rocker cracked it off.

I'm sure there's literature on the Doppler effect in a Leslie, but
Doppler it's a very small component of the "sound", most of the tone
comes from the combing. You need to spend some time in front of one of
those beasts to appreciate it. I read in here once that "recording a
Leslie is like taking a picture of a sunset." Not quite the same
dimension as the original experience.



Kurt Riemann

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.

I don't follow this.

(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
specifically say about Doppler distortion?


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

"William Sommerwerck" wrote in message

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.

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

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.

OK, now I see the problem. Frequency modulation doesn't
require and, in fact, is independent of, non-linearity in
the sense used here.

FM sidebands are Bessel functions generated by expanding
the right hand side of an expression that includes angular
velocities and frequencies *only*. IOW, "linear".

Chris Hornbeck

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

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

"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

On Wed, 11 Aug 2004 16:58:54 -0700, Bob Cain
wrote:

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

I don't know what amplitude non-linearity is. I described
what linearity is in another post. When distributed linear
and non-linear factors are all mixed up with an energy
source driving the whole thing there isn't a whole lot that
can be said about what can come out of it.

By amplitude non-linearity I only mean the stuffs in the
transfer function errors that don't include time.
Harmonic and intermodulation distortions; like that.

FM doesn't require any amplitude non-linearity. That may
be the source of several posters' confusions. It's an
interesting topic. (May you live in interesting topics!)

Chris Hornbeck

On Wed, 11 Aug 2004 18:26:42 -0700, "William Sommerwerck"
wrote:

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?

Exactly right. This can be restated as "air is very low impedance".
Conventional speakers operate into something close to a short
circuit.

Chris Hornbeck

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

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.

OK, now I see the problem. Frequency modulation doesn't
require and, in fact, is independent of, non-linearity in
the sense used here.

FM sidebands are Bessel functions generated by expanding
the right hand side of an expression that includes angular
velocities and frequencies *only*. IOW, "linear".

Right. The whole system is completely linear (if you assume perfect
drivers and noncompressable air), and can be modelled in a linear
fashion.

The easiest way to do it is to take a coaxial speaker as your example.
You got two parts, first a way to determine the woofer excursion as
an instantaneous function of input signal, which is easy to do and
a matter of some simple box modelling, and secondly a way to take the
output of that and use it to modulate the tweeter signal. And that is
just a Bessel function. You should be able to knock this out in Matlab
in fairly short order.

Doing it with a full-range driver is harder because you can't easily
just draw a line and say below this point is modulating signal and
above this point is modulated.

But yes, I don't see any reason why we have to assume anything but a
linear model.
--scott

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

Bob Cain wrote in
:

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.

That equates to saying that a train whistle moving toward you at 20 mph
will have no pitch shift if it's in a 20 mph tailwind.

Try again.

On Wed, 11 Aug 2004 14:18:01 -0700, Bob Cain
wrote:



Ben Bradley wrote:



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.

Doesn't a whistle do this, make sound without any movement of
anything but the air itself? Or are we talking past each other...

Increasing and
decreasing the air pressure results in totally predictable
changes in the velocity of the air.

Right. See the second "pressure =" equation in the other post I
just posted...

The are simply
proportional through the (real) characteristic impedence of air.

Yes, if you detect it as I describe below.

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.

Agreed, and I am assuming SPL levels that are not unusually high.

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.

To measure it with no distortion, you would have to 'follow' the
pressure wave: (this is impractical except for the lowest frequencies,
it ignores the mass of the mic diaphragm [as well as the rest of the
mic!], and lots of other detailed problems, but bear with me) have a
mic mounted on a servo (such as a voice coil of a loudspeaker) that
moves the mic back when it senses an increase in pressure and forward
when it senses a decrease, so there is practically no change in the
pressure sensed by the mic diaphragm. The servo signal to move the mic
will reproduce the acoustic wave impressing on the mic.

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
address his post.

Okay, I was obviously going on previous experience. Posts from AMHS
were nonexistent for a month or two (I can only imagine Bellsouth's
feed for AMHS dried up), then I all of a sudden saw them showing up
again in the last few days.

Bob

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

On Wed, 11 Aug 2004 22:28:36 -0400, Ben Bradley
wrote:

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.

Doesn't a whistle do this, make sound without any movement of
anything but the air itself? Or are we talking past each other...

Also the modulated arc "ion" speakers and the modulated flame
(I **** thee not) speakers used in Vietnam for propaganda flights.

The latter weren't high fi but were loud enough to allow you to
fly high enough to not be seen. A definite advantage given the
mood of the crowd.

Chris Hornbeck

On 11 Aug 2004 22:14:41 -0400, (Scott Dorsey) wrote:

The whole system is completely linear (if you assume perfect
drivers and noncompressable air), and can be modelled in a linear
fashion.

One other assumption for "perfect" linearity is infinite bandwidth.
It's a given for our models, but I wonder how significant it may be
in the context of related questions of audibility.

Chris Hornbeck

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

Carey Carlan wrote:

Bob Cain wrote in
:


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.


That equates to saying that a train whistle moving toward you at 20 mph
will have no pitch shift if it's in a 20 mph tailwind.

Try again.

Ok. If the whistle is moving at 20 miles an hour, and so is
the wind, and you are standing on the ground then the medium
is moving with respect to you. That's the same physics as
being on the moving train listening to a stationary whistle.
Doppler shift will result.


Bob
--

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

A. Einstein

On Thu, 12 Aug 2004 02:56:06 GMT, Chris Hornbeck
wrote:

I wonder how significant it may be
in the context of related questions of audibility.

On second thought, this is irrelevant ("It's not irrelevant;
it's a hippopatamus!").

Note: you have to say the quote above with the cheesiest
possible faux Viennese accent.

Anyway, just ignore me; I'm an idiot.

Chris Hornbeck

One other assumption for "perfect" linearity is infinite bandwidth.
It's a given for our models, but I wonder how significant it may be
in the context of related questions of audibility.

Not so. Linearity and bandwidth are not related. To put it another way, lack of
infinite bandwidth is not considered "distortion."

On Wed, 11 Aug 2004 21:00:38 -0700, "William Sommerwerck"
wrote:

One other assumption for "perfect" linearity is infinite bandwidth.
It's a given for our models, but I wonder how significant it may be
in the context of related questions of audibility.

Not so. Linearity and bandwidth are not related. To put it another way, lack of
infinite bandwidth is not considered "distortion."

For FM they're (only) related in the context of a complete
modulation and demodulation. That's a poor fit to the models
we're discussing. Best to just ignore my ravings.

OTOH.....

Nahhh...

Chris Hornbeck

William Sommerwerck wrote:

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.


That's the problem. There is no difference.

Ah, but there is.

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?


Nope, I'm afraid Newtonian Relativity says otherwise.

Hmmm, do you mean that these two quite different physical
systems are going to behave in the same way? Please explain
what Newtonial relativity says about these different systems
that makes them indistinguishable.


Bob
--

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

A. Einstein

Kurt Riemann
"Arny Krueger"

It is this added velocity that causes the Doppler distortion.

Except that I disagree that there IS any velocity added to the higher
wave. The wave IS velocity. No more, no less. Complex but coherent.


** The source of the wave has a velocity - you moron.

That alters the frequency in the air.

The wave velocity in air is fixed.



Given the degree to which Doppler shift is a measurable phenomena
regulated by the speed of sound in air, and is very auduble from
objects traveling at relatively low velocities

AND

Given that a speaker moves at a high rate of speed,


** Nope - 1 m/S at most.

About 2 mph.



Shouldn't doppler distortion be garishly apparent?


** No - you jerk off.


If it is so subtle
that it has escaped everyone's attention, it must be violating some of
Doppler's own physical laws.


** False assertion - thence a false conclusion.



Even a Sawtooth wave would theoretically show doppler distortion. Not
only that, but if you were to take the harmonic components of a
sawtooth wave and play them all out of phase with each other, there
would be no difference in sound, but they would theoretically be
modulating each other.


** Ignorant bull****.

Equates summing with multiplying.





Anyway, I stand by my assertions.


** Where the lunatic stands is a place for others to instantly evacuate.




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

On Wed, 11 Aug 2004 21:45:56 -0700, Bob Cain
wrote:



William Sommerwerck wrote:

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.

How so, Bob?

That's the problem. There is no difference.

Ah, but there is.

Bob, what's the difference if the cone is moved by an electrically
supeimposed signal of two sine waves, and if it is moved electrically
by one sine wave and the whole speaker frame is moved mechanically by
another sine wave? Does the cone not go through the same motion in
both cases?

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?

The plane will have more surface area than the speaker cone, so the
plane would make a louder sound for the same depth of motion.

But if the speaker were emitting a high frequency signal, it would
be emitted on a surface that's moving back and forth at a lower
frequency to a large depth (whether it's just the cone or the driver
and plane), and it would be frequency-modulated just the same.



Nope, I'm afraid Newtonian Relativity says otherwise.

Hmmm, do you mean that these two quite different physical
systems are going to behave in the same way? Please explain
what Newtonial relativity says about these different systems
that makes them indistinguishable.


Bob
--

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

A. Einstein

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

Haiku for my new newsgroup stalker
--------------------------------------------------------

I wake up each day
Happy and refreshed
For I am not Phil

A great stereo
must never be listened to
only analyzed

innacuracies
in all trivial matters
make his head explode

The burden of his knowledge
Drives him to lash out
oddly, at Rivers

no social graces
and yet he knows everything
alone in his cult

Australia is home
To Phil and the vast outback
Thank God for oceans

His perfect knowlege
Hidden in his dark replies
Never sees the point

His perfect newsgroup
Would be all Phil Allisons
All noise? Or silence?

His nasty retorts
drive away the questioners
Now he will be Plonked


----------------------------------------------------------

I am Kurt Riemann
No longer seeing that jerk
On my newsreader

"Bob Cain" wrote in message


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.

Can't air pressure be changed by thermal means?

Kurt Riemann wrote in message

On Wed, 11 Aug 2004 21:51:48 -0400, "Arny Krueger"
wrote:


Are you thinking the 50Hz is a modulator?

Yes, the 50 Hz is the modulator.

It isn't moving identically to a pure 50Hz tone, it has 4k *mixed*
in which means that the speaker changes it's excursion to represent
the 4k tone.

Agreed.

If there is no IM distortion, then the two waveforms merely
follow the waveform.

That's what the cone does. However you must look at the situation
from the viewpoint of the receiver/listener, not the viewpoint of
the cone.

Interesting.


The receiver/listener *sees* a 4 KHz source that is moving back and
forth in accordance with the 50 Hz sine wave. The position of the
cone as a function of time is correct at all times. However, the 4
KHz source is apparently moving from the viewpoint of the listener.
Therefore it is Doppler-shifted.

It is not "pushing" the waves of the 4k tone.

No, but it is moving he source of the 4 KHz tone.

It is here where great minds disagree.

Disagreement can be good.

The position of the cone is analogous to the amplitude of the cone.
The position of the cone is correct, so there is no amplitude
distortion and no amplitude distortion. However, when the cone
correctly follows the electrical energy applied to it, the cone
moves a 4 KHz acoustical source (itself) back and forth with respect
to the receiver/listener at a 50 Hz rate. It is this added velocity
that causes the Doppler distortion.

Except that I disagree that there IS any velocity added to the higher
wave. The wave IS velocity. No more, no less. Complex but coherent.

You're right, there is no velocity added to the wave in the air. It moves at
the same speed as any other sound. It's the source that picks up the added
velocity.

Given the degree to which Doppler shift is a measurable phenomena
regulated by the speed of sound in air, and is very auduble from
objects traveling at relatively low velocities

AND

Given that a speaker moves at a high rate of speed,

Shouldn't doppler distortion be garishly apparent?

Depends on the situation.

I don't think that a speaker cone motion due to bass is really all that
fast. A woofer cone operating at 50 Hz will move at a peak speed of about
314 inches per second, or about 27 feet per second. This is only about 2% of
the speed of sound.

If it is so subtle that it has escaped everyone's attention, it must be
violating some of
Doppler's own physical laws.

Doppler has not escaped the attention of the technical community. There are
a number of JAES papers about it. Audio Glossaries on the web contain
up-to-date information about it. Thing is, Doppler is a relatively simple
thing, and the issue is thought to be more-or-less settled within learned
circles. I think the last paper I found about it in the JAES archive was
from the early 1980s.

Even a Sawtooth wave would theoretically show doppler distortion.

Yes.

Not only that, but if you were to take the harmonic components of a
sawtooth wave and play them all out of phase with each other, there
would be no difference in sound, but they would theoretically be
modulating each other.

I don't know about the "no difference in sound" in every case. What we have
learned is that Doppler FM distortion always seems to create artifacts that
in reasonable worst case real-world speakers, are always submerged in AM
effects. Perhaps when we reduce AM effects by an order of magnitude, we'll
have to look more seriously at Doppler-related effects.

"Phil Allison" wrote in message



Given that a speaker moves at a high rate of speed,

** Nope - 1 m/S at most.

About 2 mph.

Do the math Phil. The largest stroke woofers around have about 2" linear
stroke which can happen at 50 Hz. The frequency at which the maximum stroke
can be achieved is limited, because the woofer becomes heavily mass-loaded
at higher frequencies, but 50 Hz can be below that frequency for woofers
like these.

50*2*pi*2 = 628 ips = about 50 fps = a peak cone velocity about 15 m/S

In my other example, I used 1" stroke, and still came up with 27 FPS or
about 8 m/S

In fact there are commercial woofers with a lot more than 25.6 mm Xmax, and
some of them can go a bit higher than 50Hz without becoming so mass-loaded
that they can't do their full linear stroke. Speaker cones can also
sometimes substantially exceed their Xmax.

Bottom line Phil, you're off by about an order of magnitude on maximum cone
velocity. But your heart is in the right place - these aren't what could be
reasonably called "a high rate of speed".

"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.

"William Sommerwerck" wrote in message

One other assumption for "perfect" linearity is infinite bandwidth.
It's a given for our models, but I wonder how significant it may be
in the context of related questions of audibility.

Not so. Linearity and bandwidth are not related. To put it another
way, lack of infinite bandwidth is not considered "distortion."

Agreed. However, the phrase "Linear Distortion" applies to things like lack
of bandwidth.

"Chris Hornbeck" wrote in message

On Wed, 11 Aug 2004 18:26:42 -0700, "William Sommerwerck"
wrote:

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?

Exactly right. This can be restated as "air is very low impedance".
Conventional speakers operate into something close to a short
circuit.

I don't think so. Speakers are suspension and/or enclosure air compliance
loaded below resonance. They usually become cone mass-loaded around and
above resonance.

Loudspeaker horns are acoustical transformers that match the high compliance
of the air to the relatively low source impedance of most conventional
loudspeaker drivers.

Horn-loaded drivers are the only ones that operate into an acoustical
impedance low enough to be called anything like a matched impedance, and it
still isn't anything like an acoustical short.

A driver operating into an acoustical short circuit would be motionless.

"Ben Bradley" wrote in message


Bob, what's the difference if the cone is moved by an electrically
supeimposed signal of two sine waves, and if it is moved electrically
by one sine wave and the whole speaker frame is moved mechanically by
another sine wave? Does the cone not go through the same motion in
both cases?

Good point.

"Chris Hornbeck" wrote in message

On Wed, 11 Aug 2004 18:08:28 -0700, Bob Cain
wrote:

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.

I see two flaws here. First is that the FM exists *at the
diaphragm* and is independent of media.

The FM exists at the receiver or listener. If the speaker and the listener
have no relative velocity, no Doppler.

People who ride on trains don't hear the whistle of their train as being
Doppler-shifted. Been there, done that.

Second and lesser is in a way just a restatement of the
observation that conventional diaphragms are high impedance
and air is low impedance. Low acoustic impedance drivers
exhibit low FM distortions (by definition, in this
backwards description).

Agreed.

At some point here we're going to need to talk about horns,
but I'm dreading it. Folk get all riled up.

Sad too, its really pretty simple - a horn is an acoustical impedance
matching transformer.

"Bob Cain" wrote in message

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.

It's 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.

Well, all we need to know is "This is the sound that is coming out of the
front of the speaker".

Lets go down your list:

(1) that in the surround - doesn't matter where the Doppler comes
from, just that it is.

I don't follow this.

What does a speaker do? It makes sound. What do we do with speakers? We put
them in boxes. To make things simple let's consider a sealed box. The sealed
box is there to ensure that the only sound we hear comes out of the front of
the speaker, not its back. Therefore, all we need to do is characterize the
sound that is coming out of the front of the speaker.

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

This either.

Same story. All we need to do is characterize the sound coming out of the
front of the speaker, regardles of its source.

(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?

The general case is that there is both AM & FM distortion. The purpose of
the measurement is to determine where or not there is FM distortion.

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?

It's performing a lot different than the simulation that predicts chaos.

What does it specifically say about Doppler distortion?

Our test finds some Doppler distortion.


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.

It's not a problem here because we do have a working, believeable theory
about loudspeaker Doppler.

"Phil Allison" wrote in message

"Bob Cain"

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



** This article has all the maths re the Doppler effect in woofers.

http://www.geocities.com/kreskovs/Doppler1.html

I still haven't reviewed it thoroughly, but it looks a lot like some of the
JAES papers I've cited recently.

But, he blew the experiment, because his results could be and probably are
dominated by AM effects.

The expeirment part of the article was deconstructed last week in that other
forum you participate in, Phil. Forgot?

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.

"Arny Krueger"
"Phil Allison"

Given that a speaker moves at a high rate of speed,

** Nope - 1 m/S at most.

About 2 mph.

Do the math Phil.


** Go pull your tiny dick - Arny.


The largest stroke woofers around have about 2" linear
stroke which can happen at 50 Hz.


** The OP mentioned simply "speaker" - not sub woofer.

You come back with an excursion number for the most extreme sub woofer that
exists.

Subs are not used to produce frequencies in the kHz range.



50*2*pi*2 = 628 ips = about 50 fps = a peak cone velocity about 15 m/S



** WRONG: V = 2*pi*f * X-max.


In my other example, I used 1" stroke, and still came up with 27 FPS or
about 8 m/S


** WRONG.


Bottom line Phil, you're off by about an order of magnitude on maximum
cone
velocity.


** But I was talking of a "speaker" - just as the OP was.

Speakers have an X-max of about 6mm which is reached at about 30 Hz.

2*pi*.006*30 = 1.13 m/S




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

"Phil Allison" wrote in message

"Arny Krueger"
"Phil Allison"

Given that a speaker moves at a high rate of speed,

** Nope - 1 m/S at most.

About 2 mph.

Do the math Phil.

** Go pull your tiny dick - Arny.

How do you know what size it is, Phil? Been fantasizing about me? ;-)

The largest stroke woofers around have about 2" linear
stroke which can happen at 50 Hz.

** The OP mentioned simply "speaker" - not sub woofer.

Oh Phil are you saying that subwoofers aren't speakers?

You come back with an excursion number for the most extreme sub
woofer that exists.

No, that one has Xmax that is about 40% more than 1" - about 36 mm if I
recollect properly. I was giving you a break!

Subs are not used to produce frequencies in the kHz range.

Agreed, but due to their long stroke, some people think they might be
candidates for Doppler distortion.

50*2*pi*2 = 628 ips = about 50 fps = a peak cone velocity about 15
m/S

** WRONG: V = 2*pi*f * X-max.

Agreed, so now we're back to my original example of about 7 m/S


Bottom line Phil, you're off by about an order of magnitude on
maximum cone velocity.

** But I was talking of a "speaker" - just as the OP was.

Phi,l are you saying that subwoofers aren't speakers?

Speakers have an X-max of about 6mm which is reached at about 30 Hz.

Phil, are you saying that subwoofers aren't speakers?

2*pi*.006*30 = 1.13 m/S

But to quote you Phil,

"Nope - 1 m/S at most."

Phil, even your example, as limited as it is, is 1 m/S