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Currently planning my second build. Its gonna be an OLF SJ.

The plans give the option of either ladder bracing or X bracing for the back.

What difference does this make ?

Thanks

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Richard

I'm very interested in some opinions as well. I used an X brace on my latest back just to try something different and it seemed to me that the X would give the back a little better chance of creating an actual dome instead of only a   cylinder that ladder bracing can provide.

I also chose not to use a back joint reinforcement after checking my Martin that had none. I did put a small reinforcement elliptical 'shape' over the largest joint on the lower bout.

Unfortunately sound wise I have no idea what those change will portend.

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Thank You and Best To All

Richard,

Try this thread.

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

What do you want from you back?

Do you believe it should reflect sound by being very rigid, or do you want it to move with the top and add to the tone?

You can brace either way to make it reflective, just keep it all pretty heavy.
Both ways will work to make it active, but you'll obviously need to make everything lighter so that it can move.   

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"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

From what I've been able to find out from measuring guitars, it seems as though the 'main back' resonance, the lowest pitched tap tone, is the only one that can contribute to the power of the guitar. Thus, I think you want it to move some at a low frequency, near the pitch of the 'main top' resonant mode, but otherwise you want the back to be a stationary reflector. Of course, you can't have it both ways.

I X-brace backs because it makes it easier for me to 'tune' them to work with the top. I can shave the back braces and check the resonant modes with it off the sides, so everything is easy to get at and I can see the effects of small changes. It still takes a while to figure it all out, though.    

Alan, when you tune your top and the back, do you tune them off from the sides first and then put the whole box togehter? If so, does the tuning relationship change at all once they are attached to the sides, and therefore need some fine tuning, or does it works out OK?

I remember you mentioning that you tune the top and back to the same resonance, because when you put the bridge on it, it drops by half note.

[QUOTE=Alan Carruth] ........ but otherwise you want the back to be a stationary reflector.... [/QUOTE]

Alan,
I am curious if you have tested or played a guitar with a real active back that was pretty thin and lightly braced. If you have, what was the bracing scheme and how did it seem to work?

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"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

Thanks for the input guys

So as far as I can see youre saying that using x braces in itself doesn't give a different sound. Rather you chose to use this method because it makes it easier to tune the back to give the sound you want. Right ?

So what are you looking (listening) for when you tune the back and top before assembly ? Specific notes or an interval between the 2 plates?

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Richard

Main reason? Holds the dome better.

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

[QUOTE=SteveS] What do you want from you back?

   [/QUOTE]

Good question...... I don't really know yet.

I guess thats why I'm thinking of trying the x brace option - to try and get one step nearer to forming an opinion.

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Richard

[QUOTE=Colin S] Main reason? Holds the dome better.

Colin[/QUOTE]

Colin.

I'm gonna risk looking realy dumb now (just for a change )

What does the dome do actually ?

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Richard

    The dome allows for movement of the wood through humidity changes. It is also stronger than a flat braced piece. As wood dries it shrinks. With it glued to the braces , the wood will pull in the top or back . As it dries more it will actually cause the wood to crack.
   Domeing allows more movement and strength with less matterial , though that being said if the wood dries out to extreems it will still crack. Martin used the flatter back braces through the 80's and changed to the higher stiffer brace they use now.
   The thinner bracing of the past allowed alot more movement but also caused some problems from the back sinking.
     There are surely other contribution the back can make to the guitar because of shape but it is difficult to test . Alan has made a lifetime study and can contribute more than I to this disscussion
john hall
blues creek guitars

What John said and a domed back adds stiffness.

You ask great question here. The back of the guitar is probably the least understood part on the guitar. Almost all the effort in making the guitar has been put into the top. There could be some great things learned by exploring the possibilities that the back can add to the guitar.
Unfortunately, most of us don't have the time for that.

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"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

microsmurf asked:
"Alan, when you tune your top and the back, do you tune them off from the sides first and then put the whole box togehter?"

Yes. The pitches of the 'free' plate modes are much different from the tap tones of the assembled box, and you have to get some experience with a given design to be able to predict where things will end up. As you go along there's less fine tuning needed.

Cachalote asked:
"I am curious if you have tested or played a guitar with a real active back that was pretty thin and lightly braced."

Mahogany backs, in general, end up much lighter than rosewood; often not weighing much more than the top does. A rosewood back, by comparison, can weigh three times as much as the top. This is part of what give mahogany guitars their 'punch': the back moves more, because it's lighter, and pumps more air through the soundhole. An extreme example of this would be the cypress back on a Flamenco, optimised for attack, without a lot of sustain.