Doppler Distortion - What Started the Discussion?

[Mike Rivers]

I guess I must have missed the first message about this. Worked all
day Wednesday (tough for a retired guy) and came home to find close to
100 postings about it (most of which I didn't read).

Did someone publish an article? Did Phil Allison make a declaration?

Is this something that crept in here from rec.audio.opinion or
..high-end?

I care more about the psychology of this thread than the actual
content. Call me nuts again.


--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo

[Chris Hornbeck]

On 12 Aug 2004 11:35:10 -0400, (Mike Rivers)
wrote:

>I care more about the psychology of this thread than the actual
>content. Call me nuts again.

It came from a mistaken assumption about non-linearity in the
generation of FM. Honest.

From little acorns,

Chris Hornbeck

[JoVee]

in article , David Morgan (MAMS) at
wrote on 8/12/04 1:13 PM:

>
> "Mike Rivers" > wrote in message...
>
>> I care more about the psychology of this thread than the actual
>> content. Call me nuts again.
>
> Hey nuts again. I'm fine over here - never read a single word of
> it after the initial post. Too foggy for me out there. Thanks...
>
> DM

me too... Bob Cain posted the initial query but it went weird way too fast.
Most practical early post was about DD being SO much smaller relative to
IM/THD/Whatever as well as the overdriving effects of drivers stuff that it
was pretty moot no matter what. I got Bonnie and Charlie coming over this
weekend and need to prep the house.

[Eric K. Weber]

Bob Cain posted the initial query in reply to a thread on rec.audio.tech
...... possibly by mistake? The thread started by Arny Krueger on
rec.audio.tech August 5....

Rgds:
Eric


"JoVee" > wrote in message
...
> in article , David Morgan (MAMS) at
> wrote on 8/12/04 1:13 PM:
>
> >
> > "Mike Rivers" > wrote in message...
> >
> >> I care more about the psychology of this thread than the actual
> >> content. Call me nuts again.
> >
> > Hey nuts again. I'm fine over here - never read a single word of
> > it after the initial post. Too foggy for me out there. Thanks...
> >
> > DM
>
> me too... Bob Cain posted the initial query but it went weird way too
fast.
> Most practical early post was about DD being SO much smaller relative to
> IM/THD/Whatever as well as the overdriving effects of drivers stuff that
it
> was pretty moot no matter what. I got Bonnie and Charlie coming over this
> weekend and need to prep the house.
>

[Eric K. Weber]

Bob Cain posted the initial query in reply to a thread on rec.audio.tech
...... possibly by mistake? The thread started by Arny Krueger on
rec.audio.tech August 5....

Rgds:
Eric


"JoVee" > wrote in message
...
> in article , David Morgan (MAMS) at
> wrote on 8/12/04 1:13 PM:
>
> >
> > "Mike Rivers" > wrote in message...
> >
> >> I care more about the psychology of this thread than the actual
> >> content. Call me nuts again.
> >
> > Hey nuts again. I'm fine over here - never read a single word of
> > it after the initial post. Too foggy for me out there. Thanks...
> >
> > DM
>
> me too... Bob Cain posted the initial query but it went weird way too
fast.
> Most practical early post was about DD being SO much smaller relative to
> IM/THD/Whatever as well as the overdriving effects of drivers stuff that
it
> was pretty moot no matter what. I got Bonnie and Charlie coming over this
> weekend and need to prep the house.
>

[George Perfect]

In this place, Mike Rivers was recorded saying ...
>
> I guess I must have missed the first message about this. Worked all
> day Wednesday (tough for a retired guy) and came home to find close to
> 100 postings about it (most of which I didn't read).
>
> Did someone publish an article? Did Phil Allison make a declaration?
>
> Is this something that crept in here from rec.audio.opinion or
> .high-end?
>
> I care more about the psychology of this thread than the actual
> content. Call me nuts again.
>

I confess! I may be the guilty party via a throwaway remark I made in an
unrelated discussion over on alt.music.home-studio that Rany took
exception to.

You don't want a link to the thread now, doya? ;)

--
George
Newcastle, England

Problems worthy of attack
Prove their worth by hitting back - Piet Hein

[George Perfect]

In this place, Mike Rivers was recorded saying ...
>
> I guess I must have missed the first message about this. Worked all
> day Wednesday (tough for a retired guy) and came home to find close to
> 100 postings about it (most of which I didn't read).
>
> Did someone publish an article? Did Phil Allison make a declaration?
>
> Is this something that crept in here from rec.audio.opinion or
> .high-end?
>
> I care more about the psychology of this thread than the actual
> content. Call me nuts again.
>

I confess! I may be the guilty party via a throwaway remark I made in an
unrelated discussion over on alt.music.home-studio that Rany took
exception to.

You don't want a link to the thread now, doya? ;)

--
George
Newcastle, England

Problems worthy of attack
Prove their worth by hitting back - Piet Hein

[Bob Cain]

Mike Rivers wrote:

> I guess I must have missed the first message about this. Worked all
> day Wednesday (tough for a retired guy) and came home to find close to
> 100 postings about it (most of which I didn't read).
>
> Did someone publish an article? Did Phil Allison make a declaration?
>
> Is this something that crept in here from rec.audio.opinion or
> .high-end?
>
> I care more about the psychology of this thread than the actual
> content. Call me nuts again.

:-) It was entirely my doing. It was mentioned in another
group and the idea has never sat well with me for reasons I
hadn't probed very well. I decided to take a harder look
from simple physics and wave mechanics and came to the
conclusion that it is a myth with a hand waving argument
only in its support. I wanted either to be beaten out of
that by a complete theory that worked or to give it the
coupe da grass.

Jury's out AFAIC, I don't think any point I've made has
been refuted and there is just one from the believers that
I've not found a flaw with yet. There is still no
indication that a real, predictive theory supports it and I
take that as strongly indicative that there isn't one.


Bob
--

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

A. Einstein

[Bob Cain]

Mike Rivers wrote:

> I guess I must have missed the first message about this. Worked all
> day Wednesday (tough for a retired guy) and came home to find close to
> 100 postings about it (most of which I didn't read).
>
> Did someone publish an article? Did Phil Allison make a declaration?
>
> Is this something that crept in here from rec.audio.opinion or
> .high-end?
>
> I care more about the psychology of this thread than the actual
> content. Call me nuts again.

:-) It was entirely my doing. It was mentioned in another
group and the idea has never sat well with me for reasons I
hadn't probed very well. I decided to take a harder look
from simple physics and wave mechanics and came to the
conclusion that it is a myth with a hand waving argument
only in its support. I wanted either to be beaten out of
that by a complete theory that worked or to give it the
coupe da grass.

Jury's out AFAIC, I don't think any point I've made has
been refuted and there is just one from the believers that
I've not found a flaw with yet. There is still no
indication that a real, predictive theory supports it and I
take that as strongly indicative that there isn't one.


Bob
--

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

A. Einstein

[George Perfect]

In this place, Bob Cain was recorded saying ...
>
> :-) It was entirely my doing. It was mentioned in another
> group and the idea has never sat well with me for reasons I
> hadn't probed very well. I decided to take a harder look
> from simple physics and wave mechanics and came to the
> conclusion that it is a myth with a hand waving argument
> only in its support. I wanted either to be beaten out of
> that by a complete theory that worked or to give it the
> coupe da grass.
>
> Jury's out AFAIC, I don't think any point I've made has
> been refuted and there is just one from the believers that
> I've not found a flaw with yet. There is still no
> indication that a real, predictive theory supports it and I
> take that as strongly indicative that there isn't one.

But Bob, unless your position has changed (or I misunderstood what you
wrote in the original discussion on amhs) your problem is with the
existence of Doppler per se.

From what I've seen you write so far, I think your misunderstanding
arises from the position (sic) you've taken as observer on the driver
cone - or within the moving air mass which it excites.

As I (and plenty of others) have said, Doppler occurs as a distortion in
the time domain (ie, FM) as a result of relative motion between source
and receiver. IOW, I think you need to factor in an observation point at
some distance from the driver and consider the variation in distance
caused by the large amplitude excursion of the cone at low frequencies
modulating a (any) higher frequency signal.

Perhaps consider this: A single driver reproduces a 2kHz tone. Heard at
some distance, there will be no Doppler distortion as the only motion of
the cone is that which produces the sound waveform (your proposition as
I understand it).

Now add a LF signal (say 20Hz) to the driver at sufficient amplitude to
cause significant cone excursion (figures between 5mm and 50mm have been
mentioned - pick one!).

The *spatial* position from which the higher frequency tone is issued is
now varying according to the cone deflection caused by the LF signal.

As Ben Bradley (I think) wrote, the driver is still vibrating and
issuing the 2kHz tone when it is at both extremes of the excursion
caused by the LF tone. IOW, the *distance* between the origin of the
2kHz tone and the listener is varying.

As the speed of sound is constant (for this argument at least) and
finite, it follows that the time taken for the 2kHz tone to reach the
listener will vary acording to cone position.

In this way, the LF signal will impose itself as FM modulation on the
higher signal.

I believe you are missing this difference between cone velocity and the
effect it has on air - and failing to factor in the speed of sound - to
your equations.

I also believe that the Linkwitz description (whose link I posted a
while ago) provides all the mathematical descrption needed to explain
the effect.

Your maths might be right - it's your understanding of the mechanism you
are trying to describe that seems faulty.

--

George
Newcastle, England

Problems worthy of attack
Prove their worth, by hitting back [Piet Hein]

[George Perfect]

In this place, Bob Cain was recorded saying ...
>
> :-) It was entirely my doing. It was mentioned in another
> group and the idea has never sat well with me for reasons I
> hadn't probed very well. I decided to take a harder look
> from simple physics and wave mechanics and came to the
> conclusion that it is a myth with a hand waving argument
> only in its support. I wanted either to be beaten out of
> that by a complete theory that worked or to give it the
> coupe da grass.
>
> Jury's out AFAIC, I don't think any point I've made has
> been refuted and there is just one from the believers that
> I've not found a flaw with yet. There is still no
> indication that a real, predictive theory supports it and I
> take that as strongly indicative that there isn't one.

But Bob, unless your position has changed (or I misunderstood what you
wrote in the original discussion on amhs) your problem is with the
existence of Doppler per se.

From what I've seen you write so far, I think your misunderstanding
arises from the position (sic) you've taken as observer on the driver
cone - or within the moving air mass which it excites.

As I (and plenty of others) have said, Doppler occurs as a distortion in
the time domain (ie, FM) as a result of relative motion between source
and receiver. IOW, I think you need to factor in an observation point at
some distance from the driver and consider the variation in distance
caused by the large amplitude excursion of the cone at low frequencies
modulating a (any) higher frequency signal.

Perhaps consider this: A single driver reproduces a 2kHz tone. Heard at
some distance, there will be no Doppler distortion as the only motion of
the cone is that which produces the sound waveform (your proposition as
I understand it).

Now add a LF signal (say 20Hz) to the driver at sufficient amplitude to
cause significant cone excursion (figures between 5mm and 50mm have been
mentioned - pick one!).

The *spatial* position from which the higher frequency tone is issued is
now varying according to the cone deflection caused by the LF signal.

As Ben Bradley (I think) wrote, the driver is still vibrating and
issuing the 2kHz tone when it is at both extremes of the excursion
caused by the LF tone. IOW, the *distance* between the origin of the
2kHz tone and the listener is varying.

As the speed of sound is constant (for this argument at least) and
finite, it follows that the time taken for the 2kHz tone to reach the
listener will vary acording to cone position.

In this way, the LF signal will impose itself as FM modulation on the
higher signal.

I believe you are missing this difference between cone velocity and the
effect it has on air - and failing to factor in the speed of sound - to
your equations.

I also believe that the Linkwitz description (whose link I posted a
while ago) provides all the mathematical descrption needed to explain
the effect.

Your maths might be right - it's your understanding of the mechanism you
are trying to describe that seems faulty.

--

George
Newcastle, England

Problems worthy of attack
Prove their worth, by hitting back [Piet Hein]

[Phil Allison]

"George Perfect"

> As the speed of sound is constant .....


** Only in still air - this is where your case falters.

When the medium ( or a part of it) is in motion you cannot just ignore
that fact.





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

[Phil Allison]

"George Perfect"

> As the speed of sound is constant .....


** Only in still air - this is where your case falters.

When the medium ( or a part of it) is in motion you cannot just ignore
that fact.





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

[George Perfect]

In this place, Phil Allison was recorded saying ...
>
> "George Perfect"
>
> > As the speed of sound is constant .....
>
>
> ** Only in still air - this is where your case falters.
>
> When the medium ( or a part of it) is in motion you cannot just ignore
> that fact.

G'day

Plonk!

--

George
Newcastle, England

Problems worthy of attack
Prove their worth, by hitting back [Piet Hein]

[George Perfect]

In this place, Phil Allison was recorded saying ...
>
> "George Perfect"
>
> > As the speed of sound is constant .....
>
>
> ** Only in still air - this is where your case falters.
>
> When the medium ( or a part of it) is in motion you cannot just ignore
> that fact.

G'day

Plonk!

--

George
Newcastle, England

Problems worthy of attack
Prove their worth, by hitting back [Piet Hein]

[Phil Allison]

"George Perfect"
Phil Allison .
> >
> > "George Perfect"
> >
> > > As the speed of sound is constant .....
> >
> >
> > ** Only in still air - this is where your case falters.
> >
> > When the medium ( or a part of it) is in motion you cannot just ignore
> > that fact.
>
> G'day
>
> Plonk!


** What an absolute moron Mr Perfect has proved to be.

He must think the speed of sound is just like the speed of light.





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

[Phil Allison]

"George Perfect"
Phil Allison .
> >
> > "George Perfect"
> >
> > > As the speed of sound is constant .....
> >
> >
> > ** Only in still air - this is where your case falters.
> >
> > When the medium ( or a part of it) is in motion you cannot just ignore
> > that fact.
>
> G'day
>
> Plonk!


** What an absolute moron Mr Perfect has proved to be.

He must think the speed of sound is just like the speed of light.





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

[Mike Rivers]

In article > writes:

> :-) It was entirely my doing. It was mentioned in another
> group and the idea has never sat well with me for reasons I
> hadn't probed very well. I decided to take a harder look
> from simple physics and wave mechanics and came to the
> conclusion that it is a myth with a hand waving argument
> only in its support. I wanted either to be beaten out of
> that by a complete theory that worked or to give it the
> coupe da grass.

I never thought to give it a name, but it's always been my conjecture
that the Doppler effect contributed to what people hear when they try
my acoustic polarity demo - a 20 Hz sawtooth that inverts polarity
halfway through the playback.

In one polarity, the nearly-vertical edge of the sawtooth is going
positive, causing the speaker to move toward the listener as fast as
possible. When the polarity is inverted, the cone moves toward the
listener slower. The difference that most people hear is a difference
in high frequency (or low frequncy) content.

I have no proof that this is a Doppler effect, nor do I really care. I
just wanted to demonstrate to the skeptics that inverting polarity of
the signal driving a speaker can actualy sound different. Still,
skeptics being skeptics have problems accepting that there isn't some
issue with phase response or non-linearity with the speaker. Seems
like those with highest-falootin' speakers hear less of a change (or
no change) when the polarity changes. But then I've always been a bit
suspicious of people who spend unconscionable amounts of money on
their home audio systems and try to find things that might be wrong
(or arguably right) about their gear rather than enjoying music in
fine fidelity.




--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo

[Mike Rivers]

In article > writes:

> :-) It was entirely my doing. It was mentioned in another
> group and the idea has never sat well with me for reasons I
> hadn't probed very well. I decided to take a harder look
> from simple physics and wave mechanics and came to the
> conclusion that it is a myth with a hand waving argument
> only in its support. I wanted either to be beaten out of
> that by a complete theory that worked or to give it the
> coupe da grass.

I never thought to give it a name, but it's always been my conjecture
that the Doppler effect contributed to what people hear when they try
my acoustic polarity demo - a 20 Hz sawtooth that inverts polarity
halfway through the playback.

In one polarity, the nearly-vertical edge of the sawtooth is going
positive, causing the speaker to move toward the listener as fast as
possible. When the polarity is inverted, the cone moves toward the
listener slower. The difference that most people hear is a difference
in high frequency (or low frequncy) content.

I have no proof that this is a Doppler effect, nor do I really care. I
just wanted to demonstrate to the skeptics that inverting polarity of
the signal driving a speaker can actualy sound different. Still,
skeptics being skeptics have problems accepting that there isn't some
issue with phase response or non-linearity with the speaker. Seems
like those with highest-falootin' speakers hear less of a change (or
no change) when the polarity changes. But then I've always been a bit
suspicious of people who spend unconscionable amounts of money on
their home audio systems and try to find things that might be wrong
(or arguably right) about their gear rather than enjoying music in
fine fidelity.




--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo

[Bob Cain]

George Perfect wrote:


> But Bob, unless your position has changed (or I misunderstood what you
> wrote in the original discussion on amhs) your problem is with the
> existence of Doppler per se.

Yes.

>
> From what I've seen you write so far, I think your misunderstanding
> arises from the position (sic) you've taken as observer on the driver
> cone - or within the moving air mass which it excites.

No, my POV has been stationary with respect to the system.

>
> As I (and plenty of others) have said, Doppler occurs as a distortion in
> the time domain (ie, FM) as a result of relative motion between source
> and receiver. IOW, I think you need to factor in an observation point at
> some distance from the driver and consider the variation in distance
> caused by the large amplitude excursion of the cone at low frequencies
> modulating a (any) higher frequency signal.

That's the usual heuristic (which doesn't seem to lead to a
theory capable of prediction.)

>
> Perhaps consider this: A single driver reproduces a 2kHz tone. Heard at
> some distance, there will be no Doppler distortion as the only motion of
> the cone is that which produces the sound waveform (your proposition as
> I understand it).

If you take the heuristic argument to its conclusion, even
this is not true. The single tone will be distorted by the
same motion that generates it.

>
> Now add a LF signal (say 20Hz) to the driver at sufficient amplitude to
> cause significant cone excursion (figures between 5mm and 50mm have been
> mentioned - pick one!).

Yes, I understand the common heuristic argument for it. I
just think it wrong in a way that I have yet to fully pin
down. Again, the fact that it has not lead to a general
predictive theory for "Doppler distortion" that applies to
any signal tells me it can't and is thus not valid. If in
fact it exists, and anyone can locate or derive that theory
I'd love to look at it. This is not string theory, folks.

I'll repeat my argument again for the non-existence of
Doppler distortion in the hope that, if there is a flaw,
someone who can find the flaw will do so. It's pretty
darned simple (and I think air tight.)

1) Assuming a plane wave confined within and propegating on
the axis of an acoustic waveguide (a tube), if you place a
test piston in it (borrowed from the idea of a test particle
or test mass in theoretical physics) stiff and acoustically
opaque with no mass, infinite compliance and no fricton, it
will move in lock step with the particle velocity of the
air. It does this because it must or else a pressure
differential would be developed across it which would make
it accelerate at an infinite rate because of its zero impedence.

[attack point]

2) If the velocity of the test piston is measured and
recorded and that recording used to control the velocity of
an active piston, then, by reciprocity, the exact same
particle velocity will be induced in the air as was measured
by the test piston and if the test piston is left in place
at a distance from it, it will move identically to what was
recorded with some appropriate, fixed time offset.

[attack point]

3.) No restriction has been placed on the nature of the
acoustic signal involved in 2) and 3) or on the impedence of
the driven piston. Some driving signal will exist that can
move it with any desired velocity as a function of time and
that signal is calculable from the desired motion and its
actual impedence.

[attack point]

4) From 1), 2) and 3) it can be seen that perfect
reconstruction of any acoustic signal can be accomplished
without introduction of any non-linear phenomenon. "Doppler
distortion" does not exist.

[attack point]


Bob
--

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

A. Einstein

[Bob Cain]

George Perfect wrote:


> But Bob, unless your position has changed (or I misunderstood what you
> wrote in the original discussion on amhs) your problem is with the
> existence of Doppler per se.

Yes.

>
> From what I've seen you write so far, I think your misunderstanding
> arises from the position (sic) you've taken as observer on the driver
> cone - or within the moving air mass which it excites.

No, my POV has been stationary with respect to the system.

>
> As I (and plenty of others) have said, Doppler occurs as a distortion in
> the time domain (ie, FM) as a result of relative motion between source
> and receiver. IOW, I think you need to factor in an observation point at
> some distance from the driver and consider the variation in distance
> caused by the large amplitude excursion of the cone at low frequencies
> modulating a (any) higher frequency signal.

That's the usual heuristic (which doesn't seem to lead to a
theory capable of prediction.)

>
> Perhaps consider this: A single driver reproduces a 2kHz tone. Heard at
> some distance, there will be no Doppler distortion as the only motion of
> the cone is that which produces the sound waveform (your proposition as
> I understand it).

If you take the heuristic argument to its conclusion, even
this is not true. The single tone will be distorted by the
same motion that generates it.

>
> Now add a LF signal (say 20Hz) to the driver at sufficient amplitude to
> cause significant cone excursion (figures between 5mm and 50mm have been
> mentioned - pick one!).

Yes, I understand the common heuristic argument for it. I
just think it wrong in a way that I have yet to fully pin
down. Again, the fact that it has not lead to a general
predictive theory for "Doppler distortion" that applies to
any signal tells me it can't and is thus not valid. If in
fact it exists, and anyone can locate or derive that theory
I'd love to look at it. This is not string theory, folks.

I'll repeat my argument again for the non-existence of
Doppler distortion in the hope that, if there is a flaw,
someone who can find the flaw will do so. It's pretty
darned simple (and I think air tight.)

1) Assuming a plane wave confined within and propegating on
the axis of an acoustic waveguide (a tube), if you place a
test piston in it (borrowed from the idea of a test particle
or test mass in theoretical physics) stiff and acoustically
opaque with no mass, infinite compliance and no fricton, it
will move in lock step with the particle velocity of the
air. It does this because it must or else a pressure
differential would be developed across it which would make
it accelerate at an infinite rate because of its zero impedence.

[attack point]

2) If the velocity of the test piston is measured and
recorded and that recording used to control the velocity of
an active piston, then, by reciprocity, the exact same
particle velocity will be induced in the air as was measured
by the test piston and if the test piston is left in place
at a distance from it, it will move identically to what was
recorded with some appropriate, fixed time offset.

[attack point]

3.) No restriction has been placed on the nature of the
acoustic signal involved in 2) and 3) or on the impedence of
the driven piston. Some driving signal will exist that can
move it with any desired velocity as a function of time and
that signal is calculable from the desired motion and its
actual impedence.

[attack point]

4) From 1), 2) and 3) it can be seen that perfect
reconstruction of any acoustic signal can be accomplished
without introduction of any non-linear phenomenon. "Doppler
distortion" does not exist.

[attack point]


Bob
--

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

A. Einstein

[Bob Cain]

Bob Cain wrote:


>
> 3.) No restriction has been placed on the nature of the acoustic signal
> involved in 2) and 3)

That should be 1) and 2). A final point that needs to be
made is that the hueristic that is used to justify "Doppler
distortion" applies fully to the described test system.


Bob
--

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

A. Einstein

[Bob Cain]

Bob Cain wrote:


>
> 3.) No restriction has been placed on the nature of the acoustic signal
> involved in 2) and 3)

That should be 1) and 2). A final point that needs to be
made is that the hueristic that is used to justify "Doppler
distortion" applies fully to the described test system.


Bob
--

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

A. Einstein

[Chris Hornbeck]

On Fri, 13 Aug 2004 15:29:42 -0700, Bob Cain
> wrote:

>> Perhaps consider this: A single driver reproduces a 2kHz tone. Heard at
>> some distance, there will be no Doppler distortion as the only motion of
>> the cone is that which produces the sound waveform (your proposition as
>> I understand it).
>
>If you take the heuristic argument to its conclusion, even
>this is not true. The single tone will be distorted by the
>same motion that generates it.

This is literally true. But the sidebands have no delta F.

And all else, no disagreements here.

The FM occurs as a math construct, PFM (pure friggin' magic).

Chris Hornbeck

[Chris Hornbeck]

On Fri, 13 Aug 2004 15:29:42 -0700, Bob Cain
> wrote:

>> Perhaps consider this: A single driver reproduces a 2kHz tone. Heard at
>> some distance, there will be no Doppler distortion as the only motion of
>> the cone is that which produces the sound waveform (your proposition as
>> I understand it).
>
>If you take the heuristic argument to its conclusion, even
>this is not true. The single tone will be distorted by the
>same motion that generates it.

This is literally true. But the sidebands have no delta F.

And all else, no disagreements here.

The FM occurs as a math construct, PFM (pure friggin' magic).

Chris Hornbeck

[Bob Cain]

Chris Hornbeck wrote:

> This is literally true. But the sidebands have no delta F.
>
> And all else, no disagreements here.

Then you accept the conclusion? Without finding flaw in the
steps, it's unavoidable. You raise the possiblity above
that reciprocity doesn't apply to acoustic systems and if
so then a flaw exists but I think that possibility can be
dismissed. At least, we've finally found the physical
principle on which it all rests.

> The FM occurs as a math construct, PFM (pure friggin' magic).

So there's a ghost in the machine, eh? Or spooky action at
a distance. :-)


Bob
--

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

A. Einstein

[George Perfect]

In this place, Bob Cain was recorded saying ...
>

Bob - did I miss the dismissal of the link I gave to the Linkwitz
article?

> > But Bob, unless your position has changed (or I misunderstood what you
> > wrote in the original discussion on amhs) your problem is with the
> > existence of Doppler per se.

> Yes.

And ... just so everyone is clear, you are claiming that the Doppler
effect does not exist. Is that right?

--
George
Newcastle, England

Problems worthy of attack
Prove their worth by hitting back - Piet Hein

[Bob Cain]

George Perfect wrote:

> In this place, Bob Cain was recorded saying ...
>
>
> Bob - did I miss the dismissal of the link I gave to the Linkwitz
> article?

I looked at it, it's the same description that appears
everywhere. It's hard to attack because it doesn't say
much. Nothing at all predictive comes out of it in a
general sense. Hand waving theories are notoriously hard to
disprove because there's no place to really grab a hold of them.

> And ... just so everyone is clear, you are claiming that the Doppler
> effect does not exist. Is that right?

Based on my current reasoning, and pending proof that
reciprocity applies to acoustic systems, that's right.

The physics groups wouldn't touch "Doppler distortion", at
least those that are known to know their stuff, but they
might be a bit more willing to help me with the simple
question of proving that reciprocity applies should I not
find the key. As I said earlier in response to Chris, I
think the simplest proof appeals to the conservation of energy.


Bob
--

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

A. Einstein

[S O'Neill]

Bob Cain wrote:
>

> 2) If the velocity of the test piston is measured and recorded and that
> recording used to control the velocity of an active piston, then, by
> reciprocity, the exact same particle velocity will be induced in the air
> as was measured by the test piston and if the test piston is left in
> place at a distance from it, it will move identically to what was
> recorded with some appropriate, fixed time offset.
>
> [attack point]


Doesn't this depend on air being incompressible? Put another way, how
likely is a perfect mechanical step function executed by the active
piston to be likewise in the air and at the test piston? Or is that
beside the point?

[Bob Cain]

S O'Neill wrote:

> Bob Cain wrote:
>
>>
>
>> 2) If the velocity of the test piston is measured and recorded and
>> that recording used to control the velocity of an active piston, then,
>> by reciprocity, the exact same particle velocity will be induced in
>> the air as was measured by the test piston and if the test piston is
>> left in place at a distance from it, it will move identically to what
>> was recorded with some appropriate, fixed time offset.
>>
>> [attack point] >

> Doesn't this depend on air being incompressible?

No, that just leads to an infinite speed of sound.

> Put another way, how
> likely is a perfect mechanical step function executed by the active
> piston to be likewise in the air and at the test piston? Or is that
> beside the point?

With qualification, that is an equivalent question. It
would have to be a band limited step or else the air would
cavitate immediately into its non-linear regime. If it were
band limited so as to keep the air within its linear regime,
the motion of the test piston (microphone) should exactly
follow that of the driven piston. If reciprocity holds, any
acoustic signal should be exactly reproducable by a piston
that moves the same way that the test piston does in
response to it. There's no room in this simple picture for
"Doppler distortion."


Bob
--

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

A. Einstein