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Why are neodium magnets not bigger

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  • Why are neodium magnets not bigger

    Neodium magnets can be smaller but still have the same force as bigger ferrite magnets but why doesn't manufactures make the neodium magnets the same size as the ferrite versions? Yes it would be more expensive but the efficiency would also be greater or doesn't work this way?

    Like the dayton ND series, they are very powerfull and only with a small magnet wich could be much bigger! Would be ideal for portable speakers with high efficiency but they aren't available so probably it don't work this way?

  • #2
    It's usually a cost equation. Why use more magnet than is necessary?

    But when they can, yes the neo magnets can be big as a ferrite. I have such a midrange sitting right here. The magnet strength BL would go go way up, sensitivity would go up, but in a woofer/fullrange other things will go down...

    Comment


    • Scarface1
      Scarface1 commented
      Editing a comment
      Thanks, what will go down in woofer/fullrange? I have a small 2 inch "fullrange" using for a bluetooth speaker and was wondering what a bigger magnet could do. Still i have nothing i can do about it but let's say 2 db efficiency more is a lot for a battery powered speaker!

  • #3
    Originally posted by Scarface1 View Post
    Neodium magnets can be smaller but still have the same force as bigger ferrite magnets but why doesn't manufactures make the neodium magnets the same size as the ferrite versions? Yes it would be more expensive but the efficiency would also be greater or doesn't work this way?
    It doesn't work that way. With higher flux Qes would go down, but that doesn't give increased sensitivity across the board. Response gets tilted towards the high frequencies.

    www.billfitzmaurice.com
    www.billfitzmaurice.info/forum

    Comment


    • #4
      What Bill said. When you see huge magnets, it's because the gap is very long, like in a subwoofer, so more total magnetic flux is needed.
      Francis

      Comment


      • Scarface1
        Scarface1 commented
        Editing a comment
        Ok i see, so the magnetic force become less efficient and is solved with a bigger magnet?

      • fpitas
        fpitas commented
        Editing a comment
        The greater area of the gap needs that much more energy.

    • #5
      Neodymium.

      Comment


      • fpitas
        fpitas commented
        Editing a comment
        Yes. Neodium is a VERY rare earth.

    • #6
      Large neodymium magnets are dangerous and can cause injuries. I played with two small ones each about the same size as a Ritz cracker. Them darn things crashed together so hard that they shattered and sparks flew!

      Comment


      • fpitas
        fpitas commented
        Editing a comment
        Yeah, you have to be careful. For a driver, usually you magnetize them in place, after they're positioned and glued.

    • #7
      Originally posted by djg View Post
      Neodymium.
      I guess it went over his head, he didn't get it.

      Comment


      • fpitas
        fpitas commented
        Editing a comment
        The spelling of neodymium isn't uhm, elementary ;)

    • #8
      Thanks guys!! Just curious

      Comment


      • #9
        I will comment, when I first saw neodymium drivers I was a little amused how small the magnets are. But I've designed with it, and the stuff has tremendous energy density, especially compared to ferrites.
        Francis

        Comment


        • #10
          Originally posted by fpitas View Post
          I will comment, when I first saw neodymium drivers I was a little amused how small the magnets are. But I've designed with it, and the stuff has tremendous energy density, especially compared to ferrites.
          Exactly this is why i'm thinking why not bigger? I guess when they say the greater the erea( dept ) of the gap the more energy is needed but this is about dept, you also can make it wider, wich you don't see that much with neodymium ( i haven't seen it at all )

          Comment


          • billfitzmaurice
            billfitzmaurice commented
            Editing a comment
            As I said, higher flux gives lower Qes. Model two woofers with specs that are very close except for Qes, say one with 0.35 and another with 0.20. You'll have your answer why large neo magnets aren't used. As for not using deeper neo magnets versus ceramic that's all about price.

          • fpitas
            fpitas commented
            Editing a comment
            The optimum aspect ratio of the magnet is also determined by the B/H ratio, if I recall my magnet design from 30 years ago. Ferrites favor a short, wide magnet. Alnico (for example) tends to be more square.

        • #11
          https://totalelement.com/pages/2022-...rice-increases

          Comment


          • fpitas
            fpitas commented
            Editing a comment
            It went from an obscure laboratory curiosity to being the darling of modern electromagnetics. Would have been nice to invest.

          • billfitzmaurice
            billfitzmaurice commented
            Editing a comment
            Supply and demand. Until fairly recently the main use of neo magnets was in computer hard drives. Now the primary use is in electric car motors and wind powered generators. It takes a lot more neo to meet that demand.
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