OM size 12-string?

[Dale Gulick]

I’m considering an OM size 12-string (my standard OM is 14-frets to the body and closer to dred depth, Sitka). I’m interested in opinions concerning overall characteristics relative to a dred or GA box.

[Alan Carruth]

I used to make all of my 12s on the 17" Jumbo platform. A few years ago I made a 16" one, and it was a cannon. I've made another since, and a couple of my students have as well, and although the newer ones aren't quite of the same caliber, they are still pretty heavy artillery. So that's one aspect of it: it's easier to make a loud small guitar than a loud big one.

As you go to a smaller platform you tend to get more 'treble balance'. The smaller box volume can't support the low air resonance with as much power, and usually the 'air' pitch is higher too. You can drop the pitch by making the soundhole smaller, at the cost of some more power, and you can also make the box deeper, which has something of the same effect, but the fact remains that the best and easiest way to get a 'big' guitar sound is to make a big guitar.

Don't over build it. You need to make the top about twice as stiff to handle the added tension, but, thanks to the 'cube rule', that means you only need to make it about 25% thicker, and use bracing that's 25% taller, than you would normally use. That's one reason 12s can be such good noise makers: you've got about twice the power, but only have to move a little more than 25% more weight to move (the bridge and bridge plate are bigger, remember?).

IMO,the OM is 'God's size' for the steel string guitar. I can't imagine a well made OM not sounding terrific.

Alan Carruth /Luthier

[Barry Daniels]

So maybe we should rename it the OMG.

[Freeman Keller]

Here is, from left to right, a standard Martin short scale dread, my short scale OM 12 and my very long scale ladder braced 000. The OM is my go to finger picker, the ladder braced one my slide and blue axe. The Martin sits in the closet.



The OM has 5/16 non scalloped braces, a third tone bar, and the top was thinned to about 0.120. The body is a little deeper than a standard OM. It is happy tuned down two semi tones to D (the ladder braced one is usually tuned to C or some open tuning). Tuned to D the OM doesn't have the usual 12 string jangle and is very well balanced across the strings.

Another size to consider, particularly for a strummer, would be a jumbo. Many people think that Taylors best 12's are the x55 jumbos (or the incredible LKSM) and there are plans available for a Taylor clone.

[Dale Gulick]

What should the target ring-and-a-half mode frequency be for the top? I'm assuing the added thickness and taller bracing will raise the pitch. Also, what, if anything, should be done to change the back tap tone?

[Alan Carruth]

The ring+ pitch on the top rises, but maybe not as much as you might think. I don't have a huge number of samples on this, but looking at a few records pulled from the file it seems as though the 6-string SJs I've made tend to have ring+ frequencies around 280, while the 12s have been closer to 300. Given the range of results I'd hazard that 12 would be about 10% higher. I'd make the back about that much higher, too. Remember that assembled tap tones don't track 'free' plate pitches very closely at all.

Alan Carruth / Luthier