So I was thinking, I have a tv that is very sensitive to magnetic flux and I also have a Tumult. It wouldnt be a great combination if either of them were on the same side of the room which makes placement limited.
How could I sheild this?
My ideas:
Thick sheet metal wrapped into a cylinder with an endcap welded on. I was thinking this could perhaps need to be double thick sheet metal wrap to absorb all the stray flux.
I have no idea on what dimensions would be good however.
How might the sheilding effect the flux if it was close enough? I would imagine adding metal around the magnet would only increase flux in the gap? I dont know exactly what kind of metal is proper for it, but I was thinking some sort of soft steel.
Will it work?
Is it possible?
How shall I make it?
How could I sheild this?
My ideas:
Thick sheet metal wrapped into a cylinder with an endcap welded on. I was thinking this could perhaps need to be double thick sheet metal wrap to absorb all the stray flux.
I have no idea on what dimensions would be good however.
How might the sheilding effect the flux if it was close enough? I would imagine adding metal around the magnet would only increase flux in the gap? I dont know exactly what kind of metal is proper for it, but I was thinking some sort of soft steel.
Will it work?
Is it possible?
How shall I make it?
I thought about the idea of bucking magnets, but the fact of the matter is, the Tumult has a giant magnet and a bucking magnet of adequate size would get expensive. I have heard of mu metals before, but I dont think I can buy them at any of the local hardware stores. The whole idea of this project was to find a cheap way to sheild subwoofers, if it gets over $50, I'll just be happy with what I have. I suppose I will send an email to adire and ask what they think.
Thanks for the responses
Thanks for the responses
Has anyone had luck with the bucking magnets from Parts Express? They're cheap enough.
http://www.partsexpress.com/webpage.cfm?webpage_id=3&CATID=48&ObjectGroup_ID=825
http://www.partsexpress.com/webpage.cfm?webpage_id=3&CATID=48&ObjectGroup_ID=825
NVMDSTEvil said:
A faraday cage has no effect on a static magnetic field.
[edit] there's no known material that will "block" static flux, all you can do is re-direct it (which is what magnetic "shielding" does, offering a path of lower resistance for the flux compared to the surrounding air)
Faraday cages shield from exterior electric fields. Gaussian shields shield from exterior magnetic fields. If a Faraday cage is made of a material such as Iron (or Liquid Oxygen or ...) with positive magnetic susceptibility (in other words, a permeability > 1), it will provide some magnetic shielding. Soft Iron shields well because of its permeability. MuMetal has an ultrahigh permeability, and therefore shields very well.
How much steel? I tried sticking a 2" dia x 1/4" thick (along the axis of the poles) NeFeB N42 (1.33 Tesla) magnet to a 1/4" steel plate, and it feels 99% shielded on the back side of the steel. I tried the same magnet with some 16ga steel, and I felt almost no shielding happening on the back side of the steel.
Note: When you shield magnetically, you also change the strength (by changing the effective length) of the magnet you're shielding. On the magnet side of my magnet/steel contraption, the magnetic field appears to be close to as strong as it would be if I had a magnet 2x as long (along the axis of flux) as the one I started with. What does this mean? That it's also in your interest to move the shielding as far away from the magnet you're shielding as possible to minimize the changes you make to the magnet.
If you're interested, there are some awesome Electricity and Magnetism lectures online from the MIT OpenCourseware site. Excellent demos to go along with the in-depth mathematics behind all of this (including the LOX sticking to a magnet that I mentioned above).
http://ocw.mit.edu/OcwWeb/Physics/8-02Electricity-and-MagnetismSpring2002/VideoLectures/
Bryan A. Thompson
bryan@batee.com
How much steel? I tried sticking a 2" dia x 1/4" thick (along the axis of the poles) NeFeB N42 (1.33 Tesla) magnet to a 1/4" steel plate, and it feels 99% shielded on the back side of the steel. I tried the same magnet with some 16ga steel, and I felt almost no shielding happening on the back side of the steel.
Note: When you shield magnetically, you also change the strength (by changing the effective length) of the magnet you're shielding. On the magnet side of my magnet/steel contraption, the magnetic field appears to be close to as strong as it would be if I had a magnet 2x as long (along the axis of flux) as the one I started with. What does this mean? That it's also in your interest to move the shielding as far away from the magnet you're shielding as possible to minimize the changes you make to the magnet.
If you're interested, there are some awesome Electricity and Magnetism lectures online from the MIT OpenCourseware site. Excellent demos to go along with the in-depth mathematics behind all of this (including the LOX sticking to a magnet that I mentioned above).
http://ocw.mit.edu/OcwWeb/Physics/8-02Electricity-and-MagnetismSpring2002/VideoLectures/
Bryan A. Thompson
bryan@batee.com
What would it take the shield a typical 12" subwoofer such as AE speakers AV12 and similar?
I had a look at the PE bucking magnets. The biggest is around 100mm x 45mm x 18mm and they mention the size should be around 1/2 - 2/3 the size. So lets say the magnet in question is 140mm diam and 35mm deep, what size should I use? 75mm diam x 12mm (2 stacked?)
Or just the biggest size a single?
Where do you place the bucking magnet if not on the back of the driver magnet?
I had a look at the PE bucking magnets. The biggest is around 100mm x 45mm x 18mm and they mention the size should be around 1/2 - 2/3 the size. So lets say the magnet in question is 140mm diam and 35mm deep, what size should I use? 75mm diam x 12mm (2 stacked?)
Or just the biggest size a single?
Where do you place the bucking magnet if not on the back of the driver magnet?
paulspencer said:
Magnet area is the primary determing factor in magnet strength (all else being equal), not so much the thickness, the only reason manufactures stack magnets is because magnets are cheaper than the high grade steel they'd have to use otherwise.
So in choosing a suitable bucking magnet I would use one the same diameter as on the driver, or failing that the largest diameter one I could get my hands on.
My peerless tweeters have a bucking magnet that's exactly the same diameter as on the tweeter motor only half the thickness.
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