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The Ghost
 
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Default Basic Acoustic Derivation/Proof Needed

Bob Cain wrote in message ...
Bob Cain wrote:


snip.....snip

The answer turns out to be simple. If the velocity and
position of the particles moving about their rest position
at the origin are
Vp(t) = Sp'(t)


snip......snip

The Doppler distortion in a plane wave is a consequence of
the non-linear relationship between the signal motion
imparted to the air by the driver and the flow velocity
(pressure) at a point about which that motion is manifest
and measured.

For a two tone Vd(t), one at 40 Hz and another at 2 kHz and
allowing a motion of 2 cm (a reasonable Xmax for a two way
system) the RMS IM distortion sidebands about the 2 kHz
fundamental near the speaker face are on the order of .2% of
that fundamental. While of some signifigance compared to
other portions of an audio chain, it probably isn't for a
loudspeaker given its other distortion mechanisms.
Bob


Does your prediction of 0.2% distortion apply to the situation of a
piston in a tube or a piston in an infinite baffle, or doesn't it
matter?
  #2   Report Post  
Bob Cain
 
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The Ghost wrote:

Does your prediction of 0.2% distortion apply to the situation of a
piston in a tube or a piston in an infinite baffle, or doesn't it
matter?


First, that prediction is incorrect (I realized this
morning.) I accidentally plugged the 2 cm in as velocity
rather than displacement when doing the calculation but .2%
is correct for a magnitude .01 m/sec LF velocity.

The correct figure for 40 Hz at 2.53 m/s (2 cm throw) and 2
kHz at .05 m/sec (approximately equal acceleration, as is
closer to the situation with a driver in a cabinet) is about
25.4% RMS IM distortion. I find this rather startling.

The sidebands around the 2 kHz signal are -15 dB, -36 dB,
-60 dB, -87 dB.

These figures would obtain in a tube were it possible to
generate LF displacements that large when so loaded, and
they would not be distance dependant.

This simple plane wave analysis says nothing at all about a
piston in a baffle or a cabinet. The assumption of constant
characteristic impedence that it makes is no longer the case
even at the piston/air interface. A correct analysis would
have to take into account the radiation impedence seen by
the piston. I'm not sure whether the effect would be more
or less than in a tube when that difference is accounted
for. That's what I should look at next but I've fallen far
enough behind in what I really should be doing that I must
defer that.

As far as dependancy on distance from a speaker in a baffle,
I now don't think there will be much, if any, but thats only
a SWAG based on thinking that the frequencies of the IM
terms are close enough to the fundamental that they will
propegate from the plane of the speaker pretty much the same
as the fundamental so that the distortion as a percent of
the fundamental should not change much with distance.

Yes, this is a complete reversal of my thinking. The trap I
fell into was the false belief that the flow velocity at a
plane and the particle velocity about that plane were the
same. Having finally thought my way out of that
misconception and seeing that in fact they aren't even
related linearly (in free space as well as near a driver), I
see that I was wrong in what I believed followed from it.

This brings me back to the reason I began trying to
understand this to begin with, the quantitative
determination of how signifigant the effect really is. It
now seems to be more signifigant than has been assumed, not
less. Whether or not that remains true for more realistic
speaker couplings is an open question.


Bob
--

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

A. Einstein
  #3   Report Post  
Bob Cain
 
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The Ghost wrote:

Bob Cain wrote in message ...

Bob Cain wrote:



snip.....snip


Just realized that you copied only part of what I said in
sci.physics to everywere else this discussion had become
active (except your home group alt.sci.physics.acoustics
oddly enough), so to rectify that the full sci.physics post
follows.

Bob Cain wrote:

For the case of a propegating sinousiodal plane wave (or
more generally oscillating plane waves if at all possible)
where

v(d,t) = Vp cos(w(t-d/c)) or a general v(t-d/c)

describes the planar particle velocity at a position d
relative to some origin, I need a rock solid
proof/derivation of the state equations, position and
velocity, of the particles which are at rest in a plane d
when the field is quiescent. I cannot believe how elusive
this has remained for me and need help.


The answer turns out to be simple. If the velocity and
position of the particles moving about their rest position
at the origin are

Vp(t) = Sp'(t)

then the flow velocity of the particles in the plane of the
origin is

Vf(t) = Vp(t + Sp(t)/c)

and the pressure there is

P(t) = Ra*Vf(t)

This implies that there is a non-linear relationship between
particle velocity about a point and the flow velocity at
that point. In acoustics texts this relationship is swept
away in the approximation that Vf(t) = Vp(t) when motion is
small relative to the wavelength of the sound.

If there is a driver at the origin which imparts its motion
Vd(t) and Sd(t) to the air then

Vp(d,t) = Vd(t-d/c)
Sp(d,t) = Sd(t-d/c)

where d is the distance from the driver's rest position to
the point about which the motion is of interest. The flow
velocity (and proportional pressure) at that point is

Vf(t,d) = Vd(t-(d-Sd(t-d/c))/c)

The Doppler distortion in a plane wave is a consequence of
the non-linear relationship between the signal motion
imparted to the air by the driver and the flow velocity
(pressure) at a point about which that motion is manifest
and measured.

For a two tone Vd(t), one at 40 Hz and another at 2 kHz and
allowing a motion of 2 cm (a reasonable Xmax for a two way
system) the RMS IM distortion sidebands about the 2 kHz
fundamental near the speaker face are on the order of .2% of
that fundamental. While of some signifigance compared to
other portions of an audio chain, it probably isn't for a
loudspeaker given its other distortion mechanisms.


Bob
--

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

A. Einstein
  #4   Report Post  
The Ghost
 
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Bob Cain wrote in
:



The Ghost wrote:

Does your prediction of 0.2% distortion apply to the situation of a
piston in a tube or a piston in an infinite baffle, or doesn't it
matter?


First, that prediction is incorrect (I realized this
morning.) I accidentally plugged the 2 cm in as velocity
rather than displacement when doing the calculation but .2%
is correct for a magnitude .01 m/sec LF velocity.



Yes, I know. I asked the question because I knew the prediction was
incorrect for a tube and because I wanted you to confirm that it was for a
tube before I called attention to what was a very glaring and clearly
incorrect prediction.


The correct figure for 40 Hz at 2.53 m/s (2 cm throw) and 2
kHz at .05 m/sec (approximately equal acceleration, as is
closer to the situation with a driver in a cabinet) is about
25.4% RMS IM distortion. I find this rather startling.

The sidebands around the 2 kHz signal are -15 dB, -36 dB,
-60 dB, -87 dB.



Since you failed to mention prior work on this problem, or acknowledge its
validity, I will simply state that the -15dB sideband level is in good
agreement with the prediction of Art Ludwig's prior analysis of Doppler
distortion in a tube.


  #5   Report Post  
The Ghost
 
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Bob Cain wrote in
:


Just realized that you copied only part of what I said in
sci.physics to everywere else this discussion had become
active (except your home group alt.sci.physics.acoustics
oddly enough), so to rectify that the full sci.physics post
follows.




I didn't cross-post it to alt.sci.physics.acoustics because I didn't want
to be responsible for initiating another firestorm of cross-posting of ad
hominem attacks from you and your scum-bag buddies who admire and respect
me so much. Also, I didn't cross-post it to alt.sci.physics.acoustics
because of the generally sloppy presentation involving undefined terms, the
use of non-standard terminology and a a complete lack of coherence. We all
familiar what can happen (statistically speaking) if enough typewriters are
put in the hands of enough monkeys. Until such time as you clean up your
so-called analysis, I will remain unconvinced that the analysis is valid
and that your predictions are anything other than accidental and/or the
haphazard result of an even number of favorable errors.



  #6   Report Post  
The Ghost
 
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Bob Cain wrote in
:


What I find most strange is that with all the specialists
that had comments on all of this (other than in
sci.physics), the simple analysis I finally saw relating
flow velocity at a plane to particle velocity about it which
leads to the general, quantitative answer was never offered
by anyone else. Had it been, the issue could have been put
to bed much sooner.



There is no such thing as a problem that has only one method of solution.
Art Ludwig provided the analysis and the solution weeks ago, but you
rejected his analysis because you clearly couldn't understand it. You now
claim to have obtained the same result by different means. Even if your
sloppy, alternative analysis is correct, it adds nothing in the way of
understanding. It does however provide you with the personal gratification
that you did it yourself.....which is clearly what this has been about all
along.



The general, quantitative solution is as I've written it.
It is exact and can be applied to any physically realizable
signal. I will not drag this on any further unless there
are questions to answer (and until/unless I can come back
with a quantitative solution for a piston in a baffle.)
Bob


What do you mean by "flow velocity?" It's not discussed or defined in any
of my reference books on acoustics, and I have most if not all of them.
Define your terms........Sp'(t), Ra, Vd, etc. If you have a closed form
solution, present it.







  #7   Report Post  
Bob Cain
 
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The Ghost wrote:

What do you mean by "flow velocity?" It's not discussed or defined in any
of my reference books on acoustics, and I have most if not all of them.
Define your terms........Sp'(t), Ra, Vd, etc. If you have a closed form
solution, present it.


I'm not an acoustics specialist, as is obvious, and am not
terribly concerned about satisfying them with terms. What I
mean is the velocity of the acoustic air flow passing a plane
in units of distance/time. If there is a more correct term
I'd be happy to know it.

Definition of terms:

Vp(t) is the velocity of a particle normally at rest at the
origin as an acoustic wave goes through it in MKS units of
meter/second.

Sp(t) is the position of that particle in meters.

Vf(t) = Vp(t+Sp(t)/c) is the flow velocity at the origin
as a function of the particle velocity Vp(t) and position
Sp(t) defined above. This relationship holds everywhere,
not just near a driver.

Vd(t) is the velocity of a driver face at rest at the origin.

Sd(t) is it the position of the driver face.

Vp(d,t) = Vd(t-d/c) is the velocity of a particle normally
at rest at the position d as an acoustic wave created by a
driver at the origin goes past it. It is also in MKS units
of meter/second.

Sp(d,t) = Sd(t-d/c) is the positon of that same particle
about position d in units of the meter.

Ra is the acoustic impedence of air in Pascal*sec/meter. In
a tube it is homogenious and isoptropic with an approximate
value of 300 Pascal*sec/meter.

Vf(d,t) = Vd(t-(d-Sp(d,t))/c) is the velocity of particles
passing a plane at d in meter/sec.

P(d,t) = Ra*Vf(d,t) is the pressure at that plane.


On closed forms:

If the driver velocity function of time has a closed form
indefinite integral, the application of my expression for
Vf(d,t) to obtain a closed form for the flow velocity and
pressure should be obvious.

For example if the velocity function of the driver is

Vd(t) = Al*sin(Wl*t) + Ah*sin(Wh*t)

then

Sd(t) = -((Al/Wl)cos(Wl*t) + (Ah/Wh)cos(Wh*t))

and

Sp(d,t) = -((Al/Wl)cos(Wl*(t-d/c)) + (Ah/Wh)cos(Wh*(t-d/c))

Vp(d,t) = Al*sin(Wl*(t-(d-Sp(d,t))/c)) + Ah*sin(Wh*(t-(d-Sp(d,t))/c))

I haven't bothered to do the algebraic substitution of the
penultimate equation into the final one. With that, it is an
exact closed form solution for two sinusoids.


Bob
--

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

A. Einstein

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zigoteau
 
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Bob Cain wrote in message ...

Hi, Bob,

Good to see that you're still sticking with it.


Since you failed to mention prior work on this problem, or acknowledge its
validity, I will simply state that the -15dB sideband level is in good
agreement with the prediction of Art Ludwig's prior analysis of Doppler
distortion in a tube.


Presuming it built on them, I had not gone past the
unmotivated equations 4) and 5) in his note to see that he
had proposed something similar for two sinusoids as an
approximation further on without regard to those equations.
What I wrote was determined without refering to anything
in that note following equations 4) and 5). The discussion
in sci.physics with Zigoteau was invaluable in leading me to
the answer and that discussion is on the record if not
crossposted to every group in which the discussion found itself.


extracted from previous post

For a two tone Vd(t), one at 40 Hz and another at 2 kHz and allowing
a motion of 2 cm (a reasonable Xmax for a two way system) the RMS IM
distortion sidebands about the 2 kHz fundamental near the speaker
face are on the order of .2% of that fundamental. While of some
signifigance compared to other portions of an audio chain, it
probably isn't for a loudspeaker given its other distortion
mechanisms.


I presume that these are the values given by Art Ludwig that I asked
for. Thanks.

I've improved my value for the acoustic impedance of air, from values
given on

http://hypertextbook.com/facts/2000/RachelChu.shtml and

http://www.rfcafe.com/references/gen..._still_air.htm

The values c=343 m.s^-1 and rho=1.25 kg.m^-3 give Z=429 Pa.m^-1.s

Art must like it loud. At 40Hz, let's say the speaker diaphragm has an
rms amplitude of 1e-2 m. Its rms velocity excursion v is 2.4 m.s^-1,
and hence the power flux is Z*v^2 = 2471 W.m^-2. Sound intensities are
normally expressed in dB wrt 1 pW.m^-2. This works out at 154 dB. This
may be compared to the following table from
http://www.nidcd.nih.gov/health/educ...cibel_text.asp

Decibel level What we hear
10 dB Normal breathing
20 dB Rustling leaves, mosquito
30 dB Whisper
40 dB Stream, refrigerator humming
50-60 dB Quiet office
50-65 dB Normal conversation
60-65 dB Laughter
70 dB Vacuum cleaner, hair dryer
75 dB Dishwasher
78 dB Washing machine
80 dB Garbage disposal, city traffic noise
Prolonged exposure to any noise above 90 dB can cause gradual hearing
loss.
84 dB Diesel truck
70-90 dB Recreational vehicle
88 dB Subway, motorcycle
85-90 dB Lawnmower
100 dB Train, garbage truck
97 dB Newspaper press
98 dB Farm tractor
Regular exposure of more than 1 minute risks permanent hearing loss.
103 dB Jet flyover at 100 feet
105 dB Snowmobile
110 dB Jackhammer, power saw, symphony orchestra
120 dB Thunderclap, discotheque/boom box
110-125 dB Stereo
110-140 dB Rock concerts
130 dB Jet takeoff, shotgun firing
145 dB Boom cars

Cheers,

Zigoteau.
  #9   Report Post  
Daydream Electric
 
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Your abuse of the English language is disgusts me. When's the last time you
heard music performed inside a tube? Never? Exactly.

We all familiar what can happen (statistically speaking) if enough

typewriters are
put in the hands of enough monkeys.



  #10   Report Post  
Bob Cain
 
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zigoteau wrote:

Bob Cain wrote in message ...

Hi, Bob,

Good to see that you're still sticking with it.


I think I got it, finally, and I thank you again for the
fruitful discussion.

For a two tone Vd(t), one at 40 Hz and another at 2 kHz and allowing
a motion of 2 cm (a reasonable Xmax for a two way system) the RMS IM
distortion sidebands about the 2 kHz fundamental near the speaker
face are on the order of .2% of that fundamental. While of some
signifigance compared to other portions of an audio chain, it
probably isn't for a loudspeaker given its other distortion
mechanisms.



I presume that these are the values given by Art Ludwig that I asked
for. Thanks.


Those aren't his. I used the parameters I did because they
more closely relate to real world speakers in enclosures
(even though the analysis is for a plane wave.) The .2%
distortion figure I gave was an error caused by my
accidentally plugging .01 as the velocity rather than the
position magnitude. With that corrected, the distortion
becomes a whopping 25%.

I thought I had posted his for you. Sorry if I failed to do
that (ah, I see that post still in my drafts folder.)

He has recently used 100 Hz, 8000 Hz, .04 m/s, .0004 m/s.
In a plane wave that would be 119 dB SPL and 77 dB SPL in a
tube. That only gives a LF excurison of 6.4 E-5 meters.
The ratio of RMS IM distortion to the HF signal for those
parameters is 0.66%. Even this small amount is signifigant
compared to other factors in the recording/reproduction
chain were it the only source of speaker distortion.


I've improved my value for the acoustic impedance of air, from values
given on

http://hypertextbook.com/facts/2000/RachelChu.shtml and

http://www.rfcafe.com/references/gen..._still_air.htm

The values c=343 m.s^-1 and rho=1.25 kg.m^-3 give Z=429 Pa.m^-1.s


Thank you. I took my approximate values from Pierce's text.
Not sure why he'd have used Z=300 Pa.m^-1.s which is quite
different.


Art must like it loud. At 40Hz, let's say the speaker diaphragm has an
rms amplitude of 1e-2 m. Its rms velocity excursion v is 2.4 m.s^-1,
and hence the power flux is Z*v^2 = 2471 W.m^-2. Sound intensities are
normally expressed in dB wrt 1 pW.m^-2. This works out at 154 dB.


Again, it was I who plugged in that number because it is a
reasonable excursion in real world situations due to poor LF
coupling to the air. I am hardly sure, however, that mixing
apples with oranges by using a plane wave analysis with
nearly point source conditions leads to anything meaningful
so that 25% figure needs be taken with a grain of salt.
I.E. I'm not sure how well LF piston velocity in an
enclosure is coupled to motion of the air immediately in
front of it.


Thanks,

Bob
--

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

A. Einstein


  #11   Report Post  
Art Ludwig
 
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"zigoteau" wrote in message
om...
Bob Cain wrote in message

...

[snips]
Art must like it loud. At 40Hz, let's say the speaker diaphragm has an
rms amplitude of 1e-2 m. Its rms velocity excursion v is 2.4 m.s^-1,
and hence the power flux is Z*v^2 = 2471 W.m^-2. Sound intensities are
normally expressed in dB wrt 1 pW.m^-2. This works out at 154 dB. This
may be compared to the following table from


First off, this is not the example I include on my site. I use a velocity of
1 m/s at 50 Hz, and this is just to generate some convenient numbers which
can easily be scaled. Second, the relationship you use is valid for a
piston in a tube, but for the real world case of a piston in a baffle the
sound output is much less because the real part of the impedance seen by the
diaphragm is much less than your Z. At 50 Hz a 1 m/s velocity corresponds to
a peak displacement of 3 millimeters which is quite realistic for a woofer.
I invite any educated physicist to look at my site and decide for him or her
self if my derivation is valid. It can be seen at

http://www.silcom.com/~aludwig/Physi...on/dopdist.htm

As you pointed out, I assume the linear wave equation in this derivation,
and for very high velocities, or for propagation in a tube, the
non-linearity of air can be important. I have now analyzed the solution to
the nonlinear acoustic equations as well. That analysis is at

http://www.silcom.com/~aludwig/Physi..._acoustics.htm

Art Ludwig


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The Ghost
 
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"Daydream Electric" wrote in
:

Your abuse of the English language is disgusts me. When's the last
time you heard music performed inside a tube? Never? Exactly.

We all familiar what can happen (statistically speaking) if enough

typewriters are
put in the hands of enough monkeys.




"Your abuse of the English language IS disgusts me?" Right on, moron!
The topic of discussion involves a theoretically ideal situation of a
piston in a tube. Since you clearly have **** for brains, I don't expect
you to understand why that theoretically ideal situation is being
discussed. Nonetheless, why don't you do both of us a favor and simply not
read my posts, you stupid idiot.



  #13   Report Post  
zigoteau
 
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"Art Ludwig" wrote in message news:O__7d.3313$gk.2647@okepread01...

Hi, Art,

"zigoteau" wrote in message
om...
Bob Cain wrote in message

...

[snips]
Art must like it loud. At 40Hz, let's say the speaker diaphragm has an
rms amplitude of 1e-2 m. Its rms velocity excursion v is 2.4 m.s^-1,
and hence the power flux is Z*v^2 = 2471 W.m^-2. Sound intensities are
normally expressed in dB wrt 1 pW.m^-2. This works out at 154 dB. This
may be compared to the following table from


First off, this is not the example I include on my site. I use a velocity of
1 m/s at 50 Hz, and this is just to generate some convenient numbers which
can easily be scaled. Second, the relationship you use is valid for a
piston in a tube, but for the real world case of a piston in a baffle the
sound output is much less because the real part of the impedance seen by the
diaphragm is much less than your Z. At 50 Hz a 1 m/s velocity corresponds to
a peak displacement of 3 millimeters which is quite realistic for a woofer.
I invite any educated physicist to look at my site and decide for him or her
self if my derivation is valid. It can be seen at

http://www.silcom.com/~aludwig/Physi...on/dopdist.htm

As you pointed out, I assume the linear wave equation in this derivation,
and for very high velocities, or for propagation in a tube, the
non-linearity of air can be important. I have now analyzed the solution to
the nonlinear acoustic equations as well. That analysis is at

http://www.silcom.com/~aludwig/Physi..._acoustics.htm


I hope my response didn't sound too disrespectful, but Bob was
complaining that my formula gave distortion figures which were too
high. My point was that the values plugged in to the formula
correspond to extremely high acoustic intensities, so large distortion
is not unreasonable.

I take your point about the difference between a loudpeaker in a
conventional enclosure and a highly idealized one in a tube.

I am interested if you have managed to solve the nonlinear wave
equations. I haven't got time to digest it just now, but will look at
your website ASAP.

Cheers,

Zigoteau,
  #14   Report Post  
Vladan
 
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After so many words spent on the effect in regard to speaker, when are
you to start examining it in regard to (dynamic) microphone.

And don't forget the air. Molecules are moving. There must be some
dopler there, too.
  #16   Report Post  
Bob Cain
 
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The Ghost wrote:

Thank you for pointing out the fact that Bob Cain used your formula to
predict the Doppler IM distortion levels that he provided. Knowing that
fact certainly clears up my confusion over Bob Cains ability to provide
seemingly correct distortion numbers and his total inability to present
either a sensible and coherent verbal or mathematical explanation of how
the distiotion numbers were calculated.


Please notice the difference between what I wrote and what
Zigoteau wrote. His approach, a first order approximation
using a M-T power series, yields (using common symbols and
frames of reference):

Vp(d,t) = Vd(t - (d - Sd(t-d/c))/(c - Vd(t-d/c)))

Mine, which involves no approximation, yields:

Vp(d,t) = Vd(t - (d - Sd(t-d/c))/c)

I answered you as to precisely what my symbols mean and how
to get from that relationship to a closed form solution for
two sinusoids.

Rather than attempting an expansion of that to yield an
approximation for the distortion products, I simply generate
a band limited signal from that two sinusoid solution and
use a combination of Matlab and tools designed for audio
signal manipulation to measure what's in that signal in both
the frequency and time domain. I am interested in
quantitative answers to the question rather than in
demonstrating mathematical prowess.


Bob
--

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

A. Einstein
  #17   Report Post  
Bob Cain
 
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The Ghost wrote:


Bob Cain can't define or explain what he means because he doesn't know what
he means.


You have obviously not grasped the simplicty of what I wrote
and the clarification of it that you asked for. I doubt
you've even read it. It merely answers the question "what
is the pressure at a point in a plane wave as a function of
the motion of the particles about that point" in a simple
and direct way. One that even you could understand if you
wished to.

It's not at all complicated, Gary, and is the answer that
should have been given long ago when I first began asking
about it. I challenged you any number of times to produce
it if you knew it.

Enough of this. I've got what I came for.


Bob
--

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

A. Einstein
  #18   Report Post  
The Ghost
 
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Bob Cain wrote in
:



The Ghost wrote:


Bob Cain can't define or explain what he means because he doesn't
know what he means.


You have obviously not grasped the simplicty of what I wrote
and the clarification of it that you asked for. I doubt
you've even read it. It merely answers the question "what
is the pressure at a point in a plane wave as a function of
the motion of the particles about that point" in a simple
and direct way. One that even you could understand if you
wished to.


You are correct, I have not grasped the simplicity of what you wrote, and
the reason is because what you wrote is little more than nonsensical
gibberish. The fact of the matter is that the problem is not with my
inability to grasp what you have done, the problem is with your inability
to present what you have done in a coherent and sensible manner.


It's not at all complicated, Gary, and is the answer that
should have been given long ago when I first began asking
about it. I challenged you any number of times to produce
it if you knew it.



You have been insulting me in alt.sci.physics.acoustics for over four
years, and you find it odd that I would not give you the time of day if
your life depended on it? Get a reality check and stop confusing
capability with motivation. Art Ludwig gave you the analysis that you
requested and you spit in his face, walked away and came here begging for
someone else to provide you with an analysis that you might be able to
understand. If I were you, I wouldn't expect any help on other problems
from Art anytime soon.

Enough of this. I've got what I came for.
Bob



That you have, and apparently to hell with anyone else reading this thread
who might want to benefit from the help that you have received and from
what you have done (whatever that might be).



  #19   Report Post  
The Ghost
 
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Bob Cain wrote in
:


I answered you as to precisely what my symbols mean and how
to get from that relationship to a closed form solution for
two sinusoids.


You answered NOTHING. I asked you to define what you meant by flow
felocity and all you did was to restate your equation for so-called flow
velocity, Vf(t), which you seem to have pulled out of thin air. Where did
you get that equation? Did you derive it or did you make it up? If you
derived it, show the derivation. In other places you equate your so-called
flow velocity to pressure. Which is it. Pressure is force per unit area.
Velocity is distance per unit time. They are not the same. Your
terminology is not only unconventional, it is nonsensical.


Rather than attempting an expansion of that to yield an
approximation for the distortion products, I simply generate
a band limited signal from that two sinusoid solution and
use a combination of Matlab and tools designed for audio
signal manipulation to measure what's in that signal in both
the frequency and time domain. I am interested in
quantitative answers to the question rather than in
demonstrating mathematical prowess.
Bob



Great! We now know that the distortion numbers that you gave resulted from
both an undefined analysis as well as an undefined simulation. No doubt
you have a reason for keeping it all a secret? Perhaps that's because you
are just pretending to have an analysis and simulation, and that the
distortion numbers that you are providing are really from Art Ludwig's
analysis and the MatLab program that he sent to you. If not, I suggest
that you post your analysis and that you offer to provide your simulation
to anyone interested, as Art has done.

You have recently called me a fraud. Perhaps it is you who is the real
fraud? If not, prove it.








  #20   Report Post  
Jim Carr
 
Posts: n/a
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"The Ghost" wrote in message
. 29...

You have recently called me a fraud. Perhaps it is you who is the real
fraud? If not, prove it.


Hmmm...Celebrating in Art's shadow and insulting people does not help you
shed the overcoat of fraud. You've still offered nothing beyond putting
together an experiment that demonstrated what everyone in the discussion
agreed upon already.




  #21   Report Post  
The Ghost
 
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"Jim Carr" wrote in
newson8d.12144$mS1.11114@fed1read05:

"The Ghost" wrote in message
. 29...

You have recently called me a fraud. Perhaps it is you who is the real
fraud? If not, prove it.


Hmmm...Celebrating in Art's shadow and insulting people does not help you
shed the overcoat of fraud. Y


Screw you, asswipe. All you've ever offered is mindless, ignorant arm-
chair criticism. So, you don't even qualify for the fraud test.


You've still offered nothing beyond putting
together an experiment that demonstrated what everyone in the discussion
agreed upon already.


Quite the contrary, At the time everyone in your mindless camp was denying
the mere existence of dynamic Doppler shift. Shortly after I presented my
measurement results, the tune immediately changed. The new tune became
that Doppler distortion did exist, but not in a tube. Now that two people
have independently presented theoretical predicitions of the levels of
Doppler distiortion in a tube, the tune has once again changed.

Kiss my ass you technically-inept piece of ****. You are so full of it
that it is flowing out your ears.
  #22   Report Post  
Bob Cain
 
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The Ghost wrote:

Bob Cain wrote:
I answered you as to precisely what my symbols mean and how
to get from that relationship to a closed form solution for
two sinusoids.


You answered NOTHING. I asked you to define what you meant by flow
felocity and all you did was to restate your equation for so-called flow
velocity, Vf(t),


I fully explained my terms in a response to you and I gave a
detailed answer to what I mean by flow velocity in response
to Edward Green.

which you seem to have pulled out of thin air. Where did
you get that equation? Did you derive it or did you make it up?
If you derived it, show the derivation


If you will bother to understand my definitions of Vf, Vp
and Xp, then if

Vf(t) = Vp(t + Sp(t)/c)

defined at the origin of a cordinate system is not obvious
to you by inspection there is no hope of your understanding
anything else. I suppose I could draw some pretty pictures
for you if that is the level at which you require
explanation. Having understood that, everything else is
just straithtforward translation to move the origin of the
frame of reference to a driver an arbitrary distance d from
the point where conditions are to be described.

In that translation, there is an assumption I suppose you
could argue with but I don't think you will because it is
correct. That assumption is Vp(d,t) = Vd(t-d/c). I.E. the
motion of particls about position d is the same as that of
the driver face about its rest position at a time earlier by
d/c.

In other places you equate your so-called
flow velocity to pressure. Which is it.


I've explained this. It is the velocity at a point that is
related to the pressure at that point by the acoustic impedence.

Pressure is force per unit area.
Velocity is distance per unit time. They are not the same.


Of course not. The are related by a constant of proprionality
called characteristic impedence or more generally acoustic
impedence which is in units of Pascal.s.m^-1 and your
pretending that you didn't understand my explanation of that
in the definition of terms I gave is nothing but baiting.

Great! We now know that the distortion numbers that you gave resulted from
both an undefined analysis as well as an undefined simulation.


You are simply ignoring the explicit formula I gave you that
I used to generate a discrete time signal and pretending
ignorance of commonly understood methods of discrete time
signal analysis. That is your problem, not mine.

So that you cannot continue to pretend you haven't seen it,
here again, copied from a prior response to you with a bit
more elaboration of what I call flow velocity, is the
definition of the terms I use and the results I obtain.

Definition of terms:

Vp(t) is the velocity of a particle normally at rest at the
origin as an acoustic wave goes through it in MKS units of
meters/second.

Sp(t) is the position of that particle in meters.

Vf(t) = Vp(t+Sp(t)/c) is the flow velocity at the origin
as a function of the particle velocity Vp(t) and position
Sp(t) defined above. This relationship holds everywhere,
not just near a driver. What I call flow velocity is
the velocity of whatever particle happens to be at the
origin at any point in time.

Vd(t) is the velocity of a driver face at rest at the origin.

Sd(t) is it the position of the driver face.

Vp(d,t) = Vd(t-d/c) is the velocity of a particle normally
at rest at the position d as an acoustic wave created by a
driver at the origin goes past it. It is also in MKS units
of meter/second.

Sp(d,t) = Sd(t-d/c) is the positon of that same particle
about position d in units of the meter.

Vf(d,t) = Vd(t-(d-Sp(d,t))/c) is the velocity of particles
passing a plane at d in meter/sec.

P(d,t) = Ra*Vf(d,t) is the pressure at that plane.

Ra is the acoustic impedence of air in Pascal*sec/meter. In
a tube it is homogenious and isoptropic with an approximate
value of 429 Pascal*sec/meter.


On closed forms:

If the driver velocity function of time has a closed form
indefinite integral, the application of my expression for
Vf(d,t) to obtain a closed form for the flow velocity and
pressure should be obvious.

For example if the velocity function of the driver is

Vd(t) = Al*sin(Wl*t) + Ah*sin(Wh*t)

then

Sd(t) = -((Al/Wl)cos(Wl*t) + (Ah/Wh)cos(Wh*t))

and

Sp(d,t) = -((Al/Wl)cos(Wl*(t-d/c)) +
(Ah/Wh)cos(Wh*(t-d/c))

Vp(d,t) = Al*sin(Wl*(t-(d-Sp(d,t))/c)) +
Ah*sin(Wh*(t-(d-Sp(d,t))/c))

I haven't bothered to do the algebraic substitution of the
penultimate equation into the final one. With that, it is
an exact closed form solution for two sinusoids.

Final note; the last two formulas are what I used to
generate a discrete time signal (by, of all things,
calculating it for discrete values of time) for analysis
using standard tools with which I am familiar. There are no
secrets in doing this that even a near novice to discrete
time signal processing would fail to know.


Bob
--

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

A. Einstein
  #23   Report Post  
Bob Cain
 
Posts: n/a
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The Ghost wrote:

If I were you, I wouldn't expect any help on other problems
from Art anytime soon.


Do you speak for Art Ludwig now? Have you, at any point,
spoken _as_ Art Ludwig?


Bob
--

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

A. Einstein
  #24   Report Post  
Porky
 
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"The Ghost" wrote in message
. 29...
"Jim Carr" wrote in
newson8d.12144$mS1.11114@fed1read05:

"The Ghost" wrote in message
. 29...

You have recently called me a fraud. Perhaps it is you who is the real
fraud? If not, prove it.


Hmmm...Celebrating in Art's shadow and insulting people does not help

you
shed the overcoat of fraud. Y


Screw you, asswipe. All you've ever offered is mindless, ignorant arm-
chair criticism. So, you don't even qualify for the fraud test.


You've still offered nothing beyond putting
together an experiment that demonstrated what everyone in the discussion
agreed upon already.


Quite the contrary, At the time everyone in your mindless camp was

denying
the mere existence of dynamic Doppler shift. Shortly after I presented my
measurement results, the tune immediately changed. The new tune became
that Doppler distortion did exist, but not in a tube. Now that two people
have independently presented theoretical predicitions of the levels of
Doppler distiortion in a tube, the tune has once again changed.

Kiss my ass you technically-inept piece of ****. You are so full of it
that it is flowing out your ears.


I would suggest that you take a bottle or two of Immodium AD, your oral
diarrhea is really getting out of control again. You're losing the race, the
human race, that is...


  #25   Report Post  
Porky
 
Posts: n/a
Default


"Vladan" wrote in message
...
After so many words spent on the effect in regard to speaker, when are
you to start examining it in regard to (dynamic) microphone.

And don't forget the air. Molecules are moving. There must be some
dopler there, too.

In a microphone, the diaphragm excursion is so small that any possible
Doppler shift would be negligable, even assuming that there is Doppler shift
in a mic. BTW, if there is Doppler shift in a microphone because of
diaphragm excursion, then there must also be Doppler shift in the human ear
because of the excursion of the eardrum, and if that is true, our hearing
mechanism must have compensation built in, so, since the amount of excursion
in the mic and the eardrum are similar, if there is any Doppler shift in a
mic, it can be disregarded.




  #26   Report Post  
Jim Carr
 
Posts: n/a
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"The Ghost" wrote in message
. 29...

Screw you, asswipe. All you've ever offered is mindless, ignorant arm-
chair criticism. So, you don't even qualify for the fraud test.


I have stated from day one that I understand the concept of Doppler
distortion in a speaker as repeatedly described. I also commented that if it
happens as described, then microphones suffer from it. Instruments like
guitars and pianos must also suffer from it as well. However, because of the
short distances in the vibrations, it must not be much.

What bothered me was that I could not (and still cannot) see how a speaker
really works. Yeh, I can describe the mechanics involved, but I still don't
fully understand the exact physics where the diaphragm creates the sound
wave. Is it at the start of the throw? The end? The middle? If it's in the
middle of a long throw for a loud low frequency, how does it make the higher
frequencies at the same time?

The speaker pushes air and makes a breeze, but it also transfers energy to
individual molecules which start bouncing into each other in a wave, which
is what we ultimately perceive as sound. I accept that it works, but the
physics escape me. I can live with that.

So, when Bob suggested that there might be something more involved with
Doppler distortion due the physics described above, I thought that was a
fair question to ask. He conducted himself quite well and took the humble
step of expanding the discussion out of a.m.h-s and into groups where people
with expertise greater than his might answer the question.

It was going quite well until some home-schooled, insecure mamma's boy (that
would be you) started venting his years of frustration and feelings of
inadequacy. It's been a fun little game watching you yap like a poodle while
several of us kicked the fence. FYI, Porky and I are far from being pals.
Check the Google archives if you don't believe me.

I have stated repeatedly that I have neither the training nor the experience
to even begin to answer the questions myself. Quite frankly I couldn't care
less if it's there or not. First, I cannot hear it. Second, even if I could,
there's nothing I could do about it anyway. Of the issues in the processes
required for me to produce good music on my home computer, Doppler
distortion is at the bottom of the list.

So, there is no fraud test for me to pass or fail. Well, maybe there is.
Maybe I am lying and really do have a degree in physics, and I'm just
playing dumb. Sorta like you, I guess.

As for your blustering about threats, give it a rest. There's no way you
have the balls to say in person any of the things you've written. You might
have when you were younger, but now you're too big to hide in your mother's
apron when things get tough. You know deep down I'm right, so don't even
bother playing the "if we met in person" game. Chances are it would never
happen. If it did, we all know how you'd behave.

Kiss my ass you technically-inept piece of ****. You are so full of it
that it is flowing out your ears.


Try something new, will ya? That one is getting old.


  #27   Report Post  
Porky
 
Posts: n/a
Default


"The Ghost" wrote in message
. 6...
"Daydream Electric" wrote in
:

Your abuse of the English language is disgusts me. When's the last
time you heard music performed inside a tube? Never? Exactly.

We all familiar what can happen (statistically speaking) if enough

typewriters are
put in the hands of enough monkeys.




"Your abuse of the English language IS disgusts me?" Right on, moron!
The topic of discussion involves a theoretically ideal situation of a
piston in a tube. Since you clearly have **** for brains, I don't expect
you to understand why that theoretically ideal situation is being
discussed. Nonetheless, why don't you do both of us a favor and simply

not
read my posts, you stupid idiot.

The original discussion was about possible Doppler shift in a
loudspeaker. Theoretical ideals do not necessarily equate to real world
situations, and even if they do, the relationship is often tenuous at best.
The whole reason for using a piston in a tube is to reduce a fiendishly
complex issue to simplest terms so that a mathematical solution might be
considered (and from the length of this discussion, it's still extremely
complex).
In a real listening room with a real loudspeaker, one must not only
consider the possible phase shifts in the soundwaves that travel directly
from the speaker to the ear, but also the phase relationships of all the
soundwaves that are reflected off the walls, floor, ceiling, and any item in
the room that is capable of reflecting sound toward the ear, and then
refraction also must be taken into account. Since even the largest anechoic
chambers aren't anechoic at very low frequencies, the situation is still
hoplessly complex even there.
I would suggest that until someone builds a computer model of a real
loudspeaker reproducing real music in a real room, comes up with the
necessary algorythms and runs the simulation, no accurate, or even
approximate solution for the real world issue is going to be found.
From a practical standpoint, the question isn't whether Doppler shift
exists in a loudspeaker, the real issue is whether or not it's audible, and
if it is audible, whether or not our hearing has a mechanism to compensate
for it.


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



Porky wrote:

"Vladan" wrote in message
...

After so many words spent on the effect in regard to speaker, when are
you to start examining it in regard to (dynamic) microphone.

And don't forget the air. Molecules are moving. There must be some
dopler there, too.


In a microphone, the diaphragm excursion is so small that any possible
Doppler shift would be negligable, even assuming that there is Doppler shift
in a mic.


Nonetheless, even if the mic can measure pressure or
velocity at a point with zero excursion there is still a
non-linear relationship between the motion of a tiny
zero-mass test particle normally at rest at that point and
the pressure/velocity measured there. Remaining tubular for
the nonce, if we had a mixture of a 40 Hz and a 2 kHz wave
each at 94 dB SPL and if the motion of the test particle is
that of the signal then the pressure at its rest position
will show about 0.024% IM distortion relative to the HF
fundamental and sidebands about -75 dB down from it.

The thing that concerns me, now that I can put numbers to at
least the tube conditions and see that they can get big, is
that if conditions are such that in the very near field of a
speaker a signifigant percentage of its LF velocity is
coupled to the air then the Doppler effect can get _very_
signifigant because of the large excursions needed to offset
the poor far field coupling. My hope is that a retarded
wave cancels most of that up close so that it won't grow to
too great a signifigance.

The degree of near field LF coupling for a given far field
measure from a speaker in an enclosure is the next thing I
want to know.


Bob
--

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

A. Einstein
  #29   Report Post  
Jim Carr
 
Posts: n/a
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"Porky" wrote in message
t...
From a practical standpoint, the question isn't whether Doppler shift
exists in a loudspeaker, the real issue is whether or not it's audible,

and
if it is audible, whether or not our hearing has a mechanism to compensate
for it.


How could the ear/brain possibly compensate for it? There's no way to
analyze a sound to know if it's distorted unless you know how the sound is
supposed to be in the first place. Take the classic whistle on a train.
Unless you know the pitch is supposed to stay constant, how can you know the
sound is affected by Doppler? You can't.

As for the "real" issue the discussion always been esoteric. I don't think
anyone really thinks there is anything practical that can be done about it.


  #30   Report Post  
TonyP
 
Posts: n/a
Default


"Porky" wrote in message
...
In a microphone, the diaphragm excursion is so small that any possible
Doppler shift would be negligable, even assuming that there is Doppler

shift
in a mic. BTW, if there is Doppler shift in a microphone because of
diaphragm excursion, then there must also be Doppler shift in the human

ear
because of the excursion of the eardrum, and if that is true, our hearing
mechanism must have compensation built in, so, since the amount of

excursion
in the mic and the eardrum are similar, if there is any Doppler shift in a
mic, it can be disregarded.


What a load of crap. Whilst I agree that any doppler in a microphone would
be minute, it would not be compensated for by the ear/brain just because it
may be similar magnitude to the eardrum.

TonyP.





  #31   Report Post  
Porky
 
Posts: n/a
Default


"Bob Cain" wrote in message
...


Porky wrote:

"Vladan" wrote in message
...

After so many words spent on the effect in regard to speaker, when are
you to start examining it in regard to (dynamic) microphone.

And don't forget the air. Molecules are moving. There must be some
dopler there, too.


In a microphone, the diaphragm excursion is so small that any possible
Doppler shift would be negligable, even assuming that there is Doppler

shift
in a mic.


Nonetheless, even if the mic can measure pressure or
velocity at a point with zero excursion there is still a
non-linear relationship between the motion of a tiny
zero-mass test particle normally at rest at that point and
the pressure/velocity measured there. Remaining tubular for
the nonce, if we had a mixture of a 40 Hz and a 2 kHz wave
each at 94 dB SPL and if the motion of the test particle is
that of the signal then the pressure at its rest position
will show about 0.024% IM distortion relative to the HF
fundamental and sidebands about -75 dB down from it.


If we get into Doppler shift due to motion in air molecules, I suspect
we're getting down to "the bumble bee doesn't really fly because the math
says it can't" point.

The thing that concerns me, now that I can put numbers to at
least the tube conditions and see that they can get big, is
that if conditions are such that in the very near field of a
speaker a signifigant percentage of its LF velocity is
coupled to the air then the Doppler effect can get _very_
signifigant because of the large excursions needed to offset
the poor far field coupling. My hope is that a retarded
wave cancels most of that up close so that it won't grow to
too great a signifigance.

The degree of near field LF coupling for a given far field
measure from a speaker in an enclosure is the next thing I
want to know.


If the equations show that all that much Doppler distortion in a speaker,
why can't we hear it?
By Occam's Rasor, either our hearing mechanism has built in compensation,
so Doppler distortion doesn't matter, or the math is wrong and it needs to
be revised. That isn't to say that it doesn't happen in the
piston-in-an-infinite-tube model, it just means that the speaker/room model
is a totally different animal.



  #32   Report Post  
Porky
 
Posts: n/a
Default


"TonyP" wrote in message
u...

"Porky" wrote in message
...
In a microphone, the diaphragm excursion is so small that any possible
Doppler shift would be negligable, even assuming that there is Doppler

shift
in a mic. BTW, if there is Doppler shift in a microphone because of
diaphragm excursion, then there must also be Doppler shift in the human

ear
because of the excursion of the eardrum, and if that is true, our

hearing
mechanism must have compensation built in, so, since the amount of

excursion
in the mic and the eardrum are similar, if there is any Doppler shift in

a
mic, it can be disregarded.


What a load of crap. Whilst I agree that any doppler in a microphone would
be minute, it would not be compensated for by the ear/brain just because

it
may be similar magnitude to the eardrum.

It seems that you missed the point, which was that if there is Doppler
shift in a mic because of diaphragm motion, then there must also be Doppler
shift in the human ear
because of eardrum motion. If that is true then the hearing mechanism must
have a method of compensation for it.


  #33   Report Post  
Porky
 
Posts: n/a
Default


"Jim Carr" wrote in message
news:tVq8d.12196$mS1.2969@fed1read05...
"Porky" wrote in message
t...
From a practical standpoint, the question isn't whether Doppler shift
exists in a loudspeaker, the real issue is whether or not it's audible,

and
if it is audible, whether or not our hearing has a mechanism to

compensate
for it.


How could the ear/brain possibly compensate for it? There's no way to
analyze a sound to know if it's distorted unless you know how the sound is
supposed to be in the first place. Take the classic whistle on a train.
Unless you know the pitch is supposed to stay constant, how can you know

the
sound is affected by Doppler? You can't.


The point is that everyone hears the Doppler shift in a train whistle,
but when comparing a "live" sound to it's replica being reproduced by a very
accurate loudspeaker system, under the closest to ideal conditions possible,
there is a great deal of disagreement as to whether there is any audible
distortion produced by the speaker system, and even more as to whether any
of that is due to Doppler shift. J B Lansing, Altech and others have done
considerable experimentation with "live vs reproduced" sound, and the matter
of realism seems to get very close under the best conditions, so close that
even highly trained expert listeners have trouble telling the difference. If
it were otherwise, we wouldn't be having this discussion! :-) That argues
that either our hearing mechanism compensates for any Doppler distortion
that might be present, or that it isn't audible even if it does exist.


As for the "real" issue the discussion always been esoteric. I don't think
anyone really thinks there is anything practical that can be done about

it.

As to it being an esoteric discussion, it has certainly become one, but
the original question was "Do speakers create Doppler distortion when
producing both a HF tone and an LF tone at the same time?", and there is
nothing esoteric about that question. If audible Doppler distortion does
occur in a speaker, then there must a number of ways to minimize it, so this
discussion does have some possible practical application, assuming that
anyone can prove that we actually hear Doppler distrotion in a speaker when
listening to music.


  #34   Report Post  
zigoteau
 
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Default

Bob Cain wrote in message ...

Hi, Bob,

Just a minor correction.

Please notice the difference between what I wrote and what
Zigoteau wrote. His approach, a first order approximation
using a M-T power series, yields (using common symbols and
frames of reference):

Vp(d,t) = Vd(t - (d - Sd(t-d/c))/(c - Vd(t-d/c)))

Mine, which involves no approximation, yields:

Vp(d,t) = Vd(t - (d - Sd(t-d/c))/c)


I am sorry, Bob, but the second equation does involve an approximation.

Cheers,

Zigoteau.
  #35   Report Post  
TonyP
 
Posts: n/a
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"Porky" wrote in message
...
It seems that you missed the point, which was that if there is Doppler
shift in a mic because of diaphragm motion, then there must also be

Doppler
shift in the human ear
because of eardrum motion. If that is true then the hearing mechanism must
have a method of compensation for it.


It seems you've missed my point. The brain "compensates" for the auditory
system itself, because you have NO other point of reference.

TonyP.




  #36   Report Post  
Porky
 
Posts: n/a
Default


"TonyP" wrote in message
u...

"Porky" wrote in message
...
It seems that you missed the point, which was that if there is Doppler
shift in a mic because of diaphragm motion, then there must also be

Doppler
shift in the human ear
because of eardrum motion. If that is true then the hearing mechanism

must
have a method of compensation for it.


It seems you've missed my point. The brain "compensates" for the auditory
system itself, because you have NO other point of reference.


Sure you do, ever hear of bone conduction? That bypasses the eardrum
totally. There is also considerable evidence that we can "hear" the audio in
audio modulated RF at certain frequencies, which would seem to bypass the
physical hearing mechanism entirely. However, my point was that if one can
tell the difference between a "live" sound and the same sound reproduced on
a very high quality sound system, then either there is no audible distortion
present, or our ears have a mechanism that compensated for whatever
distortion is present, including any Doppler distortion.


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



Porky wrote:


If we get into Doppler shift due to motion in air molecules, I suspect
we're getting down to "the bumble bee doesn't really fly because the math
says it can't" point.


Huh? That's exactly what Doppler distortion is due to.
There is a mild non-linear relationship everywhere in a
soundfield between particle velocity about a point and the
fluid velocity at that point. That was my epiphany. Not
much as epiphanies go but, hey, they get fewer and fewer
every year. :-)

If the equations show that all that much Doppler distortion in a speaker,
why can't we hear it?


Who says we can't? It's sorta hard to get rid of to do an
ABX test on.

By Occam's Rasor, either our hearing mechanism has built in compensation,
so Doppler distortion doesn't matter, or the math is wrong and it needs to
be revised. That isn't to say that it doesn't happen in the
piston-in-an-infinite-tube model, it just means that the speaker/room model
is a totally different animal.


Sure it is but it should get signifigantly worse with a
driver in an enclosure rather than in a tube because of the
large excursions demanded at the low frequencies to couple
anything from an enclosed speaker to a room. You can get
real high SPL low frequencies in a tube without much
excursion, which is what causes it, but not so with an
enclosed speaker in a room. You have to push a whole lot of
LF air up close to get what's in the signal to reach you at
any distance.

Dunno what you mean by built in compensation nor why there
would be anything like that. It's not the kind of thing
evolution would have devoted much energy to. There weren't
many broadband sound sources to work with even if it had
been deemed important for some reason.


Bob
--

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

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



Porky wrote:

It seems that you missed the point, which was that if there is Doppler
shift in a mic because of diaphragm motion, then there must also be Doppler
shift in the human ear
because of eardrum motion. If that is true then the hearing mechanism must
have a method of compensation for it.


There is none of _any_ signifigance with either. Excursions
in either case are more than a few orders of magnitude
away from signifigance.


Bob
--

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

A. Einstein
  #39   Report Post  
TonyP
 
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"Porky" wrote in message
...

"TonyP" wrote in message
It seems you've missed my point. The brain "compensates" for the

auditory
system itself, because you have NO other point of reference.


Sure you do, ever hear of bone conduction? That bypasses the eardrum
totally.


Not at all. It is concurrent with the eardrum. Audioligists must use large
masking signals just to get some figure for bone conduction, but it is less
than via the eardrum. I know of no way to seperate the two for comparison
purposes, do you? (The worlds audiologists await your reply :-)


There is also considerable evidence that we can "hear" the audio in
audio modulated RF at certain frequencies, which would seem to bypass the
physical hearing mechanism entirely.


Some level of diode detection has been demonstated in some cases, usually
connected with metal fillings. This couples audio signals via bone
conduction.

However, my point was that if one can
tell the difference between a "live" sound and the same sound reproduced

on
a very high quality sound system, then either there is no audible

distortion
present, or our ears have a mechanism that compensated for whatever
distortion is present, including any Doppler distortion.


???

TonyP.


  #40   Report Post  
Art Ludwig
 
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[snips]
"zigoteau" wrote in message
om...
Bob Cain wrote in message

...
Mine, which involves no approximation, yields:

Vp(d,t) = Vd(t - (d - Sd(t-d/c))/c)


I am sorry, Bob, but the second equation does involve an approximation.

Zigoteau.


I agree completely, and I would like to point out that if you evaluate the
above equation at d=0 you get an result identical to my equation (8) in my
analysis at
http://www.silcom.com/~aludwig/Physi...on/dopdist.htm, which has
been posted for quite a while now. Rod Elliot presented the same equation
before I did. I present this equation as an approximate analysis, but show
that it is quite accurate. I also show that this equation is completely
equivalent to the good old fashioned "Doppler distortion" that folks have
been using for years. Just follow the link under "interesting issues" for a
proof of this statement. As far as I am aware you are not claiming your
analysis is novel, Zigoteau, so I don't mean this as a personal criticism.
I just want to set the record straight for people not familiar with the
history.
Art Ludwig


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