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Multi-Way Conventional loudspeakers with crossovers

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Old 25th July 2010, 01:14 PM   #6821
mige0 is offline mige0  Austria
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To give a qualitative picture on how „dry friction“ affects movement of of the diaphragm I set up a simplified simu

This simu assumes that there is 100% rigidity from VC to the points of velocity independent friction (spider and surround) – which is kind a optimistic – and also shows static and dynamic friction being the same (for simplicity of simulation).


First a plot that shows the situation when roughly 10% of the given max force is eaten up by friction.

Starting out with a 2Vpp source signal – membrane movement looks like that:

Click the image to open in full size.



lowering source signal to 1Vpp signal – membrane movement looks like that:

Click the image to open in full size.



lowering source signal to 500mVpp signal – membrane movement looks like that:

Click the image to open in full size.



lowering source signal to 250mVpp signal – membrane movement looks like that:

Click the image to open in full size.



lowering source signal to 200mVpp signal – membrane movement looks like that:

Click the image to open in full size.



We see that distortion due to velocity independent friction starts to stick out as signal falls.
Right to the point where weak signals are no longer able to move the diaphragm at all.

We also see that movement starts delayed as the force has to reach a certain level first before movement begins.
Also we see that movement stops before reaching peak points as there is no longer enough force to pull to sine top.

The DC shift seen here would level out in reality of course – and we would more clearly see the rest position to be offset...


Well this might be a „little bit“ exaggerated – as we hardly would see it happen in such pure form and at such level – but the basic principle clearly is shown IMO.




Michael

Last edited by mige0; 25th July 2010 at 01:28 PM.
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Old 25th July 2010, 03:09 PM   #6822
mige0 is offline mige0  Austria
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Quite in contrary to above – friction that depends on velocity does not show such ill behaviour.

An example for „velocity dependent friction“ could be the air that is pushed through the VC gap by the cup.

Both types of friction contribute to Qms, but have way different impact sonically.

Michael
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Old 25th July 2010, 04:27 PM   #6823
badman is offline badman  United States
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Ah the evil zero crossing again!

We don't like that! It's why some of us charge couple our capacitors a la jbl, something other people using CD 2-ways may wish to consider given that they're mostly already using high Qms drivers and Dr. Geddes recommends low crossover distortion amplifiers
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Old 25th July 2010, 05:31 PM   #6824
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Soongsc, can you simplify that to a yes or no? I'm not sure what you are saying now. You start out sounding like it's a "yes", but then it seems to go to maybe a "no" or a "maybe".

Man, I thought Californians were perplexing,

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Old 25th July 2010, 05:47 PM   #6825
mige0 is offline mige0  Austria
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Quote:
Originally Posted by badman View Post
Ah the evil zero crossing again!

We don't like that!
....and Dr. Geddes recommends low crossover distortion amplifiers
he might have been shooting the wrong suspects.. but thats an old story ...


Michael

Last edited by mige0; 25th July 2010 at 05:52 PM.
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Old 26th July 2010, 08:44 AM   #6826
soongsc is offline soongsc  Taiwan
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Quote:
Originally Posted by dantheman View Post
Soongsc, can you simplify that to a yes or no? I'm not sure what you are saying now. You start out sounding like it's a "yes", but then it seems to go to maybe a "no" or a "maybe".

Man, I thought Californians were perplexing,

Dan
If you just want a judgement which is better, I really can't tell with the graphs flipping like that. I'm used to laying them side by side and studying them that way. The only thing I can tell from the way they are is that they will sound different.
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Old 26th July 2010, 10:12 AM   #6827
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Quote:
Originally Posted by mige0 View Post
Quite in contrary to above – friction that depends on velocity does not show such ill behaviour.

An example for „velocity dependent friction“ could be the air that is pushed through the VC gap by the cup.

Both types of friction contribute to Qms, but have way different impact sonically.

Michael
I'm starting to doubt that coulomb friction is significant. If it were THD measurements would surely show it.
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Old 26th July 2010, 12:28 PM   #6828
dlr is offline dlr  United States
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Quote:
Originally Posted by john k... View Post
I'm starting to doubt that coulomb friction is significant. If it were THD measurements would surely show it.
How would it be evident in the measurements?

Dave
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Old 26th July 2010, 12:32 PM   #6829
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Wouldn't a low-level nearfield THD measurement pick up this artifact?
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Old 26th July 2010, 12:48 PM   #6830
soongsc is offline soongsc  Taiwan
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Quote:
Originally Posted by john k... View Post
I'm starting to doubt that coulomb friction is significant. If it were THD measurements would surely show it.
If this kind of friction is measureable, smaller test signals will reveal it more significantly, thus the THD measurements would show higher levels of distortion with smaller test signals. Wouldn't it?
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