Question About Rod Magnet Size

Discussion in 'Just Pickups' started by micpoc, Oct 26, 2018.

  1. micpoc

    micpoc Friend of Leo's

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    I was wondering what sonic differences using different size rod magnets in a pickup will make, all other things being equal.
     
  2. DCW74

    DCW74 Tele-Meister

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    I imagine it would just make a hotter or cooler pickup based on the size of the magnetic field. A bigger magnet with the same amout of coils would necessarly have a stronger field.
     
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  3. Teleterr

    Teleterr Friend of Leo's

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    Attack. Big magnet vs small is different, so is beveled vs non.
     
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  4. Antigua Tele

    Antigua Tele Friend of Leo's

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    Unlike most other magnets, AlNiCo has a lower coercivity and a higher permeability, which means the shape of AlNiCo impacts the strength of the magnet. The get the greatest amount of strength, the length of the magnet has be to about four times the width of the polar faces. Ceramic and rare earth magnets have a high coercivity and a low permeability, so they can be formed as flat buttons, but AlNiCo requires more length in order to work well. So if you simply make an AlNiCo pole piece wider, like a Seymour Duncan Quarter Pound, becuase the length is not increased to account for the added width, the overall strength is not that much greater. That's why you don't see crazy "stratitus" effects with those pickups, the magnets are much larger, but not much different in terms of strength. Some people assume the Quarter Pound is a loud pickup because of the large pole pieces, but it's the high turn count coil that is the cause of that, the magnets are not especially strong, and if you tap a Quarter Pound coil to half the turns, it then produces a tone similar to any other Fender single coil . So in this respect, the diameter alone doesn't matter so much as the overall dimensions of the AlNiCo pole piece.

    The other impact of pole piece diameter is the degree of "focus" it yields. The guitar string is divided up into harmonics, each harmonic has an actual physical width associated with it. The higher the frequency, the smaller the physical harmonic width. If the harmonic width is smaller than the diameter of the pole piece, than they start to cancel out (treble), which places more emphasis in on the lower harmonics (mids and bass). It's analogous to losing detail due to reduced focus. With this tool http://www.till.com/articles/PickupResponseDemo/ , you can change the "width" value of the pickup, which is effectively the same as changing the pole piece diameter, and as you increase the value, you can see that the amplitudes increasingly drop off in the higher frequencies. The thing is, the pole piece has to be really wide, like an inch or greater, in order to have a significant effect within the audible spectrum, and no production pickup on the market that I know of has that wide of pole pieces. Humbuckers come close, but because it's two distinct fields side by side, and not a single, wide magnetic field, they let through high frequencies in bands. Using that Tillman demo, you can click "Add Pickup" and put two smaller coils side by side to see what that looks like. The pole piece diameters are about 0.18", so you can input that value to get a realistic simulation.

    In practice, the pole piece diameter doesn't matter, aside from what it means to the overall strength of the magnetic field. The reason the diameter is what it is, is because it yielded optimal strength for a given depth.
     
    Last edited: Oct 27, 2018
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  5. micpoc

    micpoc Friend of Leo's

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    Excellent info... thanks!
     
  6. Teleterr

    Teleterr Friend of Leo's

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    The rods diameter determines the coils aperture size which effects how it sounds. Wide aperture gives a smoother attack.The width of the magnet may or may not have a magnetic difference , but it certainly effects the sound due to the physical constrants it imposes on the coil gap.. I had a wide appature coil and tried various magnet sizes in the gap. A little difference, but the gap was the dominate feature.
     
  7. micpoc

    micpoc Friend of Leo's

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    It makes sense that, in actual practice, it would affect some other physical aspects of the pickup, which is why I said, perhaps unclearly, "all other things being equal", i.e., nothing else changes at all. Sorry, I should have been clearer, my mistake.
     
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