On 13 Aug 2004 22:20:04 -0400, (Scott Dorsey) wrote:

The Doppler issue isn't one of wave propagation at all, it's an issue
that results from the breakdown of reciprocity, where the motion of the
speaker to produce a given wave in air is different than the motion of
the microphone diaphragm that picked it up.

I have a theory! This is at least (couldn't really follow it all)
the third major paradigm shift in this discussion. So:

1. Bob Cain, notorious trickster, bon vivant and fan of Albert
Einstein, posts a challenging conceptual thread in August 2004.

2. One hundred years ago, in a land far, far away, an unknown
clerk with a day job in the Zurich patent office was thinking
about train whistles, the much earlier Michealson-Morley C
experiments, and Lorentz's recent E=MC^2 conclusions.

3. Said clerk decides, hey! I could get the babes if I just
pretended that all this hockus-pockus was true. Turns out to be
right! Who knew?! Rock-n-Roll.

4. Said notorious trickster tosses bomb into newsgroup as part
homage, part Summer Blockbuster.

5. Lots is learned, (He who cannot be named) contributes (!),
some new blood arrives. All good.

"That is my theory, and what it is too." - Anne Elk

Chris Hornbeck

On 13 Aug 2004 22:20:04 -0400, (Scott Dorsey) wrote:

The Doppler issue isn't one of wave propagation at all, it's an issue
that results from the breakdown of reciprocity, where the motion of the
speaker to produce a given wave in air is different than the motion of
the microphone diaphragm that picked it up.

I should also have said in my earlier frivolous post that this is
the most elegant viewpoint I've yet heard. It includes everything
that matters and excludes the Ghafla.

Chris Hornbeck

Scott Dorsey wrote:

The Doppler issue isn't one of wave propagation at all, it's an issue
that results from the breakdown of reciprocity, where the motion of the
speaker to produce a given wave in air is different than the motion of
the microphone diaphragm that picked it up.

I'd need to see a real good reason for reciprocity to
breakdown. Hand waving about waves riding waves just
doesn't hack it I'm afraid.


Bob
--

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

A. Einstein

Phil Allison wrote:

[some nonsense]

Go away, troll. Your utter ignorance is a heavy weight on
this discussion, and most it seems. You really enjoy that
don't you. No more for feed for ya, son.


Bob
--

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

A. Einstein

Chris Hornbeck wrote:

My Kyper _FM Simplified_ is out on loan, but should be back soon,
and I can give you a better pointer.

But for a heavy math guy like you, the Terman-level description
might be even better. His 1947 3rd ed. of _Radio Engineering_
chapter 9 section 5 has two equations applicable:

9.6 gives a description of instantaneous amplitude of a wave as
a function of angular velocities and frequencies, and

9.9 gives the Bessel function of the first kind expansion for the
sum of the two angles.

Chris, I'm a bit confused here. Is Termen's description
that of the basic principles of frequency modulation or does
he relate that to loudspeaker motion and show how it
produces it with mathematical rigor?

The question here is whether or not a loudspeaker comprises
a frequency modulator at all and if so, what's the full
mathematical description rigorously tied to physical principles.

Doesn't it puzzle you too that it hasn't been produced to
kill my thesis? If it exists and can predict the behavior
quantitatively that would pretty much put an end to it. It
hasn't been produced or referenced here or in any of the
physics or acoustics related forums I've asked.

I am persuaded that the absence of a theory in this case
provides at least one good theory for the absence of the
phenomenon.

That an ideal piston would move in some way in response to
an acoustic wave but not produce that wave when moved the
same way seems utterly absurd. I'm not up to it tonight but
I'll bet that reciprocity can be proven to be required by an
appeal to the conservation of energy.

I guess that is the final step of my argument, though, to
show on first principles that conservation of energy (or
some basic physical conservation law) requires the
reciprocity on which the argument is based. Heavy sigh.
That seems as obvious to me without proof as the argument
for "Doppler distortion" does to others. At least it
appears reasonably amenable to proof.


Bob
--

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

A. Einstein

On Fri, 13 Aug 2004 23:40:44 -0700, Bob Cain
wrote:

The Doppler issue isn't one of wave propagation at all, it's an issue
that results from the breakdown of reciprocity, where the motion of the
speaker to produce a given wave in air is different than the motion of
the microphone diaphragm that picked it up.

I'd need to see a real good reason for reciprocity to
breakdown. Hand waving about waves riding waves just
doesn't hack it I'm afraid.

But that's the thing I like best about it; it's an algebraic ratio
of diaphragm sizes divided by field strength.

Yes: everything moving has FM issues.

But: smaller things move less in the same field.

I'll have to get some sleep on this, but crudely: the originating
diaphragm must move (some) to do its job. The receiving diaphragm
must move (some less) to do its job.

Chris Hornbeck

On Sat, 14 Aug 2004 00:11:20 -0700, Bob Cain
wrote:

Chris, I'm a bit confused here. Is Termen's description
that of the basic principles of frequency modulation or does
he relate that to loudspeaker motion and show how it
produces it with mathematical rigor?

Terman only describes the results, not the machinery. He
assumes that one believes the machinery to be applicable.
(Well, it is for an FM transmitter, so he's fairly confident!).


The question here is whether or not a loudspeaker comprises
a frequency modulator at all and if so, what's the full
mathematical description rigorously tied to physical principles.

Can you accept that the (moving, of course) diaphragm
defines the system output? Or must we move further downstream?

If you can't accept the diaphragm's motion as definitive
then I'm lost. If you can, then we can move on to the receiving
diaphragm.

But if you can....



Doesn't it puzzle you too that it hasn't been produced to
kill my thesis? If it exists and can predict the behavior
quantitatively that would pretty much put an end to it. It
hasn't been produced or referenced here or in any of the
physics or acoustics related forums I've asked.

OTOH, that's what makes a great topic. The easy stuff gets
laughed off and the impossible stuff gets bull****ted off.

But! the great stuff lies right under the surface. And so
encourages discussion. Everybody *thinks* they know how
transformers work....

But really, nobody does. Our intuitively useful models are,
not to put too fine a point on it, wrong. Tough titty; we
get along.

I am persuaded that the absence of a theory in this case
provides at least one good theory for the absence of the
phenomenon.

Or: the theory exists someplace else. I just don't think
audio is the place to look. It's a radio theory.

That an ideal piston would move in some way in response to
an acoustic wave but not produce that wave when moved the
same way seems utterly absurd. I'm not up to it tonight but
I'll bet that reciprocity can be proven to be required by an
appeal to the conservation of energy.

I guess that is the final step of my argument, though, to
show on first principles that conservation of energy (or
some basic physical conservation law) requires the
reciprocity on which the argument is based.

Do microphones exhibit FM distortion? If so, how much?
(See S. D. above)

That seems as obvious to me without proof as the argument
for "Doppler distortion" does to others. At least it
appears reasonably amenable to proof.

The answer to Scott's posed question is simply "It's bigger."
The scale makes it significant.

Chris Hornbeck

"Chris Hornbeck" wrote in message


I'll have to get some sleep on this, but crudely: the originating
diaphragm must move (some) to do its job. The receiving diaphragm
must move (some less) to do its job.

If you had two diaphragms that had to move equal distances in the same
direction to accomplish their respective functions of receiving or sending,
there would be no Doppler distortion. We would be back to the listener
riding on the same train as the whistle.

"Bob Cain" wrote in message


If it exists and can predict the behavior
quantitatively that would pretty much put an end to it. It
hasn't been produced or referenced here or in any of the
physics or acoustics related forums I've asked.

I believe that Goofball has the math and experimental data that does that.

Bob Cain wrote:
Scott Dorsey wrote:

The Doppler issue isn't one of wave propagation at all, it's an issue
that results from the breakdown of reciprocity, where the motion of the
speaker to produce a given wave in air is different than the motion of
the microphone diaphragm that picked it up.

I'd need to see a real good reason for reciprocity to
breakdown. Hand waving about waves riding waves just
doesn't hack it I'm afraid.

It's in the nature of speaker cabinets. Look at the woofer excursion on
a 20 Hz note vs. a 50 Hz note. Now look at what happens to a microphone
given the same two notes. The ratios are not even a little bit the same.
You can plug-and-chug with the formulae in the Dickason book if you want
to know the maximum excursion of a given driver in a given cabinet at a
given frequency.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

"Bob Cain"


Phil Allison wrote:

[some nonsense]


** Some very much sense was rudely snipped by a NG ****wit who makes the
world's perpetual motion imbeciles look sane.






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

If it exists and can predict the behavior quantitatively that
would pretty much put an end to it. It hasn't been produced
or referenced here or in any of the physics or acoustics
related forums I've asked.

I believe that Goofball has the math and experimental data that does that.

Are you talking audibility or existence?


Several days ago I reduced the issue to a simple thought-experiment -- given a
driver producing a high frequency, is there a fundamental difference between
moving the driver as a whole at a much lower frequency and moving the cone
itself at a much lower frequency?

If there is none, then Doppler distortion exists. If there is, then it might or
might not.

I understand (and sympathize with) Bob's desire for a mathematical treatment.
But I much prefer the "clever insight" ahem that points to the real issue, and
cuts the Gordian knot.

Speaker cones reach their greatest velicities at low frequencies
and large excursions while making the same SPL as at higher
frequencies with lower velocities.

Uh... If you double the frequency and halve the excursion, you have exactly the
same velocity.

Electrodynamic speakers are velocity devices.

On Sat, 14 Aug 2004 06:27:18 -0700, "William Sommerwerck"
wrote:

Speaker cones reach their greatest velicities at low frequencies
and large excursions while making the same SPL as at higher
frequencies with lower velocities.

Uh... If you double the frequency and

halve the excursion,

Oops-a-daisy.

y ou have exactly the
same velocity.

Electrodynamic speakers are velocity devices.

"William Sommerwerck"

Speaker cones reach their greatest velicities at low frequencies
and large excursions while making the same SPL as at higher
frequencies with lower velocities.

Uh... If you double the frequency and halve the excursion, you have
exactly the
same velocity.


** But not the same SPL.

" F = mA " rules.





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

** But not the same SPL.

" F = mA " rules.

No, I believe you do have the same SPL. Correct me if I'm wrong, but doubling
the frequency also doubles the acoustic impedance (???) and you get the same
power transfer to the air.

I'm weak on this. Somebody fill me in.

On Sat, 14 Aug 2004 07:39:18 -0700, "William Sommerwerck"
wrote:

** But not the same SPL.

" F = mA " rules.

No, I believe you do have the same SPL. Correct me if I'm wrong, but doubling
the frequency also doubles the acoustic impedance (???) and you get the same
power transfer to the air.

I'm weak on this. Somebody fill me in.

http://www.google.com/groups?selm=EK...utput=gpla in

"William Sommerwerck" wrote in message

** But not the same SPL.

" F = mA " rules.

No, I believe you do have the same SPL. Correct me if I'm wrong, but
doubling the frequency also doubles the acoustic impedance (???) and
you get the same power transfer to the air.

I'm weak on this. Somebody fill me in.

Goofball's cite of Pierce's article is the real thing.

All other things being equal, excursion goes up by four when the frequency
goes down by two.

"William Sommerwerck" wrote in message

If it exists and can predict the behavior quantitatively that
would pretty much put an end to it. It hasn't been produced
or referenced here or in any of the physics or acoustics
related forums I've asked.

I believe that Goofball has the math and experimental data that does
that.

Are you talking audibility or existence?

Existence.

Several days ago I reduced the issue to a simple thought-experiment
-- given a driver producing a high frequency, is there a fundamental
difference between moving the driver as a whole at a much lower
frequency and moving the cone itself at a much lower frequency?

I thought it was a great question with an obvious answer.

If there is none, then Doppler distortion exists. If there is, then
it might or might not.

There is none from the perspective of the listener.

I understand (and sympathize with) Bob's desire for a mathematical
treatment. But I much prefer the "clever insight" ahem that points
to the real issue, and cuts the Gordian knot.

Well yesterday I cited about a jillion AES articles that are all positive
for Doppler distortion in speakers, but generally negative for it being a
serious audible problem, if they grant an opinion on that topic at all.

On Sat, 14 Aug 2004 00:11:20 -0700, Bob Cain
wrote:

...

The question here is whether or not a loudspeaker comprises
a frequency modulator at all and if so, what's the full
mathematical description rigorously tied to physical principles.

Doesn't it puzzle you too that it hasn't been produced to
kill my thesis? If it exists and can predict the behavior
quantitatively that would pretty much put an end to it. It
hasn't been produced or referenced here or in any of the
physics or acoustics related forums I've asked.

I am persuaded that the absence of a theory

The absence of a theory? What would a theory look like that would
convince you? I've seen some good arguments here and have tried to
present some on my own...

in this case
provides at least one good theory for the absence of the
phenomenon.

Here's my attempt at something almost semi-rigorous. It has
equations, so maybe that will help convince you.

H = frequency of high-pitch tone
L = frequency of low-pitch tone
w = 2 pi * t generally called omega and used a conversion factor
from cycles to radians, the 'natural' unit for trig functions.
t = time, a continuously increasing value.

From those you can surely come up with this equation of the voltage
that would be put across the terminals of a speaker to generate these
pitches:

voltage = sin (wH) + sin (wL)

(there's of course a gain constant multiplier in front of each sin,
but we'll set them to 1 to keep things simple)
Presuming the loudspeaker (or driver, or whatever you call it) is
perfectly linear, the voice coil will move in proportion to the
voltage across it and its position .. well, actually, at frequencies
above resonance, I think it's the force the voice coil pushes with, or
the pressure the cone pushes on the air, that is proportional to the
impressed boltage, but regardless, we agree that it's all linear (that
all else the same, a higher voltage gives a proportionally higher
amplitude) in this theoretically perfect speaker driver.

pressure = sin (wH) + sin (wL)

where of course "pressure" is defined as relative to the ambient
air pressure, which is considered the zero reference point.

Put a microphone at some distance, maybe 10cm from the speaker.
Suppose the low frequency signal causes a total cone displacement of
10mm (5mm toward the mic, and 5mm away from the mic, in reference to
the cone's rest position). The high tone is also present, but for the
reasons given in the previous paragraph, it moves the cone a much
smaller distance (maybe .05mm), which we will ignore for the moment.
This means that at the positive peak of the low tone, the cone (which
is the source of the high tone - do we agree with that?) is closer to
the microphone. Due to the finite speed of sound, the mic picks up the
high tone in less time than when the cone is in its rest position, so
the high tone is phase-advance at the mic. Likewise at the negative
peak of the low tone, the distance between the cone and the mic is
greater than at rest position, so the high tone is phase-retarded at
the mic.
So the phase of the high tone as picked up by the (stationary) mic
is phase-modulated by the low pitch, and the formula becomes:

pressure = sin (wH + k * sin (wL)) + sin (wL)

where K is a constant that depends on (among other things) the
speed of sound. (It would be an inverse relationship - the faster the
speed of sound, the lower the value of k).

To truly complete the model, we should also indicate the phase
modulation of the low tone by the high tone (the 0.05mm distance I
mention above):

pressure = sin (wH + k * sin (wL)) + sin (wL + k2 * sin (wH))

where k2 is another constant similar to k (it should actually be
the same constant with a frequency dependence).

Of course, phase modulation, while not being the same as frequency
modulation, is equivalent. IIRC, it only takes an integral or a
derivative (of the modulating signal) to convert from one to the
other.

If you actually run this formula through something that generates
..wav files, small values of k amd k2 (perhaps barely audible, if at
all, compared to a value of 0) will give something similar to what a
full-range driver will do, and larger values will sound like a patch
on a Yamaha DX series synth (if you really want it to sound cool, have
k and k2 decrease exponentially). So to simulate a speaker, keep the
numbers low.

So that's my "theory" (I hesitate to use the word because there are
so many definitions, and I'm not sure any of them are right for this)
of FM in loudspeaker drivers.

If that doesn't convince you, I've got a boat oar in the water
making waves analogy, then I'll suggest you physically connect a train
whistle to a speaker cone...

That an ideal piston would move in some way in response to
an acoustic wave but not produce that wave when moved the
same way seems utterly absurd. I'm not up to it tonight but
I'll bet that reciprocity can be proven to be required by an
appeal to the conservation of energy.

I guess that is the final step of my argument, though, to
show on first principles that conservation of energy (or
some basic physical conservation law) requires the
reciprocity on which the argument is based. Heavy sigh.
That seems as obvious to me without proof as the argument
for "Doppler distortion" does to others. At least it
appears reasonably amenable to proof.


Bob

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

Chris Hornbeck wrote:

Can you accept that the (moving, of course) diaphragm
defines the system output? Or must we move further downstream?

If you can't accept the diaphragm's motion as definitive
then I'm lost. If you can, then we can move on to the receiving
diaphragm.

But if you can....

Yes, I can. The question is what that motion does to the
air in front of it.

Doesn't it puzzle you too that it hasn't been produced to
kill my thesis? If it exists and can predict the behavior
quantitatively that would pretty much put an end to it. It
hasn't been produced or referenced here or in any of the
physics or acoustics related forums I've asked.


OTOH, that's what makes a great topic. The easy stuff gets
laughed off and the impossible stuff gets bull****ted off.

LOL! That's the thing. If it exists, it shouldn't take a
John Baez or an Ed Whitten (prominent mathematical
physicists) to write it down.

Our intuitively useful models are,
not to put too fine a point on it, wrong. Tough titty; we
get along.

All too often, and they can be very seductive too.


I am persuaded that the absence of a theory in this case
provides at least one good theory for the absence of the
phenomenon.


Or: the theory exists someplace else. I just don't think
audio is the place to look. It's a radio theory.

It's supposedly an acoustics phenomenon which is a branch of
classical mechanics. I've inquired of those community's
usenet presence and no answer has been forthcoming in those
forums either. I'm fair to middlin with physics myself
having degrees in both EE and Engineering Physics and
looking up close at it, nothing emerges but the simple
linear transmission of energy from piston to air.

Do microphones exhibit FM distortion? If so, how much?
(See S. D. above)

Dunno what the lore says but my analysis says no more so
than speakers, which is zero.



That seems as obvious to me without proof as the argument
for "Doppler distortion" does to others. At least it
appears reasonably amenable to proof.


The answer to Scott's posed question is simply "It's bigger."
The scale makes it significant.

Can't see any basis in physics for that. Seems to be
another of those intuitive things that can't really be
justified when push comes to shove. (With all due respect,
Scott.)


Bob
--

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

A. Einstein

William Sommerwerck wrote:

Several days ago I reduced the issue to a simple thought-experiment -- given a
driver producing a high frequency, is there a fundamental difference between
moving the driver as a whole at a much lower frequency and moving the cone
itself at a much lower frequency?

Not even sure the thought experiment casts any light on the
problem.


If there is none, then Doppler distortion exists. If there is, then it might or
might not.

If and only if the applied reasoning proves correct. I
don't think it does. I've given another line of reasoning
that shows conclusively that it doesn't exist if the law of
reciprocity applies to acoustic phenomenon. I see
absolutely no reason in physics why it shouldn't but that
remains to be proven or if that fails what law replaces it
that yields this "Doppler distortion."


I understand (and sympathize with) Bob's desire for a mathematical treatment.
But I much prefer the "clever insight" ahem that points to the real issue, and
cuts the Gordian knot.


I've begun to think that the problem with the intuitive
description, that is so seductive, boils down to the belief
that a signal is physically made up of sinusoids and then
drawing false conclusions from that false belief.

While it's a whole 'nother argument that need not be taken
up here, a physical signal is no more composed of complex
exponentials (sins with phase) than it is of wavelets which
offer an infinite number of equivalent orthogonal basis
sets. The physical signal is what it is, no more, no less.
Fourier analysis isn't about physical reality, it's about
a mathematical tool that can, in the proper circumstances,
give insight and calculational advantage.

As such, if it exists, the phenomenon should be describable
without appeal to fourier analysis and that description
should yield quantifiable predictions that apply to any
signal. So far as I can determine, no such description
exists. Don't you find that puzzling? As I've said before,
this isn't string theory and shouldn't require a John Baez
or Ed Whitten to figure out.

John and I were close friends with frequent face time once
but that's been somewhat distanced by time and geography.
I'm tempted to ask him for his analysis of this but his
prominence has so skyrocketed since those days and our
friendship so lapsed that I am hesitant to even approach him
with something so trivial now. "I know I haven't been in
touch in many years, John, but I need you now to settle a
trivial classical physics argument", somehow doesn't sit
well with me. Besides, he'd probably just tell me "Bob,
that's something you shouldn't need my help with." He's
known for that. :-)


Bob
--

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

A. Einstein

Scott Dorsey wrote:

It's in the nature of speaker cabinets.

Scott, the intuitive argument commonly presented to justify
"Doppler distortion" doesn't appeal in any way to cabinets
or other imperfections in the emitter. It is described as a
mechanism that occurs at the piston/air interface regardless
of how that piston gets driven.


Bob
--

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

A. Einstein

Arny Krueger wrote:

If you had two diaphragms that had to move equal distances in the same
direction to accomplish their respective functions of receiving or sending,
there would be no Doppler distortion. We would be back to the listener
riding on the same train as the whistle.

Bingo. Bob leaves the stage to thunderous applause :-)


Bob
--

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

A. Einstein

William Sommerwerck wrote:

Speaker cones reach their greatest velicities at low frequencies
and large excursions while making the same SPL as at higher
frequencies with lower velocities.


Uh... If you double the frequency and halve the excursion, you have exactly the
same velocity.

Electrodynamic speakers are velocity devices.

Hey, William, we agree on something. I think the occasion
warrents a party. But then, I think that of most occasions.
:-)


Bob
--

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

A. Einstein

Several days ago I reduced the issue to a simple thought-experiment --
given a driver producing a high frequency, is there a fundamental
difference between moving the driver as a whole at a much lower
frequency and moving the cone itself at a much lower frequency?

Not even sure the thought experiment casts any light on the
problem.

Then you need to rethink it. It cuts right to the heart of the issue.


I've begun to think that the problem with the intuitive
description, that is so seductive, boils down to the belief
that a signal is physically made up of sinusoids and then
drawing false conclusions from that false belief.

The Principle of Superposition states that, in a linear system, the output for a
complex input is equal to the simple sum of the outputs for the sinusoidal
inputs that make up the complex input.

This is true for the cone motion, but it says nothing about the medium in front
of the cone.


As such, if it exists, the phenomenon should be describable
without appeal to fourier analysis and that description
should yield quantifiable predictions that apply to any
signal. So far as I can determine, no such description
exists. Don't you find that puzzling? As I've said before,
this isn't string theory and shouldn't require a John Baez
or Ed Whitten to figure out.

You're confusing the motion of the cone with the motion of the air in front of
it. They're not necessarily the same thing.

William Sommerwerck wrote:

** But not the same SPL.

" F = mA " rules.


No, I believe you do have the same SPL. Correct me if I'm wrong, but doubling
the frequency also doubles the acoustic impedance (???) and you get the same
power transfer to the air.

I'm weak on this. Somebody fill me in.

Sound pressure emitted by a piston is proportional to and in
phase with its velocity. Piston velocity alone determines SPL.

The F = mA applies to what happens to a piston with mass m
when a force F is applied to it in the absence of air. It
doesn't say anything about what happens to air in response
to the motion of a piston. That's independant of how the
piston gets its motion.


Bob
--

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

A. Einstein

Bob Cain wrote:


I've begun to think that the problem with the intuitive description,
that is so seductive, boils down to the belief that a signal is
physically made up of sinusoids and then drawing false conclusions from
that false belief.

While it's a whole 'nother argument that need not be taken up here, a
physical signal is no more composed of complex exponentials (sins with
phase) than it is of wavelets which offer an infinite number of
equivalent orthogonal basis sets. The physical signal is what it is, no
more, no less. Fourier analysis isn't about physical reality, it's
about a mathematical tool that can, in the proper circumstances, give
insight and calculational advantage.

While I will maintain until the end that the last paragraph
is true, I see that the consideration is a dead end. It's
much simpler than that.


Bob
--

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

A. Einstein

Ben Bradley wrote:


Put a microphone at some distance, maybe 10cm from the speaker.
Suppose the low frequency signal causes a total cone displacement of
10mm (5mm toward the mic, and 5mm away from the mic, in reference to
the cone's rest position). The high tone is also present, but for the
reasons given in the previous paragraph, it moves the cone a much
smaller distance (maybe .05mm), which we will ignore for the moment.
This means that at the positive peak of the low tone, the cone (which
is the source of the high tone - do we agree with that?) is closer to
the microphone. Due to the finite speed of sound, the mic picks up the
high tone in less time than when the cone is in its rest position, so
the high tone is phase-advance at the mic. Likewise at the negative
peak of the low tone, the distance between the cone and the mic is
greater than at rest position, so the high tone is phase-retarded at
the mic.

Here is the problem. Since the distance between driver and
detector is actually the distance from the rest position of
the driver to the detector, which is true because the driver
face is riding the wave it creates, there is really no phase
modulation because there is no distance modulation.

Any math that starts from the assumption that the distance
from the driver to the detector is the instantaneous
position of the piston will end at the wrong place.


Bob
--

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

A. Einstein

"Goofball_star_dot_etal"
On Sat, 14 Aug 2004 07:39:18 -0700, "William Sommerwerck"
wrote:

** But not the same SPL.

" F = mA " rules.

No, I believe you do have the same SPL. Correct me if I'm wrong, but
doubling
the frequency also doubles the acoustic impedance (???) and you get the
same
power transfer to the air.

I'm weak on this. Somebody fill me in.

http://www.google.com/groups?selm=EK...utput=gpla in


" Above resonance, where the system is mass controlled, for a given drive
level, acceleration is
constant with frequency. Integrate that w.r.t. frequency and you find the
velocity then goes as the inverse frequency. Now integrate the velocity
w.r.t. frequency and you then find that displacement goes as the inverse
square of frequency. "



** QED



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

"Bob Cain"

William Sommerwerck wrote:

** But not the same SPL.

" F = mA " rules.


No, I believe you do have the same SPL. Correct me if I'm wrong, but
doubling
the frequency also doubles the acoustic impedance (???) and you get the
same
power transfer to the air.

I'm weak on this. Somebody fill me in.

Sound pressure emitted by a piston is proportional to and in
phase with its velocity. Piston velocity alone determines SPL.


** Mr Cain has applied Goebbel's theories of propaganda to science.



The F = mA applies to what happens to a piston with mass m
when a force F is applied to it in the absence of air.


** It also applies to a speaker cone ( above resonance) in the presence of
air.



It doesn't say anything about what happens to air in response
to the motion of a piston. That's independant of how the
piston gets its motion.


** Purest gobbledegook.



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

"Bob Cain"


William Sommerwerck wrote:

Speaker cones reach their greatest velicities at low frequencies
and large excursions while making the same SPL as at higher
frequencies with lower velocities.


Uh... If you double the frequency and halve the excursion, you have
exactly the
same velocity.

Electrodynamic speakers are velocity devices.

Hey, William, we agree on something.



** LOL




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

"Bob Cain"


Ben Bradley wrote:


Put a microphone at some distance, maybe 10cm from the speaker.
Suppose the low frequency signal causes a total cone displacement of
10mm (5mm toward the mic, and 5mm away from the mic, in reference to
the cone's rest position). The high tone is also present, but for the
reasons given in the previous paragraph, it moves the cone a much
smaller distance (maybe .05mm), which we will ignore for the moment.
This means that at the positive peak of the low tone, the cone (which
is the source of the high tone - do we agree with that?) is closer to
the microphone. Due to the finite speed of sound, the mic picks up the
high tone in less time than when the cone is in its rest position, so
the high tone is phase-advance at the mic. Likewise at the negative
peak of the low tone, the distance between the cone and the mic is
greater than at rest position, so the high tone is phase-retarded at
the mic.

Here is the problem. Since the distance between driver and
detector is actually the distance from the rest position of
the driver to the detector, which is true because the driver
face is riding the wave it creates, there is really no phase
modulation because there is no distance modulation.


** The low frequency tone changes the effective rest position of the driver
for the high frequency tone. The simplest test set up will show that the
time of arrival is being modulated and hence creating varying phase shift in
the high tone.

You only need to synch the scope's time base to a frequency source and watch
the phase change on the screen as a mic is moved near a speaker fed the same
frequency.

Add a low frequency into the game and the phase of the high one shimmers in
proportion to the **excursion** of the cone.

Use a lissajous pattern for enhanced effect.




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

"Phil Allison" wrote in message
...
"Bob Cain"
Phil Allison wrote:

Ok. The false assumption is that the pressure wave created
by a piston is proportional to its acceleration. It isn't;
it's proprotional to the piston velocity.

** You have evidence ????

Better than that, I have a proof by the principle of
reciprocity (not at all the same as analogy since it only
considers the actual system in question.) If you missed it,
I'll be happy to repeat it.


** You have no proof - only your own a mad ideas.

Bob is correct: instantaneous acceleration numbers don't mean much
unless you're doing materials analysis on the cone, suspension, or
motor structure. It doesn't matter if the cone is pulling 100 G's
at some arbitrary point in time (it could have stopped...); it
matters that it moved from point A to point B in X microseconds. It
might not have accelerated _at_all_ during X, but it will still
produce a positive or negative pressure wave.

Speaker cones reach their greatest velicities at low frequencies
and large excursions while making the same SPL as at higher
frequencies with lower velocities.

This is true, but not for the reason you seem to be stating.

The real reason for this is that conventional direct radiator
dynamic loudspeakers lose air coupling efficiency at at about the
frequency whose quarter wavelength is equal to the diameter of the
cone. Excursion has to approximately double for each octave below
this point achieve the same SPL.

-DrBoom

On Sat, 14 Aug 2004 15:24:25 -0700, Bob Cain
wrote:

"Doppler distortion" is described as a
mechanism that occurs at the piston/air interface regardless
of how that piston gets driven.

Not by me. I'm leaning towards saying that the mechanism
occurs at the linear distance between radiating and receiving
diaphragms. Because it's the linear distance that's modulated.

Chris Hornbeck

"Chris Hornbeck" wrote in message

On Sat, 14 Aug 2004 15:24:25 -0700, Bob Cain
wrote:

"Doppler distortion" is described as a
mechanism that occurs at the piston/air interface regardless
of how that piston gets driven.

Not by me. I'm leaning towards saying that the mechanism
occurs at the linear distance between radiating and receiving
diaphragms. Because it's the linear distance that's modulated.

The mechanism IS the change in linear distance between radiating and
receiving
diaphragms. Because it's the linear distance that's modulated.

"DrBoom"
"Phil Allison"

Speaker cones reach their greatest velocities at low frequencies
and large excursions while making the same SPL as at higher
frequencies with lower velocities.

This is true, but not for the reason you seem to be stating.

The real reason for this is that conventional direct radiator
dynamic loudspeakers lose air coupling efficiency at at about the
frequency whose quarter wavelength is equal to the diameter of the
cone. Excursion has to approximately double for each octave below
this point achieve the same SPL.


** So you are claiming constant cone excursion with frequency above some
low frequency is the norm ?? That means all drivers have rising cone
velocity with frequency - doubling every octave. The very highest
velocities would then be found at the top of their operating range. Not so.

The formula " F = m.a " describes the effect of drive force on the voice
coil.

To this, add the formula for the displacement of an accelerating mass: s
= u.t + a.t.t / 2

The squared " t " shows that displacement quadruples when a force operates
for double the time on a given mass.

So, if the drive force (or amplifier current ) remains unchanged but
operates for twice the time before reversing direction ( ie operates at half
the frequency) the cone will move four times as far before it changes
direction.




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

On Sat, 14 Aug 2004 14:42:57 -0700, Bob Cain
wrote:

If you can't accept the diaphragm's motion as definitive
then I'm lost. If you can, then we can move on to the receiving
diaphragm.

Yes, I can. The question is what that motion does to the
air in front of it.

Suppose the moving diaphragm itself, referenced to the position
of the receiving diaphragm, generated the Doppler effect?
And the diaphragm to air translation were only linear; no
special pleadings in the translation needed?


LOL! That's the thing. If it exists, it shouldn't take a
John Baez or an Ed Whitten (prominent mathematical
physicists) to write it down.

Whenever I've seen Joan Baez, her recitative has leaned more
towards the polemical, but she does let the occasional
trig function slip in.

The answer to Scott's posed question is simply "It's bigger."
The scale makes it significant.

Can't see any basis in physics for that. Seems to be
another of those intuitive things that can't really be
justified when push comes to shove. (With all due respect,
Scott.)

The problem is all in my very, very poor expression of it.
The two moving diaphragms are asymmetrical in their "absolute"
motion, therefore they have some relative motion.

And their relative motion is *all* that's needed for the
Doppler effect.

Maybe what I'm missing is why the audio case must be different
from the case of other waves? Red shift, blue shift, etc.
You're obviously getting at something, but I'm not seeing
it yet.

Chris Hornbeck

"Chris Hornbeck" wrote in message


Maybe what I'm missing is why the audio case must be different
from the case of other waves? Red shift, blue shift, etc.
You're obviously getting at something, but I'm not seeing
it yet.

It's all the same, more or less. Doppler with light, doppler with sound...
At the core is relative motion.

On Sat, 14 Aug 2004 18:04:47 -0700, Bob Cain
wrote:

Here is the problem. Since the distance between driver and
detector is actually the distance from the rest position of
the driver to the detector, which is true because the driver
face is riding the wave it creates, there is really no phase
modulation because there is no distance modulation.

Wow. You can't leave it with just this much. What does
this mean?

Perhaps you would start with: does a single motion modulate
distance? and move on to multiple imbedded motions.

Truely stunned,

Chris Hornbeck