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Doppler distortion doesn't make sense (Edit: It actually does!)

March Audio

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One is totally in the electrical domain.

This example is half electrical domain, modulating the physical domain with respect to the actual position of the sound emanating source (the vc and its acceleration characteristics) in real time.

Well we all have experienced real world examples with sirens. Just in this case the ambo* is going back and forth past us rapidily instead of just approaching and then leaving. The pitch (frequency) goes up then down. The movement distance (amplitude of the lower frequency) is like the FM deviation.

I'm struggling to see the difference between electrical and an acoustic wave. As I said thats probably me being dumb :) so Im not saying Im right, just struggling today to engage brain :)

* Australian. For those who are uninitiated in the intricacies of Australian English, everything possible is abbreviated. If at all possible using a "o" .

Straya - Australia
Ambo - Ambulance.
Arvo - afternoon.
Devo - devastated
Defo - definitely
Servo - Service (gas) station
Bottlo - liquor store
Tradie - Tradesman
Firey - Fireman
Avo - Avacado
Smoko - work break



Slang with Margot Robbie

 
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Julf

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Not in a multidriver system though.

Indeed. For the doppler effect to be a factor you need two (or more) signals reproduced by the same driver.

How big would the amplitude difference need to be before it becomes audible (assuming linear transducer)

I am sure I could calculate it if I had a few more coffees. Of course the question "how large does a pitch modulation need to be to be audible" is tricky. Anyway, it is not a question of amplitude difference as much as absolute amplitude (cone movement) at the lower frequency.
 

DonH56

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I think @March Audio is saying FM modulation of an electrical signal is essentially the same as Doppler modulation of an audio (electromechanical driver) signal. Look at the equations posted by @SIY in post #7 (https://www.audiosciencereview.com/...sense-edit-it-actually-does.8994/#post-228911 ) and compare to e.g. Wikipedia's (somewhat long and confusing) description of FM modulation https://en.wikipedia.org/wiki/Frequency_modulation (I have a much better description in my old RF books but not with me at the moment.) Similar, and similar in spectral results, but not quite the same though you could mash them together (I have a vague memory of being forced to do that in a RADAR class ages ago but have mercifully forgotten the details).

They are closer in this context of speaker modulation than the basic equations SIY showed as the velocity is time-varying with the signal. I think. It's early yet here, and my test just finished, so back to work.

HTH - Don
 

Julf

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I think @March Audio is saying FM modulation of an electrical signal is essentially the same as Doppler modulation of an audio (electromechanical driver) signal.

And I would agree with that.
 

March Audio

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I think @March Audio is saying FM modulation of an electrical signal is essentially the same as Doppler modulation of an audio (electromechanical driver) signal. Look at the equations posted by @SIY in post #7 (https://www.audiosciencereview.com/...sense-edit-it-actually-does.8994/#post-228911 ) and compare to e.g. Wikipedia's (somewhat long and confusing) description of FM modulation https://en.wikipedia.org/wiki/Frequency_modulation (I have a much better description in my old RF books but not with me at the moment.) Similar, and similar in spectral results, but not quite the same though you could mash them together (I have a vague memory of being forced to do that in a RADAR class ages ago but have mercifully forgotten the details).

They are closer in this context of speaker modulation than the basic equations SIY showed as the velocity is time-varying with the signal. I think. It's early yet here, and my test just finished, so back to work.

HTH - Don

Yes that's what my fuzzy brain is thinking :)
 

DonH56

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Comment how? It can create steady-state flow and pulses of air that can modulate the sound (changes the transmission medium) as well as add interesting reflections. Some use the effect to advantage, e.g. http://www.rotarywoofer.com/ .
 

DonH56

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So I gather you've heard it and don't like it? I've only ever seen one AFAIK and it was pretty impressive but I did not have much time with it.

Whatever, except for the relation to a fan, not relevant to this thread.
 

scott wurcer

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Intermod shows as bands at f1-f2, f1+f2, and combinations of nf1+/-mf2, where n and m are integers.

Doppler will show frequency shift that's velocity dependent. So if the the bands don't broaden and the broadening isn't a function of the lower frequency amplitude, it's not Doppler.

To get back to the original problem, velocity is in quadrature with the amplitude so the phase of the sidebands is important. The Hilbert transform can separate the AM from the FM which is what we did to plot the instantaneous frequency of an LP using the 3.15kHz tone on a test LP. This is pretty easy to do maybe you could take some data and send it to me, it's just a few lines in one of the free signal processing packages.

BTW the plots being addressed looked like 6kHz and 800Hz not 80Hz.
 

scott wurcer

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As for the speakers, the 6k tone alone looked like this (left speaker only):
View attachment 33556


And 80 hz added:
View attachment 33555


It's interesting, because the 6k alone already produces a sideband. Maybe it's due to the tweeter itself or the internal amplifier, I don't know how distortion free It should be. And when I add the 80 hz tone, the existing sideband stays pretty much the same, and it adds another, higher one. It's about the same level as the one present in the Lcd2c. Not sure what to make of this. Could be the microphone itself is distorting or some other effect I missed. At any case, the Clears show significantly more distortion (whether doppler or IMD) than the rest, which is how it sounded like to my ear.

I was away at the Miami/Patriots game or I would have responded earlier. If you look very carefully the right "sideband" in the second plot could be actually split and the first plot does not actually have one sideband but a signal artifact that is additive in the second plot. This is of course an educated guess from experience of something that needs to be entertained as a possibility.
 

gene_stl

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So I gather you've heard it and don't like it? I've only ever seen one AFAIK and it was pretty impressive but I did not have much time with it.
Whatever, except for the relation to a fan, not relevant to this thread.

No, I plead guilty to never having seen one of these. I wouldn't know where to see one. With all due respect to mr or dr Thigpen who invented it I am also not particularly interested in it. A little bit too goofy for me and way way too high priced. ($14k without the box) But that's just me.

Maybe I should not have referred to it as a POS. I apologize. It's just an absurdly overpriced transducer for a range that there is not much music in.
BTW I can also simulate an earthquake rather interestingly with my large boxes and eight woofers.
 

freddi

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I think I've heard it on headphones on Youtube videos such as those where there's continuous high amplitude LF along with a tune and that IEM are more guilty of it than competent on-ear/over ear headphones which have much more surface area. Its heard as "gargle" such as one would hear talking or singing up close to an electric fan and can be a problem with coaxial speakers where music which could expose it has long held LF notes while say a flute is playing versus a speaker where the tweeter is not directly in front of the low freqyency cone.
 

steve_b_in_az

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and think of any signal being frequency modulated by a sine wave. does it not do the same thing? Sorry I am probably having a dumb day :)

so with the speaker the higher frequency wave is being compressed and rarefied by the lower frequency signal. Its frequency is going up and down.
My question about this phenomenon comes from the fact that when multiple simple acoustic sources are simultaneously emitting sound, the sources combine into a complex (summed) waveform. When a listener hears this complex waveform, the acoustic processing area of the brain 'decomposes' this complex waveform back into a perceived set of simple sources once again (similar to a Fourier decomposition, but done using the neuronal processing within the auditory center of the brain). Therefore a speaker driver must follow this complex waveform precisely, so that the emitted pressure wave is a faithful copy of the complex (superimposed) waveform that impinged upon the recording media in the first place. As long as the driver can follow the complex waveform, the brain should be able to decompose the complex signal back into the perception of a set of simple sources once again. In this understanding, the "modulation" of one of the components of the summed waveform other components of the summed waveform is supposed to happen - since this is what produces the complex waveform in the first place. Is this not correct?
 

steve_b_in_az

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My question about this phenomenon comes from the fact that when multiple simple acoustic sources are simultaneously emitting sound, the sources combine into a complex (summed) waveform. When a listener hears this complex waveform, the acoustic processing area of the brain 'decomposes' this complex waveform back into a perceived set of simple sources once again (similar to a Fourier decomposition, but done using the neuronal processing within the auditory center of the brain). Therefore a speaker driver must follow this complex waveform precisely, so that the emitted pressure wave is a faithful copy of the complex (superimposed) waveform that impinged upon the recording media in the first place. As long as the driver can follow the complex waveform, the brain should be able to decompose the complex signal back into the perception of a set of simple sources once again. In this understanding, the "modulation" of one of the components of the summed waveform other components of the summed waveform is supposed to happen - since this is what produces the complex waveform in the first place. Is this not correct?
For example, here is the sum of four simple (sinusoidal) sources. This just seems like a complex waveform that would have to be traced out by the loudspeaker driver, and then 'decomposed' back into simple sources by the listener.

1667197535554.png
 

Geert

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As long as the driver can follow the complex waveform, the brain should be able to decompose the complex signal
How is the brain supposed to decompose a signal that has been distorted by a speaker? How is it going to compensate for the distortion if it doesn't know the nature and amount of distortion? How is it even going know the sound is not as intented?
 

NTK

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It took me awhile to understand how Doppler distortion came about. Doppler distortion is most noticeable when the same driver is reproducing a loud low frequency signal simultaneously with a high frequency one. It also happens in coax drivers where the moving outer cone acts as an oscillating reflector for the inner driver.

The cause of Doppler distortion is that the "source" (radiating surface) of the sound is the loudspeaker diaphragm. When the driver diaphragm is reproducing a low frequency signal and cycles back and forth. If it is also playing a higher frequency signal, the "source" of the higher frequency is in reality no longer a "stationary" source but a moving/oscillating one.

It is similar to a train moving towards you while blasting its horn. You hear the horn at a higher pitched -- the Doppler effect. Imagine, if the "driver diaphragm" is moving towards you at a constant speed and it is playing a tone, you will hear the tone at an elevated pitch due to the Doppler effect.

Now, the diaphragm is instead oscillating playing a bass tone. When it is also playing a higher frequency tone, the "radiator" of the higher frequency signal is no longer stationary but a moving one. The frequency of the higher frequency tone is now modulated by the diaphragm movement due to the lower frequency tone, and we have Doppler distortions.

As the modulation is proportional to the speed of the diaphragm movement, it would be logical that a larger size driver will have lower Doppler distortions than a smaller one at the same output SPL.
 

fpitas

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garyrc

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When excursion is minimized, modulation distortion (sidebands) occurring when two tones, often a midrange tone and a bass tone, are played using the same diaphragm, seems to be of lower magnitude than when a greater excursion is allowed. Excursion can be minimized by proper horn loading and other strategies.

Here are some early photos by Paul W. Klipsch
1682156740639.png

1682156890002.png

1682157270006.png

1682157507492.png

Note that at 1 watt, at 1 meter, where the IM was determined to be 1% by Heyser, the SPL would be 101 dB without room or boundary gain, or perhaps 105 dB in a typical living room.

From Heyser's review of the Klipschorn in Audio, November, 1986
 

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