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Thread: Practical knowledge of interaction between strings and pickups?

  1. #1

    Default Practical knowledge of interaction between strings and pickups?

    I want to understand more about acoustic mechanics or what it can be called. I have not found much information that is usable for me. Can you help me find information regarding string dimension, distance to pick up pole piece etc. versus loudness (acoustic), electric output from pick up etc?
    I would wish for information like “if the cross area of a string is increased with 25% then the loudness will increase with 25% and the pick up output will increase with 50% implied the same pitch, and the same pluck force”. I believe that I would be able to profit such information.
    By the way, do you pull an A-string with the same force as an E-string?
    And what is the difference between playing e.g. a g2 on the A-string with the g2 on the E-string when it comes to loudness and electric output?

  2. #2
    Registered User Tom Wright's Avatar
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    Default Re: Practical knowledge of interaction between strings and pickup

    With luck Pete Mallinson of Almuse will add more info and correct my mistakes but here's what I've learned. I hope I'm not telling you stuff you already know.

    A text on electromagnetic field calculation would give you the precise relationships, but in practice the math is not necessary. This work has been done, through trial and experience. If you intend to design pickups, find one you like and make changes in that design.

    The general relationship is that fatter strings do make more output, but this is not a linear ratio, since it is reduced by the higher tension of those strings. Players do not want to compensate for different string response so they choose gauges that balance to a good approximation. The electrical response will be very close to the mechanical (acoustic) response, and the g2 on the A should be the same as g2 on the E. It will be the same mechanically, but in that special case the E tends to be weak in most pickups, whether mandolin or guitar.

    An important factor in pickup tone will be the shape and strength of magnet field, other things being equal. A wide, mild field will be clean, no clipping distortion. Strong, narrow fields will clip but be louder. Separate pole magnets have a certain tone, and allow for string loudness compensation. A bar magnet with screw pole pieces will also allow that, but needs more depth to include the magnet under the coil. Keeping a pole-magnet pickup farther from the strings will make for a clean tone and OK coverage when bending the string.

    Unequal things include double-coil hum-suppressing pickups. These lose some high harmonics since neighboring harmonic nodes are not picked up (being motionless) so a large amount of harmonics is missing. Single-row pickups lose fewer harmonics. Missing some harmonics is not a bad thing, since this is the source of magnetic pickup tone, less complicated than the acoustic sound.

    Also important is that the standard design only responds to vertical movement, at right angles to the plane of the coil. The explanation is that the magnet induces field in the string, so the coil sees a moving magnet and responds to changes in distance. Total output will depend on all the above and the number of turns in the coil, so the normal gauge is 47 or so to allow for many turns and DC resistance of a few thousand ohms.

    An interesting design is making the strings the coil and have them simply move in a magnetic field (moving-coil design). For an electric mandolin it is probably a metal bridge, so one would connect two groups of strings behind the nut, and make that the output. Weak, low-impedance output, but fun to do since you can hold any kind of magnet near the strings and get signal. I tried this for alternative violin pickups; it works but is unwieldy for an add-on, and sounded too magnetic for violin.
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    Registered User rockies's Avatar
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    Default Re: Practical knowledge of interaction between strings and pickup

    Gunwald, one of the most often misunderstood items I ran into in my repair business was complaints of low volume and thin tone. Usually the cause was the use of phosphor bronze strings such as j74's instead of monel or nickle strings such as J67's made for electric instruments. Once proper strings were used a remarkable difference.
    Dave
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  4. #4

    Default Re: Practical knowledge of interaction between strings and pickup

    Quote Originally Posted by Tom Wright View Post
    The general relationship is that fatter strings do make more output, but this is not a linear ratio, since it is reduced by the higher tension of those strings. Players do not want to compensate for different string response so they choose gauges that balance to a good approximation. The electrical response will be very close to the mechanical (acoustic) response, and the g2 on the A should be the same as g2 on the E. It will be the same mechanically, but in that special case the E tends to be weak in most pickups, whether mandolin or guitar.
    Thanks Tom, very interesting, so using a heavier string will increase the output some but not much. Or that is how I interpret what you've written. If the E string gives less output than the A string would it then be beneficial to add e.g. a nut on the E pole piece if it's fixed?
    Secondly, how or what will be clipped by a stronger narrower magnetic field? Peak of the amplitude?

  5. #5
    Registered User Tom Wright's Avatar
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    Default Re: Practical knowledge of interaction between strings and pickup

    Yes, adding a piece of metal is sometimes used to compensate instead of pushing pole up.

    Amplitude is clipped, sounds like distortion. The pickups on my Ryder will do that if too close to the large strings, mainly the C.
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