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Shield speaker magnet from activating reed

  1. Feb 16, 2012 #1
    My question pertains to model trains. I use a magnet under my last car to activate computer commands via a reed switch. One locomotive has a speaker placed near the bottom and the magnet of the speaker activates the reed switch - which I don't want it to do. One thought to correct this is to place a thin substance under the locomotive, between the speaker and the reed, this substance would block/distort/weaken the magnetic strength. It would need to be thin. Is there such a material. I tried aluminum paper but that did not work.


  2. jcsd
  3. Feb 16, 2012 #2


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    Staff: Mentor

    It needs to be ferrous (like iron) in order to deflect/route the magnetic field.

    Try bending a flat piece of iron so that it forms a 4-sided box around your speaker. Drill holes in the diaphram side of the iron strip before you bend it around the speaker. This will divert the external magnetic field lines closer to the speaker, instead of letting them spray out farther where they can affect your reed switch. Try to use the thickest iron strip you can, to avoid having it saturate from the magnetic field so close to the speaker magnet.
  4. Feb 16, 2012 #3

    Thanks for the quick reply. One question I have regarding iron is whether this would eventually become magnetized?

  5. Feb 16, 2012 #4

    jim hardy

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    Science Advisor
    Gold Member

    i used a peach can to shield a subwoofer that was making my TV screen purple.
    It was just right diameter to go around the speaker magnet. I cut it tall enough to cover the exposed part of the speaker magnet's bottom and sides.

    Ordinary iron wont become strongly magnetized. But i think you want sides on your shield ,as Berkeman suggested.

    Many cans are aluminum these days- check with a refrigerator magnet.
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