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From: Ross
Remote Name: 76.101.10.136
Date: 10 Apr 2007
Time: 09:04:36 -0400
Luthier’s Weblog 4/10/07 Today, the luthier takes a walk along the shoreline. For a long time now, I have mentally used the term “shoreline” as a description of the outline of an instrument body, the shore being what the Spanish luthier would refer to as the “Plantilla”. The ribs delineate this shape, and the top overlays it. Using an enclosed body of water, or lake, as a model, we see that the regularity of the shoreline determines the ratio of the length of the shoreline to the area of the length. For a fixed water area, the smallest ratio will be described as a circle. Elongating the circle into an oval, or introducing irregularities into the arc of the circle (such as coves, inlets, bays, or peninsulas) increases the ratio. Moving this model to the guitar, we see that, relatively speaking, the dreadnought guitar has a smaller ratio than a tight-waisted jumbo body style. Introducing a cutaway further increases the ratio. A banjo, of course has the smallest ratio possible. So what are the advantages of a lower ratio to a higher ratio and vice versa? Most obviously, a smaller ratio requires less material and simpler construction than a sound box of identical volume but greater ratio. Further, it is easier to locate the bridge “island” in a location that maximizes distance to “shore”, thereby assisting lower frequency propagation. On the other hand, a greater shoreline : area ratio provides more rigidity to the sides, making for a more solid top support. Also, when the shoreline is thoughtfully manipulated, top area can be arranged to maximize distance of the bridge “island” to shore, while simultaneously increasing rib rigidity in the areas that most require rigidity. And of course the area that requires the most rigidity and the stability it imparts is…the neck block area. By closing the ribs in on the neck block and using the tight curve of the cutaway to decrease side deflection, neck/body stability may be increased. A smaller upper bout results, (if, indeed, one incorporates a waist). Which means that the lower bout may be larger. Since proximity to the bridge determines the acoustic active-ness of a particular unit of top area, it may reasonably be supposed that diminishing the area of the less acoustically active upper bout in order to increase the prime real estate of the lower bout will result in tonal gains. Can the reduction in area of the neck/body region really make the neck joint more stable? After all, there is strength imparted by the extra tone wood of the top and back of the larger upper bout design. I believe that the loss of this material is more than offset, way more, by tightly bent side material in closer proximity to the neck block. The increased support of the neck block by the cutaway alone results in a marked strengthening. The luthier licks his chops in anticipation of what he can do with all that extra volume and area he can shift to the lower bout! Ross Teigen 9:06 am