Banjo skin for guitar

ShawnShawn Boise, Idaho✭✭✭✭
This may seem an odd idea, but I have been contemplating the function of one for awhile now...mainly to achieve a tone between the spectrum of a guitar and a banjo. What I intend to do is make a removable sounhole banjo head that can slip in and/or out of the larger D-Hole size of a Maccaferri. I realize how difficult this may be to accomplish, but I think I can work out a usable design that would fit smoothly over the soundhole.

Now for the big question (for any experimenters or luthiers)...will this achieve the tone of a banjo somewhat? Or, alternatively, will I end up with with an odd looking and sounding guitar?


  • KlezmorimKlezmorim South Carolina, USANew
    Posts: 160
    If I understand your scenario correctly, you are going to plug the soundhole with a taut membrane? Where does the sound come out? The "soundhole" is just that; the hole where the sound comes out of a guitar.

    On a banjo, the "soundhole" is/are the openings between the tone ring (upon which the head is fastened) and the resonator. The tone of a banjo is due to a very thin bridge resting a very tight membrane; quite different than the wooden top and relatively massive bridge of a guitar.
  • ElliotElliot Madison, WisconsinNew
    Posts: 551
    I say try it - I have a cigar box guitar made by a guy in Kentucky and it has 2 soundholes at the top with small kitchen sink drains in them - the cheap ones with holes not sieves - that work perfectly as resonators.

    A small aluminum pie dish with holes in it glued to the inside I bet would work.... :)
  • ShawnShawn Boise, Idaho✭✭✭✭
    Posts: 325
    I'm not really wanting to plug the soundhole so much as create a thin percussive removable membrane over a portion of its size. This means I would of course leave areas for the sound to escape, but create a "sort of" internal resonator made of calf skin or plastic stretched and pulled like a banjo head.

    I'm not really trying to recreate the sound of a banjo with this project, but rather giving a Maccaferri a slight percussive edge for greater tonal nuances. I play a bit of banjo on the side once in awhile, and was trying to think of how to incorporate that percussive edge into the framework of a guitar. Essentially taking the idea of the original internal resonator and making a removable one out of banjo head material.

    At this point, I know I can make a suitable device to fit in the soundhole, but I'm not 100% sure it will yield the correct tonal qualities I seek.
  • Bob HoloBob Holo Moderator
    Posts: 1,250
    Hi Shawn, The soundhole is a port which tunes the resonance of the body cavity. Google "Helmholz Resonator" and you'll find information on it. By plugging or partially occluding the hole you're changing the tuning frequency and pushing the guitar closer to an aperiodic (lossy) or completely sealed enclosure. To make a long story short, you lose bass doing this. Depending on how heavy your resonator is and how you attach it to the soundboard you will weight the soundboard which will reduce its efficiency and lower its resonance frequency... so it'll be softer and have less snap. As to whether the skin vibrates and has some tone - who knows - it probably will. Instead of mounting something to the soundhole or the soundboard. It sounds like the concept you're tossing around is a horn loading situation - or at least some kind of wave-guide. I'm sure you can google this too. About the banjo tone - for the most part, the banjo sound comes from the extremely light soundboard (skin) that is under extreme stress (stretched) and unbraced. Hence it is very efficient, has a high resonance frequency - and has tons & tons of undampened harmonics. Skin is somewhat elastic, very split resistant, and isotropic (same strength along all axes) and so you can just stretch it and put the pressure of a bridge on any point much as you'd change the pitch of a tom-tom by digging into it with your elbow or hand. Wood wouldn't fare so well if a person did this ;)

    The Mac resonators were interesting devices which had a cool function that wasn't what Mario Maccaferri intended. They worked because they partitioned the internal cavity of the guitar into multiple chambers and altered the body/port tuning. Guitar resonators (like steel guitars) are another interesting concept - take a look at the design of Dobros and you'll sort of see what they're doing and it might inspire you.
    You get one chance to enjoy this day, but if you're doing it right, that's enough.
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