Determining Oval Hole sizing? Template?

[sish]

I just wrapped up my first f-hole kit build and am considering trying to make an oval holed kit using the un-cut IV Mandolin Kit. The problem though... I have no idea what the dimensions on the oval hole should be? Is there a template out there that I haven't found with Google? Is there some nice person on here that has an oval hole and can get me some specs?

If I could make a nice template I imagine I could route the hole out, otherwise it would be go really slow on my scroll saw with a very fine blade.

If you've done one, or know someone else who did, what worked?

Thanks!

Matt

[David Houchens]

I have a set of plans for a Gibson teens A model. I'll see if I can see where they came from. I've had them on the wall forever. I can trace the top profile if they're not available anymore.

[Dave Cohen]

Your IV kit will not have the same body shape or body dimensions as a vintage Gibson oval hole mandolin. Consequently, you have some latitude about positioning the oval hole, as well as its' size and shape. Also, your kit will likely require you to make a suspended fingerboard extension, as it did for your ff-hole mandolin. The way to find the position for your oval hole is to do a full-size drawing of the body and fretboard, complete with fret positions. Decide how many frets you want, then position your soundole so that it is not obstructed (or at least not obstructed too much) by the end of the fretboard.

The single "oval" soundhole is an ellipse. The vintage oval hole mandolins had total soundhole areas in the range from 2.6 sq. in. to around 3.0 sq. in. I have used larger hole areas with some success, about 3.5 sq. in. area. You can also play with the "ellipticity" of the ellipse. That is, you can make a "squashed" ellipse that deviates a lot from a circle, or a rounder ellipse that looks closer to a circle. The more "squashed" you make it, the more you can keep it from being too close to the bridge, but that also depends on how you like the way it looks. If you are not comfortable with simple analytic geometry, you can do your drawing on graph paper to help in estimating your area. You can draw a simple ellipse by placing two pins along the major semiaxis, i.e., the longer axis of the ellipse, making a loop of string or fishing line, placing the loop outside the two pins, place your pencil inside the loop, pull tight, and trace around the perimeter of the ellipse. Too big? Make the loop smaller. Too small? Make the loop larger.

http://www.Cohenmando.com/

[Jim Hilburn]

After I made the only oval I've ever made I discovered the eclipse tool in MS paint. You can easily make any shape oval you want and print it. I'm sure many other illustration programs have the same thing.

[StuartGold]

Just curious. To the who have made a bunch of oval holed mandolins, just what are the tonal implications of the hole being larger or smaller and also closer or farther from the bridge?

[Dave Cohen]

Just curious. To the who have made a bunch of oval holed mandolins, just what are the tonal implications of the hole being larger or smaller and also closer or farther from the bridge?

"Tonal implications" are difficult to talk about, partly because tone is so subjective, and partly because tone is not easily quantified. Nevertheless, there are a few things that can be said. First, the soundhole position has structural implications. Put the hole too close to the bridge, and you compromise the structural stability somewhat. The top plate will more easily collapse in the region from the bridge to the soundhole, and the tendency to bulge in the area between the bridge and the tail will be greater. Neither of those tendencies are certainties, but are more likely when the hole is closer to the bridge.

Make the soundhole area smaller, and you lower the frequency of the main air resonance; larger, and you raise the frequency of the main air resonance. Move the soundhole position toward the heel and you lower the frquency of the main air resonance slightly. Move the position toward the bridge, and you raise the frquency slightly. What does that mean for "tone"? Imo, lower air resonance frequencies tend toward a more "tubby" sound. Higher air resonance frequencies tend toward a more projective, but less warm, low end. All of that assumes everything else is equal. Those qualities are not determined by air resonance frequency alone. Rather, they depend on the interaction of the air resonance with body resonances. There is quite a bit of data on this in my chapter in the 2010 Rossing book, "The Science of String Instruments".

http://www.Cohenmando.com/

[Ron Cox]

Just the thread I was hoping would show up! I too plan on taking on an IV kit (without holes cut) and was wondering where to get this kind of info.

I am anxiously awaiting my copy of the Siminoff book and hoping there are some more answers there as well.