Self-centering Magnetic Suspension?

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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.
 
Stocker said:
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
 
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.

I_F
 
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
 
diyAudio Moderator Emeritus
Joined 2001
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.
 
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.
 
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.
 
diyAudio Moderator Emeritus
Joined 2001
To compensate the powerhandling of alu windings also damping and centering i thought ferrofluid can achieve all these.

Here is the US patent number for a spiderless, ferrofluid woofer used in Bogen utility speakers and manufactured by NEAR, which was, (still is?) a very reputable loudspeaker system manufacturer known for fine home loudspeakers.

US005335287

Just go to United States Patent and Trademark Office and see the patent.

Please do keep us posted, this is very interesting.

PS: Apparently Bogen and NEAR are now one and ferrofluid woofers are now used on selected Bogen speakers below. I don't think they are too expensive. Here's their web page. The woofer on the professional 12" and 15" does not have the ferrofluid, but several other models do.

http://www.bogen.com/products/NEARspeakers/
 
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Sorry but I can't find the patent listed above US005335287. I have searching the entire site on spiderless but can't find it. Do I oversee something?
Maybe next week I gonna test the new setup. If it is not what i hoped for I wil post also the drawing on how I made the EM suspension. For now it is classified ;-)
Some DIY'rs already tried to make EM-suspension with a coile above and beneath the magnetic gap but this is not near lineair on the "zero" spot (almost undo-able) because the magnetic field don't stop at the end of the gap it fade out. There is a better yet simple and cost effective solution. I search the internet for months if someone has also the same solution to this but for now nobody found (yet). I will post a youtube video for you guys to see it in action...
 
diyAudio Moderator Emeritus
Joined 2001
Jef:

Sorry for sending you on the search. This referral to patents thing is more complicated than I thought. Turns out that US00.... number is not the form the patent website likes. This should get you there.

Method 1:
Please go here-this will bring you to the patent and drawings.
United States Patent: 5335287

Method 2:
This should bring you to the patent search page:
US Patent Full-Text Database Boolean Search

Copy this number and fill it in on the Term 1 search box:
5,335,287

There will be several choices, look for this title:
Loudspeaker utilizing magnetic liquid suspension of the voice coil

Method 3:
www.uspto.gov
patents, (written in white in blue-green box)
Search Patents, (box in bottom third of page)
Quick Search, (might have to scroll down to see it)

Copy this number and fill it in on the Term 1 search box:
5,335,287

There will be several choices, look for this title:
Loudspeaker utilizing magnetic liquid suspension of the voice coil

Best of luck on this fascinating project and we look forward to you keeping us posted! :)
 
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Jef:

Sorry for sending you on the search. This referral to patents thing is more complicated than I thought. Turns out that US00.... number is not the form the patent website likes. This should get you there.

Method 1:
Please go here-this will bring you to the patent and drawings.
United States Patent: 5335287

Method 2:
This should bring you to the patent search page:
US Patent Full-Text Database Boolean Search

Copy this number and fill it in on the Term 1 search box:
5,335,287

There will be several choices, look for this title:
Loudspeaker utilizing magnetic liquid suspension of the voice coil

Method 3:
www.uspto.gov
patents, (written in white in blue-green box)
Search Patents, (box in bottom third of page)
Quick Search, (might have to scroll down to see it)

Copy this number and fill it in on the Term 1 search box:
5,335,287

There will be several choices, look for this title:
Loudspeaker utilizing magnetic liquid suspension of the voice coil

Best of luck on this fascinating project and we look forward to you keeping us posted! :)

Thanks for helping me out. I have found the correct patent. The fluid is on it's way 4 days remaining. Maybe this weekend I can give you the first results... For me, it is a extra stimulant to continue with this project if there are people who are actually intrested in my work. So thx and see you soon...
 
diamagnetic interaction can apparently enable stable "passive" magnetic suspension:

http://www.mae.ncsu.edu/courses/Mae...Scientist Online - Diamagnetic Levitation.htm

(from American Scientist online, search: diamagnetic levitation

American Scientist Online

in case they pull the classroom link to the article)

You can put together a demo with bismuth plates as the diamagnetic material a neat experiment but VERY touchy the diamagnetic effect is orders of magnitude less than the magnetic one.
 
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