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would something like this even work? I know the Larson Brothers built two twelve fret classical dreadnoughts, but not a 14 fret one.

I dunno, but if you try it, let us know how it turns out

My guess is that it would be too quiet and boomy/muffled sounding at such a large size. A larger soundhole might help some.

Are you thinking X bracing, or fan bracing with a cross strut below the soundhole like most classicals? That lower cross strut is what determines whether 12 fret or 14 fret bridge position is closer to the sweet spot.

I've been a little tempted to try an X braced nylon stringer. Probably more OM sized (~15" lower bout), and with 4 or so fan braces in place of the usual tone bars. But first I need to just build a regular classical, since it's pretty unlikely that my fiddling around with designs would sound as good as one that's been so heavily refined

If you want to stay with fan braces and a lower transverse brace (below the soundhole) as in most classicals, you will want to stay with a 12 fret to the body neck, to move the bridge further back towards the sweet spot of the lower bout. There is a good discussion in Somogyi Volume 1 about why an X-braced 14 fret guitar works with the bridge shifted so far towards the neck - the vibrating area of the surface is also shifted forward by virtue of the absence of the lower transverse brace, which most people think is a vibrational show-stopper. (Note that the Smallman-style lattice brace guitars are basically totally rigid in the top on the neck side of the lower transverse brace position.

Check out the Rodriguez plan from GAL. It is a big guitar, and the design seems to successfully deal with the potential boominess of the large body (as I would attest to, having built three). Rodriguez uses an additional treble bar that spans the entire width of the top, intersecting the lower transverse brace diagonally at the center line of the top. I'm not sure I'd want to go a lot bigger than this box (or some of the correspondingly large Madrid guitars) and still be driving the top with nylon strings. I will say that I recently saw Pepe Romero playing his Rodriguez unamplified in a hall holding about 400 people, and the guitar produced enough sound to work in that space (but perhaps requiring close attention).

I would hesitate to bring an X-brace to a nylon string instrument, as I've read too much about the nylon strings not having enough energy to move the top if the cross-dipole is damped too much, but heh, I've never tried it, so what do I know? I think Al Carruth has indicated positive results with a few X-braced classicals. I'd love to see specifics of that design.

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Jim Kirby
kirby@udel.edu

Yeah, you'd probably want to make the X pretty light, especially on the lower legs where the fans could handle much of the necessary stiffening. The idea would be to free up more vibrating area and get a richer tone, especially in the low range, plus allowing the 14 fret neck.

I wonder though, would it be better to stick with the tight long dipole and loose cross dipole, or do the "dipole role swap" and loosen the long dipole as much as possible? Might be tricky to loosen the long one enough without the bridge bubbling up. Maybe do a triple-X bracing layout? The main X, plus a light double X in the lower quadrant to distribute the bridge force around without tightening the long dipole too much. I'm thinking very thin top as well.

Loose long dipole would probably also work good in a parlor shape.

But back to the original topic, another option for a 14 fret neck is to simply shorten the upper bout to make room for it with the normal bracing. Might look a little funky though, especially on a dreadnought.

Wouldn't really loose long dipole = ladder bracing, which of course does indeed work really well for parlor guitars?
Any number of non-Spanish, baroque to romantic era guitars are ladder braced, but these are also all very small bodied instruments, and so this may not be much guidance for a dreadnaught sized guitar.

A lot of 14 fret instruments were indeed 12 fret instruments with truncated upper bouts, yes? 000's?

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Jim Kirby
kirby@udel.edu

A dreadnought classical is not a great idea...............Bigger is not neccessarily better when it comes to classicals because there's not enough energy in nylon strings to efficiently drive a body much bigger than around 15".
Martin introduced the large 000-28C classical in the early sixties and dropped it a few years later in favor of a 00 size in the same style.
They recently came out with one in 000 size which used an "X" brace which worked surprisingly well. The guitar itself was mahogany with a cedar top.
The other important factor here is that the larger the body, the lower the resonance. Thus a larger body will lack the brightness in the treble which is the whole point of the classical guitar in my opinion.
There is a reason that every good classical guitar you will see falls within around 10mm of every other one in every measurement.
A 14 fret neck can work fairly well on a classical provided you make some fairly major adjustments in the body due to the new bridge location. My 14 fret model uses a 15" body to keep the top flexible at the 14 fet bridge location and is both shallower and with a larger sound hole to keep the body from being too bass resonant.

David answered well. But my question is "Why?" What are you hoping to accomplish?

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Expectation is the source of all misery; comparison the thief of joy.
http://redrivercanoe.ca/

Sorry double post

The reason I want to use a dreadnought is because The Larson Brothers built two classical's/steel string guitars that according to what I have heard from George Gruhn and Bob Hartman, The X Braced Dreadnoughts sound great as classicals. The reason I started this thread is because I wanted to know how well a 14 fret classical would work. I don't really care how the guitar sounds, I have no intention of selling the guitar when it is finished. Oh and I forgot to mention, Dreadnoughts are awesome!!!

?? What other criterion is there? If the guitar doesn't sound good, in what other sense would you judge it to be "working"?

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Jim Kirby
kirby@udel.edu

I once played a regular dred with nylon strings on it (belonged to a lady having issues with steel strings). I was amazed by how "Spanish" it sounded, but the volume was only marginally better than that of an unplugged electric )

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Build log

If this is a personal investigation I say go right ahead!

I would offer if you are going to build it, to build it to optimize nylon strings as well as possible. Don't just build a Dred like a SS and expect it to be good as a nylon string guitar.

The photo is of a 12 fret neck.

I would go 12 fret neck and use the X brace but much lighter than for SS.

It is still amazing to me just how much sound a smaller body classical can put out. I remain to be convinced that a Dred size body will offer any real improvement.

_________________
Expectation is the source of all misery; comparison the thief of joy.
http://redrivercanoe.ca/

"The Larson Brothers built two classical's/steel string guitars that according to what I have heard from George Gruhn and Bob Hartman, The X Braced Dreadnoughts sound great as classicals"

As compared to what??

With all due respect to George and Bob, I'm not sure their frame of reference is what it might be.

If this project is just a personal bit of self indulgence, have fun! (I'm all for self indulgence) especially considering that you're not too concerned about the results.

This guitar is just going to be an experiment. I just really like the larson brothers and have a strong desire to try something different.

Classical guitar strings don't necessarily have less energy than steel strings. The energy in a vibrating string goes as the tension and the square of the amplitude. Classical strings do carry less tension, but they are also normally set for a higher action, and the extra height can more than make up for the lower tension.

What nylon strings lack is high frequency energy. If you pluck a steel string and a nylon string in the same place they will start off with the same mix of partials with the same relative power. However, nylon itself has a much higher damping factor than steel (try tapping plates of each some time) and the thicker nylon string has to move more air in order to vibrate. This doesn't help it produce sound, any more than trying to run in water up to your knees produces much of a current. It just takes work to make it happen. The result is that after a second or so the nylon string will have almost no energy above 2000 Hz, while the steel string will have plenty of energy out to 8k.

So, the central problem is different for steel string and nylon string guitars. With steel you're trying to get enough bass to balance out all of that treble. With nylon you're trying to make the best use of the little bit of treble you have, and not overpower it with too much bass. Generally speaking, it's easier to get bass than treble: you make the guitar bigger.

It's actually easier to make a loud small guitar than it is to make a loud big one. You need to have a structure in the top that can keep the bridge from folding up too soon. All else equal, the smaller the span the stiffer, so as you increase the size of the top you need to beef up the structure, both the top thickness and the bracing. In general, for a given structural geometry, the weight of the vibrating area goes up faster than the area as you make the span bigger, and it's the ratio of Area/mass that establishes how loud the guitar can get. So, for a given structual setup and set of wood, the smaller top will tend to have a higher A/m ratio, and be louder.

X-bracing is somewhat more efficient structurally, so you can make a larger top with X bracing for a given weight and stiffness. The thing that changes is the relative pitch of the 'cross dipole' resonant mode. Usually both steel string and nylon string guitars that I consider good (YMMV) have their monopole mode at around 180-200, and the long dipole somewhere near 350. However, on nylon string guitars the cross dipole is usually around 250 Hz or lower, and it's as low as 220 on some Flamencos I've looked at. Steel strings usually have the cross dipole up around 300. This seems to have an effect on the band width of the 'main top' (top monopole) peak in the output spectrum: it's often wider on steel strings than nylon because the cross dipole is not stealing energy from the monopole. A narrow 'main top' peak tends to give a 'cutting' or even 'harsh' sound. Flamencos like that, and classicals can often use a bit of it as well.

I have built two 12-fret 000 classicals, both with BRW B&S, one with a Red spruce top and the other with cedar. The Red was a bit 'edgy' for me when new, although it may have 'played in' to a more mellow sound. The cedar top has worked nicely. I used 1/4" bracing, and kept it quite low. I do think the BRW helped keep the trebles from getting lost. You might try Osage or Padauk if the bank account can't swing Brazilian.

Alan, I'd appreciate it if you would flesh that out for those of us who are engineering challenged. I'm assuming you're making some assumptions when you say "a given structural geometry". Are you scaling top thickness and brace height equally? How and where are you measuring stiffness?

It seems that one way to match the stiffness a of a shorter span to that of a longer span is keep the top the same thickness and increase the brace height. Wouldn't you then end up with less mass per square inch on the larger top?

Not arguing but I'm guessing you have a good reason for thinking in terms of adding top thickness and brace height on a larger body.

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http://www.chassonguitars.com

I'm engineering challenged, too! I've dug out a bit of the math, but not everything I'd like.

Stiffness, in this case, is the ability of the top to resist deforming at the bridge from the static load of the strings. This is what sets the limit on how lightly you can build the top.

According to my copy of 'Luthier's Toolbox Light' that Charles Fox gave me back when world was younger, doubling the length of a given beam gives eight times the deflection under a given load, and I'm pretty sure the same holds true for a top. To get the deflection back down to the initial value, you need to double the height of the beam or the thickness of the top. That's because the stiffness of a beam goes as the cube of the height.

Let's assume we're looking at the lower bout only, and it's close enough to a circle for government work. We'll call the initial area one square foot, and the mass one ounce. Doubling the span gives you four times the area: four square feet. To keep the stiffness up, you need to also double the thickness; so four times the area times twice the thickness gives eight times the mass. The ratio of area to mass has gone from 1/1 to 4/8=1/2.

If you have settled on some standard bracing scheme, you'll need to double the height of the braces as well. You might also want to make them a little wider, to keep the relationship between the brace stiffness and the gluing area, and that adds some weight too.

So there's no getting around it; bigger tops are heavier for a given stiffness, assuming you use the same material and don't find a more efficient brace layout.

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