Doppler and Loudspeakers

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#21
davidsrsb said:
You would get doppler effects if a woofer had a tweeter attached to the cone. The tweeter cone position is then modulated by the woofer position. Nobody does this.
An ideal single driver driven by two signals is in a position determined by the two signals, with the same reference point, so the sum pressure exactly tracks the drive voltage - no doppler shifts.
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Okay, you've convinced me! Well that's one thing I don't have to worry about any more.
 
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#24
Busdriver02 said:
a whole page on this topic: LInk
Not sure who Rod Elliott is, so take it with an internet grain of salt

Edit to add: if this set of tests is to be believed. Doppler effects on speaker output isn't a thing
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Rod is an extremely good engineer -with some strong opinions, most of which he backs up.

Still good from Klipsch (yes, that one):
http://www.readresearch.co.uk/loudspeaker_papers/klipsch_modulation_distortion_article_1.pdf
http://www.readresearch.co.uk/loudspeaker_papers/klipsch_modulation_distortion_article_2.pdf
http://www.readresearch.co.uk/loudspeaker_papers/klipsch_modulation_distortion_article_3.pdf
Roy Childs in Audio:
https://www.worldradiohistory.com/Archive-All-Audio/Archive-Audio/70s/Audio-1970-08.pdf
 
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#25
Interesting how useful shared information is dismissed by members of the comunity. The guy writing the article has actually done some research that is way above the capabilities on most of us here. I happen to agree with his findings and I am very glad that others are researching the issue as well. Please enjoy the hobby, if you can't contribute anything useful don't obstruct the others doing so. Follow my lead 🙂
 
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#27
cracked case said:
What if you had a tweeter output reflecting off a woofer cone, this would double the affect.
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That ought to be my cue, but I've been too busy to explicitly follow up on this test for Doppler. Near-field, I did not hear a "tight vibrato" on the too-loud organ high notes over the deepest long closing chord, but too much detail-overload which included pitch fluctuation (not fast vibrato). A specific test track may be needed.

W

Post in thread 'Full Range Speaker Photo Gallery'

cracked case said:
If the tweeter output is bouncing off the dust cap, would that double the "doppler" affect? Perhaps this could be used to our advantage, by using a very directional horn or ring tweeter, bounding several times between a driver and stationary reflector, magnifying the affect, allowing us to hear how it changes the sound.
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I listened for doppler and IMD on Englskyts final bottom note-chord. JBL 2226H was incredible. There was so much (loud) detail I couldn't tell which if any were distortion.... Need to devise a test. I understand your "scheme" and will ponder it, thanks.
 
#28
cracked case said:
What if you had a tweeter output reflecting off a woofer cone, this would double the affect.
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If you made measurements of the tweeter dispersion, while applying a dc voltage to the woofer, you would find the directivity pattern going all over the place with the woofer position.
In my opinion, this is the biggest downside of coaxial drivers. In particular the Kef LS50, with a relatively small and therefore high movement woofer cone is noted to not handle loud bass well, benefiting from a sub woofer and high-pass.
The big Tannoys work better because the massive cone moves very little at sane volumes
 
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#30
davidsrsb said:
An ideal single driver driven by two signals is in a position determined by the two signals, with the same reference point, so the sum pressure exactly tracks the drive voltage - no doppler shifts.
Click to expand...
If the frequencies are not the same the voltages for the two are not proportional to the excursion of the cone, its frequency dependent. Thats whay you can have doppler shifts
 
#32
A full LF cycle goes through: at max outward excursion zero speed; at zero excursion max inward speed; at max inward excursion zero speed; at zero excursion max outward speed. Different things are happening at different places i.e. distance to the listener, position and velocity of voicecoil -- as HF cycles fold into/on top of it -- creating different distortions.
 
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#35
I think there is a misunderstanding of the nature of waves. The signal coming out of the amplifier is one superimposed wave not two independent waves. It is Wave 1 plus Wave 2. Simple math. This resultant wave, the product of two waves, is applied to a loudspeaker and it produces a variation in air pressure, the speaker produces one longitudinal wave not two independent waves. The earlier example of a woofer with a tweeter on it would produce 'Doppler' distortion because there are two waves being created with one loudspeaker dependent on the position of the other. One loudspeaker in mono can not create 'Doppler' distortion because it is reproducing a superimposed wave.

The reason @john k... 's example produces distortion in the last example is the loudspeaker was driven to distort. "In this case the signal level was increased untill distortion componens appeared in the result." Well, dugh! There was no distortion at lower levels. The distortion was caused by the loudspeaker being driven beyond it's capabilities. Of course that will cause distortion. This is clearly a case of confirmation bias.

Figure_17_10_04a.jpg


Ref: https://courses.lumenlearning.com/suny-physics/chapter/16-10-superposition-and-interference/

EDIT: Woofers don't speed up and slow down either, they for the most part, make sinusoidal waves at a constant rate.
 
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#36
john k... said:
Been there, done that. Call if what you like. A high frequency signal radiating from a slower moving source has a frequency shift. http://geocities.com/kreskovs/Doppler1.html
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That is my tweeter mounted on the woofer cone example. No sane designer would actually make a coaxial driver like this. Real world examples have the (compression) tweeter using the same chassis reference as the woofer. Then the resulting pressure waveform is superimposed as in @Arthur Jackson post above.
 
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#37
Ha, my insane bouncing-off-convex-dustcap reflector-coaxial virtual point source... Of course it was 15" near-field etc., and by supporting tweeter(s) on the up-firing cone (one tested configuration) some distortions didn't apply. I always mentioned "mitigation" with a bridge/reflector, if needed.

Sure all frequencies are superimposed in the soundwave hence combined in the cone movement. I think (participatng in this thread) we all know that.
 
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