Intermodulation-distortion and Doppler-distortion ?? - diyAudio
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Old 21st December 2012, 08:34 PM   #1
aarvin2 is offline aarvin2  Mauritius
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Default Intermodulation-distortion and Doppler-distortion ??

Dear enthusiasts and experts of DIY, would you mind and care explaining how and why those distortions happen in certain speaker designs and how they are eliminated ??

I would also be very curious to know in simple words, what happens "sonically" as a result of those distortions ??


Thank you in advance guys
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Old 21st December 2012, 08:43 PM   #2
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Here is a link to some work I did back in 2001 on this. The revise version of the paper is not archived.

Copy and past the link in your browser.

"http://web.archive.org/web/20090809205449/http://www.geocities.com/kreskovs/Doppler1.html"
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Old 21st December 2012, 08:47 PM   #3
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Here's another one.
Doppler Distortion in loudspeakers
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Old 21st December 2012, 08:56 PM   #4
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Originally Posted by Melo theory View Post
Good to see the Rod corrected his initial article.

[edit] I would argue that whether it is rightly called Doppler distortion or not is some what of a moot point as it would not occur if the cone was not moving at the modulation frequency.

[edit 2] It kind of interesting to look bad at the history. I wrote my initial artical back in 2001. Then, some time later Rod wrote an artical some waht at odds with mine. When I became aware of Rod's articel I wrote my revised article in response. At point SL and Art L. apparently got in the loop with Rod and the issue was straightend out. It would have been a lot simpler if Rod had contacted me before posting the his initial rersponse to my artical. I guess that's what happens when you don't belong to the "club".
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Old 21st December 2012, 09:33 PM   #5
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Yes, this is a confusing topic (as far as what to call it)
It's basically this aarvin.....think of the loudspeaker driver as a spring, when a bass tone is playing, it makes a large swing. Now a treble makes a little swing, if the tones play at the same time, you will get phase distortion because the treble swing is fighting the inertia of the bass tone swing. This gets worse with greater amplitude (because the swings are larger). The remedy for this is to not let the higher frequencies swing to much by implementing a crossover.
This is the main problem with having a full range driver cover the entire FR.
I'm still confused as whether or not to call it Doppler distortion because 1 swing in itself should cause a higher or lower pitch when moving toward or away from you. I guess we could find out by comparing a driver pointing to the listener vs. one pointing upwards. I don't think it would ever be perceivable though.
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Old 21st December 2012, 10:05 PM   #6
jcx is online now jcx  United States
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Klippel's site: Introduction is a great source for serious articles on loudspeaker driver distortion
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Old 21st December 2012, 10:47 PM   #7
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Originally Posted by Melo theory View Post
.
I'm still confused as whether or not to call it Doppler distortion because 1 swing in itself should cause a higher or lower pitch when moving toward or away from you. I guess we could find out by comparing a driver pointing to the listener vs. one pointing upwards. I don't think it would ever be perceivable though.
I have a hard time accepting Rod's position that it is not Doppler distortion, or rather that calling it Doppler distortion is incorrect. Perhaps it might be more accurate to call it Doppler induced phase modulation distortion. It is definitely a Doppler effect since if the driver is not moving it does not occur. Rod makes the comment that "it takes time" and the "driver is not actually moving through the medium (air)". I can not agree with that. For example, if I hold my hand up and move it to the left and right, at what frequency and at what amplitude is it suddenly not moving through the air? It is its motion that disturbs the air and generates acoustic wave. Or, suppose that in the conventional Doppler explanation where the carrier is moving at constant velocity, if the carrier suddenly starts to broadcast a sound does it take time for the frequency to be shifted? No! Even when you start with the idea of phase modulation, that phase modulation is the result of the cone motion. So call it what you like, it is motion induced. And, like Doppler shift, the magnitude of the shift is dependent on the velocity, with max shift occurring at max cone velocity. Also note that in my analysis, when the velocity of the source becomes constant (carrier frequency is zero or DC) the basic Doppler result is recovered.
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Old 21st December 2012, 11:06 PM   #8
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I don't want to start thinking about this again. It's really squeezing my mind grapes!
hahaha!
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Old 22nd December 2012, 01:07 AM   #9
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Originally Posted by Melo theory View Post
I don't want to start thinking about this again. It's really squeezing my mind grapes!
hahaha!
Well, at least you could make wine
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