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Thread: Mandocello nut

  1. #1
    Certified! Bernie Daniel's Avatar
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    Default Mandocello nut

    Hello,

    I'm going to do a "reset up" and a K-5 style mandocello that made some years ago. I think that I want to move the four courses more to the center of the nut thus reducing the inter-string and inter-course distances. I think bar chords will be easier to make with that set up?

    To that end I modified an Excel program for calculating nut configurations so that it would plot out how the nut would look if properly slotted. (the base program was originally written by Jerry Beyers a Cafe member). The top image shows the proposed new nut configuration the bottom image is the nut arrangement that I have now.

    My concern is that I could end up with the C strings too close together? They could interfere with each other when vibrating?

    Anyone know off hand a rule of thumb that relates string diameter (e.g., C string 074") to minimum inter-string distance in a course?

    Here in the new set up I am proposing a distance of 0.23" (center C1 to center C2 string). This translates to a distance between the inner sides of the two C strings of 0.17". (that is 0.23" - 0.074")

    Could there be a problem?

    Open C on the mandocello is C2 fourth the wave frequency (f) is known to be 65.41 Hz. The length of its sound wave would be: λ = Vs/f (where Vs is the speed of sound and λ = wave length). Further we can get the amplitude (a) of the wave (trough to peak) by a = λ/f. So going through the numbers I get an amplitude of about 0.081" for the mandocello C-string. That seems reasonable to me?

    So the two strings might have to be separated by 2X 0.081 = 0.162" to avoid touching

    So maybe I'm on the edge of what might work with this set up? That a separation of 0.17"?

    Or should I not equate amplitude of the sound wave with that actual movement of the string? I'm going to look into that but maybe someone else already has?

    Click image for larger version. 

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    Bernie
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  2. #2

    Default Re: Mandocello nut

    I have no experience with any double strung instrument larger than an octave mandolin. My guess is that you may be OK, provided the spacing at the bridge does not change. The widest arc of string vibration will be at the octave fret and at that point the difference in spacing will be 1/2 what it is at the nut.

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  4. #3

    Default Re: Mandocello nut

    Amplitude is not related other than to how hard you pluck the string. Rule of thumb might be if, at the midpoint, the inter-string distance is more than or comparable to twice the non-buzz action height, you should be good. (The two strings can buzz against each other since they’re not in phase, so twice). If my imitation mandola is any example, you’re probably good at less than that separation.

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