Hi,

The link provided below is a company that provides Mu Metal at reasonable prices and smaller quantites. Their product includes different thicknesses of Mu Metal and High Permeability materials for magnet shielding. You would be surprised what some of the thin materials will do.

I have used them for past projects at work and they work well.

If you make a Mu Metal cage for the CRT, it will take a lot of material. It may affect the deflection yoke or the mask behind the CRT screen. Watch out for high voltage and don't get it too near the yoke. I recommend source suppression at the speakers.

Sometimes it is easier to shield the source of the magnetic interference rather than the victim.

The idea as has been correctly stated is similar to "shorting out" the magnetic flux path. This provides a preferred return path for the flux lines to follow (around the inside of the Mu Metal material instead of allowing it to extend out to other metal objects to return to the source). This provides the field containment that you are looking for. The high permeability provides the ability to contain the field.

This company will provide you sheets of the material which you could wrap the material around the speaker magnet assembly. Be aware that the speaker frame may also be part of the problem. Don't cover the rear cone area though if you want any low frequency performance (grin).

In working with Mu Metal, it is not a good idea to hammer on it, just form it to the shape you want and test it out. If you hammer it, it will probably need to be re-anealed (heat treating process that re-polarizes the material).

http://www.lessemf.com/mag-shld.html

I am not affiliated with the company, I do Signal Integrity & EMC design.

Ross Wellington