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Old 10th November 2002, 02:16 AM   #1
halojoy is offline halojoy  Sweden
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Question Vibration Isolators - Air, Magnets or other materials

I found an approach for decoupling of electronic apparatus I have never seen before.

Opposing magnets in the corners makes the apparatus "levitate"
The Levitator

I'd like to know more about different things we can do
to make our Audio-equipment lead a comfortable life without being disturbed by the surroundings

Air, magnets, rubber and MDF. Many materials are being used.
In various constructions. What do you have to say?
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Old 10th November 2002, 07:07 AM   #2
dice45 is offline dice45  Germany
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halojoy,
i saw these gadgets recently at the local AAA show in Frankfurt. They seemed to work fine, but the magnetic force only was used for the vertical levitation.

Horizantal positioning was done by friction elements, o-rings made from teflon or rubber or whatever..

I thot this was not completely thot-tru from the POV that if mechanical decoupling from the ground is done via magnets, one should go the whole path on and use magnets throughout to get rid of the mechanical contact completely. OTOH, a product using 20 Nd magnets can no longer be offered at this comparatively low price and still make money.

I bookmarked this idea however as the idea-in-itself is brilliant: as highly progessive springs the magnets do the mechanical insulating with probably the lowest space consumption by far, considered the low natural resonance frequency achievable. However, one should use the Levitator with the highest mass it can still carry. Put a sandsack on top if necessary. okokok, doesn't look nice.
I am intending to build such a gadget for myself using magnets only. Having no mechanical contact to the ground at all.
Our local surplus shop stocks Nd magnets at reasonable costs; i came up with a solution needing needing 8 magnets for vertical and 12 magnets for horizontal aligning to take all forces and momentums. I doubt one could do it with a smaller magnet count. I followed the hole&pin/slotted hole&pin stategy to avoid over-constraining. hole&pin enforce cartesian alignment, slotted hole&pin enforce angular alignment.

In order not to weaken the topplate (carrying potentially heavy equipment) one could mount 4 magnets on a cylinder mounted to the top plate and reaching into a hole in the bottom plate, carrying the oppposing magnets. This is the hole / pin.
The same with a fin carrying 2 magnets and a slotted hole having the opposing magnets. This is the slotted hole 7 pin.

Avoiding over-constraining is a practice i shall always follow, be it in electronics or in mechanics.


Airborne platform: still musing about how to do this properly. Air springs have the clear advantage that the air pressure can be adjusted to **just** carry the load, yielding in the lowest-possible natural resonance frequency achievable with the load's mass and thus being most effective in overcritical damping: the natural resonance frequency of the system being located way below the lower bandwidth of the operating frequency range, this being 20Hz-20kHz for a phono turntable.
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Bernhard
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Old 10th November 2002, 01:12 PM   #3
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Default LEVITATION

Hi guys,

Many years ago I had tinkered with this idea as well as it seems to provide good isolation from the environment.

My dad used to have a very similar base for his electronic weighing device.
It needs such a base for weighing micrograms of chemical stuff.

As far as I can tell the Levitator still couples to the environment due do the need for horizontal alignment of the opposing fields.

I have no idea what the presence of these strong magnetic fields would do to electronic stuff but I am skeptical.

Now what this base used to align horizontally were simply opposing magnetic fields fixed to the sides of the topplate.

To reduce the influence of the magnetic fields on the topplate I think it should be possible to lower them,putting them closer to the bottomplate by using posts fixed around the topplate and placing these on the corners of the rectangle.

For the really heavy stuff one could possibly use electromagnets to lift a ferrous top- or bottomplate.

I never actually tried any of this so these are just loose thoughts to be taken at face value.

Another very effective isolator is lead (remember the "Lead Balloon?)
which has very good damping properties and low self resonance
Q= ~ 3Hz depending on alloy.
It has to be sandwiched between two hard slates (glass or wood) since it is easily dented by supporting equipment feet etc.

Cheers,
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Old 10th November 2002, 01:37 PM   #4
SY is offline SY  United States
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Not such a brilliant idea. By getting a bit more isolation from floor-borne vibration, the tradeoff is greater susceptibility to air-borne vibration.

First things first, though- if tapping on your component (with the strereo powered up and the volume turned a bit past the loudest you ever listen) doesn't result in any sound from the speakers, it probably doesn't need any kind of fancy vibration isolation. Other than turntables and amps that have microphonic tubes, money is usually best spent elsewhere.

My one exception was a preamp I built where the high-end shielded cable (nominally PTFE insulated) was microphonic! Needless to say, I pulled out all that fancy stuff, replaced it with plain old shielded cable, and all was well- except for the bucks I spent for the high-priced spread.
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Old 10th November 2002, 03:20 PM   #5
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A friend of mine asked about magnetic suspension of a platform to place his turntable on. I did some internet research and came upon a web page by a physics professor which went into detail, formulas included, explaining why no combination/placement of magnets alone can suspend a platform.

I'ts reasonable to assume that if this could be done it would have been made into a commercial product long ago.

Years ago, I built a turntable isolation platform which hung from bungee cords at each corner. Regardless of where in the room I placed the platform/turntable, including on top of the woofer box, I could not induce acoustic feedback. The sprung platform had a resonant frequency of about 2Hz.
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Old 10th November 2002, 04:12 PM   #6
dice45 is offline dice45  Germany
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All,
before i heap scorn on you UN (halojoy excluded), i am curious what Danny has to say to that, the guy who manufactures the Levitator.
He might have tried it out. and dumped for reason.
I have observed that he registered at diyAudio.

Bill,
as i am as stubborn as you and as i already had an idea how it could be done, i might try it, ignoring the fact it can't be done.

For the record: i prefer a rubber/air supsension. But no matter how i do it, it costs a lot of space.

BTW, your 2Hz bungee cord suspension does better than most TTs. 2Hz is very low and almost as low as needed.

------------
Greets,
Bernhard


PS:
UN= united naysayers
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Old 10th November 2002, 04:19 PM   #7
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Default MAGLEV

Hello,

Here's a link to related info:

http://members.aol.com/marctt/links.htm

Greetz,
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Old 10th November 2002, 04:20 PM   #8
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More info about magnetic suspension :
http://www-hfml.sci.kun.nl/levitation-possible.html
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Old 10th November 2002, 04:48 PM   #9
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dice 45 said

"2 Hz is almost as low as needed "

So, what is needed?
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Old 10th November 2002, 06:38 PM   #10
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Quote:
Originally posted by Bill Fitzpatrick
Years ago, I built a turntable isolation platform which hung from bungee cords at each corner. Regardless of where in the room I placed the platform/turntable, including on top of the woofer box, I could not induce acoustic feedback. The sprung platform had a resonant frequency of about 2Hz.
Bill,

An old trick that works well - i'm glad you brought it up. When i did it i used surgical tubing. Had lots of it around because we used it for strength training when i was swimming competitively.

A cheap Frugal-phile(tm) trick is to use squash or tennis balls cut in half under your kit.

dave
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