Self-centering Magnetic Suspension? - diyAudio
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Old 6th February 2006, 02:59 AM   #1
Stocker is offline Stocker  United States
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Default Self-centering Magnetic Suspension?

Is it possible to make a magnetic suspension that is self-centering? mrjam's amazing CDP has me wondering if the vertical centering component could be eliminated by a DIYer.

Using three, four or more as required magnets, arranged as if in a bowl shape, with poles appropriately opposed; to suspend a similarly anti-bowl shaped suspended object

clear-as-mud ascii rendering
--\__/--
-\___/-

And the big question: would it still transmit vibrations? Would many small magnets be better than a few strong ones? Could the setup be arranged slightly less than perfectly and still work?

Maybe with some platic bump-stops to prevent large shocks from damaging things.
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Old 6th February 2006, 03:45 AM   #2
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Default Re: Self-centering Magnetic Suspension?

Quote:
Originally posted by Stocker
Is it possible to make a magnetic suspension that is self-centering? mrjam's amazing CDP has me wondering if the vertical centering component could be eliminated by a DIYer.

Using three, four or more as required magnets, arranged as if in a bowl shape, with poles appropriately opposed; to suspend a similarly anti-bowl shaped suspended object

clear-as-mud ascii rendering
--\__/--
-\___/-

And the big question: would it still transmit vibrations? Would many small magnets be better than a few strong ones? Could the setup be arranged slightly less than perfectly and still work?
Well, to date Earnshaw's Theorem still holds and no static array of magnets will be stable.

If it were stable, it would still transmit vibrations at and below its resonant frequency and isolate from vibration above its resonant frequency.

That's really all this stuff is anyway, simple mechanical resonant systems, i.e. spring/mass combinations. Ideally what you want is a resonant frequency that is well below the lowest frequency you want it to isolate and you want the resonance to be very high Q (i.e. very little loss).

se
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Old 6th February 2006, 10:59 PM   #3
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Even if you could make it work, you'd get no end of grief from the golden ears who would complain about audio pollution due to the stray magnetic fields all over the place.

The magnets are really just acting as springs and WILL transfer vibration across the air space between them, as a spring would.

If you must use magnets, you could suspend the object from a single wire (balancing will be a problem) and restrict its motion using magnets located under, over, or around it...

Another thing to consider is that the whole system is undamped whether you use springs or magnets. I think you would want to damp any vibrations that are transferred so they don't keep things ringing.

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Old 7th February 2006, 01:28 AM   #4
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Old 7th February 2006, 01:32 PM   #5
jcx is online now jcx  United States
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diamagnetic interaction can apparently enable stable "passive" magnetic suspension:

http://www.mae.ncsu.edu/courses/Mae5...Levitation.htm

(from American Scientist online, search: diamagnetic levitation

http://www.americanscientist.org/tem.../assetid/35120

in case they pull the classroom link to the article)
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Old 8th February 2006, 12:56 PM   #6
Stocker is offline Stocker  United States
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interesting. thanks guys.
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Old 2nd January 2013, 07:13 AM   #7
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Hello,

I read this old post and maybe you guys can help me. I have made a driver (that really works on this moment) with a adjustable magnetic damping system. But I have a problem on this. I use a surround and spider to center the cone and voicecoil. When i reverse the current in the damping coil i can loosen up the damping or i can tighten the damping. My question... I wan't to eleminate the spider and maybe the surround because the magnetic damping is 100% lineair over the whole range. Good spiders also over 80% but most surrounds not. The problem is to magnetic center the whole coil. I tried differtent things but without succes. Thx
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Old 6th January 2013, 04:27 AM   #8
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I see that nobody has answered your question yet so I will just throw this in even though it is not quite what you asked for.

I read a review in the now-passed Audio magazine of a commercially produced speaker with a suspension of air instead of a spider. The review said it provided a linear suspension as opposed to a spider, which does not.

I do not recall the make of the speaker, but perhaps some old Audio reader remembered the review.
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Old 6th January 2013, 05:44 AM   #9
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Nothing is 100% linear. Conventional suspension arrangements are extremely linear over short excursions. It would be hard to produce a magnetic suspension, passive or active, that didn't cause a significant reduction in acoustic output efficiency due to increased moving mass. That's ignoring the power consumption of an active EM suspension. Giving up the cone edge termination of a conventional surround is going to be a problem for anything but the sub-frequency range. Linearity at high power is more practically achieved with larger or more drivers. If it's just a science project that's cool, but making it higher performance overall compared to some optimal arrangement of conventional drivers would be an impressive trick.
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Old 6th January 2013, 09:13 AM   #10
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It was started as a science project till i found a solution for a active magnetic suspension that worked better that i hoped for (the goal was to adjust the damping of the speaker in function of a dc current). the only problem was like andrew said, the moving mass. It is the same as an overhung system but i want to make it better. Therefore i have to use alu windings, no spider, no surround and untherhung with neo magnets and very thin voicecoil also alu. To compensate the powerhandling of alu windings also damping and centering i thought ferrofluid can achieve all these. The extra single winding for damping is 1 inch in height. Maybe there is a problem to consider, a moving coil generates a current in a magnetic field so the dampimg changes in function of the freq. This is also near lineair i think but i'm not sure. For know i use a battery for driving the damping winding.
One interesting thing i found out... Almost none damping to a verry stif damping changes the sound almost unnoticeable. Strange i didn't expect that hmm... That put a second Discussion in the world, is the spider so important like everyone think of? I think not, i think moving mass and cone material are the main factors... In my opinion The less parts, the less resonaces makes it only better... I ordered the ferrofluid i keep you posted about my Findings.
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