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Doppler Distoriton?

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Anonymous
August 6, 2004 2:19:23 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

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?

More about : doppler distoriton

Anonymous
August 6, 2004 2:19:24 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

Arny Krueger wrote:

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

Many thanks, Arny. Experimentalist that you are, I had a
feeling you were off doing that. :-)

My question is, wouldn't the kind of distortion claimed as
"Doppler" distortion, which is claimed to be FM, have a
continuous harmonic structure around that 4k peak rather
than the discrete one you are seeing?

Is there any way you can think of to exactly simulate an FM
modulation of 50 Hz on top of 4 kHz to compare?


Bob
--

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

A. Einstein
Anonymous
August 6, 2004 9:33:46 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

"Bob Cain" <arcane@arcanemethods.com> wrote in message
news:ceuvcj01nrh@enews3.newsguy.com
> Arny Krueger wrote:
>
>> While I've got this set up, any other data that anyone would find
>> interesting?
>
> Many thanks, Arny. Experimentalist that you are, I had a
> feeling you were off doing that. :-)

> My question is, wouldn't the kind of distortion claimed as
> "Doppler" distortion, which is claimed to be FM, have a
> continuous harmonic structure around that 4k peak rather
> than the discrete one you are seeing?

No, because the modulating frequency is a pure tone/

> Is there any way you can think of to exactly simulate an FM
> modulation of 50 Hz on top of 4 kHz to compare?

Sure 2 independent ways. First generate a FM-modulated tone in Audition 1.x
/CE.2.x

These parameters will get you close:

Base frequency: 4000 Hz
Modulate by 1 Hz
Modulation frequency 50 Hz
dB volume -15 dB

FFT analysis with 65536 points, Blackman-Harris windowing

Then, to zoom in on the frequency range around 4 KHz with enough resolution,
right click and drag around 4 KHz on the frequency scale.

The web page at http://www.pcavtech.com/techtalk/doppler/ has been updated
to include the results of this simulation, and the one below:

You can also run the FM modulation model at
http://contact.tm.agilent.com/Agilent/tmo/an-150-1/clas...

with the following parameters:

Wc = 5.0
Wm = 0.5
m= 1.02
Related resources
Anonymous
August 6, 2004 10:49:53 AM

Archived from groups: rec.audio.tech (More info?)

On Thu, 5 Aug 2004 22:19:23 -0400, "Arny Krueger" <arnyk@hotpop.com>
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?
>

Well, speakers generally are nonlinear, so what you are seeing here is
intermod. Doppler distortion in speakers is supposedly a "built-in"
effect - nothing to do with non-liearity - that is caused by the same
cone reproducing two frequencies simultaneously. The argument goes
that if a speaker is reproducing a 1kHz tone, but is simultaneously
moving back and forth at 50Hz, the 1kHz tone must be modulated by the
Doppler effect. Of course, if you do the maths of superposition, this
doesn't happen - the tones coexist perfectly without any doppler.

So this is simple, stright-forward intermodulation between the two
tones.

d

Pearce Consulting
http://www.pearce.uk.com
Anonymous
August 6, 2004 11:30:49 AM

Archived from groups: rec.audio.tech (More info?)

"Don Pearce" <donald@pearce.uk.com> wrote in message
news:gv66h0loblg05pacohrql6uti3frveipn9@4ax.com

> Well, speakers generally are nonlinear, so what you are seeing here is
> intermod.

Really?

> Doppler distortion in speakers is supposedly a "built-in"
> effect - nothing to do with non-linearity - that is caused by the same
> cone reproducing two frequencies simultaneously.

Agreed.

>The argument goes
> that if a speaker is reproducing a 1kHz tone, but is simultaneously
> moving back and forth at 50Hz, the 1kHz tone must be modulated by the
> Doppler effect. Of course, if you do the maths of superposition, this
> doesn't happen - the tones coexist perfectly without any doppler.

Tell that to the AES! ;-)

> So this is simple, straight-forward intermodulation between the two
> tones.

Two reasons I think this really is predominantly FM:

(1) The sideband structure looks a lot more like FM than AM, per the
simulations I added to http://www.pcavtech.com/techtalk/doppler/ .

(2) I redid the experiment using high frequency tones at 1 KHz and 4 KHz.

All other things being equal, AM is frequency-independent. FM is
frequency-dependent. Since the stimulus for the IM is the 50 Hz tone, the
stimulus for 50 Hz sidebands for both the 1 KHz tone and the 4 KHz tone is
the same.

I did a simulation in Audition of pure FM, and the sidebands on the 1 KHz
tone were about 12 dB lower than the ones on the 4 KHz tone, which exactly
follows this theory.

However, speakers don't have just one kind of distortion.

I have added the results of triple tone test results to
http://www.pcavtech.com/techtalk/doppler/ .

Comparing the amplitudes of the first two sidebands around 1 KHz and 4 KHz,
I find that there is an approximate difference of 6 dB. The sidebands around
the 4 KHz average about 6 dB higher than those around the 1 KHz tone. If
this was pure FM distortion, I would expect a 12 dB difference. I conclude
that there is a mixture of AM and FM.
Anonymous
August 6, 2004 11:45:21 AM

Archived from groups: rec.audio.tech (More info?)

"Arny Krueger" <arnyk@hotpop.com> wrote in message
news:Q6ednUF7Gthb9o7cRVn-qA@comcast.com

Correction:

> Comparing the amplitudes of the first two sidebands around 1 KHz and
> 4 KHz, I find that there is an approximate difference of 2 dB in levels
relative to the carriers. The
> sidebands around the 4 KHz average about 2 dB higher than those
> around the 1 KHz tone. If this was pure FM distortion, I would expect
> a 12 dB difference. I conclude that there is a mixture of AM and FM,
predominantly AM.
Anonymous
August 6, 2004 1:34:38 PM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

"Arny Krueger" <arnyk@hotpop.com> wrote in message
news:Cq2dnZqzYY_FzY7cRVn-sA@comcast.com...
> These parameters will get you close:
>
> Base frequency: 4000 Hz
> Modulate by 1 Hz
> Modulation frequency 50 Hz
> dB volume -15 dB
>
> FFT analysis with 65536 points, Blackman-Harris windowing

You know, I don't really mind you using my original work, but you could have
at least asked first. My band used to open with the above tone. The college
kids loved it.
Anonymous
August 6, 2004 4:06:55 PM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

"Arny Krueger" <arnyk@hotpop.com> writes:

> "Bob Cain" <arcane@arcanemethods.com> wrote in message
> news:ceuvcj01nrh@enews3.newsguy.com
> > Arny Krueger wrote:
> >
> >> While I've got this set up, any other data that anyone would find
> >> interesting?
> >
> > Many thanks, Arny. Experimentalist that you are, I had a
> > feeling you were off doing that. :-)
>
> > My question is, wouldn't the kind of distortion claimed as
> > "Doppler" distortion, which is claimed to be FM, have a
> > continuous harmonic structure around that 4k peak rather
> > than the discrete one you are seeing?
>
> No, because the modulating frequency is a pure tone/

That's right. Specifically, you will have sidebands at
integer multiples of the modulating frequency, thus the
spectrum will be discrete. The magnitude of the nth sideband
is given by a Bessel function of the first kind, J_n(B), where
B is the amplitude of the modulating signal.

[From Mischa Schwartz's "Information, Transmission, Modulation,
and Noise," 4th ed.]
--
Randy Yates
Sony Ericsson Mobile Communications
Research Triangle Park, NC, USA
randy.yates@sonyericsson.com, 919-472-1124
Anonymous
August 6, 2004 4:35:06 PM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

"Jim Carr" <jim@azwebpages.com> wrote in message
news:FnOQc.3226$yh.1571@fed1read05
> "Arny Krueger" <arnyk@hotpop.com> wrote in message
> news:Cq2dnZqzYY_FzY7cRVn-sA@comcast.com...

>> These parameters will get you close:
>>
>> Base frequency: 4000 Hz
>> Modulate by 1 Hz
>> Modulation frequency 50 Hz
>> dB volume -15 dB
>>
>> FFT analysis with 65536 points, Blackman-Harris windowing
>
> You know, I don't really mind you using my original work, but you
> could have at least asked first. My band used to open with the above
> tone. The college kids loved it.

LOL!
Anonymous
August 6, 2004 4:37:30 PM

Archived from groups: rec.audio.tech (More info?)

On Fri, 6 Aug 2004 07:30:49 -0400, "Arny Krueger" <arnyk@hotpop.com>
wrote:

>"Don Pearce" <donald@pearce.uk.com> wrote in message
>news:gv66h0loblg05pacohrql6uti3frveipn9@4ax.com
>
>> Well, speakers generally are nonlinear, so what you are seeing here is
>> intermod.
>
>Really?
>
>> Doppler distortion in speakers is supposedly a "built-in"
>> effect - nothing to do with non-linearity - that is caused by the same
>> cone reproducing two frequencies simultaneously.
>
>Agreed.
>
>>The argument goes
>> that if a speaker is reproducing a 1kHz tone, but is simultaneously
>> moving back and forth at 50Hz, the 1kHz tone must be modulated by the
>> Doppler effect. Of course, if you do the maths of superposition, this
>> doesn't happen - the tones coexist perfectly without any doppler.
>
>Tell that to the AES! ;-)
>
A great deal of BS has emanated from that organ!

>> So this is simple, straight-forward intermodulation between the two
>> tones.
>
>Two reasons I think this really is predominantly FM:
>
>(1) The sideband structure looks a lot more like FM than AM, per the
>simulations I added to http://www.pcavtech.com/techtalk/doppler/ .
>
>(2) I redid the experiment using high frequency tones at 1 KHz and 4 KHz.
>
>All other things being equal, AM is frequency-independent. FM is
>frequency-dependent. Since the stimulus for the IM is the 50 Hz tone, the
>stimulus for 50 Hz sidebands for both the 1 KHz tone and the 4 KHz tone is
>the same.
>
>I did a simulation in Audition of pure FM, and the sidebands on the 1 KHz
>tone were about 12 dB lower than the ones on the 4 KHz tone, which exactly
>follows this theory.
>
>However, speakers don't have just one kind of distortion.
>
>I have added the results of triple tone test results to
>http://www.pcavtech.com/techtalk/doppler/ .
>
>Comparing the amplitudes of the first two sidebands around 1 KHz and 4 KHz,
>I find that there is an approximate difference of 6 dB. The sidebands around
>the 4 KHz average about 6 dB higher than those around the 1 KHz tone. If
>this was pure FM distortion, I would expect a 12 dB difference. I conclude
>that there is a mixture of AM and FM.
>
>
>

The only way to verify this is to look at the phase as well as the
amplitude of the sidebands.

d

Pearce Consulting
http://www.pearce.uk.com
Anonymous
August 6, 2004 4:37:31 PM

Archived from groups: rec.audio.tech (More info?)

"Don Pearce" <donald@pearce.uk.com> wrote in message
news:i7r6h05nig0locvnk9e82n904oo9jf2pjv@4ax.com
> On Fri, 6 Aug 2004 07:30:49 -0400, "Arny Krueger" <arnyk@hotpop.com>
> wrote:
>
>> "Don Pearce" <donald@pearce.uk.com> wrote in message
>> news:gv66h0loblg05pacohrql6uti3frveipn9@4ax.com
>>
>>> Well, speakers generally are nonlinear, so what you are seeing here
>>> is intermod.
>>
>> Really?
>>
>>> Doppler distortion in speakers is supposedly a "built-in"
>>> effect - nothing to do with non-linearity - that is caused by the
>>> same cone reproducing two frequencies simultaneously.
>>
>> Agreed.
>>
>>> The argument goes
>>> that if a speaker is reproducing a 1kHz tone, but is simultaneously
>>> moving back and forth at 50Hz, the 1kHz tone must be modulated by
>>> the Doppler effect. Of course, if you do the maths of
>>> superposition, this doesn't happen - the tones coexist perfectly
>>> without any doppler.
>>
>> Tell that to the AES! ;-)
>>
> A great deal of BS has emanated from that organ!
>
>>> So this is simple, straight-forward intermodulation between the two
>>> tones.
>>
>> Two reasons I think this really is predominantly FM:
>>
>> (1) The sideband structure looks a lot more like FM than AM, per the
>> simulations I added to http://www.pcavtech.com/techtalk/doppler/ .
>>
>> (2) I redid the experiment using high frequency tones at 1 KHz and 4
>> KHz.
>>
>> All other things being equal, AM is frequency-independent. FM is
>> frequency-dependent. Since the stimulus for the IM is the 50 Hz
>> tone, the stimulus for 50 Hz sidebands for both the 1 KHz tone and
>> the 4 KHz tone is the same.
>>
>> I did a simulation in Audition of pure FM, and the sidebands on the
>> 1 KHz tone were about 12 dB lower than the ones on the 4 KHz tone,
>> which exactly follows this theory.
>>
>> However, speakers don't have just one kind of distortion.
>>
>> I have added the results of triple tone test results to
>> http://www.pcavtech.com/techtalk/doppler/ .
>>
>> Comparing the amplitudes of the first two sidebands around 1 KHz and
>> 4 KHz, I find that there is an approximate difference of 6 dB. The
>> sidebands around the 4 KHz average about 6 dB higher than those
>> around the 1 KHz tone. If this was pure FM distortion, I would
>> expect a 12 dB difference. I conclude that there is a mixture of AM
>> and FM.

> The only way to verify this is to look at the phase as well as the
> amplitude of the sidebands.

That's one way, but it's a very hard row for me to hoe.

So, you decline to believe that the relative amplitudes of the sidebands are
different and relevant, as the frequency has increased?
Anonymous
August 6, 2004 4:37:32 PM

Archived from groups: rec.audio.tech (More info?)

"Arny Krueger" <arnyk@hotpop.com> wrote in message
news:taudnYpxQ9008o7cRVn-og@comcast.com
>
>> The only way to verify this is to look at the phase as well as the
>> amplitude of the sidebands.
>
> That's one way, but it's a very hard row for me to hoe.
>
> So, you decline to believe that the relative amplitudes of the
> sidebands are different and relevant, as the frequency has increased?

BTW, I added some simulations of the triple tone test, showing the differing
results for AM and FM distortion.

The simulations have a darker blue-green border around them, while the lab
measurements have a lighter blue border.

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

Between the differences in the sideband structure and the amplitudes of the
first two sidebands, it seems like this triple-tone test might have some
general application. I'm thinking about jitter testing...
Anonymous
August 6, 2004 7:08:21 PM

Archived from groups: rec.audio.tech (More info?)

On Fri, 6 Aug 2004 07:47:24 -0400, "Arny Krueger" <arnyk@hotpop.com>
wrote:

>> The only way to verify this is to look at the phase as well as the
>> amplitude of the sidebands.
>
>That's one way, but it's a very hard row for me to hoe.
>
>So, you decline to believe that the relative amplitudes of the sidebands are
>different and relevant, as the frequency has increased?
>

No, not at all. But I am not convinced that with the complex
interactions of a speaker you can reach your conclusion as simply as
you have. Non-linearities of various orders can cause a multiplication
function which results in phase modulation. But to put this down to
Doppler effect is a leap too far for me.

d

Pearce Consulting
http://www.pearce.uk.com
Anonymous
August 6, 2004 7:08:22 PM

Archived from groups: rec.audio.tech (More info?)

"Don Pearce" <donald@pearce.uk.com> wrote in message
news:1347h0demfl0c5a8kjvaperbjoabec215t@4ax.com
> On Fri, 6 Aug 2004 07:47:24 -0400, "Arny Krueger" <arnyk@hotpop.com>
> wrote:
>
>>> The only way to verify this is to look at the phase as well as the
>>> amplitude of the sidebands.
>>
>> That's one way, but it's a very hard row for me to hoe.
>>
>> So, you decline to believe that the relative amplitudes of the
>> sidebands are different and relevant, as the frequency has increased?
>>
>
> No, not at all. But I am not convinced that with the complex
> interactions of a speaker you can reach your conclusion as simply as
> you have. Non-linearities of various orders can cause a multiplication
> function which results in phase modulation. But to put this down to
> Doppler effect is a leap too far for me.

I agree that the actual acoustical measurements may or may not show a
Doppler effect. At best the Doppler distortion is relatively small in the
face of the massive AM effects.

If I turn the volume up, the AM effects seem to get stronger, both overall
and proportionately. And, this is a relatively linear driver being driven
over a wider frequency range than it would be used in a good design.

If I got anything worthwhile out of this, it is the concept of using 3 tones
to separate AM distortion from FM distortion. But you still need an
underlying clear instance of FM distortion to make it worth the trouble. I
suspect that a lot of the purported jitter measurements we've seen are
actually pretty suspect because the common measurements confuse AM and FM
distortion.
Anonymous
August 6, 2004 7:31:35 PM

Archived from groups: rec.audio.tech (More info?)

On Fri, 6 Aug 2004 10:18:35 -0400, "Arny Krueger" <arnyk@hotpop.com>
wrote:

>"Don Pearce" <donald@pearce.uk.com> wrote in message
>news:1347h0demfl0c5a8kjvaperbjoabec215t@4ax.com
>> On Fri, 6 Aug 2004 07:47:24 -0400, "Arny Krueger" <arnyk@hotpop.com>
>> wrote:
>>
>>>> The only way to verify this is to look at the phase as well as the
>>>> amplitude of the sidebands.
>>>
>>> That's one way, but it's a very hard row for me to hoe.
>>>
>>> So, you decline to believe that the relative amplitudes of the
>>> sidebands are different and relevant, as the frequency has increased?
>>>
>>
>> No, not at all. But I am not convinced that with the complex
>> interactions of a speaker you can reach your conclusion as simply as
>> you have. Non-linearities of various orders can cause a multiplication
>> function which results in phase modulation. But to put this down to
>> Doppler effect is a leap too far for me.
>
>I agree that the actual acoustical measurements may or may not show a
>Doppler effect. At best the Doppler distortion is relatively small in the
>face of the massive AM effects.
>
>If I turn the volume up, the AM effects seem to get stronger, both overall
>and proportionately. And, this is a relatively linear driver being driven
>over a wider frequency range than it would be used in a good design.
>
>If I got anything worthwhile out of this, it is the concept of using 3 tones
>to separate AM distortion from FM distortion. But you still need an
>underlying clear instance of FM distortion to make it worth the trouble. I
>suspect that a lot of the purported jitter measurements we've seen are
>actually pretty suspect because the common measurements confuse AM and FM
>distortion.
>

Certainly in terms of spectrum, narrowband FM is virtually
indistinguishable from AM unless you can get at the relative phase of
the sidebands.

But as for Doppler distortion. Do the sums, assuming a perfectly
linear driver (which should still show the phenomenon if it exists,
since it needs no non-linearity). You will find that the sum of the
tones exactly matches what the trajectory of the cone should be to
prevent such distortion.

d

Pearce Consulting
http://www.pearce.uk.com
Anonymous
August 6, 2004 7:31:36 PM

Archived from groups: rec.audio.tech (More info?)

"Don Pearce" <donald@pearce.uk.com> wrote in message
news:vb57h0lm7dbc6kg3ommtu10b308apcsjts@4ax.com
> On Fri, 6 Aug 2004 10:18:35 -0400, "Arny Krueger" <arnyk@hotpop.com>
> wrote:
>
>> "Don Pearce" <donald@pearce.uk.com> wrote in message
>> news:1347h0demfl0c5a8kjvaperbjoabec215t@4ax.com
>>> On Fri, 6 Aug 2004 07:47:24 -0400, "Arny Krueger" <arnyk@hotpop.com>
>>> wrote:
>>>
>>>>> The only way to verify this is to look at the phase as well as the
>>>>> amplitude of the sidebands.
>>>>
>>>> That's one way, but it's a very hard row for me to hoe.
>>>>
>>>> So, you decline to believe that the relative amplitudes of the
>>>> sidebands are different and relevant, as the frequency has
>>>> increased?
>>>>
>>>
>>> No, not at all. But I am not convinced that with the complex
>>> interactions of a speaker you can reach your conclusion as simply as
>>> you have. Non-linearities of various orders can cause a
>>> multiplication function which results in phase modulation. But to
>>> put this down to Doppler effect is a leap too far for me.
>>
>> I agree that the actual acoustical measurements may or may not show a
>> Doppler effect. At best the Doppler distortion is relatively small
>> in the face of the massive AM effects.
>>
>> If I turn the volume up, the AM effects seem to get stronger, both
>> overall and proportionately. And, this is a relatively linear driver
>> being driven over a wider frequency range than it would be used in a
>> good design.
>>
>> If I got anything worthwhile out of this, it is the concept of using
>> 3 tones to separate AM distortion from FM distortion. But you still
>> need an underlying clear instance of FM distortion to make it worth
>> the trouble. I suspect that a lot of the purported jitter
>> measurements we've seen are actually pretty suspect because the
>> common measurements confuse AM and FM distortion.
>>
>
> Certainly in terms of spectrum, narrowband FM is virtually
> indistinguishable from AM unless you can get at the relative phase of
> the sidebands.

Measuring the phase of acoustical signals, and signals in general, can be a
vale of tears. I've played this game many times, and while I've had some
success, I feel like I earned it! ;-)

It appears that one can differentiate AM and FM based on the amplitudes of
the sidebands for carriers that have significantly different base
frequencies.

A given AM process will produce sidebands with the same amplitudes over a
wide variety of carrier frequencies. FM processes are very dependent on the
frequency of the carrier.

For a given rate of change in timing, the higher frequency carrier will show
a larger shift in frequency. This increases the Modulation Index, which is
the quotient of the maximum deviation/divided by the modulating frequency.
The higher modulation index increases the size and number of sidebands.
Therefore, higher frequency carriers will produce more sidebands and
sidebands that have a larger amplitude.

My Audition/CoolEdit simulations show this quite clearly.

> But as for Doppler distortion. Do the sums, assuming a perfectly
> linear driver (which should still show the phenomenon if it exists,
> since it needs no non-linearity).

That would be a more complex theoretical exercise.

>You will find that the sum of the
> tones exactly matches what the trajectory of the cone should be to
> prevent such distortion.

I don't see it. And as I've now pointed out several times, the JAES doesn't
seem to see it, either. IOW, there are a goodly number of refereed papers
that give abundant positive evidence that it does exist. I see that train
coming towards me, and I see that cone coming towards me!
Anonymous
August 7, 2004 5:54:05 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

On Thu, 5 Aug 2004 22:19:23 -0400, "Arny Krueger" <arnyk@hotpop.com>
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?

Knowing that the amplitude of the sidebands should be proportional
(or at least some type of direct relation) to the amplitude of the 50
Hz signal. lower it by 10 or 20dB, and let's see how the sidebands
drop, hoping they don't fall into the noise. Regardless, you already
have me convinced you're measuring doppler distortion.
-----
http://mindspring.com/~benbradley
Anonymous
August 7, 2004 10:15:07 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

In article <q9OdneD0KqQXd4_cRVn-jQ@comcast.com>,
"Arny Krueger" <arnyk@hotpop.com> 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?

Paul Klipsch used to do a doppler distortion comparison between some
arbitrary 12" direct radiator and one of his big horns. Even when the
difference in amplitudes was 10dB (the K-Horn being louder), the
difference in sideband amplitude was significant (the horn being a much
lower percentage). He was careful to keep the higher tone low enough in
frequency so that both tones were emitted by the woofer.

There was an obvious audible difference between the two, with the direct
radiator sounding "rougher", even when 10dB lower in amplitude.

As I remember, he wanted to find some way to determine the relative AM
to FM contributions, but couldn't figure out how to do it with the
technology of the times (late '60s to early '70's, AFAIR).

I think he published at least one paper on it.

Isaac
Anonymous
August 7, 2004 11:02:36 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

"Isaac Wingfield" <isw@witzend.com> wrote in message
news:isw-68029A.23150806082004@netnews.comcast.net


> Paul Klipsch used to do a doppler distortion comparison between some
> arbitrary 12" direct radiator and one of his big horns.

Modulation Distortion in Loudspeakers
Author(s): Klipsch, Paul W.
Publication: Preprint 562; Convention 34; April 1968

Abstract: When comparing 2 loudspeakers, one with direct radiator bass
system and the other with horn loaded bass, a subjective judgment was that
the one with the horn loaded bass is ·cleaner.· Both speakers were by the
same manufacturer. Various tests were applied and by process of elimination
it appears the difference in listening quality is due to frequency
modulation distortion. Beers and Belar analyzed this form of distortion in
1943, but since that time the effect has been almost ignored. Now, with
amplifiers and source material reaching new lows in distortion, differences
between good loudspeakers begin to appear significant. The mathematical
analysis has been reviewed, and measurements have been made using a spectrum
analyzer. These have been correlated with listening tests by preparing tapes
of oscillator tones and music with and without a low frequency source to
produce frequency modulation distortion. The spectrum analyses corroborate
the mathematical analysis and the listening tests offer a subjective
evaluation. The conclusion is that frequency modulation in loudspeakers
accounts in large measure for the masking of ·inner voices.· As Beers and
Belar put it, ·The sound is just not clean.· Reduction of diaphragm
excursions at lower frequencies reduces FM distortion. Horn loading,
properly applied, offers the greatest reduction, while simultaneously
improving bass power output capability. Tentatively it is wondered if FM
distortion in loudspeakers may be the last frontier in loudspeaker
improvement.


> Even when the
> difference in amplitudes was 10dB (the K-Horn being louder), the
> difference in sideband amplitude was significant (the horn being a
> much lower percentage). He was careful to keep the higher tone low
> enough in frequency so that both tones were emitted by the woofer.

As things evolve, this makes it harder to prove that the modulation
distortion at hand is FM, mot AM

> There was an obvious audible difference between the two, with the
> direct radiator sounding "rougher", even when 10dB lower in amplitude.

Direct radiator drivers have improved considerably since then. For example,
the spec Xmax was introduced some decades later.

> As I remember, he wanted to find some way to determine the relative AM
> to FM contributions, but couldn't figure out how to do it with the
> technology of the times (late '60s to early '70's, AFAIR).

The paper I cited was published in 1968. Ironically, the FFT-based
measurement technology we enjoy today was just becoming well-known at that
time.

I think that the triple tone test and modern spectrum analyzer technology
provides valuable insights into this area. I think that I've established
that when there are two upper-frequency probe tones, FM distortion will
produce sidebands with a higher amplitude with the highest frequency tone,
all other things being equal. This finding can be, and probably should be
applied to investigations relating to both Doppler distortion and jitter.
Anonymous
August 7, 2004 3:09:51 PM

Archived from groups: rec.audio.tech (More info?)

On Fri, 6 Aug 2004 10:54:46 -0400, "Arny Krueger" <arnyk@hotpop.com> wrote:

>> But as for Doppler distortion. Do the sums, assuming a perfectly
>> linear driver (which should still show the phenomenon if it exists,
>> since it needs no non-linearity).

>That would be a more complex theoretical exercise.

>>You will find that the sum of the
>> tones exactly matches what the trajectory of the cone should be to
>> prevent such distortion.

>I don't see it. And as I've now pointed out several times, the JAES doesn't
>seem to see it, either. IOW, there are a goodly number of refereed papers
>that give abundant positive evidence that it does exist. I see that train
>coming towards me, and I see that cone coming towards me!

FWIW, a friend of mine (a pretty sharp physics dude) claims he
became interested in this topic around the time Klipsch was
talking about it, and worked it out, and came to the same conclusion
that Don Pearce does.

He tried to explain it to my dumb brain by saying that the sound
source is not the cone, but an area out in front of the cone, which
is not moving. Doesn't make sense to me of course :) 

--
Steve Maki
Anonymous
August 7, 2004 4:13:22 PM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

Arny Krueger wrote:


> As things evolve, this makes it harder to prove that the modulation
> distortion at hand is FM, mot AM

Right. The horn loaded system has a smaller excursion so
that AM would be reduced to a similar, and perhaps greater
degree.



Bob
--

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

A. Einstein
Anonymous
August 7, 2004 4:29:08 PM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

Would you technical guys agree that the two tone interaction
we are hypothesizing can be approximated to low order by:

l*sin((wh+wld*sin(wl*t))*t) + h*sin((wl+whd*sin(wh*t))*t)

with h and l related to the amplitudes of the HF and LF
components respectively, wh the frequency of the HF tone, wl
the frequency of the LF tone and wld and whd a measure of
the "depth" in Hz of the cross modulations that are related
to the relative strength of the two tones?

If so, I'd appreciate input on what might be a reasonable
set of parameters.


Bob
--

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

A. Einstein
Anonymous
August 7, 2004 5:08:08 PM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

"Ben Bradley" <ben_nospam_bradley@mindspring.com> wrote in message
news:0er8h0dhdavvgdutsf4pn3mvfrmecouup2@4ax.com
>
> Knowing that the amplitude of the sidebands should be proportional
> (or at least some type of direct relation) to the amplitude of the 50
> Hz signal. lower it by 10 or 20dB, and let's see how the sidebands
> drop, hoping they don't fall into the noise.

OK, the data from 10 dB lower input is the second set of triple-tone
experimental data (light yellow background) at
http://www.pcavtech.com/techtalk/doppler/

>Regardless, you already
> have me convinced you're measuring Doppler distortion.

Well, a mixture. I'm convinced that AM distortion usually dominates, but
that Doppler is also always there, if its large enough to find.
Anonymous
August 7, 2004 5:08:09 PM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

Arny Krueger wrote:

> Well, a mixture. I'm convinced that AM distortion usually dominates, but
> that Doppler is also always there, if its large enough to find.

Arny, are you aware of any mathematical model of the typical
loudspeaker non-linearity? Just the transducer part, not
Doppler.


Bob
--

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

A. Einstein
Anonymous
August 7, 2004 10:11:34 PM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

"Bob Cain" <arcane@arcanemethods.com> wrote in message
news:cf38uu1m33@enews4.newsguy.com
> Arny Krueger wrote:
>
>> Well, a mixture. I'm convinced that AM distortion usually dominates,
>> but that Doppler is also always there, if its large enough to find.
>
> Arny, are you aware of any mathematical model of the typical
> loudspeaker non-linearity? Just the transducer part, not
> Doppler.

http://www.gedlee.com/Audio_trans.htm
Anonymous
August 7, 2004 10:11:35 PM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

Arny Krueger wrote:

>>
>>Arny, are you aware of any mathematical model of the typical
>>loudspeaker non-linearity? Just the transducer part, not
>>Doppler.
>
>
> http://www.gedlee.com/Audio_trans.htm

Thanks, Arny. Looks like a pretty comprehensive book but
outside my immediate means. I did note that in the chapter
on distortion there was nothing in the contents that
indicated a treatment of Doppler. If you have it, is that true?


Bob
--

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

A. Einstein
Anonymous
August 8, 2004 12:04:29 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

Bob Cain <arcane@arcanemethods.com> writes:

> Right. The horn loaded system has a smaller excursion so that AM
> would be reduced to a similar, and perhaps greater degree.

Agreed - the Klipschorn will perform better either way.

--A Klipschorn pair owner

--
% Randy Yates % "Remember the good old 1980's, when
%% Fuquay-Varina, NC % things were so uncomplicated?"
%%% 919-577-9882 % 'Ticket To The Moon'
%%%% <yates@ieee.org> % *Time*, Electric Light Orchestra
http://home.earthlink.net/~yatescr
Anonymous
August 8, 2004 12:10:56 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

Bob Cain <arcane@arcanemethods.com> writes:

> Would you technical guys agree that the two tone interaction we are
> hypothesizing can be approximated to low order by:
>
> l*sin((wh+wld*sin(wl*t))*t) + h*sin((wl+whd*sin(wh*t))*t)
>
> with h and l related to the amplitudes of the HF and LF components
> respectively, wh the frequency of the HF tone, wl the frequency of the
> LF tone and wld and whd a measure of the "depth" in Hz

wld and whd would be depths in radians.
--
% Randy Yates % "I met someone who looks alot like you,
%% Fuquay-Varina, NC % she does the things you do,
%%% 919-577-9882 % but she is an IBM."
%%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO
http://home.earthlink.net/~yatescr
Anonymous
August 8, 2004 12:10:57 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

Randy Yates wrote:

> Bob Cain <arcane@arcanemethods.com> writes:
>
>
>>Would you technical guys agree that the two tone interaction we are
>>hypothesizing can be approximated to low order by:
>>
>> l*sin((wh+wld*sin(wl*t))*t) + h*sin((wl+whd*sin(wh*t))*t)
>>
>>with h and l related to the amplitudes of the HF and LF components
>>respectively, wh the frequency of the HF tone, wl the frequency of the
>>LF tone and wld and whd a measure of the "depth" in Hz
>
>
> wld and whd would be depths in radians.

Right, my bad.


Bob
--

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

A. Einstein
Anonymous
August 8, 2004 4:47:48 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

Bob Cain <arcane@arcanemethods.com> writes:

> Randy Yates wrote:
>
>> Bob Cain <arcane@arcanemethods.com> writes:
>>
>>>Would you technical guys agree that the two tone interaction we are
>>>hypothesizing can be approximated to low order by:
>>>
>>> l*sin((wh+wld*sin(wl*t))*t) + h*sin((wl+whd*sin(wh*t))*t)
>>>
>>>with h and l related to the amplitudes of the HF and LF components
>>>respectively, wh the frequency of the HF tone, wl the frequency of the
>>> LF tone and wld and whd a measure of the "depth" in Hz
>> wld and whd would be depths in radians.
>
> Right, my bad.

And also my bad(der)! That should have been radians/second!
--
% Randy Yates % "Remember the good old 1980's, when
%% Fuquay-Varina, NC % things were so uncomplicated?"
%%% 919-577-9882 % 'Ticket To The Moon'
%%%% <yates@ieee.org> % *Time*, Electric Light Orchestra
http://home.earthlink.net/~yatescr
Anonymous
August 8, 2004 10:51:19 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

"Bob Cain" <arcane@arcanemethods.com> wrote in message
news:cf3orj01vg9@enews3.newsguy.com
> Arny Krueger wrote:
>
>>> Arny, are you aware of any mathematical model of the typical
>>> loudspeaker non-linearity? Just the transducer part, not
>>> Doppler.

>> http://www.gedlee.com/Audio_trans.htm

> Thanks, Arny. Looks like a pretty comprehensive book but
> outside my immediate means.

The author graciously gave me a copy, probably partially because of our
discussions about nonlinear distortion, based on an earlier manuscript.

The book is highly mathematical, and attacks AM nonlinear distortion for all
it's worth. It's not a big book, but it's very detailed and pithy.

> I did note that in the chapter
> on distortion there was nothing in the contents that
> indicated a treatment of Doppler. If you have it, is that true?

Yes, and I confirmed that with the author a few days ago.

I would say that the author has the orthodox view, which is that Doppler
distortion definately exists, but it is submerged in the relatively immense
amounts of AM distortion present in speakers under the operational
conditions where Doppler might be a concern. He has no regrets about
ignoring it.
Anonymous
August 8, 2004 5:18:16 PM

Archived from groups: rec.audio.tech (More info?)

On Fri, 06 Aug 2004 06:49:53 +0100, Don Pearce <donald@pearce.uk.com>
wrote:

>On Thu, 5 Aug 2004 22:19:23 -0400, "Arny Krueger" <arnyk@hotpop.com>
>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?
>>
>
>Well, speakers generally are nonlinear, so what you are seeing here is
>intermod. Doppler distortion in speakers is supposedly a "built-in"
>effect - nothing to do with non-liearity - that is caused by the same
>cone reproducing two frequencies simultaneously. The argument goes
>that if a speaker is reproducing a 1kHz tone, but is simultaneously
>moving back and forth at 50Hz, the 1kHz tone must be modulated by the
>Doppler effect. Of course, if you do the maths of superposition, this
>doesn't happen - the tones coexist perfectly without any doppler.
>

I don't think anyone intended that "superposition" be used
willie-nilly. How about an explanation of why a moving "tweeter"
does not produce doppler.


>So this is simple, stright-forward intermodulation between the two
>tones.
>
>d
>
>Pearce Consulting
>http://www.pearce.uk.com
Anonymous
August 8, 2004 5:22:28 PM

Archived from groups: rec.audio.tech (More info?)

On Sun, 8 Aug 2004 06:51:19 -0400, "Arny Krueger" <arnyk@hotpop.com>
wrote:

>"Bob Cain" <arcane@arcanemethods.com> wrote in message
>news:cf3orj01vg9@enews3.newsguy.com
>> Arny Krueger wrote:
>>
>>>> Arny, are you aware of any mathematical model of the typical
>>>> loudspeaker non-linearity? Just the transducer part, not
>>>> Doppler.
>
>>> http://www.gedlee.com/Audio_trans.htm
>
>> Thanks, Arny. Looks like a pretty comprehensive book but
>> outside my immediate means.
>
>The author graciously gave me a copy, probably partially because of our
>discussions about nonlinear distortion, based on an earlier manuscript.
>
>The book is highly mathematical, and attacks AM nonlinear distortion for all
>it's worth. It's not a big book, but it's very detailed and pithy.
>
>> I did note that in the chapter
>> on distortion there was nothing in the contents that
>> indicated a treatment of Doppler. If you have it, is that true?
>
>Yes, and I confirmed that with the author a few days ago.
>
> I would say that the author has the orthodox view, which is that Doppler
>distortion definately exists, but it is submerged in the relatively immense
>amounts of AM distortion present in speakers under the operational
>conditions where Doppler might be a concern. He has no regrets about
>ignoring it.
>
>

John's dad say: "Speaker at 50 Hz much like LP doing 3000 rpm.

I've got the radio if you get the urge to broasdcast the raw data,
Anonymous
August 8, 2004 10:45:54 PM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

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.


Bob
--

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

A. Einstein
Anonymous
August 8, 2004 10:47:31 PM

Archived from groups: rec.audio.tech (More info?)

"Goofball_star_dot_etal" <who@needs.email.anyhow> wrote in message
news:4116290a.1067014@usenet.plus.net

> I've got the radio if you get the urge to broadcast the raw data...

Sounds like an idea. I'm going to try to not pull an John Atkinson
hide-the-data trick on you. I didn't save the data from the two three-tone.
I'm going to do several tests in quick succession so that the acoustical
setup remains the same. I'll also try to do it when its acoustically quiet.
Anonymous
August 8, 2004 11:14:50 PM

Archived from groups: rec.audio.tech (More info?)

"Goofball_star_dot_etal" <who@needs.email.anyhow> wrote in message
news:411626b4.469516@usenet.plus.net...
> On Fri, 06 Aug 2004 06:49:53 +0100, Don Pearce <donald@pearce.uk.com>
> wrote:
>
> >On Thu, 5 Aug 2004 22:19:23 -0400, "Arny Krueger" <arnyk@hotpop.com>
> >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?
> >>
> >
> >Well, speakers generally are nonlinear, so what you are seeing here is
> >intermod. Doppler distortion in speakers is supposedly a "built-in"
> >effect - nothing to do with non-liearity - that is caused by the same
> >cone reproducing two frequencies simultaneously. The argument goes
> >that if a speaker is reproducing a 1kHz tone, but is simultaneously
> >moving back and forth at 50Hz, the 1kHz tone must be modulated by the
> >Doppler effect. Of course, if you do the maths of superposition, this
> >doesn't happen - the tones coexist perfectly without any doppler.
> >
>
> I don't think anyone intended that "superposition" be used
> willie-nilly. How about an explanation of why a moving "tweeter"
> does not produce doppler.

IM effects, of which doppler summation are a part IMO, are also dependant on
total piston excursion. Thus large diameter woofers suffer less from such
effect at low frequencies. Since cone excursion is reduced inversely with
increasing frequency, IM effects become progressively more negligable.
Arny's 2 different frequency suites seem to show this. Also a two tone test
suite is never free of FM affects because a complete higher frequency cycle
will always originate at different excursion locations within the excursion
pattern governed by the low frequency leading to the lower frequency
modulated phase shifting. Ideally one would want to use a non-harmonic or
randomized stimulus at a low frequency/high excursion and then measure the
effect on the higher signal.

Wessel
>
>
> >So this is simple, stright-forward intermodulation between the two
> >tones.
> >
> >d
> >
> >Pearce Consulting
> >http://www.pearce.uk.com
>
Anonymous
August 9, 2004 12:10:00 AM

Archived from groups: rec.audio.tech (More info?)

On Sun, 8 Aug 2004 19:14:50 +0200, "Wessel Dirksen"
<wdirksen@p-we.com> wrote:

>
>"Goofball_star_dot_etal" <who@needs.email.anyhow> wrote in message
>news:411626b4.469516@usenet.plus.net...
>> On Fri, 06 Aug 2004 06:49:53 +0100, Don Pearce <donald@pearce.uk.com>
>> wrote:
>>
>> >On Thu, 5 Aug 2004 22:19:23 -0400, "Arny Krueger" <arnyk@hotpop.com>
>> >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?
>> >>
>> >
>> >Well, speakers generally are nonlinear, so what you are seeing here is
>> >intermod. Doppler distortion in speakers is supposedly a "built-in"
>> >effect - nothing to do with non-liearity - that is caused by the same
>> >cone reproducing two frequencies simultaneously. The argument goes
>> >that if a speaker is reproducing a 1kHz tone, but is simultaneously
>> >moving back and forth at 50Hz, the 1kHz tone must be modulated by the
>> >Doppler effect. Of course, if you do the maths of superposition, this
>> >doesn't happen - the tones coexist perfectly without any doppler.
>> >
>>
>> I don't think anyone intended that "superposition" be used
>> willie-nilly. How about an explanation of why a moving "tweeter"
>> does not produce doppler.
>
>IM effects, of which doppler summation are a part IMO, are also dependant on
>total piston excursion. Thus large diameter woofers suffer less from such
>effect at low frequencies. Since cone excursion is reduced inversely with
>increasing frequency, IM effects become progressively more negligable.
>Arny's 2 different frequency suites seem to show this. Also a two tone test
>suite is never free of FM affects because a complete higher frequency cycle
>will always originate at different excursion locations within the excursion
>pattern governed by the low frequency leading to the lower frequency
>modulated phase shifting. Ideally one would want to use a non-harmonic or
>randomized stimulus at a low frequency/high excursion and then measure the
>effect on the higher signal.
>

Well, this is all very interesting but it does not address whether The
Pinciple of Linear Superposition is applicable to this case.

Don Pearce claims, in effect, to have THE LAWS OF PHYSICS and MATHS on
his side. However, he argues that (he wishes) there is no FM
therefore superposition proves that he is correct in his original wish
that the system is linear, so that superposition applies, and
therefore no FM occurs.


>Wessel

I note that you did not take the hint (in the thread "Speaker
transient analysis") that I thought your statement:

"So yes,the acoustical output is directly proportional to the velocity
(not the force applied)" was incorrect.

Svante wrote:

p=U*rho0*w/(4*pi*r)

where U is the volume flow in m3/s (=surface*velocity), rho0=1.2kg/m3,
w is the angular frequency, and r is the distance.
After some thinking about this equation, one can realise that sound
pressure is roportional to the piston *acceleration* (comes from w*U,
ie derivative of the flow).

Nobody else seemed to notice that these two statements were different.
.. .


>>
>>
>> >So this is simple, stright-forward intermodulation between the two
>> >tones.
>> >
>> >d
>> >
>> >Pearce Consulting
>> >http://www.pearce.uk.com
>>
>
>
Anonymous
August 9, 2004 12:26:58 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

Aargh! I sent that by accident. It is a work in progress and
The final conclusion remains to be written or justified. That
conclusion is, however, that a pressure signal, such as is
present in recordings, is just as linearly reproduced by a force
driven piston and that Doppler distortion doesn't exist.
I really love that hat.

In the mean time I'd appreciate it if any tech-heads
can find flaw so far. The three points on which the last
paragraph is based should be enough to support it and seem,
to me anyway, to be unassailable. Have at it.


Bob

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 was 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.
>
>
> Bob

--

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

A. Einstein
Anonymous
August 9, 2004 12:37:10 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

"Bob Cain" <arcane@arcanemethods.com> wrote in message
news:cf6kgl026b0@enews1.newsguy.com...

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

Disclaimer: I am *not* stating anything here as an expert in this field.
Other than being a musician and doing some recording at home, my only other
"experience" in mathematical acoustics was building my own bass cabinet
years ago. I used some formulas from a book to cut in the proper port for
this particular woofer and cabinet volume. I'm just trying to use logic and
imagination.

With that said, I respectfully disagree with #1. :-)

First, the piston will stop moving at some point and return to its starting
position. The air molecules will keep moving until they run out of energy.

Second, think about there being two pulses. If the second pulse arrives
after the piston returns to its starting position, then the duration between
the pulses will be exactly known. Therefore, the frequency of the pulses is
exactly known. If the second pulse arrives while the piston is still moving
forward with the first pulse, then the second pulse strikes the piston while
it's in a different position than when the first pulse struck it. That pulse
has traveled farther than in our first scenario. If you were to measure the
duration between the pulses in this scenario, it would be greater.
Therefore, a form of distortion is introduced.

Another way to imagine this is if the piston did *not* return to its
starting point. Assume at some known point in relation to the energy of the
wave that the wave can no longer push the piston. The piston then becomes
stationary at that new position. The next pulse that came along would strike
it at some distance X from where the first pulse struck it. This pulse in
turn would carry it some distance. Then the next pulse and so forth. No one
would argue that such a piston would accurately reflect the frequency of the
pulses. That would be Doppler in its truest form, right?

Let's resolve this premise before we move on.
Anonymous
August 9, 2004 1:45:54 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

Jim Carr wrote:

>
> With that said, I respectfully disagree with #1. :-)

Respectfully accepted as such. :-)

>
> First, the piston will stop moving at some point and return to its starting
> position. The air molecules will keep moving until they run out of energy.

No, I specified that the piston have infinite compliance and
zero mass and I should have added, no friction. If that is
true, it will follow the motion of the air just because
there is no reason for it not to.

Piston motion is in response to the difference in pressure
on each side. Since mass, compliance and friction are not
restraining it, it moves so that the pressure differential
is always zero. To do that, it must move with the air
particles because not doing so is the only way to generate a
pressure differential. This is a key point.

This part is only gendanken to come up with a signal to be
reproduced. If the driven, reproducing piston contains
mass, non-zero compliance or friction, which are all linear,
then the driving signal can be pre-compensated by the
inverse of the resulting mechanical impedence so as to
eliminate their effects and result in the motion required by
the signal. These things are all logically between the
signal and the piston/air interface so have no effect on
what happens there in the sense of a distortion mechanism.

>
> Second, think about there being two pulses. If the second pulse arrives
> after the piston returns to its starting position, then the duration between
> the pulses will be exactly known. Therefore, the frequency of the pulses is
> exactly known. If the second pulse arrives while the piston is still moving
> forward with the first pulse, then the second pulse strikes the piston while
> it's in a different position than when the first pulse struck it. That pulse
> has traveled farther than in our first scenario. If you were to measure the
> duration between the pulses in this scenario, it would be greater.
> Therefore, a form of distortion is introduced.

If the principle is true for any arbitrary pulse, and that
was a starting propositon, then it is true for the
superpostion of any number of pulses because any
superposition is just another arbitrary pulse.


Bob
--

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

A. Einstein
Anonymous
August 9, 2004 1:48:11 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

Jim Carr wrote:

> Disclaimer: I am *not* stating anything here as an expert in this field.

You will be when I'm done with you. :-)


Bob
--

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

A. Einstein
Anonymous
August 9, 2004 3:09:39 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

"Bob Cain" <arcane@arcanemethods.com> wrote in message
news:cf6v2402e1q@enews4.newsguy.com...
> > First, the piston will stop moving at some point and return to its
starting
> > position. The air molecules will keep moving until they run out of
energy.
>
> No, I specified that the piston have infinite compliance and
> zero mass and I should have added, no friction. If that is
> true, it will follow the motion of the air just because
> there is no reason for it not to.

Let's start here. Air is made up of a bunch of loosely packed molecules
constantly and randomly banging into one another. Am I correct?

If so, suppose I manage to start a single pulse by some method that is
hopefully immaterial. Air molecules start banging into each other in
essentially one direction. Now, I grant they spread out, but there is a
pattern when compared to the normal random collisions. Each collision uses
up some energy. Eventually there's not enough energy for any more
collisions. Would you agree or disagree that this happens?

If you agree, then we can say that a sound wave is not really a set of air
molecules going from point A to point B but rather *energy* traveling from
point A to point B through a series of air molecules colliding in an
identifiable pattern we call a wave. Can we agree on that? Again, I want to
repeat that I am simply building up a theory from a relatively small base of
knowledge and what I hope is some sound logic. If I sound condescending,
then I am doing so to myself, not you. I am trying to lay this out so *I*
understand what I'm talking about. :-)

So let's shove your piston in there. By definition the piston is not really
following the motion of the air because the air really isn't moving like a
breeze. It has to react to the energy hitting it just like the air molecules
do. Therefore, to say the piston "follows the motion of the air" is
imprecise.

What I think you are trying to say is that the piston is acted upon by the
energy of the sound wave in the *exact* same way as the air molecules. So,
how far does it move? The exact same distance as one molecule of air moves?
If so, I doubt we could induce a voltage in a coil.

Since we are in fact talking about inducing voltage in a coil and and in the
case of a speaker the subsequent movement of a piston in reaction to that
voltage, we have to include that parameter as part of the discussion.
Doppler distortion wouldn't exist if the piston *only* moved like a single
molecule.

The piston must move the coil to induce a voltage. It has to move a finite
and extremely limited distance compared to distance the energy from a sound
wave travels. The piston also must move backwards at some point otherwise it
would only react to the first pulse.

In my opinion there is no possible way to find a formula to describe Doppler
Distortion without these limiting factors of the piston. Without using any
formula I would say that Doppler Distortion comes about *because* the piston
moves a greater distance and at a slower speed than energy through the air
and because the piston also has a device which pulls it back to center
whereas the air molecules do not.

It sounds like you're trying to say that your imaginary piston (which can
never exist, BTW) would behave exactly as the air molecules do, therefore,
there is no distortion. Of course not. Your constraints on the piston
essentially describe a single molecule of air. There's no way to pick a
molecule of air and say that's distortion. The movement of the molecule as
the energy passes through it is what we're trying to measure in the first
place.

The reality is that the piston does *not* act like an air molecule, so you
need to look for a way to explain the vibration of the piston and contrast
that against the vibration of air molecules. It's that difference that
causes Doppler Distortion as I understand it.
Anonymous
August 9, 2004 3:11:49 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

"Bob Cain" <arcane@arcanemethods.com> wrote in message
news:cf6v6d12e1q@enews4.newsguy.com...
>
>
> Jim Carr wrote:
>
> > Disclaimer: I am *not* stating anything here as an expert in this field.
>
> You will be when I'm done with you. :-)

LOL! You guys make me think, that's for sure. I contrast this against the
football newsgroup I'm in that spent the off-season arguing the question: If
you were filming Hillary Clinton swimming and you saw she was drowing, what
would you do?
Anonymous
August 9, 2004 5:17:11 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

Jim Carr wrote:

>>No, I specified that the piston have infinite compliance and
>>zero mass and I should have added, no friction. If that is
>>true, it will follow the motion of the air just because
>>there is no reason for it not to.
>
>
> Let's start here. Air is made up of a bunch of loosely packed molecules
> constantly and randomly banging into one another. Am I correct?

At the lowest level, but for the purposes of acoustics, and
other than in consideration of noise, they can be
statistically treated as a continuous compressible gas from
which the acoustic laws are derived. In brief you need not
consider the molecular compostion in working with its dynamics.

> If you agree, then we can say that a sound wave is not really a set of air
> molecules going from point A to point B but rather *energy* traveling from
> point A to point B through a series of air molecules colliding in an
> identifiable pattern we call a wave. Can we agree on that? Again, I want to
> repeat that I am simply building up a theory from a relatively small base of
> knowledge and what I hope is some sound logic. If I sound condescending,
> then I am doing so to myself, not you. I am trying to lay this out so *I*
> understand what I'm talking about. :-)

With that, I think you stated what I did above in a
different way. Yes I agree.

>
> So let's shove your piston in there. By definition the piston is not really
> following the motion of the air because the air really isn't moving like a
> breeze. It has to react to the energy hitting it just like the air molecules
> do. Therefore, to say the piston "follows the motion of the air" is
> imprecise.

Not so. It is constrained by the condition that no pressure
differential, dP, is allowed across it because of its ideal
definition. If it did, it would accelerate at infinite
rate. A=dP*D/M. A is infinite because M is zero. D is the
diameter. The only way it can maintain that is to move with
the bulk velocity of the air so as to keep dP equal to zero.
Think of it as a compressible fluid. If you think of an
infinitessimal volume of that fluid, the piston will move in
concert with those volumes that are in contact with it. To
do otherwise would create a pressure difference from one
side to the other and it would move to zero it without
delay. That's what it is doing, moving without delay to
keep the pressure differential at zero. Since it is never
at any other value than zero, it is moving precisely with
the bulk velocity of the air.

> Since we are in fact talking about inducing voltage in a coil and and in the
> case of a speaker the subsequent movement of a piston in reaction to that
> voltage, we have to include that parameter as part of the discussion.

What parameter is that?

>
> The piston must move the coil to induce a voltage. It has to move a finite
> and extremely limited distance compared to distance the energy from a sound
> wave travels. The piston also must move backwards at some point otherwise it
> would only react to the first pulse.

We need not consider coils or voltages at the point of
determining the velocity of that ideal piston.

>
> In my opinion there is no possible way to find a formula to describe Doppler
> Distortion without these limiting factors of the piston. Without using any
> formula I would say that Doppler Distortion comes about *because* the piston
> moves a greater distance and at a slower speed than energy through the air
> and because the piston also has a device which pulls it back to center
> whereas the air molecules do not.

But you can't say that without writing some formula. I say
it can't be written because it would violate the conditions
I described which are due to physical laws.

>
> It sounds like you're trying to say that your imaginary piston (which can
> never exist, BTW)

Doesn't matter because if the ideal case can't generate
Doppler distortion then nothing can that contains linear
components of friction, mass and compliance. I showed how
their effects could be eliminated in the reproducer in the
post you are responding to. The ideal measuring device just
tells you what the velocity is without disturbing the
acoustic field it measures.

> would behave exactly as the air molecules do, therefore,
> there is no distortion. Of course not. Your constraints on the piston
> essentially describe a single molecule of air. There's no way to pick a
> molecule of air and say that's distortion. The movement of the molecule as
> the energy passes through it is what we're trying to measure in the first
> place.

To refute my argument you have to show that an ideal passive
piston wouldn't track the bulk velocity of the medium.
You don't need to interact with it in a signifigant way to
measure it's velocity, you could use a laser interferometer,
for example (which has in fact been proposed for a
microphone sensor.) All I've really described is a large,
ideal microphone.

>
> The reality is that the piston does *not* act like an air molecule, so you
> need to look for a way to explain the vibration of the piston and contrast
> that against the vibration of air molecules. It's that difference that
> causes Doppler Distortion as I understand it.

If you followed it, you should be able to see by now why it
would. Remember, we are considering the net effect of a
whole lot of these molecules.

If you won't accept any of these arguments would you accept
that there is some way in principle to measure the bulk
velocity without distrubing what you are measuring, at least
for all practical purposes? How about tracking the motion
of a smoke particle?

If you can then we can move on to the reproduction half of
the problem. It wasn't really necessasary to employ the
piston for measurement but it illustrates the principle of
reciprocity of measurement and transduction which is well known.


Bob
--

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

A. Einstein
Anonymous
August 9, 2004 5:20:35 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

Jim Carr wrote:

> "Bob Cain" <arcane@arcanemethods.com> wrote in message
> news:cf6v6d12e1q@enews4.newsguy.com...
>
>>
>>Jim Carr wrote:
>>
>>
>>>Disclaimer: I am *not* stating anything here as an expert in this field.
>>
>>You will be when I'm done with you. :-)
>
>
> LOL! You guys make me think, that's for sure. I contrast this against the
> football newsgroup I'm in that spent the off-season arguing the question: If
> you were filming Hillary Clinton swimming and you saw she was drowing, what
> would you do?

I give.


Bob
--

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

A. Einstein
Anonymous
August 9, 2004 5:56:15 AM

Archived from groups: alt.music.home-studio,rec.audio.tech (More info?)

"Bob Cain" <arcane@arcanemethods.com> wrote in message
news:cf7bkm01rbo@enews2.newsguy.com...

> > LOL! You guys make me think, that's for sure. I contrast this against
the
> > football newsgroup I'm in that spent the off-season arguing the
question: If
> > you were filming Hillary Clinton swimming and you saw she was drowing,
what
> > would you do?
>
> I give.

The general consensus was to let her drown. A good part of the crowd wanted
to rescue her, then shoot her.

Personal, I wanted to throw her a cigar shaped flotation device.
Anonymous
August 9, 2004 12:03:09 PM

Archived from groups: rec.audio.tech (More info?)

On Fri, 6 Aug 2004 10:54:46 -0400, "Arny Krueger" <arnyk@hotpop.com>
wrote:

>"Don Pearce" <donald@pearce.uk.com> wrote in message
>news:vb57h0lm7dbc6kg3ommtu10b308apcsjts@4ax.com
>> On Fri, 6 Aug 2004 10:18:35 -0400, "Arny Krueger" <arnyk@hotpop.com>
>> wrote:
>>
>>> "Don Pearce" <donald@pearce.uk.com> wrote in message
>>> news:1347h0demfl0c5a8kjvaperbjoabec215t@4ax.com
>>>> On Fri, 6 Aug 2004 07:47:24 -0400, "Arny Krueger" <arnyk@hotpop.com>
>>>> wrote:
>>>>
>>>>>> The only way to verify this is to look at the phase as well as the
>>>>>> amplitude of the sidebands.
>>>>>
>>>>> That's one way, but it's a very hard row for me to hoe.
>>>>>
>>>>> So, you decline to believe that the relative amplitudes of the
>>>>> sidebands are different and relevant, as the frequency has
>>>>> increased?
>>>>>
>>>>
>>>> No, not at all. But I am not convinced that with the complex
>>>> interactions of a speaker you can reach your conclusion as simply as
>>>> you have. Non-linearities of various orders can cause a
>>>> multiplication function which results in phase modulation. But to
>>>> put this down to Doppler effect is a leap too far for me.
>>>
>>> I agree that the actual acoustical measurements may or may not show a
>>> Doppler effect. At best the Doppler distortion is relatively small
>>> in the face of the massive AM effects.
>>>
>>> If I turn the volume up, the AM effects seem to get stronger, both
>>> overall and proportionately. And, this is a relatively linear driver
>>> being driven over a wider frequency range than it would be used in a
>>> good design.
>>>
>>> If I got anything worthwhile out of this, it is the concept of using
>>> 3 tones to separate AM distortion from FM distortion. But you still
>>> need an underlying clear instance of FM distortion to make it worth
>>> the trouble. I suspect that a lot of the purported jitter
>>> measurements we've seen are actually pretty suspect because the
>>> common measurements confuse AM and FM distortion.
>>>
>>
>> Certainly in terms of spectrum, narrowband FM is virtually
>> indistinguishable from AM unless you can get at the relative phase of
>> the sidebands.
>
>Measuring the phase of acoustical signals, and signals in general, can be a
>vale of tears. I've played this game many times, and while I've had some
>success, I feel like I earned it! ;-)
>
>It appears that one can differentiate AM and FM based on the amplitudes of
>the sidebands for carriers that have significantly different base
>frequencies.
>
>A given AM process will produce sidebands with the same amplitudes over a
>wide variety of carrier frequencies. FM processes are very dependent on the
>frequency of the carrier.
>
>For a given rate of change in timing, the higher frequency carrier will show
>a larger shift in frequency. This increases the Modulation Index, which is
>the quotient of the maximum deviation/divided by the modulating frequency.
>The higher modulation index increases the size and number of sidebands.
>Therefore, higher frequency carriers will produce more sidebands and
>sidebands that have a larger amplitude.
>
>My Audition/CoolEdit simulations show this quite clearly.
>
>> But as for Doppler distortion. Do the sums, assuming a perfectly
>> linear driver (which should still show the phenomenon if it exists,
>> since it needs no non-linearity).
>
>That would be a more complex theoretical exercise.
>
>>You will find that the sum of the
>> tones exactly matches what the trajectory of the cone should be to
>> prevent such distortion.
>
>I don't see it. And as I've now pointed out several times, the JAES doesn't
>seem to see it, either. IOW, there are a goodly number of refereed papers
>that give abundant positive evidence that it does exist. I see that train
>coming towards me, and I see that cone coming towards me!
>
>
>
OK, the definitive test has just occurred to me, and it is easy. Turn
the speaker through 90 degrees and make the test again. The motion of
the cone is now normal to the measuring axis and there can be no
doppler distortion. Anything that now remains is due to other effects.
What vanishes is possibly doppler.

d

Pearce Consulting
http://www.pearce.uk.com
Anonymous
August 9, 2004 12:03:10 PM

Archived from groups: rec.audio.tech (More info?)

"Don Pearce" <donald@pearce.uk.com> wrote in message
news:ja8eh0t20avm86391p3q5s3b2m81v2dq82@4ax.com

> OK, the definitive test has just occurred to me, and it is easy. Turn
> the speaker through 90 degrees and make the test again. The motion of
> the cone is now normal to the measuring axis and there can be no
> doppler distortion. Anything that now remains is due to other effects.
> What vanishes is possibly doppler.

Care to comment on the polar response of speakers at 90 degrees?

The word messy, comes to mind.
Anonymous
August 9, 2004 3:43:13 PM

Archived from groups: rec.audio.tech (More info?)

"Arny Krueger" <arnyk@hotpop.com> wrote in message
news:jKadnf0WmNJqMIvcRVn-iA@comcast.com

> "Goofball_star_dot_etal" <who@needs.email.anyhow> wrote in message
> news:4116290a.1067014@usenet.plus.net

>> I've got the radio if you get the urge to broadcast the raw data...

Yes Goofball, you do have those specialized programs that look at the phase
of sidebands, right?

> Sounds like an idea. I'm going to try to not pull a John Atkinson
> hide-the-data trick on you.

I collected the data at 16/44 to keep the data files a little shorter.

> I didn't save the data from the two three-tone tests.

But I did this time.

> I'm going to do several tests in quick succession so that
> the acoustical setup remains the same.

OK, I redid the tests at 3 different levels, picked to be more
standard-like.

I just posted the revised graphic results and links to the raw test data
files at:

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

Enjoy!

> I'll also try to do it when its acoustically quiet.

I wish.
Anonymous
August 9, 2004 4:40:19 PM

Archived from groups: rec.audio.tech (More info?)

On Mon, 09 Aug 2004 08:03:09 +0100, Don Pearce <donald@pearce.uk.com>
wrote:


>OK, the definitive test has just occurred to me, and it is easy. Turn
>the speaker through 90 degrees and make the test again. The motion of
>the cone is now normal to the measuring axis and there can be no
>doppler distortion. Anything that now remains is due to other effects.
>What vanishes is possibly doppler.
>

An interesting idea but taken to its logical conclusion might suggest
that there would be no sound either. If the sound diffracts then the
path taken by the 4kHz has to bend and the path length will change as
the speaker moves at 50 Hz.
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