F hole vs Oval hole thickness graduations.

[Roger Kunkel]

I had a good experience building a Stewmac A-5 kit. The plan included with this kit depicts a f hole build with parallel tone bars or an oval hole build with X bracing, but suggests the same thickness graduations for both. I'm wondering if it is typical for a hybrid F4/F5 oval hole to use the same graduations. Thinking of building the oval hole version so I thought I'd see if folks have opinions on this. Thanks.

[mandobassman]

That's interesting. Based on what I've seen from Gibson F-hole and oval-hole models, I was always under the impression that the tops on oval hole models were thicker. Not being a builder, I have no evidence of this, it always just seemed this way. I'm curious to hear from the builders on this.

[sunburst]

Here (http://www.mandolincafe.com/forum/showthread.php?89383-Building-an-A-Style-Mandolin-F-hole-vs-Oval-Hole&highlight=oval+hole) is a recent thread.

[Rob Grant]

FWIW: This (below) is how I brace my F style ovals... I graduate to pretty much the same specs as a standard Loar style F5, but I strengthen the area between the top of the hole and the neckblock. I usually reinforce this area with a 2 ply reversed laminate (from the same timber as the top plate) applied to the inside of the top plate in the area specified by the "red X" ( below attachment 94366). I then "feather" the edges of the applied laminate with sand paper and blend it into the the top contours. I do the additional reinforcement because I use an F5 style fretboard extension that doesn't touch the top.

94366

[mandobassman]

Here (http://www.mandolincafe.com/forum/showthread.php?89383-Building-an-A-Style-Mandolin-F-hole-vs-Oval-Hole&highlight=oval+hole) is a recent thread.

John, Is there any specific reason that the oval hole tops are thicker than the F hole tops. It's the same amount of pressure on each, I would think that the top would be more responsive if made to the same thickness as F hole mandos. As I stated earlier, I'm not a builder, I'm just wondering, do most builders just copy the Gibson A model forumla? I'm sure there are builders who have thought this through. Are there any current buliders who build with thinner tops for oval hole models? I haven't examined oval hole models from any of the current big builders, such as Wewber, Breedlove, Collings, etc..., Do they all use thicker tops than on the F hole equivelants?

[Marty Jacobson]

I believe a quote from Dr. Rossing (http://www.amazon.com/Science-String-Instruments-Thomas-Rossing/dp/1441971092) concerning oval-hole instruments is that they are almost completely different instruments than ff-hole models. At least in terms of the way they produce sound.

So they are all thicker, generally speaking, though Rob has already chimed in and says he doesn't do that. So much for that generalization. Though as you can see he offsets that with a his own bracing solution.

Wood matters, too. I have a Western Yellow Cedar top which is actually thinner than Loar specs. But it's a very, very strong, dense top, so the dimensions are kind of misleading.

The problem with oval-hole tops (any top plates, really) which are too thin is that they just don't produce a strong treble range. Everything has to be balanced.

[sunburst]

Not only do we call upon the top of a mandolin to be the first (along with the bridge) component to get the whole sound-producing mechanism of the instrument going, but we call upon it to resist the compressive load of 8 steel strings lengthwise the top while also counteracting the downward force of those strings pressing the bridge into the center of top at something like 50 pounds. The center of the top, from head block to tail block, is the structural part that must deal with all that load from the strings. Now imagine we decide to cut a hole right in that center-line part of the top... or instead, we decide to cut two holes over to the side where the structural aspect of the top is less important. Which top would need to be thicker to perform it's structural role? How should we compensate for the removed wood of the hole(s) with bracing to keep the structure intact for hundreds of years under that kind of string load? Those are some of the structural considerations involved other than response. It is a balancing act. Too thin leads to structural problems (like the ubiquitous sinking tops of old Gibson ovals) or even collapse. To thick leads to a mandolin with longevity that sounds fine inmost cases unless the thickness is really overdone.

As for response and sound, the mechanisms at work in an oval hole mandolin are enough different from those at work in an f-hole mandolin (mostly the air modes and how they interact with the top and back) because of the hole position, that thicker tops tend to help control the sound of oval hole mandolins and keep them more balanced and less "boomy" or "bass heavy".

[Roger Kunkel]

Thanks for the replies. Looks like the Siminoff plan would be a good place to start. I see he offers a F4 kit which might be a good choice for me.

[mandobassman]

Thanks for the explanation John.

[Dave Cohen]

Marty. Tom Rossing didn't say anything about mandolins in the 2010 book. That was his initial comment to me in DeKalb, back in 1999 (or was it 2000?), which makes it an anecdote at any rate. Anyway, I wrote the chapter on mandolin family instruments in that book.

We have come around to a more moderate position re the two types of mandolins. The body modes are very similar, and so are the air modes. What is different about the two types is the way in which the body modes and the air modes interact. The really huge difference is between Neapolitans (bowlbacks) and all the rest of the mandolin types.

http://www.Cohenmando.com