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Just wondered if anyone has made a 12 string acoustic. And if the bracing is the same or different from a regular 6-string.

Thanks
Neil

I've built a number of them over the years. There are various ways to go about it, but the basic thing to remember is that you should plan on about twice the tension of a 6-string.

Whatever else you do you'll probably want to leave the top thicker. Fortunately, it won't have to be twice as thick, since the limitoing factor will be bending stiffness, rather than the actual compression strength of the top. Since the bending stiffness goes as the cube of the thickness, making the top 25% thicker will make it about twice as stiff, all else equal.

You can use the same rule for the bracing: make it 25% taller and it will be twice as stiff. I always worry about the gluing area on a tall narrow brace, so I like to make them a little wider as well. This increase the stiffness a bit, of course, but not as much as the extra height.

If you're using 'standard' X bracing, you can use an extra 'tone bar' behind the bridge, which spaces them a bit closer together. Another addition that helps is a small brace along the back edge of the bridge plate, to help keep the bridge from bellying upward as much in the center.

All of this adds weight, which cuts down on volume, and stiffness, which can alter the timbre of the instrument as compared to your six-string. With all of the extra horsepower available from the added strings the power loss is not usually a problem. As for the other; it's not going to sound like a six anyway.

Hey Neil, a while back, KiwiCraig posted some pictures of his Myrtle/Englemann 12. One of the nicer 12s I've seen lately. There's some good inside-the-box pictures... ought to answer your bracing question. Look here:
http://www.luthiersforum.com/forum/viewtopic.php?f=10102&t=13971

_________________
Jim Womack

"Be thankful we're not getting all the government we're paying for. "
Will Rogers

http://www.dreamguitars.com/sold/Greven_DX-12_1118.htm Here is a link to an interesting John Greven 12 string sold a while back. If you click the "hear this guitar" link, you will hear an unusually warm sounding 12 string - to my ears anyway. I would love to know how Mr. Greven goes about bracing his 12 vs. his 6 string guitars.

Neil, I know the above info doesn't help you but Mr. Greven is very generous with his knowledge. You could do a lot worse than contacting him about how he braces his 12 strings. I have emailed him a few times - he was always willing to help. He's a nice guy. Good luck.

_________________
John Lewis
Wannabe builder owned by 2 crazy dachshunds

Neil,

Heres the bracing on my current build.

Cheers Martin