Official Luthiers Forum!

I've noticed many custom builders use a 15' radius for the back of their guitars as opposed to a 25' radius used by some mfgs like Martin. I'm curious why the custom builders choose to do this.

Is it for strength? I'm sure a tighter radius will be a little stronger and should resist deformation more. It also makes the sound box a little deeper which may affect the sound a little. Since it is stiffer, some say it resists or maybe deadens vibration more. I've read where some claim adding stiffness helps the treble response......but hurts the bass response. Could it be some use a stiffer back trying to make up for a lightly braced top?

So why do you use a 15' radius on the back of your guitar builds? Have you found the sound is affected using the shorter radiused, stiffer back? Can you describe the changes? Using the shorter radius, can you still get a good "cut" on the bass made famous on the dreadnaught Martins? How about on a 000/OM, will the bass be hurt more on this size guitar if you use a shorter radiused back?

Appreciate your thoughts.

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Formerly known as Adaboy.......

You sure Martin uses 25' for the back? I was under the impression they use either 25 or 28 for the top, and 15 for the back. The greater 'dish' provides more strength/stiffness than a flatter radius would, and I think it looks good, too.

Mattia, no, I could very well be wrong about the radius on Martin guitars.......but I thought the top used a 28' radius and the back used a 25' radius. Anyone feel free to correct me.

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Formerly known as Adaboy.......

Darryl my friend I think that Mattia is correct.

I use a 15' dish for my backs because I have one......

I wanted to add and with no disrespect intended toward Martin - not everyone wants their guitars to sound like a Martin - Martin does that just fine.

Darryl--

I use a 15 foot radius for my backs also. To me its more of a structural issue -- creating a hedge against future humidity fluxuations. I suspect that the back radius may affect tone a little bit, but as I am coming to understand guitar building in a small way, I try to think of the whole and not the collection of bits. The body shape, top wood, sound hole size and placement along with bracing style are what is going to make up 95% of your tone production.

Best --Jim

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Jim Howell
Charlotte, NC

From what I learned on this forum (or MIMF not sure) Martin uses 28' radius for their tops and 25' radius for the back on the dreadnought and similar size. For the smaller guitars they uses 20' radius for the back.

Alain, I also thought I had read Martin uses a 25' radius for the back of their guitars......though I didn't realize it was a different radius on the smaller guitars. (wonder which radius is used on the OM/000?) This is what led to my question, why do many custom builders use the 15' radius.......sound, strength, resistance to humidity, or what?

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Formerly known as Adaboy.......

I just got a 25' dish that I will use for both top and back. Saves a lot of money this way since I can't really make a dish right now due to lack of space...

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Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

I'm using a 15 for the back mainly because I think it looks better. I personally don't believe that it will have enough of an effect on the sound to warrant much concern. I do, however, believe that it is more structurally sound. All in all, as Hesh said, most of us aren't too concerned with emulating Martin. Just because something works for them doesn't necessarily mean it's the best way (or even a good way) to do things. Many factors besides sound contribute to Martin's design decisions.

Thanks for the coments everyone! I'm "green" and learn from all your posts. I'm sure everyone tires of answering these type posts from newbies but I sure appreciate everyones patience and willingness to help other interested parties.

Sorry if I implied guitars should sound like a Martin. There is such a difference in a 15' radius that many are using and the 25' radius I've read Martin uses that I figured there must be some reason for this. I used Martin as a reference as I'm most familiar with dreadnaught sized Martins.

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Formerly known as Adaboy.......