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There's a thread going on over at AGF where people are discussing whether guitars with a 12 fret or 14 fret neck sound better. Most seem to be agreeing that 12 frets sound better, and 14 frets are easier to play... however, Ervin Somogyi's conclusion when building 12 fretters was that they sound somewhat sweeter, but not as powerful as the 14 fret. His explanation makes sense, that the 14 fret bridge is better centered between the upper transverse brace and tail, thus pumping at least the monopole and long dipole more directly. I don't imagine cross dipole would be decreased much either, since the bridge pushing on the legs of the X should transmit force downward to the wide part of the lower bout.

So this has me wondering, why do 12 frets sound better to so many people? Why would a less efficient, indirect driving of the face sound better? More overtones, due to more energy going into modes other than the 3 main ones that act around the center point? Or is it related to the bracing changes that are necessary to support the bridge further down? Perhaps the 12 fret bridge is not less efficient in all cases.

I would be willing to bet the effect is much different on dreadnoughts than on tighter waisted shapes, and that Ervin's observations are at least in part due to this, being that he is particularly famous for his modified D model. The mostly rectangular face of a dread is obviously best driven from the central 14 fret bridge location. But on something like a Gibson L-00, perhaps the waist area is so restrictive that pumping the monopole from the 12 fret position is more effective, and cross dipole almost definitely more effective. J-200's as well, definitely seem like they would be better with 12 frets. Longer body so the center is further south anyway, plus tight waist, and plenty of area to get a good low monopole even when functioning as a round drum with a little extension hanging off of it. Something like Taylor's GA shape is a little more iffy.

So to those who have actually built both 12 and 14 fret steel string guitars... what are your perceived differences in tone, particularly in context of the body shape? What are your differences in bracing?

The major difference between 12 and 14 fret guitars is in the upper bout. When designing the OM Martin "compressed" the upper bout to allow access to two more frets. Otherwise the two plantillas are almost identical, including the lower bout centres, thus bridge location. You can verify that by drawing the two templates over each other.
The "lower bridge location" on 12 fretters is another one of those internet memes.
The other difference is the splay of the x-braces, the OM is more open, the Martin 12 fretters is usually 90º, or close.
In my opinion the major difference in tone comes from the length of the neck, the 12 fretter is shorter and tends to resonate at a higher frequency, thus not "steal" as many vibrations from the soundbox.

What are monopoles, dipoles and the like?

Generally I do not think 12 fretters sound better, but they tend to have a bit more bass response and slower attack. 14 fretters have a bit more edge and projection, and I think this is mostly due to the smaller soundbox.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

Laurent and Todd,
What you say is true for Martins but not for Gibsons. In particular the L-00's. They started with 12 frets and then moved to a 14 fret. The body shape is the same but the sound hole is moved quite a bit and so the bridge and the X was much more open. I think this is a better example to test for sound differences.
I don't know and I don't have a opinion as I haven't heard the two side by side but this is a case where there really is a lot of physical difference in the sound hole, bridge placement and X. The differences have to be appreciable. In a theoretical sense what would opening the X, moving the soundlhole and bridge down do ?
And to be clear, Gibson actually moved all of those things up to make a 14 fret.
Thanks,
Link

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Cut to size.....Beat to fit.....Paint to match.

I think I am missing something here. Todd, by your own graphic, the bridge position moved more than the soundhole by my eye and examination. Isn't this the typical "centering" of the bridge that is talked about concerning 12 fretters? T

The difference in change between the two is due to the shorter scale length of the NB and its having 19 frets instead of 20.

Pat

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formerly known around here as burbank
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http://www.patfosterguitars.com

IMO Pat, that answer will not get you to the bonus round. T

Some interesting reading on the evolution. http://www.lutherie.net/12-14-evolution.html

One detail I had noticed on Todd's pic is that the scale length of the 000-18v is a bit longer compared to the NB, thus the assumption that the 000 was an OM with the longer scale length.

I'm in the midst of discussions with a customer over whether to build him a 12-fret 000 or an OM. Below is an overlay I did to try to clear things up for him. On the left is half an OM over a 12-fret 000. On the right is a semi-transparent OM over the same 000. It shows clearly the squashing of the upper bout on the 14-fret, the identical bridge locations and a very slight change in the soundhole location.



A bit of trivia came up while talking to him—the 12-fret D-18VS has 19 frets while the 14-fret Dreadnought has 20. The 12-fret 000 and 14-fet OM both have 20. Probably more than anyone wanted to know.

Pat

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formerly known around here as burbank
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http://www.patfosterguitars.com

What is obvious to you is obscure to me. I suspect that you have not heard many 12-fret dreads.

It may surprise you to hear that Ervin's saying something does not make it so. And that focusing on the first three top modes is not the only way to conceptualize guitar design.


IMO that is a factor, but the length of the box is the major one.



You think?



On the 000, the bridge sits about 1/2 to 5/8" closer to the tail on the 12-fretter. The upper bout was not shortened by the full distance between frets 12 and 14. Less difference on the 0 and 00.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

I agree with Howard,
On Martin style guitars I think the longer length of the body has the greatest effect. The slight shift of the bridge, soundhole, depth of the box,and shape of the upper bout I think also contribute to the differences, but to a lesser degree. On the Gibson L00 guitars it is the shifting of the bridge and soundhole that makes what difference there is.
One of the best sounding guitars I built was a 12 fret dreadnought. But I think many people want those two extra frets free of the body.

Thanks guys.

Todd's first image is more what I was talking about, changing the neck length without changing the body shape. The OM has approximately equal distance above and below the bridge to the active region boundaries (upper transverse brace and tail), whereas the NB is unequal, with the distance from bridge to tail being a fair bit shorter.


Sorry, I was visualizing changing the bridge position on the 14 fret dread shape. Martin's 12 fret dread mostly just has more room above the UTB and thus doesn't affect the bridge-to-boundary relationship. Laurent is probably right about this variety of 12 fret guitar, that the difference is rather subtle, mainly relating to the increased air volume and shorter (and therefore stiffer) neck.

And by 'obvious', I mean the waist of a dread is so wide that moving the bridge up doesn't constrain it much, compared to moving the bridge up toward a tight waist. Better centering = better leverage on the low frequency modes that are important to good steel string sound, and if you still have plenty of distance between the bridge wings and the nearest point on the perimeter for it to move freely, there's no obvious penalty to gain that extra leverage.

The bridge-wing-to-perimeter distance on an L-00 is rather short, so I suspect that unless that area is made very flexible, the stiff bridge/X brace being so close to the naturally stiff perimeter would be less than ideal in terms of allowing the bridge to move at large amplitudes. Better leverage, and yet you can't use it because the perimeter is holding you back. At least, that's what it looks like would happen.


Certainly true. I suppose I'll have my own conceptualization after a while, but the better I can understand things upfront, the more I can learn from each trip around the barn.

But another point from the book that is at least worth pondering, is how the "Bermuda triangle" (triangle formed by the X intersection to the bridge) moves somewhat as a unit, rather than allowing the bridge to rock front to back by itself. So the long dipole axis may actually be a bit in front of the bridge, thus giving the 12 fret position a better chance of being the actual sweet spot... depending on how rigid the triangle is... which may be on the flexible side with the lower bridge position, if the bridge is farther from the intersection. Hmm.

I guess I'll just have to try building a few "14 fret body with 12 fret neck" guitars and see how they sound. Good thing I already have one coming up soon on my to-do list