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help i need shields

Discussion in 'Home Cinema Speakers' started by cypher007, Jan 28, 2005.

  1. cypher007

    cypher007
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    is there any way i can shield the magnets on my speakers, as there about 4ft from the telly and still affecting it :(. any sites or info much appreciated.
     
  2. eviljohn2

    eviljohn2
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    You can get shielding cans for speakers. These aren't shields as such, but magnets to oppose the field generated by the driver, it follows that these really need to be matched to the speaker in question and will change the internal volume of the speaker.

    You could try moving the speakers forward or backwards in relation to your screen, or up and down too if that's possible. Otherwise there's no simple solution other than moving the speakers further away or getting a flat panel display I'm afraid. :)
     
  3. cypher007

    cypher007
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    will lead sheet suppress the field.
     
  4. eviljohn2

    eviljohn2
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    Not really, you could try putting some big lumps of metal between them if you like. I wouldn't recommend leaving lumps of lead lying around the house though! :)
     
  5. Mylo

    Mylo
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    what speakers are they :eek: 4 ft is quite far, I'd be looking at another possible source for the interference.
     
  6. cypher007

    cypher007
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    they were wharfdale linton 3xp's. which were a 3way speaker from the seventies, but what ive done is removed the original tweaters and installed new Audax tw025a0's. so they have a much higher frequency response.
     
  7. cypher007

    cypher007
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    my friend has suggested fixing squares of metal to the inside walls of the speaker. i thought it might work but then again wouldnt the feild still be present from the front of the speaker, as i cant put a metal plate on the front.
     
  8. Paul Smith

    Paul Smith
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    Hi,
    Probably the easiest (and cheapest) way of shielding a speaker is to add bucking magnets to the rear of the drivers.
    It's the method I regularily use to shield any drivers which need to be placed close to magnetically sensitive equiptment.

    Paul.
     
  9. cypher007

    cypher007
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    i was trying to avoid using bucking magnets as this would change the way the speakers perform.
     
  10. Paul Smith

    Paul Smith
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    According to Vance Dickason author of the "loudspeaker Design Cookbook":-

    "A bucking magnet will only slightly change driver sensivity and will not radically alter the drivers T/S parameters, at least not enough to affect box design."

    But everyone to thier own, Good luck with the shielding.

    Paul.
     
  11. Mylo

    Mylo
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    I doubt it would work unless you could get hold of something like Mu-metal which is used to make magnetic shields and is very expensive. Also unless you could take one side off the speaker you would have to put several small pieces of metal inside the cabinet due to the size of the speaker holes which would be a lot of effort.
     
  12. pwood

    pwood
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    On other thing is to turn you TV off at the switch as it will degauss itself when turned on which whilst not being a cure may help slightly while you move the speakers about.
     
  13. cypher007

    cypher007
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    i read somewhere that putting metal caps on the magnets actually is worse than using bucking magnets, because it can affect the magnetic gap? anyway if i use bucking magnets where can i buy them? and what size would you recomend for some 70mm by 35mm magnets?
     
  14. Paul Smith

    Paul Smith
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    Yep that's right, a metal shielding cup will very likely change the drivers T/S parameters quite a bit,
    unlike the use of just a bucking magnet which hardly affects the T/S specs.

    The general rule of thumb for the size of bucking magnets is to have them just slightly smaller in height and/or diameter than the magnet used for the driver.

    As for where to get suitable magnets in the UK, that is the problem isn't it, I haven't yet found a supplier where I can just order the suitable size for the job (posting from the US would likely be expensive).
    Does anybody else know where they can easily be got from??? As I am sure quite a few of us would like to know.

    Anyway this is what I do to get by, I go round my local junkyard and look at appropriate sized car speakers (if they are obviously broken/faulty they should cost you very little), you just pull the cone off and then the spider, normally held by a couple of screws.
    At this point you can either just use the whole motor assembly reversed on the back of your driver, or what I do is heat up the motor till the glue softens and the front and back plates come away just leaving the magnet.

    I hope this helps.

    Paul.
     

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