Chris Hornbeck wrote:

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?

I'll try again. The argument for Doppler distortion
considers the instantaneous distance between reciever and
piston as the distance the sound travels so that as it moves
the distance is modulated and thus the frequency is.

That is incorrect. The reality is that the distance between
receiver and piston, precisely because that piston is riding
the wave, is measured from its rest position and not its
instantaneous position. If the rest position isn't moving
then there is no Doppler shift occuring.


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

Here's another place trouble sets in. There isn't any such
thing as single and multiple embedded moves. That's fuzzy
thinking from the incorrect assumption that in reality
signals are composed of something else. They aren't.

Nonetheless, you should see now that it doesn't matter what
motion the piston engages in while following the signal, it
is the rest position that determines the distance at all
times. Translate it and you have Doppler shift. Simply
oscillate about it and you don't. I think that is because
air only has zero response at DC, but that's off the cuff.


Bob
--

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

A. Einstein

"Bob Cain"

I'll try again. The argument for Doppler distortion
considers the instantaneous distance between reciever and
piston as the distance the sound travels so that as it moves
the distance is modulated and thus the frequency is.

That is incorrect. The reality is that the distance between
receiver and piston, precisely because that piston is riding
the wave, is measured from its rest position and not its
instantaneous position. If the rest position isn't moving
then there is no Doppler shift occuring.


** But the rest position for the high frequency **IS** moving - at the
low frequency.



Nonetheless, you should see now that it doesn't matter what
motion the piston engages in while following the signal, it
is the rest position that determines the distance at all
times. Translate it and you have Doppler shift. Simply
oscillate about it and you don't.


** Pure insanity.




.......... Phil

On Sat, 14 Aug 2004 23:25:51 -0700, Bob Cain
wrote:

I'll try again. The argument for Doppler distortion
considers the instantaneous distance between reciever and
piston as the distance the sound travels so that as it moves
the distance is modulated and thus the frequency is.

That is incorrect. The reality is that the distance between
receiver and piston, precisely because that piston is riding
the wave, is measured from its rest position and not its
instantaneous position. If the rest position isn't moving
then there is no Doppler shift occuring.

Very, very cool. I'm beginning to start to begin to get a
grasp on what you're after. You're still wrong, wrong, wrong!
but I may not be smart enough to describe why. Cool beans.

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

Here's another place trouble sets in. There isn't any such
thing as single and multiple embedded moves. That's fuzzy
thinking from the incorrect assumption that in reality
signals are composed of something else. They aren't.

Well, in that light, no classical analysis is possible.
And that's all we're talking about. Admittedly the request
was lame and loaded.

Nonetheless, you should see now that it doesn't matter what
motion the piston engages in while following the signal, it
is the rest position that determines the distance at all
times. Translate it and you have Doppler shift. Simply
oscillate about it and you don't. I think that is because
air only has zero response at DC, but that's off the cuff.

Just when I thought I had it, I fall off the edge of the earth
again.


I still think that this whole avenue is misguided and that the
only real component of receiving diaphragm motion is its
instantaneous differential air pressure, determined in our
model by the air pressure at the source diaphragm.

And I can't see where you're *not* saying that the train
whistle's pitch doesn't change.

In summary: I can't agree with "the piston riding the wave"
or that signals aren't composed of something else. The latter
would also invalidate non-linearity in general. My interpretation
can't be what you meant.

Chris Hornbeck

Chris Hornbeck wrote:

In summary: I can't agree with "the piston riding the wave"
or that signals aren't composed of something else. The latter
would also invalidate non-linearity in general. My interpretation
can't be what you meant.

How about this: it is the bulk velocity, the flow of air,
at the rest position that propegates out as the velocity
wave. The pressure of the wave follows as usual in phase
with the velocity.

What is the bulk velocity at the rest position as a function
of the velocity of the piston? I think they are simply
proportional.


Bob
--

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

A. Einstein

On Sun, 15 Aug 2004 08:29:38 -0700, Bob Cain
wrote:

How about this: it is the bulk velocity, the flow of air,
at the rest position that propegates out as the velocity
wave. The pressure of the wave follows as usual in phase
with the velocity.

What is the bulk velocity at the rest position as a function
of the velocity of the piston? I think they are simply
proportional.

Sure. And just to be perfectly clear, by bulk velocity you
mean what Beranek calls volume velocity, the time rate of
flow of the medium. And adiabatic conditions.

Chris Hornbeck

On Sat, 14 Aug 2004 23:25:51 -0700, Bob Cain
wrote:

Nonetheless, you should see now that it doesn't matter what
motion the piston engages in while following the signal, it
is the rest position that determines the distance at all
times. Translate it and you have Doppler shift. Simply
oscillate about it and you don't.

By distance here you mean the distance between originating
and receiving pistons?

And by translate you mean to move the rest position of the
originating piston, referenced to the receiving piston?

And by rest position, we mean the no-signal position?

So does the discussion hinge on the uniquely longitudinal
vibration of sound waves?

Can we agree that the distance between originating and
receiving diaphragms is modulated by the signal?

Chris Hornbeck

Chris Hornbeck wrote:

On Sun, 15 Aug 2004 08:29:38 -0700, Bob Cain
wrote:


How about this: it is the bulk velocity, the flow of air,
at the rest position that propegates out as the velocity
wave. The pressure of the wave follows as usual in phase
with the velocity.

What is the bulk velocity at the rest position as a function
of the velocity of the piston? I think they are simply
proportional.


Sure. And just to be perfectly clear, by bulk velocity you
mean what Beranek calls volume velocity, the time rate of
flow of the medium. And adiabatic conditions.

Yes.


Bob
--

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

A. Einstein

Chris Hornbeck wrote:


Can we agree that the distance between originating and
receiving diaphragms is modulated by the signal?

No because for the purposes of physics and acoustics, the
reference for measuring the distance is always the rest
position at either end.


Bob
--

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

A. Einstein

On Sun, 15 Aug 2004 15:25:34 -0700, Bob Cain
wrote:

Can we agree that the distance between originating and
receiving diaphragms is modulated by the signal?

No because for the purposes of physics and acoustics, the
reference for measuring the distance is always the rest
position at either end.

Are these two statements contradictory?

Well, how about: The distance between originating and
receiving diaphragms is an analog of the signal. With no
signal the reference positions of the diaphragms are
their rest positions and the distance between them is
a constant.

Signal or information is carried by varying the distance
between them and the constant is subtracted out. Conversions
from joltage to air pressure to joltage is symmetrical
and falls out.

Can we agree that this model can define the information
path?

Chris Hornbeck

Chris Hornbeck wrote:

On Sun, 15 Aug 2004 15:25:34 -0700, Bob Cain
wrote:


Can we agree that the distance between originating and
receiving diaphragms is modulated by the signal?

No because for the purposes of physics and acoustics, the
reference for measuring the distance is always the rest
position at either end.


Are these two statements contradictory?

Yes, I'm saying that at no point, at rest in the reference
frame of the rest-position of the driver, will Doppler shift
be observed. In that reference frame, the point of origin
is not modulated by piston motion.

The reason for that I've stated in other responses.


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)

On Sun, 15 Aug 2004 18:34:14 -0700, Bob Cain
wrote:

Yes, I'm saying that at no point, at rest in the reference
frame of the rest-position of the driver, will Doppler shift
be observed. In that reference frame, the point of origin
is not modulated by piston motion.

Does this require that the reference frame be co-incident
with the originating driver?

Chris Hornbeck

Chris Hornbeck wrote:

On Sun, 15 Aug 2004 18:34:14 -0700, Bob Cain
wrote:


Yes, I'm saying that at no point, at rest in the reference
frame of the rest-position of the driver, will Doppler shift
be observed. In that reference frame, the point of origin
is not modulated by piston motion.


Does this require that the reference frame be co-incident
with the originating driver?

It requires that it be anchored to the rest position of the
diaphragm. The bulk (volume) velocity at that position is
what propegates out as the acoustic wave. How is the bulk
velocity of the air at the rest position related to the
surface velocity of the piston? Here is where I see a
potential for being wrong, but I believe it is simply
proportional.

A fuller study of Al Ludwig's material should either make me
comfortable with that or talk me out of it. Hell, I think
I'll just ask him.


Bob
--

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

A. Einstein

On Sun, 15 Aug 2004 23:16:02 -0700, Bob Cain
wrote:

Does this require that the reference frame be co-incident
with the originating driver?

It requires that it be anchored to the rest position of the
diaphragm.

Is anchored the same as co-incident? Maybe the difference
is also the gulf of our understandings.


The bulk (volume) velocity at that position is
what propegates out as the acoustic wave. How is the bulk
velocity of the air at the rest position related to the
surface velocity of the piston? Here is where I see a
potential for being wrong, but I believe it is simply
proportional.

Well, sure. I'm still not grasping how this is not just a
tautology. The air moves like the piston moves; the
information in the immediately adjacent air is the same as the
information in the piston.

But it's the information in the receiving diaphragm that
should matter to us. (There's obviously no Doppler effect
at the radiating diaphragm or in the immediately adjacent
air.)

Or, as Arny and William have assured me, in a rigidly
coupled receiving diaphragm.

If there is a Doppler effect it must occur in the space
and time *between* the radiating and receiving diaphragms.

Chris Hornbeck

Chris Hornbeck wrote:

Is anchored the same as co-incident? Maybe the difference
is also the gulf of our understandings.

I think in the way you are thinking, that is correct. We
don't usually speak of coincident frames of reference unless
we are speaking of two or more of them. To be at rest in
the frame of reference of something is just fancy talk for
saying there is no relative motion. So no receiver that is
stationary WRT the rest position of the piston can observe
Doppler shift unless the volume velocity of the air at that
rest position is a non-linear function of the surface
velocity of the piston. That remains a possiblity but I
can't justify it. I do need to examine the assumption that
the relationship is linear in more depth.

If the information contained in the surface velocity of the
piston is changed on its way to the volume velocity at the
rest position, my argument is defeated.

Well, sure. I'm still not grasping how this is not just a
tautology. The air moves like the piston moves; the
information in the immediately adjacent air is the same as the
information in the piston.

That's another way of saying what I've been arguing with the
qualification that that information finds its way to the
volume velocity of the air at the rest position unchanged.


But it's the information in the receiving diaphragm that
should matter to us. (There's obviously no Doppler effect
at the radiating diaphragm or in the immediately adjacent
air.)

Not so obvious from the vernacular argument for "Doppler
distortion."

If there is a Doppler effect it must occur in the space
and time *between* the radiating and receiving diaphragms.

Some way or other.


Bob
--

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

A. Einstein

The train is the speaker cone. The train whistle is the high-frequency signal
"riding along."

Think superposition.

William Sommerwerck wrote:
The train is the speaker cone. The train whistle is the high-frequency signal
"riding along."

Think superposition.

But the hi freq signal/whistle is in the signal that's pushing the
cone/train, not being emitted by something attached to the cone/train.

If a tweeter rode on the woofer cone your analogy would be correct. If
the signal driving the cone has both the high and low freq signals both
signals are driving the cone so the mixing of the two signals has
happened at a 'stationary' point and not with the high frequency emitter
in motion, hence no Doppler shift.

I think there are other non-linearities in speakers that overpower any
possible doppler shift of high frequencies, you'll never hear it.

"Galen Watts"

William Sommerwerck wrote:
The train is the speaker cone. The train whistle is the high-frequency
signal
"riding along."

Think superposition.


But the hi freq signal/whistle is in the signal that's pushing the
cone/train, not being emitted by something attached to the cone/train.


** Utter gobbledegook.


If a tweeter rode on the woofer cone your analogy would be correct.


** There is no difference between that and the same cone also acting as the
tweeter.


If the signal driving the cone has both the high and low freq signals both
signals are driving the cone so the mixing of the two signals has
happened at a 'stationary' point and not with the high frequency emitter
in motion, hence no Doppler shift.


** I wonder if this dude can walk and chew gum at the same time ?????

If you cannot do that then Doppler is forever beyond your grasp.




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

The train is the speaker cone. The train whistle is
the high-frequency signal "riding along."

Think superposition.

But the hi freq signal/whistle is in the signal that's pushing the
cone/train, not being emitted by something attached to the cone/train.

If a tweeter rode on the woofer cone your analogy would be correct.

It does. As I said, THINK SUPERPOSITION.

On Mon, 16 Aug 2004 00:43:14 -0700, Bob Cain
wrote:

If the information contained in the surface velocity of the
piston is changed on its way to the volume velocity at the
rest position, my argument is defeated.

The Doppler effect doesn't require any non-linearity or
any loss, change or gain of information in the conversion
from electronic signal to instantaneous air pressure
(or volume velocity, etc.)

The entire conversion, at each end of the path, can be
considered to be perfectly linear and free of *any*
bad modulations, AM, FM, PM, daylight savings, none.

The Doppler effect occurs in the path *between* the
originating instantaneous air pressure (or velocity, etc.)
and the receiving instantaneous air pressure (or velocity,
etc.)

If there is a Doppler effect it must occur in the space
and time *between* the radiating and receiving diaphragms.

Some way or other.

The path between originating air pressure and receiving air
pressure is modulated by the asymmetry in their motions.
One can be a perfectly scaled version of the other and the
modulation of path length still produce sidebands.

Chris Hornbeck

On Mon, 16 Aug 2004 14:27:41 GMT, Galen Watts wrote:

William Sommerwerck wrote:
The train is the speaker cone. The train whistle is the high-frequency signal
"riding along."

Think superposition.

But the hi freq signal/whistle is in the signal that's pushing the
cone/train, not being emitted by something attached to the cone/train.

If a tweeter rode on the woofer cone your analogy would be correct.

So don't power the tweeter, but instead run the high frequency
through the woofer (presuming this will reproduce at all through the
woofer and the weight of the tweeter frame), so the high frequency is
still emitting from the tweeter cone. When the woofer cone has the low
frequency component as well, the tweeter is still emitting the high
frequency and still being moved by the low frequency.

If
the signal driving the cone has both the high and low freq signals both
signals are driving the cone so the mixing of the two signals has
happened at a 'stationary' point and not with the high frequency emitter
in motion,

Is the 'emitter' the cone? If the cone is not in motion, how does
it produce the low tone (or the high tone for that matter)?

What's so magical about a moving cone that it's considered to be at
a 'fixed point'???

hence no Doppler shift.

I think there are other non-linearities in speakers that overpower any
possible doppler shift of high frequencies, you'll never hear it.

That may be true, but that has nothing to do with the existence (or
lack thereof) of doppler distortion.
-----
http://mindspring.com/~benbradley

Chris Hornbeck wrote:
On Mon, 16 Aug 2004 00:43:14 -0700, Bob Cain
wrote:


If the information contained in the surface velocity of the
piston is changed on its way to the volume velocity at the
rest position, my argument is defeated.


The Doppler effect doesn't require any non-linearity or
any loss, change or gain of information in the conversion
from electronic signal to instantaneous air pressure
(or volume velocity, etc.)

Oh, yes it does, because once information is transfered to
the air, the only way to get Doppler shift is with
translation of the reciever.


The entire conversion, at each end of the path, can be
considered to be perfectly linear and free of *any*
bad modulations, AM, FM, PM, daylight savings, none.

Cool, then there is no "Doppler distortion."


The Doppler effect occurs in the path *between* the
originating instantaneous air pressure (or velocity, etc.)
and the receiving instantaneous air pressure (or velocity,
etc.)

How?


The path between originating air pressure and receiving air
pressure is modulated by the asymmetry in their motions.
One can be a perfectly scaled version of the other and the
modulation of path length still produce sidebands.

It is not. The distance to the transmitter is the distance
to its rest position. If that translates you get a Doppler
shift of everything in the signal. If it oscilates, that is
added linearly to the acoustic signal and you have to look
again for the real rest position because there is one.


Bob
--

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

A. Einstein

William Sommerwerck wrote:

The train is the speaker cone. The train whistle is
the high-frequency signal "riding along."


Think superposition.


But the hi freq signal/whistle is in the signal that's pushing the
cone/train, not being emitted by something attached to the cone/train.


If a tweeter rode on the woofer cone your analogy would be correct.


It does. As I said, THINK SUPERPOSITION.

Add something predictive to that simple statement and it
might be worth considering.


Bob
--

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

A. Einstein

It does. As I said, THINK SUPERPOSITION.

Add something predictive to that simple statement
and it might be worth considering.

I've already done that. But I'll do it again.

Get a single "cone" driver that can reproduce both 100Hz and, oh, 5kHz. * Feed
both frequencies to the driver, with the 100Hz strong enough to cause
substantial, visible, cone motion. Measure the FM sidebands generated around the
5kHz signal.

Now attach the driver to a shake table or something similar. Feed 5kHz into the
cone driver, and a 100Hz signal into the shake table at an amplitude that bodily
moves the whole driver as much as the cone moved in the first experiment. You
should see similar FM sidebands.

It doesn't matter whether the cone moves "under its own power" or is moved by
something else. The principle of superposition predicts that it makes no
difference whether the HF signal is produced by an object attached to the moving
surface, or the moving surface itself. Dig?

If this still isn't perfectly clear, imagine that the moving object is a truck
("Not a ****, but a truck." -- Harry Partch), and the sound source is a
transducer that "drives" the wind-shield thingy on the top of the cab. In
effect, the truck's body itself is the source of sound -- and you'd certainly
expect to hear a Doppler shift as the truck passed, right? Right.

QED.

You can argue all you want. Arguing from fundamental principles is important, of
course. But at some point you need to actually perform an experiment and "see
what happens."

* Actually, it doesn't matter whether there's any audible output at 100Hz --
only that the cone moves significantly. Right?

On Mon, 16 Aug 2004 14:29:15 -0700, Bob Cain
wrote:


The path between originating air pressure and receiving air
pressure is modulated by the asymmetry in their motions.
One can be a perfectly scaled version of the other and the
modulation of path length still produce sidebands.

It is not. The distance to the transmitter is the distance
to its rest position. If that translates you get a Doppler
shift of everything in the signal. If it oscilates, that is
added linearly to the acoustic signal and you have to look
again for the real rest position because there is one.

I see now that I've only restated the little cone on the big cone
argument, which you don't accept. You may well be right, but
I have no way to resolve it for myself conceptually.

The only thing left to do is to go to Portland for a few
weeks. PDX here I come.

Thanks for the stimulation,

Chris Hornbeck

On Tue, 17 Aug 2004 00:26:26 GMT, Chris Hornbeck
wrote:

You may well be right,

I take it all back. The diaphrams are moving in relation
to each other. Speed of sound is fixed. One moves more
than the other. As Scott says, reciprocity failure.

The relative movement of the diaphrams *alone* causes
a Doppler effect. It is not necessary for the frame of
reference of either to move.

The relative motions modulate relative distance which
modulates relative time.

But I've got to admit that your argument is very
seductive, and more importantly, a worthy centenary
tribute. Way to go (but you're still wrong, wrong, wrong!)
and I'll be reading you from PDX.

Thanks again,
ps: there must be something interesting in the uniquely
longitudinal-ness of sound waves.

Chris Hornbeck

William Sommerwerck wrote:

It does. As I said, THINK SUPERPOSITION.


Add something predictive to that simple statement
and it might be worth considering.


I've already done that. But I'll do it again.

I mean predictive in the sense of numbers that can be
compared against experiment, not more hand waving.


Bob
--

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

A. Einstein