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  #83   Report Post  
Randy Yates
 
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Default Doppler Distoriton?

ow (Goofball_star_dot_etal) writes:

On 10 Aug 2004 10:19:38 -0400, Randy Yates
wrote:

(Goofball_star_dot_etal) writes:

On Tue, 10 Aug 2004 02:39:51 GMT, Randy Yates wrote:


Wow, that's eloquent! Hey, any way you can get the idea across!

Actually the idea of superposition goes all the way out to abstract
mathematics. You can consider a "system" a mapping, call it f(.), from
one domain (the input), call it X, to another domain (the output),
call it Y. Thus Y = f(X). In abstract algebra, a mapping is
"homomorphic" if, for two inputs x1 and x2, f(x1 + x2) = f(x1) +
f(x2). Note that the operation "+" on the left side of the "=" is in
the domain X, while on the right side it is in the domain Y. A
"system" (in the engineering sense) obeys the superposition principle
if and only if the mapping corresponding to that system is
homomorphic. In other words, "homorphism" and "superposition" are the
same thing.
--

So I take it that you are not a fan of plain english. . .


If the concepts involved were just a matter of "plain english" then it
probably wouldn't have taken mathematicians, physicists, and engineers
centuries to formalize them.


I always thought they were slow.. .

Also, I have found that, while intuition (which is what I call the
level of explanation you were attempting) can be helpful at certain
stages of understanding, over-relying on it can lead to errors in
analysis.


Agreed but lean about intuition:
http://www.amazon.co.uk/exec/obidos/...293460-4259040


:It is necessary, if you want to do more than blow smoke in
front of mirrors, to formally derive the results one is asserting.
--


Feel free to imply that I am an uncouth blowhard.


Hey!?! Peace, man! I ain't trying to rain on your parade. I sorta
like you. If I'm implying you're an uncouth blowhard, then I'm also
implying I am too! There've been way too many times when I ASSUMED
my intuition was correct only to CRASH AND BURN! It ain't pretty.

I also ain't the sharpest tool in the shed, and if that is what I
implied I apologize. I made the low score (C+) in my last class (OK,
so it was a graduate engineering course on error correction with
some of the sharpest minds from China and India attending), and
my first post-high school education was DeVry (definitely more of
a "hands-on" school than a theory school).

I think the two worlds (theory vs. practice) are both way cool in
their own respects, but to actually unite the two is totally way
way way cool.... I get a hard-on trying to do that.

I've done the analysis, calculations and analysed the experimental
results, spotted some circular arguments and other errors. It ain't
"rocket science" but where were you during this time with your faultly
BS detector? I want some numbers from you now.


Sorry sir. I'll try to improve and cough up the goods from now on...
--
Randy Yates
Sony Ericsson Mobile Communications
Research Triangle Park, NC, USA
, 919-472-1124
  #85   Report Post  
Goofball_star_dot_etal
 
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Default Doppler Distoriton?

On Tue, 10 Aug 2004 19:08:29 GMT, ow
(Goofball_star_dot_etal) wrote:


Now how do we measure displacement more accurately?


I know! I know! Please sir! We could use Doppler SODAR!
Shut up, son. You are going in circles!


  #86   Report Post  
Arny Krueger
 
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Default Doppler Distoriton?

"Paul Guy" wrote in message

On Thu, 5 Aug 2004 22:19:23 -0400, "Arny Krueger"
wrote:

Here's the results of some speaker measurements that I made tonight,
based on passing 50 Hz & 4 KHz mixed 1:1 at about 1.2 volts rms,
through a Peerless 6.5 inch woofer with about 6 mm Xmax (relatively
large for a woofer its size). The speaker is mounted in a roughly
0.4 cubic foot box with no vent. The power amp is a QSC USA 850.
This is not very loud. The mic is an ECM8000 that is a few inches
from the woofer cone.

http://www.pcavtech.com/techtalk/doppler/

The first graph shows the broadband response. The large spikes at 50
Hz and 4 KHz are clearly visible. The second and third harmonics of
the 50 Hz tone are about 30 dB down. The spike for the 4 KHz tone is
about 5 dB higher than the spike for 50 Hz because the woofer is
simply that much more efficient at 4 KHz.

The second graph is taken from the same test, with the frequency
scale enlarged to show about 400 Hz on either side of 4 KHz. The
first pair of large spikes are about 50 Hz on either side of 4 KHz,
the second are about 100 Hz on either side of 4 KHz, and so on. The
distortion products are probably a mixture of AM and FM distortion,
with FM predominating, as the test is contrived to focus on FM.

While I've got this set up, any other data that anyone would find
interesting?


This is a bit late in the thread but.....
If you are trying to discriminate FM from AM, you can look at the
envelope. AM (IM) distortion should have a typical modulation pattern.


In fact we get a mixture of the two.

You might need to use some electronics to AM detect the envelope. ie.,
bandpass filter for 4000 Hz, envelope detector, then watch the AC
component at the output, just like a typical AM receiver.


I've done this on a PC using the filters in Audition/CEP

For the FM component, clip the signal, put the resultant in a 4 khz
bandpass, or just measure the sidebands around 4 KHz.


For small modulation indices you get only two sidebands for FM (that's the
formal definition of NBFM) just like AM. And, if the modulating signal is
distorted, you get multiple sidebands with AN, Just like FM.

The only difference between AM (IM) and FM (phase) modulation is the
phase of the two sidebands. AM they are both in phase (they add to the
overall amplitude). In FM they are out of phase, thus they have no
effect on the amplitude. The individual amplitudes are the same
between AM and FM, assuming the FM is of small deviation (yours is not
all that small).


Right, but measureing phase in acoustical tests can be challenging. The
poster with the nickname of Goofball has some relevant tools at his
disposal.

I've also discovered that that you can get some clues about AM versus FM
with a triple tone test. If the modulating signal is the same for two tones
in a doppler test or in the case of jitter, the tone at the higher frequency
has the higher modulation index and therefore a different sideband
configuration.

wc=carrier freq (rad/sec)
wm=modulating freq (rad/sec)
A=amplitude
M=FM modulation index
u=AM modulation factor
FM: A*cos(wc*t) + 1/2*M*A[ cos(wc + wm)*t - cos(wc - wm)*t]
AM: A*cos(wc*t) + 1/2*u*A[ cos(wc + wm)*t + cos(wc - wm)*t]
This applies to narrow band FM (M less than 0.3). Notice that the
sign of the lower sideband is the only difference.


Agreed.

A standard spectrum analyzer will not allow you to tell the AM from
FM sidebands (to the best of my limited knowledge).


Not directly.

There might be
some tricks you can play if you have a tracking generator. If your
spectrum analyzer allows you to sample the data and run math on it,
you might be able to massage the data to give you some useful results.


That's roughly the approach that is being taken.

If your existing spectrum has unequal sidebands, you can suspect a
combination of AM and FM sidebands.


Agreed. We've got 'em

One trick you might pull off, is to ADD pure AM modulated signal to
your measured signal. If there is FM modulation, you can add enough AM
such that one of the sidebands cancels out. By knowing the AM
amplitude, this will allow you to determine the FM component.


We've already got a mixture of AM & FM coming out of the test.


  #88   Report Post  
Goofball_star_dot_etal
 
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Default Doppler Distoriton?

On Wed, 11 Aug 2004 02:57:26 GMT, Randy Yates wrote:


An accelerometer, a la Velodyne?
--


And those who are not asleep will note that this is a very good
solution from an experimental point of view. Points to those that say
why.
  #89   Report Post  
Arny Krueger
 
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Default Doppler Distoriton?

"Goofball_star_dot_etal" wrote in message

On Wed, 11 Aug 2004 02:57:26 GMT, Randy Yates wrote:


An accelerometer, a la Velodyne?


And those who are not asleep will note that this is a very good
solution from an experimental point of view. Points to those that say
why.


It gives you acelleration, forthwith.

Integrate it (essentially pass it through a low pass filter) once and you
get velocity.

Integrate it again and you get position.

Every time you integrate it, a lot of spurious noise gets low-pass filtered
@ 6 dB/octave.


  #90   Report Post  
Goofball_star_dot_etal
 
Posts: n/a
Default Doppler Distoriton?

On Wed, 11 Aug 2004 15:28:45 -0400, "Arny Krueger"
wrote:

"Goofball_star_dot_etal" wrote in message

On Wed, 11 Aug 2004 02:57:26 GMT, Randy Yates wrote:


An accelerometer, a la Velodyne?


And those who are not asleep will note that this is a very good
solution from an experimental point of view. Points to those that say
why.


It gives you acelleration, forthwith.

Integrate it (essentially pass it through a low pass filter) once and you
get velocity.

Integrate it again and you get position.

Every time you integrate it, a lot of spurious noise gets low-pass filtered
@ 6 dB/octave.


OK, 2 points but remember what Svante said. . and there is more. . .
Think "one variable at a time" and "how should we record and process
the accelerometer data?"


  #92   Report Post  
Goofball_star_dot_etal
 
Posts: n/a
Default Doppler Distoriton?

On 10 Aug 2004 15:26:56 -0400, Randy Yates
wrote:

(Goofball_star_dot_etal) writes:

On 10 Aug 2004 10:19:38 -0400, Randy Yates
wrote:

(Goofball_star_dot_etal) writes:

On Tue, 10 Aug 2004 02:39:51 GMT, Randy Yates wrote:


Wow, that's eloquent! Hey, any way you can get the idea across!

Actually the idea of superposition goes all the way out to abstract
mathematics. You can consider a "system" a mapping, call it f(.), from
one domain (the input), call it X, to another domain (the output),
call it Y. Thus Y = f(X). In abstract algebra, a mapping is
"homomorphic" if, for two inputs x1 and x2, f(x1 + x2) = f(x1) +
f(x2). Note that the operation "+" on the left side of the "=" is in
the domain X, while on the right side it is in the domain Y. A
"system" (in the engineering sense) obeys the superposition principle
if and only if the mapping corresponding to that system is
homomorphic. In other words, "homorphism" and "superposition" are the
same thing.
--

So I take it that you are not a fan of plain english. . .

If the concepts involved were just a matter of "plain english" then it
probably wouldn't have taken mathematicians, physicists, and engineers
centuries to formalize them.


I always thought they were slow.. .

Also, I have found that, while intuition (which is what I call the
level of explanation you were attempting) can be helpful at certain
stages of understanding, over-relying on it can lead to errors in
analysis.


Agreed but lean about intuition:
http://www.amazon.co.uk/exec/obidos/...293460-4259040


:It is necessary, if you want to do more than blow smoke in
front of mirrors, to formally derive the results one is asserting.
--


Feel free to imply that I am an uncouth blowhard.


Hey!?! Peace, man! I ain't trying to rain on your parade. I sorta
like you. If I'm implying you're an uncouth blowhard, then I'm also
implying I am too! There've been way too many times when I ASSUMED
my intuition was correct only to CRASH AND BURN! It ain't pretty.

I also ain't the sharpest tool in the shed, and if that is what I
implied I apologize. I made the low score (C+) in my last class (OK,
so it was a graduate engineering course on error correction with
some of the sharpest minds from China and India attending), and
my first post-high school education was DeVry (definitely more of
a "hands-on" school than a theory school).

I think the two worlds (theory vs. practice) are both way cool in
their own respects, but to actually unite the two is totally way
way way cool.... I get a hard-on trying to do that.

I've done the analysis, calculations and analysed the experimental
results, spotted some circular arguments and other errors. It ain't
"rocket science" but where were you during this time with your faultly
BS detector? I want some numbers from you now.


Sorry sir. I'll try to improve and cough up the goods from now on...
--
Randy Yates
Sony Ericsson Mobile Communications
Research Triangle Park, NC, USA
, 919-472-1124


Since I am the result of a liason between Howard Ferstler and a sheep,
you should not expect too much of me:
All is revealed:
http://groups.google.com/groups?safe...&num=100&hl=en
Anyhow I have the 'flue and may be dead tomorrow, in which case could
you take a look at:
http://www.wareing.dircon.co.uk/images/Bingo.jpg
and translate it into a formula for Bob Cain.

Sorry I've got to die now, byeeee.
  #93   Report Post  
Bob Cain
 
Posts: n/a
Default Doppler Distoriton?



Bob Cain wrote:


Well, I've asked for help on the general equation for pressure at
a point removed from an ideal piston in an infinite tube as a
function of the force applied to the piston that includes the
effects of Doppler distortion in alt.sci.physicw and on the
moderated group sci.physics.research where the real guns hang
out and there has been no answer.

What I've found is that any attempt to write the expression
from conditions at the interface results in a recursion or
infinite regress unless the term included to account for
the motion of the piston is set to zero. It's really tricky.

So let's look at an argument by reciprocity. Assume an
acoustic pulse of any arbitrary shape running down the tube
with an ideal pistion (no mass, stiff, infinite compliance)
in place.

1. The piston will move exactly in step with the motion of
the air molecules as the pulse passes by it.

Now let's measure and record the velocity of that piston as
the pulse passes by. Next let's mount a voltage to velocity
transducer, again ideal with a zero mechanical impedence, on
the side of the piston from which the pulse came when we
measured it.

2. When we drive that piston so as to reproduce the velocity
that was recorded we will get the identical pulse propegating
off of it as originally measured.

3. Because air is air, the resulting pressure pulse will be
in phase with that velocity and given by p(t) = v(t) * Ra,
where Ra is the characteristic impedence or air, and that
pressure pulse will be identical to the one that the
measured pulse had.

Because this should be true with a pulse of any shape it will
be true of a supposition of any such pulses which implies that
it is true of any signal and is thus a linear transducer with
no distortion of any kind.


The only thing that needs to be said to complete this is
that any arguments relative to velocity can be equally
applied to pressure since pressure and velocity in air are
in phase and related by a constant of proportionality, Ra,
the acoustic impedence of air.

The last nail in the coffin of loudspeaker Doppler
distortion is to find the flaw in the the intuitive, and
highly persuasive, argument that has been used historically
and used a lot as a counter to my argument. The flaw just
came to me today, finally.

Doppler shift is an unquestionable phenomenon, easily proved
from first principles. The thing is that it depends on a
sound source that is moving with respect to, i.e. _within_
the medium (we assume for this that the listener is
stationary with respect to it.) A piston with two
frequencies driving it and stationary with respect to the
medium otherwise will supposedly show those frequencies
modulating each other. The flaw is that the piston is not
in any sense moving within the medium, it is moving the
medium which is fundamentally different.

If you had a little loudspeaker moving back and forth in
space with a low frequency while emitting a high frequency
you would indeed see the "Doppler distortion" phenomenon but
if you move that speaker back and forth with a large plane
to which it is attached, the low and high frequencies will
add linearly with no distortion. In the latter case it is
part of the system moving the air and in the former it is
just moving within the air.

If you move the entire plane with the sum of the two
frequencies, it moves the air the same amount and generates
a pressure wave with only those two spectral components and
no frequency modulation.

Doppler distortion in loudspeakers in indeed a myth
justified by faulty intuitive hand waving.


Bob
--

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

A. Einstein
  #94   Report Post  
Detector195
 
Posts: n/a
Default Doppler Distoriton?

"Arny Krueger" wrote in message ...
Here's the results of some speaker measurements that I made tonight, based
on passing 50 Hz & 4 KHz mixed 1:1 at about 1.2 volts rms, through a
Peerless 6.5 inch woofer with about 6 mm Xmax (relatively large for a woofer
its size). The speaker is mounted in a roughly 0.4 cubic foot box with no
vent. The power amp is a QSC USA 850. This is not very loud. The mic is an
ECM8000 that is a few inches from the woofer cone.

http://www.pcavtech.com/techtalk/doppler/

The first graph shows the broadband response. The large spikes at 50 Hz and
4 KHz are clearly visible. The second and third harmonics of the 50 Hz tone
are about 30 dB down. The spike for the 4 KHz tone is about 5 dB higher than
the spike for 50 Hz because the woofer is simply that much more efficient at
4 KHz.

The second graph is taken from the same test, with the frequency scale
enlarged to show about 400 Hz on either side of 4 KHz. The first pair of
large spikes are about 50 Hz on either side of 4 KHz, the second are about
100 Hz on either side of 4 KHz, and so on. The distortion products are
probably a mixture of AM and FM distortion, with FM predominating, as the
test is contrived to focus on FM.

While I've got this set up, any other data that anyone would find
interesting?


Could you simulate a Leslie speaker by mixing a really huge low
frequency sine wave with the regular audio program?
  #95   Report Post  
Jim Carr
 
Posts: n/a
Default Doppler Distoriton?

"Bob Cain" wrote in message
...
Doppler shift is an unquestionable phenomenon, easily proved
from first principles. The thing is that it depends on a
sound source that is moving with respect to, i.e. _within_
the medium (we assume for this that the listener is
stationary with respect to it.) A piston with two
frequencies driving it and stationary with respect to the
medium otherwise will supposedly show those frequencies
modulating each other. The flaw is that the piston is not
in any sense moving within the medium, it is moving the
medium which is fundamentally different.


I don't understand. Explain to me how the speaker actually transfers the
energy to the air. Maybe you can do that by contrast. Suppose I hit my
knuckle on the table. I can't see the table vibrate, but I know it does. The
energy moves from the molecules in the table to the molecules in the air. I
can live with that.

Then I watch the speaker diaphragm move. Sometimes it moves a lot, sometimes
a little. At one point during the movement is the sound wave created? I know
it pushes air to create a "breeze" but that's not the sound wave. I'm
guessing that when the forward movement stops, the pressure goes back to
"normal" and the sound wave is formed.

Is that how it works or am I still struggling with truly understanding the
mechanics of how a speaker works? I know how it works in layman's terms, but
I'm fuzzy about the actual mechanics of getting those molecules smacking
into each other.




  #96   Report Post  
Arny Krueger
 
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Default Doppler Distoriton?

"Randy Yates" wrote in message

ow (Goofball_star_dot_etal) writes:

On Wed, 11 Aug 2004 15:28:45 -0400, "Arny Krueger"
wrote:

"Goofball_star_dot_etal" wrote in message

On Wed, 11 Aug 2004 02:57:26 GMT, Randy Yates
wrote:

An accelerometer, a la Velodyne?

And those who are not asleep will note that this is a very good
solution from an experimental point of view. Points to those that
say why.

It gives you acelleration, forthwith.

Integrate it (essentially pass it through a low pass filter) once
and you get velocity.

Integrate it again and you get position.


Every time you integrate it, a lot of spurious noise gets low-pass
filtered @ 6 dB/octave.


Yes, and that's a good thing(TM).


Agreed.

OK, 2 points but remember what Svante said. .


I can't find that post...

and there is more. . .
Think "one variable at a time" and "how should we record and process
the accelerometer data?"


I thought I covered that.

What's the bandwidth of an accelerometer signal when stuck on a speaker

cone?

Depends on the type of acellerometer. The ones commonly used with subwoofers
have dominant poles up in the 100's of Hz. The pole is due to the mass of
the acellerometer and the compliance of the mounting. Acellerometers used
this way do somewhat change the dynamics of the cone.

No problemo at 50 Hz.

The *pro* methodology involves a laser and $$$$. The Dumax machine does it
that way.

Could you use a sound card input to digitize it?


No doubt, with suitable preamplification.

Now, I'm thinking about calibrating the accelerometer on the cone.


  #97   Report Post  
Arny Krueger
 
Posts: n/a
Default Doppler Distoriton?

"Detector195" wrote in message
om

Could you simulate a Leslie speaker by mixing a really huge low
frequency sine wave with the regular audio program?


Not in any practical way. Sorry.


  #100   Report Post  
Doug
 
Posts: n/a
Default Leslies, was Doppler Distoriton?

There is simulated Leslie sound and there is real Leslie sound.
Simulated sounds, just that, simulated. Not bad, but not like a real
Leslie. If you search on ebay you can find all sorts of Leslie stuff.
Prices vary, and they are HEAVY and expensive to ship.

I play the guitar and have always wanted to play through a real
Leslie. Never have though.

Randy Yates wrote in message ...
"Wessel Dirksen" writes:

"Randy Yates" wrote in message
...
(Detector195) writes:
[...]
Could you simulate a Leslie speaker by mixing a really huge low
frequency sine wave with the regular audio program?

But why??? You can buy a used leslie for just a few hundred bucks
and get the Real McCoy(TM).

--A 1969 Leslie 147 Owner


Aren't real classic Leslies priced through the roof these days?


I don't know - I bought mine about 3 years ago off of Ebay for $600
($200 of which was shipping charges). It had an amp problem which I
fixed. I doubt that they're much more expensive now, but I've been
inactive in buying/selling the stuff for awhile.

Unless you mean actual new leslies - yes those are extremely expensive.
($2000+?)

You might try Goff for more info,
http://www.goffprof.com/



  #101   Report Post  
Bob Cain
 
Posts: n/a
Default Doppler Distoriton?



Jim Carr wrote:

"Bob Cain" wrote in message
...

Doppler shift is an unquestionable phenomenon, easily proved
from first principles. The thing is that it depends on a
sound source that is moving with respect to, i.e. _within_
the medium (we assume for this that the listener is
stationary with respect to it.) A piston with two
frequencies driving it and stationary with respect to the
medium otherwise will supposedly show those frequencies
modulating each other. The flaw is that the piston is not
in any sense moving within the medium, it is moving the
medium which is fundamentally different.



I don't understand. Explain to me how the speaker actually transfers the
energy to the air.


By pushing and pulling on it. The velocity of the piston is
transfered to the particles (voxels) of the air in front of it.

Then I watch the speaker diaphragm move. Sometimes it moves a lot, sometimes
a little. At one point during the movement is the sound wave created?


Whenever it moves, as it moves. The air has no choice but
to go along with it and that creates a velocity and pressure
wave that are in phase and related by the characteristic
acoustic impedence of air.

When you push on air, it moves and pushes on the air in
front of it but with some delay in the transfer. That's
what causes the speed of sound. The push propegates outward
from this bit of air to the bit in front of it and that's a
wave. Same when you pull on it.

Does that help?


Bob
--

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

A. Einstein
  #102   Report Post  
Jim Carr
 
Posts: n/a
Default

"Bob Cain" wrote in message
...
When you push on air, it moves and pushes on the air in
front of it but with some delay in the transfer. That's
what causes the speed of sound. The push propegates outward
from this bit of air to the bit in front of it and that's a
wave. Same when you pull on it.

Does that help?


Sorta. From what you're saying. the *origin* of each individual wave can
take place at any point within the throw of the diaphragm. Is that correct?


  #103   Report Post  
Bob Cain
 
Posts: n/a
Default



Jim Carr wrote:

"Bob Cain" wrote in message
...

When you push on air, it moves and pushes on the air in
front of it but with some delay in the transfer. That's
what causes the speed of sound. The push propegates outward
from this bit of air to the bit in front of it and that's a
wave. Same when you pull on it.

Does that help?



Sorta. From what you're saying. the *origin* of each individual wave can
take place at any point within the throw of the diaphragm. Is that correct?


Not sure even how to define the origin of the wave in those
terms. Thanks for that. I just realized that the
assumptions which are being made about that are the flaw in
the intuitive description of "Doppler distortion."

Something that is ocuring dynamically is being described in
terms of a static piston in one sense and dynamically in
another. That doesn't work. The distance from the piston
to the the sensor isn't relevant to the argument if it is
riding the wave. In a way, it's effect is being included
twice if you do that. That's a no-no that will lead to
false prediction.

The flaw in the common argument for "Doppler distortion" has
proven very elusive but I think that this nails it. It
really is subtle which explains why it's been around so long.

I added rec.audio.pro to this because it's highly relevant
to the thread on this subject that is happening there.


Bob
--

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

A. Einstein
  #104   Report Post  
Jim Carr
 
Posts: n/a
Default

"Bob Cain" wrote in message
...

Sorta. From what you're saying. the *origin* of each individual wave can
take place at any point within the throw of the diaphragm. Is that

correct?

Not sure even how to define the origin of the wave in those
terms. Thanks for that. I just realized that the
assumptions which are being made about that are the flaw in
the intuitive description of "Doppler distortion."


I'm having a hard time envisioning just one wave being started by one thrust
of the piston. Maybe if I fully understood that rather than the quite
satisfactory "it just does and that's how a speaker works" mentality I'v
always had, I could argue intelligently one way or the other.

I added rec.audio.pro to this because it's highly relevant
to the thread on this subject that is happening there.


Great. Feed me to the wolves. Hey, RAP folks: I hold no degrees in
electronics, physics, acoustics, etc. I do not work with audio as a
profession. I just find the topic interesting and do not purport myself to
be an expert. As I noted earlier in the thread, which was not cross-posted,
if I seem condescending, it is because I am trying to explain things in
simple terms to myself. Since my logic is usually sound, my guess is that a
basic premise somewhere is wrong or incomplete, hence the detailed and
simplist explanations.

With that said, help me out here. I can't get myself away from the
assumption that since a speaker diaphragm has a throw of a certain distance,
then the waves started by the diaphragm may be started from any point in
that throw. As such two waves which are created a certain time apart may end
up traveling different distances to reach my stationary ear, thus a Doppler
shift. Measurable? I dunno. Discernible to my ear? Probably not.


  #105   Report Post  
Bob Cain
 
Posts: n/a
Default



Jim Carr wrote:

With that said, help me out here. I can't get myself away from the
assumption that since a speaker diaphragm has a throw of a certain distance,
then the waves started by the diaphragm may be started from any point in
that throw. As such two waves which are created a certain time apart may end
up traveling different distances to reach my stationary ear, thus a Doppler
shift. Measurable? I dunno. Discernible to my ear? Probably not.


To recapitulate, the problem with that intuitive view, which
is the whole basis of believing that there is "Doppler
distortion" is that it assumes that the distance from the
driver is the distance from the instantaneous position of
the piston. That's wrong. The distance from the driver,
since it is riding the wave it is creating, is the distance
from its zero or rest position, the position about which it
oscillates. That doesn't change with the nature of the
signal unless there is a DC component.

If the distance from the driver is not changing, there is no
Doppler shift. None of the proposed scenarios which have
the face of the driver oscillating about a rest position
will produce Doppler shift despite intuition.

Whew!


Bob
--

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

A. Einstein


  #106   Report Post  
Phil Allison
 
Posts: n/a
Default


"Jim Carr"

With that said, help me out here. I can't get myself away from the
assumption that since a speaker diaphragm has a throw of a certain

distance,
then the waves started by the diaphragm may be started from any point in
that throw. As such two waves which are created a certain time apart may

end
up traveling different distances to reach my stationary ear, thus a

Doppler
shift.



** A time delay or advance is just that - it is not Doppler. Any such
delay or advance depends solely on the position of the cone - not its
*velocity*. If a cone is displaced by 10mm, that will introduce a time
error of 29 uS or a phase shift of 50 degrees at 5 kHz.

Any attempt to measure Doppler frequency shifts must allow for this -
most have not.



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


  #107   Report Post  
Arny Krueger
 
Posts: n/a
Default

"Phil Allison" wrote in message

"Jim Carr"

With that said, help me out here. I can't get myself away from the
assumption that since a speaker diaphragm has a throw of a certain
distance, then the waves started by the diaphragm may be started
from any point in that throw. As such two waves which are created a
certain time apart may end up traveling different distances to reach
my stationary ear, thus a Doppler shift.



** A time delay or advance is just that - it is not Doppler. Any
such delay or advance depends solely on the position of the cone -
not its *velocity*. If a cone is displaced by 10mm, that will
introduce a time error of 29 uS or a phase shift of 50 degrees at 5
kHz.

Any attempt to measure Doppler frequency shifts must allow for this
- most have not.


That's because this time shift, more specifically the time rate of change of
this time shift, is the cause of Doppler.


  #108   Report Post  
Randy Yates
 
Posts: n/a
Default

Arny,

This information is probably in this thread somewhere, but it has
gotten so long and convoluted that it's much easier just to ask: Are
you asking whether FM (Doppler) modulation at the high frequency is
the ONLY effect that results when that high frequency in addition to a
low frequency (purposely left undefined since the actual values depend
on a number of factors in the physical setup) are reproduced in the
same transducer, or is there some amount of AM modulation as well?

"The Ghost" gave me an idea for determining this without requiring any
measurement of the instantaneous cone displacement. Perform an FM
discrimination of the received (microphone) signal at the high
frequency "carrier." Call the discriminated signal m(t). Regenerate a
perfect FM signal using the modulating signal m(t) and subtract that
from the original signal. The result is the residual modulation on the
signal, which could then be AM-detected to determine if AM is present.

Three practical issues which must be dealt with come to mind:

1) How to synchronize the regenerated FM carrier amplitude to the
original FM amplitude? Easy answer: emit a signal consisting of the
high frequency tone alone for a length of time adequate to measure the
amplitude.

2) What modulation index, or depth of modulation, should be used in
the regenerated FM signal? Said another way, what gain (if any) should
be applied to m(t) when regenerating the FM signal?

3) How do you synchronize the regenerated signal in time with the
original signal? There are actually two synchronization tasks to be
done: phase synchronization of the carriers, and delay in the modulating
signal, i.e., tau in A*m(t-tau). (A is the parameter in question 2).

Does this make any sense?
--
% Randy Yates % "My Shangri-la has gone away, fading like
%% Fuquay-Varina, NC % the Beatles on 'Hey Jude'"
%%% 919-577-9882 %
%%%% % 'Shangri-La', *A New World Record*, ELO
http://home.earthlink.net/~yatescr
  #109   Report Post  
Arny Krueger
 
Posts: n/a
Default

"Randy Yates" wrote in message


Arny,


This information is probably in this thread somewhere, but it has
gotten so long and convoluted that it's much easier just to ask: Are
you asking whether FM (Doppler) modulation at the high frequency is
the ONLY effect that results when that high frequency in addition to a
low frequency (purposely left undefined since the actual values depend
on a number of factors in the physical setup) are reproduced in the
same transducer, or is there some amount of AM modulation as well?


I'm not asking that question, because I know the answer, and I knew it
walking in the door last week.

The results of playing multiple tones through something as dirty as a
speaker produces copious amonts of both AM and FM. As a rule, the AM
dominates.

"The Ghost" gave me an idea for determining this without requiring any
measurement of the instantaneous cone displacement. Perform an FM
discrimination of the received (microphone) signal at the high
frequency "carrier." Call the discriminated signal m(t). Regenerate a
perfect FM signal using the modulating signal m(t) and subtract that
from the original signal. The result is the residual modulation on the
signal, which could then be AM-detected to determine if AM is present.


I've tried that, and a lot of other things. It has the usual problems with
nulling in the real world. You can get roughly a 2:1 to 10:1 reduction of
the unwanted distortion by that means.

Three practical issues which must be dealt with come to mind:


1) How to synchronize the regenerated FM carrier amplitude to the
original FM amplitude?


Pretty easy to do an fair job of in the digital domain.

Easy answer: emit a signal consisting of the
high frequency tone alone for a length of time adequate to measure the
amplitude.


If you've looked at the raw data page posted at
http://www.pcavtech.com/techtalk/doppler/ you'd know that finding that out
with pretty fair precision is a matter of reading numbers off a screen.

2) What modulation index, or depth of modulation, should be used in
the regenerated FM signal? Said another way, what gain (if any) should
be applied to m(t) when regenerating the FM signal?


At this point I should point out that since the AM dominates, it might make
sense to apply an AM signal to null the AM part out, leaving the FM.

3) How do you synchronize the regenerated signal in time with the
original signal? There are actually two synchronization tasks to be
done: phase synchronization of the carriers, and delay in the
modulating signal, i.e., tau in A*m(t-tau). (A is the parameter in
question 2).


Well, we know quite a bit about the signal that we are trying to clean up.

Does this make any sense?


Been there, done that. Seriously, I come back to this problem of separating
AM and FM from a real world signal every once and while, and learn a bit
more about solving it.

This time I realized that ideally, AM distortion related sidebands are
indepenendent of of the carrier frequency, but increase in amplitude with
carrier frequency for FM. Trouble is, this practical example is so heavily
dominated by the AM distortion. I hope to go back to studying jitter, and
play this card there.

I suspect that lots of people have been misidentifying AM distortion
products as jitter.


  #110   Report Post  
Jim Carr
 
Posts: n/a
Default

"Phil Allison" wrote in message
...

** A time delay or advance is just that - it is not Doppler. Any such
delay or advance depends solely on the position of the cone - not its
*velocity*.


I disagree. The time delay or advance *is* Doppler. The speed of sound is
constant in a given medium. In the classic example of the train whistle the
velocity of the train changes the distance/time between waves, but those
waves travel just as fast as if the train were still. It seems like you are
saying Doppler has to do with adding velocities together, which is untrue.




  #111   Report Post  
Ben Bradley
 
Posts: n/a
Default

In alt.music.home-studio,rec.audio.tech,rec.audio.pro,
Bob Cain wrote:



Jim Carr wrote:

With that said, help me out here. I can't get myself away from the
assumption that since a speaker diaphragm has a throw of a certain distance,
then the waves started by the diaphragm may be started from any point in
that throw. As such two waves which are created a certain time apart may end
up traveling different distances to reach my stationary ear, thus a Doppler
shift. Measurable? I dunno. Discernible to my ear? Probably not.


To recapitulate, the problem with that intuitive view, which
is the whole basis of believing that there is "Doppler
distortion" is that it assumes that the distance from the
driver is the distance from the instantaneous position of
the piston. That's wrong. The distance from the driver,
since it is riding the wave it is creating, is the distance
from its zero or rest position, the position about which it
oscillates. That doesn't change with the nature of the
signal unless there is a DC component.


Oh, goody. You want a DC component, I'll GIVE you a DC component!
insert emoticon here

Let's go to extremes. Say we got one of these big honking
high-power woofers (that I recall reading Arny's writings about a
while back) with X-max of one or two inches or so. Superimpose a 1kHz
tone (probably the highest frequency it will reasonably reproduce)
onto a "DC component", say a 1/2 Hz sine wave that slooowly moves the
cone in and out a total distance of two inches, all the while it's
also putting this 1kHz tone into the air. Don't think of it as a 0.5Hz
sine wave, think of it as a varying DC component (that's obviously
what it is, you can see the cone move back and forth with your eyes).
What will you say is the acoustic source of the 1kHz, the driver
frame, which does not move, or the cone, which DOES move?

And presuming you see this as a possible cause of doppler
distortion, how is this "DC component" any different from a higher
frequency (say 20Hz or 50Hz) that also causes substantial cone
displacement?

If the distance from the driver is not changing, there is no
Doppler shift.


The distance from which part of the driver? The frame? The cone?
Something else?

None of the proposed scenarios which have
the face of the driver oscillating about a rest position
will produce Doppler shift despite intuition.
Whew!


If you think it's frustrating for you, imagine how I feel with Phil
agreeing with me!

Bob


-----
http://mindspring.com/~benbradley
  #112   Report Post  
Phil Allison
 
Posts: n/a
Default


"Jim Carr"
"Phil Allison"


** A time delay or advance is just that - it is not Doppler. Any

such
delay or advance depends solely on the position of the cone - not its
*velocity*.


I disagree. The time delay or advance *is* Doppler.



** Doppler frequency shift is proportional to source velocity - so they
are not the same.


The speed of sound is constant in a given medium.



** If the medium is moving at some speed then that adds to, or subtracts
from, the speed of sound in still air (ie 343 m/S)


In the classic example of the train whistle the
velocity of the train changes the distance/time between waves,



** Yes, because the train is moving through the air.


but those waves travel just as fast as if the train were still.


It seems like you are
saying Doppler has to do with adding velocities together, which is untrue.



** Not at all - but the magnitude of the Doppler shift is proportional to
the velocity of the source compared to the surrounding air. A woofer cone
takes a small volume of with it for the ride.




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







  #113   Report Post  
Jim Carr
 
Posts: n/a
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"Phil Allison" wrote in message
...
I disagree. The time delay or advance *is* Doppler.



** Doppler frequency shift is proportional to source velocity - so they
are not the same.


Maybe we just have a failure to communicate. I say the actual frequency does
not shift. Assume a constant frequency at the source. If the distance
between the source and the receiver changes, then the receiver cannot
reliably determine the frequency. This is because the distance between the
sound waves (wavelength) emitted by the source changes. The receiver
determines the frequency by measuring the wavelength, which is the distance
between a given point on a wave and the corresponding point on the next
cycle of the wave.

Now, our ears don't measure distance, they are measuring time to put it
loosely. They don't care how fast the wave is moving. They sense the time
interval (a function of distance) between waves. Since movement of either
the source, observer or both can change that distance, there is an
*apparent* shift in frequency, not a "real" shift. We know this because we
already agreed the source emitted a constant frequency. It can be expressed
like this:

fo = fs . (v - vo) / (v - vs)
fo is the apparent frequency of the observer.
fs is the frequency of the source
v is the speed of sound
vo and vs are the velocities of the source and observer.

But then again, you seemed to disagree about the speed of sound being
constant when you wrote...

** If the medium is moving at some speed then that adds to, or subtracts
from, the speed of sound in still air (ie 343 m/S)


To which I say, care to cite a reference? The apparent shift is certainly a
function of the velocity of the source and/or receiver, but the speed of
sound is constant. If it's not, there is no Doppler.

Let's just reason it out by using the whistle on the train and the changing
speed of sound which you cite. Suppose further that the listener is 3,430
meters away. The sound wave has to travel 10 seconds to arrive at the
observer, right?

Train #1 is stationary and blows the whistle. A second train is moving at
100m/S. At the exact moment is parallel with train #1 it blows its whistle.
This happens to be the exact same time train #1 blew its whistle. Based on
your statement above, the first sound of the whistle is moving at 343m/S.
The second is traveling at 443m/S.

Are you saying that the second whistle will arrive at the receiver 2.25
seconds earlier and that we would hear two separate whistles?

If they did, they would sound exactly the same anyway, which would mean no
Doppler shift.

Refer to the formula above. For Doppler to work, v (speed of sound) must
remain constant in the medium. If the velocities add together, then the
distance between each wave would therefore remain constant. Hence, no shift.


  #114   Report Post  
Phil Allison
 
Posts: n/a
Default


"Arny Krueger"
"Phil Allison"
"Jim Carr"

With that said, help me out here. I can't get myself away from the
assumption that since a speaker diaphragm has a throw of a certain
distance, then the waves started by the diaphragm may be started
from any point in that throw. As such two waves which are created a
certain time apart may end up travelling different distances to reach
my stationary ear, thus a Doppler shift.



** A time delay or advance is just that - it is not Doppler. Any
such delay or advance depends solely on the position of the cone -
not its *velocity*. If a cone is displaced by 10mm, that will
introduce a time error of 29 uS or a phase shift of 50 degrees at 5
kHz.

Any attempt to measure Doppler frequency shifts must allow for this
- most have not.


That's because this time shift, more specifically the time rate of change

of
this time shift, is the cause of Doppler.



** So this is what all the Doppler Distortion fuss is about ????

A tiny bit of phase jitter, which at 5 kHz rarely amounts to more than a
few degrees ??


I was looking at it on my scope yesterday:


1. A 5 inch woofer, in box, driven by an amp fed from with two sine wave
generators with outputs summed.

2. A condenser mic feeding a pre-amp and followed by a 12 dB/oct HPF at
2 kHz thence to the scope.

3. The high frequency generator output is also linked to the scope which
operates in X-Y mode.

4. Park mic in front of woofer fed with a circa 5000 Hz sine wave at
about 10 watts. ( I used ear muffs)

5. Adjust scope and exact mic position to get a straight, diagonal line
traced on the scope screen - note that adjusting the 5000 Hz amplitude
affects the angle of the diagonal line only (ie makes it easy to visually
distinguish amplitude modulation ).

6. Turn up low frequency generator, set to say 40 Hz, and watch the line
open out to form a narrow ellipse indicating that the phase is changing as
the cone moves closer and further away from the mic.

7. Sweep low frequency generator up and down and note that cone excursion
alone controls the size of the ellipse - it never opens out more than
about 15 degrees for a linear cone excursion of 3 mm.

8. Try hard to imagine that this is the notorious, evil, Doppler
distortion before your eyes.


Wow.



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





  #115   Report Post  
Phil Allison
 
Posts: n/a
Default


"Jim Carr"
"Phil Allison"


I disagree. The time delay or advance *is* Doppler.



** Doppler frequency shift is proportional to source velocity - so

they
are not the same.



Maybe we just have a failure to communicate. I say the actual frequency

does
not shift.


Since movement of either the source, observer or both can change that

distance, there is an
*apparent* shift in frequency, not a "real" shift.



** The *observed* frequency changes - end of story.


But then again, you seemed to disagree about the speed of sound being
constant when you wrote...

** If the medium is moving at some speed then that adds to, or

subtracts
from, the speed of sound in still air (ie 343 m/S)


To which I say, care to cite a reference?



** Silly question - see any school physics text.


Let's just reason it out by using the whistle on the train and the

changing
speed of sound which you cite.
Suppose further that the listener is 3,430
meters away. The sound wave has to travel 10 seconds to arrive at the
observer, right?

Train #1 is stationary and blows the whistle. A second train is moving at
100m/S. At the exact moment is parallel with train #1 it blows its

whistle.
This happens to be the exact same time train #1 blew its whistle. Based on
your statement above, the first sound of the whistle is moving at 343m/S.
The second is traveling at 443m/S.



** That wrong conclusion simply has no connection with my statement.

Both whistle sounds travel through still air to the listener.


Are you saying that the second whistle will arrive at the receiver 2.25
seconds earlier and that we would hear two separate whistles?


** Nope.




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




  #116   Report Post  
Bob Cain
 
Posts: n/a
Default



Arny Krueger wrote:

That's because this time shift, more specifically the time rate of change of
this time shift, is the cause of Doppler.


Doesn't exist, Arny. Look he

http://www.silcom.com/~aludwig/Physi..._of_sound.html

Tellingly, as deep as the discussion goes, no mention is
made of "Doppler distortion" and if you read it you will see
why such nonsense wouldn't even have been considered.

It also directly supports what I have said recently that
distance from an oscilating piston, for the purposes of the
physics of piston interaction with air is the distance to
the rest position. I must say, that I found this link just
minutes ago, oddly enough looking for links to IR's for
Acoutic Modeler. I fingered it out earlier all by m'self.

Now about that data you posted...



Bob
--

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

A. Einstein
  #117   Report Post  
Bob Cain
 
Posts: n/a
Default



Ben Bradley wrote:


Let's go to extremes. Say we got one of these big honking
high-power woofers (that I recall reading Arny's writings about a
while back) with X-max of one or two inches or so. Superimpose a 1kHz
tone (probably the highest frequency it will reasonably reproduce)
onto a "DC component", say a 1/2 Hz sine wave that slooowly moves the
cone in and out a total distance of two inches, all the while it's
also putting this 1kHz tone into the air. Don't think of it as a 0.5Hz
sine wave, think of it as a varying DC component (that's obviously
what it is, you can see the cone move back and forth with your eyes).
What will you say is the acoustic source of the 1kHz, the driver
frame, which does not move, or the cone, which DOES move?


Doesn't matter how slow the oscilation is, it won't produce
Doppler shift.

If the distance from the driver is not changing, there is no
Doppler shift.



The distance from which part of the driver? The frame? The cone?
Something else?


The rest position, the one it will settle to when the
driving signal is removed. If the driving signal contains a
DC component, and the piston is not restrained by a
compliance, then and only then will Doppler shift occurs.
Hard to swallow, I know but it is the truth.




None of the proposed scenarios which have
the face of the driver oscillating about a rest position
will produce Doppler shift despite intuition.
Whew!



If you think it's frustrating for you, imagine how I feel with Phil
agreeing with me!


That really must be rough. I sympathize. :-)

Look here if you aquire the math to understand it.


http://www.silcom.com/~aludwig/Physi..._of_sound.html

I just found it and everything I've said is in it if not in
the same context. It doesn't consider "Doppler distortion"
because there is no reason to.


Bob
--

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

A. Einstein
  #118   Report Post  
Arny Krueger
 
Posts: n/a
Default

"Phil Allison" wrote in message

"Arny Krueger"
"Phil Allison"
"Jim Carr"

With that said, help me out here. I can't get myself away from the
assumption that since a speaker diaphragm has a throw of a certain
distance, then the waves started by the diaphragm may be started
from any point in that throw. As such two waves which are created a
certain time apart may end up travelling different distances to
reach my stationary ear, thus a Doppler shift.


** A time delay or advance is just that - it is not Doppler. Any
such delay or advance depends solely on the position of the cone -
not its *velocity*. If a cone is displaced by 10mm, that will
introduce a time error of 29 uS or a phase shift of 50 degrees at 5
kHz.

Any attempt to measure Doppler frequency shifts must allow for
this
- most have not.


That's because this time shift, more specifically the time rate of
change of this time shift, is the cause of Doppler.



** So this is what all the Doppler Distortion fuss is about ????

A tiny bit of phase jitter, which at 5 kHz rarely amounts to more
than a few degrees ??


It's not a lot. The most important thing is that its swamped by all teh AM
distortion.

I was looking at it on my scope yesterday:


1. A 5 inch woofer, in box, driven by an amp fed from with two sine
wave generators with outputs summed.


2. A condenser mic feeding a pre-amp and followed by a 12 dB/oct
HPF at 2 kHz thence to the scope.


3. The high frequency generator output is also linked to the scope
which operates in X-Y mode.


4. Park mic in front of woofer fed with a circa 5000 Hz sine wave
at about 10 watts. ( I used ear muffs)


5. Adjust scope and exact mic position to get a straight, diagonal
line traced on the scope screen - note that adjusting the 5000 Hz
amplitude affects the angle of the diagonal line only (ie makes it
easy to visually distinguish amplitude modulation ).


6. Turn up low frequency generator, set to say 40 Hz, and watch
the line open out to form a narrow ellipse indicating that the phase
is changing as the cone moves closer and further away from the mic.


7. Sweep low frequency generator up and down and note that cone
excursion alone controls the size of the ellipse - it never opens
out more than about 15 degrees for a linear cone excursion of 3 mm.

8. Try hard to imagine that this is the notorious, evil, Doppler
distortion before your eyes.


I never said it was notorious or evil. But net it out -we're saying pretty
much the same thing, Phil. The Doppler distortion is there but its small.

I think the guy who brought up Doppler as some kind of a serious problem did
so a few weeks ago. He used Doppler distortion as a justification for not
liking long-excursion woofers. In the end he admitted that he used 2-way
monitors with either 6.5 or 8" woofers, and no subwoofer. Ironic enough?


  #119   Report Post  
Arny Krueger
 
Posts: n/a
Default

"Bob Cain" wrote in message

Arny Krueger wrote:

That's because this time shift, more specifically the time rate of
change of this time shift, is the cause of Doppler.


Doesn't exist, Arny. Look he

http://www.silcom.com/~aludwig/Physi..._of_sound.html

Tellingly, as deep as the discussion goes, no mention is
made of "Doppler distortion" and if you read it you will see
why such nonsense wouldn't even have been considered.

It also directly supports what I have said recently that
distance from an oscilating piston, for the purposes of the
physics of piston interaction with air is the distance to
the rest position. I must say, that I found this link just
minutes ago, oddly enough looking for links to IR's for
Acoutic Modeler. I fingered it out earlier all by m'self.

Now about that data you posted...


Sorry Bob, but I'm not buying.


  #120   Report Post  
Phil Allison
 
Posts: n/a
Default


"Arny Krueger"
"Phil Allison"


** So this is what all the Doppler Distortion fuss is about ????

A tiny bit of phase jitter, which at 5 kHz rarely amounts to more
than a few degrees ??


It's not a lot. The most important thing is that its swamped by all the AM
distortion.



** Which, unlike the puny phase jitter, is veeerrrryy audible.




I was looking at it on my scope yesterday:


1. A 5 inch woofer, in box, driven by an amp fed from with two sine
wave generators with outputs summed.


2. A condenser mic feeding a pre-amp and followed by a 12 dB/oct
HPF at 2 kHz thence to the scope.


3. The high frequency generator output is also linked to the scope
which operates in X-Y mode.


4. Park mic in front of woofer fed with a circa 5000 Hz sine wave
at about 10 watts. ( I used ear muffs)


5. Adjust scope and exact mic position to get a straight, diagonal
line traced on the scope screen - note that adjusting the 5000 Hz
amplitude affects the angle of the diagonal line only (ie makes it
easy to visually distinguish amplitude modulation ).


6. Turn up low frequency generator, set to say 40 Hz, and watch
the line open out to form a narrow ellipse indicating that the phase
is changing as the cone moves closer and further away from the mic.


7. Sweep low frequency generator up and down and note that cone
excursion alone controls the size of the ellipse - it never opens
out more than about 15 degrees for a linear cone excursion of 3 mm.

8. Try hard to imagine that this is the notorious, evil, Doppler
distortion before your eyes.



I never said it was notorious or evil.



** I was using poetic license.


But net it out -we're saying pretty
much the same thing, Phil. The Doppler distortion is there but its small.



** I found with my test that much of it goes away if you put the woofer
cone at right angles to the mic.

Hey - I have always had my 10 inch sub mounted facing the floor.

Way to go !!!



I think the guy who brought up Doppler as some kind of a serious problem

did
so a few weeks ago. He used Doppler distortion as a justification for not
liking long-excursion woofers. In the end he admitted that he used 2-way
monitors with either 6.5 or 8" woofers, and no subwoofer. Ironic enough?



** Must just love all that IM.



.......... Phil





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