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i'm in the planning stages of laying out a 12 string acoustic. it's been a while since i've played one so i am unsure on the spacing between the pairs and over all relationship both at the nut and saddle. what makes for and playable instrument?

what adjustments are made to the bracing to support the extra tension? i understand that the tension isn't doubled but there must be enough added that would make the need for stiffer bracing somewhere.

i've just finished a maple back and side and am really happy with the note definition that i got. i'm thinking this would be a good way to go for a 12 string. though i do have a set of pau ferro that i've been thinking about but i haven't built with a rosewood yet so i don't really have an idea how to compare it with maple.

also i'm thinking of making it a 12 fret with a 24.562 scale fretboard and hoping this will allow for it be easy to play tuned standard.

many thanks for any thoughts and opinions.

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I recently put together a semi-experimental multiscale 12 string with a 24in. S.L. on the bass side and a 22 1/2in S.L. on the treble. It tunes to standard tuning with no problem, and even DADGAD doesn't sound too bad.
Pau Ferro will probably give you a sound somewhere between maple and rosewood. It might be the best of both worlds. I haven't had any bad reactions to it, but some do, so take precautions with the dust.

I own a Martin 12 and have built a couple of others based on things that I didn't like about it. First, for string spacing, most use nut width of about 1-7/8 with the strings 0.100 or so from the edge. I space the courses using the StewMac gauge for the primaries and then put the octaves about 0.100 from them. At the bridge common spacing is around 2-5/16 - some people open the gap between the primary and octave slightly.

One minor design consideration is whether to put the primaries or octave pins closest to the saddle - for most manufacturers it is the primaries - Martin traditionally did the octaves but has recently switched.

As far as bracing - depending on strings, scale and tuning you will have somewhere around 50 percent more tension (not double). It is worth doing the math before you start - that will give you and idea of what to do with the braces. My D12-28 has standard 5/16 non scalloped braces and the same top plate thickness as a six string. Taylor makes the top plate slightly thicker and adds a third tone bar and finger braces. On the LKSM (designed to be tuned to C#) the braces are very wide and deeply scalloped. On my fingerstyle OM sized 12 I made the top 0.115 thick with three non scalloped 5/16 braces - it is usually tuned to D.

Many people think mahogany is a good tonewood for a 12 - they are so complex sounding to start with that adding the overtones of something like rosewood is overkill. I can't tell you how either maple or Pau Ferro will work.

I'm not a fan of 12 string dreads - and while lots of folks like jumbos I built an OM and a 000. There is a good set of plans at Ultimate that looks pretty much like a Taylor x55 body - even if you are going to build something else that might be a really good starting point. Good luck, I'll look forward to the results.

It's been my experience that, for 12 strings, you almost can't go wrong with EIR, mahogany or mahogany-like tonewoods (khaya and sapele for instance) if you couple it with a medium stiff sitka top. As Freeman said, leave the top a little thicker than you would a comparable 6 string top, and leave the braces approximately 25% heavier. I also shift the two tone bars slightly closer to the bridge plate. As far as the string spacing at the nut, Paul Woolson has a great method. First locate your 1st and 6th double courses. Then center string number 2 1/16th" from the center of string number one, and center string number eleven 3/32" from the center of string number 12. Finally, (you need the Stew mac string spacing rule for this step), lay out the spacing of the remaining strings using the Stew Mac rule, by laying out strings 3,5,7 & 9 between nos. 1 & 11, and then strings 2,4,6,8 & 10 between nos. 2 & 12. Sounds complicated. Wish I had the capability to do a drawing. If the explanation isn't clear enough, PM me and I might be able to draw something, take a photo, and post it.

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michael propsom
www.propsomguitars.com

thank you all for the insight.

clay, a mulitiscale 12 sounds like quite the undertaking and really interesting. must have some interesting bracing.

freeman and jsmith, i'm going to have to draw out your spacing explanations, i think i understand what you are saying but will know when i see it on paper if i actually do.

you both are making me think more about going with a mahogany or saplele. i build my first 2 with mahogany, i love the sound of them!

did any of you reinforce the neck with carbon fiber rods?

i really need to play a few before i get into it but i live almost 2 hours from the nearest music store.

thanks again!

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just finished one.
I set the octaves back 1 7/8 nut
octaves spaces .080 from the primaries The body was a 66 martin D28 that needed a lot of work and my customer opted for this. Brazilain Rosewood adi top and snakewood binding.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

The only 12 I've built was a dreadnought and built for myself. Several folks have played and been blown away by it, but for most a 12 is a second guitar and most clients struggle to find the cash for their first artisanal instrument.

Like Freeman, I owned a Martin D12-28 and my 12-string build was an attempt to fix what I didn't like -- which was a lot! I felt the Martin neck configuration would make a better cricket bat -- and I was happy to unload it! My 12-string build is now 5 years old and the setup hasn't changed at all during that time (even after spending 4 months in a shipping container through the Tasman and Pacific Ocean, and sitting on a South Africa dock for 4 weeks). So structurally, the assembly is doing its job, yet the guitar is a cannon with rich yet balanced sound. I was very pleased with the result.

It's a 14-fret dread with 640 mm scale length. Neck is 46.2 mm at the nut, and 58.8 mm at the 12th fret. Overall string spacing 41.5 mm at the nut, and 58.8 mm at the saddle.

I found this response by William Cumpiano helpful in optimizing the string spacing at the nut and depth of slots: http://dolcecano.blogspot.se/2009_03_01_archive.html#4220140834614424435. At the bridge, you want to keep the pairs as narrowly spaced as is possible without interference of the rearward pinned string as it passes the forward pin. That is a function of pin head diameter and you want your strings spaced a hair wider than half the diameter of a pin (see photo of bridge).

Structurally, I made the top no more than 0.010" thicker than "normal", the bridge patch has a larger footprint, and there is an extra brace that goes along the bottom edge of the bridge patch between the legs of the X. The bracing is shown on the left, with it's sister 6-string on the right (nowadays I taper the tone bars on a 6-string, rather then scalloping -- more responsive).

Patch, I agree that you do need to play a bunch of 12 strings - they can be more different than sixers and a lot depends on how you plan to play them. Just for comparison here are my three - D12-28, home made OM and long scale ladder braced copy of a Stella.



I think the best commercial twelves on the market are made by Taylor and Guild - be sure to play some of them. Breedlove is doing some interesting work and the Martin Grand jumbos are probable their best modern 12's. When you play them remember that many 12 string players like to down tune one or two semi tones - if you want to tune to concert short scale and light strings are a good idea.

To try to describe how I lay out the string spacing - first remember that normally the first two courses are unisons tuned the same as a six string. The next four "courses" normally have the primary string "down" (closer to the floor) and the octave "up" - you hit it first with your pick. There are other ways to string but lets not get into them here.

I lay out the two outside strings whatever distance I like from the edge of the fretboard - that depends on playing technique, do you fret with your thumb, bend notes, etc - but lets just say its 0.110 from the edge. That will be the high E and the low octave E. Next make a mark on the nut 0.100 inside the low E octave - that will be the low E primary. Now space the four additional primaries using your usual approach - for me its the SM scale. Now make a mark 0.100 to the left of each of these - that will be the octaves. Look at it, fiddle with it slightly until it looks right, cut the notches.

This is a crappy picture but you get the idea maybe



I play a lot of slide on my twelves so I do two additional steps. First I like flatter than normal fretboards - I use 20 inch radius rather than 16. Second, I cut the nut slots so that the tops of the strings are roughly level rather than the bottoms. For normal fretting you want the bottoms of the strings to approach the zero fret line.

As Tim points out, spacing at the saddle is set by pin locations but can be controlled a little bit by ramping. On the Stella clone I used a tailpiece so spacing is set by slots in the saddle. Note in Tim's picture that he has compensated each string of each course - that is a lot of work but it sure helps the guitar play in tune up the neck - 12 strings are notorious for poor intonation.

Really helpful, thanks!

I'm in Tucson at the moment visiting the inlaws, I got a chance to get into one music store and they happened to have a Guild 12. It wasn't a great player but helpful to hold and measure. Hopefully I'll find another before I leave.

I'm curious why the high octaves would be closer to the saddle? I'd think you'd want the primaries closer to take advantage of the steeper break angle.

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I like the idea of a 12 string multiscale Definitely need to give that a try sometime. I'll probably keep to 1" or less difference though. But at least the wide neck helps reduce the angle on the frets.

Another idea I like is using 6 pins, with two strings per hole. And while searching for pictures of it, I ran across this old but relevant ANZLF thread: http://www.anzlf.com/viewtopic.php?t=354