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Crossover position near magnet

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  • Crossover position near magnet

    My crossover is pretty near the magnet of the woofer and I wondered if I should shield it in some way. When I was a kid in school we used MU metal in electronics cases to keep the noise lower. I don’t think that is good for magnets but I wondered if there was a way to shield things...

  • #2
    An eighth inch of mu metal will do it. Anything less isn't worth the bother. Moving the coils even an inch will help, as the flux intensity of a magnet drops as the square of the distance.
    www.billfitzmaurice.com
    www.billfitzmaurice.info/forum

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    • #3
      Originally posted by billfitzmaurice View Post
      ... Moving the coils even an inch will help, as the flux intensity of a magnet drops as the square of the distance.
      +1. Orient the XO board with the coils away from the woofer. If its a DIY XO, maybe a physical redesign/rebuild can maximize distance from the magnet. There are "rule" for XO component orientation/placement on the board. So, if you decide to re-do the XO, consult first.

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      • #4
        Click image for larger version

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        Thanks gentlemen. I may ultimately have to redo the crossover. It was in a vertical box but in my soundbar with the new boxes laying on the side, the crossover only fits on the bottom. It was on the back wall.
        I may need to make a completely new crossover...


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        • #5
          I almost always put my low pass and high pass sections on different boards. Doing so you're far less likely to make a mistake in the wiring, the smaller board sizes make it easier to mount them out of the way, and since the inductors on the high pass and low pass boards are much further apart cross talk is eliminated.
          www.billfitzmaurice.com
          www.billfitzmaurice.info/forum

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          • #6
            Originally posted by billfitzmaurice View Post
            I almost always put my low pass and high pass sections on different boards. Doing so you're far less likely to make a mistake in the wiring, the smaller board sizes make it easier to mount them out of the way, and since the inductors on the high pass and low pass boards are much further apart cross talk is eliminated.
            THanks Bill. That makes sense and what I will do in the future. Living and learning!

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            • #7
              Steve,

              If you have a DATS and a loose inductor, I'd test the inductor in it's position before going through all the trouble of re-doing anything. I did some testing on coil proximity to neo magnets on the ND91 for the Bantam crossover (air coil inductors, not laminated) and there was very little difference in it's value even just a few inches away, barely measurable.

              Of course, the magnet on your woofer there is a fair bit larger, but you might give it a test before doing a bunch of work... it may not be that big of a deal.

              TomZ
              *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
              *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

              *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

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              • #8
                Originally posted by tomzarbo View Post
                Steve,

                If you have a DATS and a loose inductor, I'd test the inductor in it's position before going through all the trouble of re-doing anything. I did some testing on coil proximity to neo magnets on the ND91 for the Bantam crossover (air coil inductors, not laminated) and there was very little difference in it's value even just a few inches away, barely measurable.

                Of course, the magnet on your woofer there is a fair bit larger, but you might give it a test before doing a bunch of work... it may not be that big of a deal.

                TomZ
                Thanks Tom. I did read about your investigation about that. Much appreciated.

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                • #9
                  It is hard to tell, and I am sure you have tried already, but it looks very close to being able to fit vertically on the right side of the photo, no?

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                  • #10
                    Originally posted by Dukk View Post
                    It is hard to tell, and I am sure you have tried already, but it looks very close to being able to fit vertically on the right side of the photo, no?
                    Thanks Dukk. I will play with that idea. You may be right and I may be left

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                    • #11
                      It's always been my understanding that Neodymium motor designs are "self shielding".

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                      • #12
                        If the magnetic field from the woofer's permanent magnet is static (which it should be) and your crossover inductor is not moving in the magnetic field (which it shouldn't be) then there will be no effect on the inductor, unless its core is already very near to saturation. I highly doubt that you are pushing those big iron cores anywhere near saturation. Electromagnetic Fields 201.
                        Craig

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                        • #13
                          I've noticed that, although neo magnets are more powerful than ferrite, their strength is focused much more closely to the magnet than with ferrite magnets. Or at least that's my observation.

                          I think that's why neo magneted drivers are considered "shielded" their sphere of influence is much closer to the magnet.
                          TomZ
                          *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                          *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                          *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

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