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Old 18th January 2006, 11:35 AM   #1
Nuutti is offline Nuutti  Finland
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Default New capacitive motional feedback method

Hi all,

After years of hard meditation, failures, retries, despair, totally destroyed loudspeaker drivers and even some success I decided to make webpages about the new capacitive motional feedback method. Pages can be found here:

www.servospeaker.com

Pages are not too pretty (web design is not exatly my strong part) , but I hope the content is understandable...

Warning: This system is potentially dangerous to your drivers, and maybe even yourself as there are some high-voltage parts involved (no current needed though) so take care of yourself (and your drivers)...

Comments are welcome!
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Old 18th January 2006, 11:48 AM   #2
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Nice !!!
The coolest part is that it is a very straightforward construction of a linear sensor. This is an important point if a technology shall be applied in large scale production.

BTW: How much did the international patent application cost you ?

Regards

harles
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Old 18th January 2006, 01:03 PM   #3
Nuutti is offline Nuutti  Finland
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Quote:
Originally posted by phase_accurate
Nice !!!
The coolest part is that it is a very straightforward construction of a linear sensor. This is an important point if a technology shall be applied in large scale production.

BTW: How much did the international patent application cost you ?

Regards

harles
Thanks for your appreciation. The cost... Well, too much to mention here.
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Old 18th January 2006, 02:04 PM   #4
AJinFLA is offline AJinFLA  United States
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This is very interesting Nuuti. Thank you for sharing all your hard work with the DIY community!

Cheers,

AJ
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Old 18th January 2006, 03:17 PM   #5
Puggie is offline Puggie  United Kingdom
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Very nice and simple, Why do you do this when I have a pair of Seas L22s that I am wondering if I can do something 'interesting' with!
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Old 18th January 2006, 03:29 PM   #6
heater is offline heater  Finland
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Amazing.

Now I guess you have a switch some where that enables/disables the motioan feedback.
So my question is how does it sound when you throw the switch to the ON position ?
Can you hear a big change ?
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Old 18th January 2006, 04:31 PM   #7
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Congratulations on the work you have put into this project. The idea of a cylindrical capacitive sensor works very well.
It is very linear and you can use various methods to measure the capacitance, including radio frequencies such as used in some condenser mics.
The ibasic idea however is not novel so I would be doubly careful with your patent application.

Andrew
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Old 18th January 2006, 04:35 PM   #8
Nuutti is offline Nuutti  Finland
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Quote:
Originally posted by heater

Now I guess you have a switch some where that enables/disables the motioan feedback.
So my question is how does it sound when you throw the switch to the ON position ?
Can you hear a big change ?
I would say that the bass sounds generally tighter. Also when playing constant, say 20 Hz note with a lot of deflection, the sound is more - should I say "convincing", since the THD is lower. You just don't hear so much of those harmonics. Also the long term compression effect due to voice coil heating is reduced. This effect I haven't measured yet, but it was actually very noticeable when I tried to get constant output for distortion measurements and the output level (without feedback) just kept dropping when adjusting the volume up.

Well, of course this was only my own opinion that may be a bit biased.

At lower levels effect is not so noticeable, since much of the speaker THD comes from spider/surround/motor nonlinearities that are proportional to cone deflection.

Puggie: I don't see any problem with SEAS L22. It seems to have the same voice coil diameter as L18RNX. Some drivers however may not have enough "depth" between top of the voice coil former and pole piece to reliable attach the outer cylinder of the capacitor. I dont know if this is the case with L22's. I have done some experimenting with L26RFX/P and atleast there is plenty of room (and 51mm voice coil).
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Old 18th January 2006, 05:57 PM   #9
KBK is offline KBK  Canada
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Very nice! I was looking to create and patent a slightly different motional feedback system. I like yours, as it is sensitve to small fluctuations of the driver cone, wheras most are only concerned with the gross level changes at high levels of deflection.

The reality of the human ear, is that it is the miniscule differences in peak levels -they are the 'intelligence' of how we actually hear. This means that your system has far more fidelity, to that 'ear' that 'we' actually use to hear things. Ie, measurements are important-- but their weighting/design is even more critical.
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Old 19th January 2006, 05:37 AM   #10
Nuutti is offline Nuutti  Finland
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Quote:
Originally posted by KBK
I was looking to create and patent a slightly different motional feedback system.
What was the operating principle in your system? Was it also capacitive?

I actually first played with simple plate capacitor with other plate connected straight to the cone and other to the basket (so that the distance between them changed with cone deflection). Didn't really work as the capacitance was unlinear and very small causing noisy signal. And cone breakup caused chaotic sounds coming out of the system (this proto was with paper cone).
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