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In looking through the bracing Martin library I see there is no standard. No doubt different builders put their X braces in different locations. In reasoning through this I have a couple of thoughts that I would like some help with the realities of this.
OK, so assuming the bridge is important in agitating the top, it seems to me that if the X came out under the short end of the bridge or even the corner it would allow the bridge to move more and so the top move more resulting in more sound. This would seem to be a benefit for smaller guitars.
On the other hand if you have a large guitar it might be better to control the top movement. If so giving the bridge more support such as sending the X out under the long end of the bridge would restrict the bridge/top movement and so reduce boominess.
Thank you for your thoughts and experiences in advance.

I'm confused.

What do you mean by long & short end of the bridge?

Do you mean putting the X off center?

Kevin Looker

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I'm not a luthier.
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Try this

http://www.kitguitarsforum.com/board/vi ... 3f2e70fa94

Brian

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My memory is so good, sometimes I remember things that never happened.

The thing I find interesting is all the 'placements' in that second video relate to the sound hole location as if the sound hole location were a constant. If that's true then where is that sound hole location? Measured from where? Same on all Martins?

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Not quite sure I understand the question. I will add that I like the wings of the bridge to overlay the
lower X legs to provide both structural support and also as a conduit for vibration through the
bridge, down the lower X legs and into the top.

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Lance@LuthiersForum.com

I think if you stick to 14 fret Martin Dreadnaughts, it's constant enough. Other than that, it doesn't make that much sense to use the soundhole as the reference for locating the X. It's just traditional. People have been describing it that way as long as I remember.

Based on my observations: if the X arms pass through the back corners of the bridge it's standard; if they come out the sides of the bridge, it's forward shifted; and if they pass under the long back edge of the bridge, it's rear shifted. (more or less)

Greg B understood what I was trying to say. For a specific scale the bridge has to be in a certain place. But if you are building you can have any x angle and put the x anywhere you want to. Using the sound hole as a reference point is useless as the sound hole is in a different place with different guitars whether factory or handbuilt ie. 19 vs 20 fret guitars.
So I was thinking that 1) if the x is lower under the bridge the guitar top will be more controlled. In contrast 2) if the the x comes out the bottom corner then the top is less controlled. If 3) the x comes out under the short edge, the wing, the top will be more free to vibrate but still be supported because the x is under the bridge.
At the beginning of the Martin video Diane said "the more the top vibrates the more sound you have". I am thinking that the 3rd option above will do that, allow the top to move more. I see all 3 in the Martin bracing library and I am assuming that there are effects of different placements.
So my question is, is that true in real life and if so what are the tonal construction consequences?

So basically your saying the wider they are spread apart from each other the more vibration?

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James W Bolan
Nashville Tennessee

No, you could have any angle x you wanted which would be an entirely different factor to discuss. I am talking about where the x comes out under the bridge and what effects that would have. Would a more supported bridge be relatively more quiet than a less supported but still supported bridge.

The X is forward of the bridge. This is about structure. If you miss the mark you can have some serious structure issues. The X braces should catch the lower corner. A slight movement will be ok but you miss the mark the bridge corners can pull a serious blister on the top. Here you will see the position in relation to the braces
http://theunofficialmartinguitarforum.y ... isL6H_16So

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

As someone pretty new to building guitars, I'm going to jump in with the thoughts I have. Please feel free to correct me (I want to learn, so if I'm wrong I'd rather learn that here than after building things the wrong way).

The bridge/bridge plate and X-braces form a triangle that provides a lot of structural strength that's needed due to string tension. And that's more the purpose of this triangle than sound production, if I understand correctly. That triangle can be made to be more resonant with changes in the height of the X-braces themselves along with the dimensions and weight of the bridge and it's bridge plate. So even with 2 guitars built side by side with the same materials and the same layout, if one is braced heavier than the other, it would be probably more choked as to volume.

Now, if you took the X and pushed it further toward the upper bout, and left the bridge in the same location, you would make the triangle larger. I don't know what effect that would have. It seems it would make it structurally stronger as long as the triangle is intact. If the legs of the braces ended up not "connected" to the bridge or it's plate, then the structure would suffer.

Since the upper bout, and everything above the X is mostly structural as well, shifting the X toward the upper bout would make the active part of the top (the lower bout) larger, which would help with volume compared to an X lower on the body.

I guess what I'm getting at is that volume has more to do with the shape and height of the braces than with where the X-braces and bridge are located in relation to each other. Within reason.

Again, I'm new. I think I'm echoing what I learned from reading and listening to others.

Bob

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Bob
From the oldest town in Texas.

Bluescreek gets what I am trying to say. On the thread he has linked you will see that the x goes up and down under the bridge. Sometimes hitting the upper corner of the bridge, sometimes the lower corner and sometimes out the back of the bridge.
One of the videos linked above called it forward, standard and back shifted. Further it was said that forward produces a more bassy sound, standard a balanced and back a more treble sound. That was helpful but my original thought is that each of those positions would allow the top to vibrate more or less producing more or less sound.
So if we wanted a guitar for a person that plays light fingerstyle on a smaller guitar, forward or as I said out the side of the bridge would be go so as to agitate the top more easily to audible volume. On the other hand a hard playing bluegrass player might benefit from the back shifted braces coming out the back of the bridge so as to control the top so its not so boomy.
So in conclusion in your opinion what is the effect of where the x comes out under the bridge? Is it just tonal or are there volume or even characteristic implications?

You've basically got it. However, as has been noted, if you go too far forward, there is a greater propensity for the top to belly, the bridge to rotate, and buckling to occur. Don't forget the structure. Also, it's possible that a thin topped guitar with a more rear shifted X brace could have more bass than a thicker top with a forward shifted X. The tone might differ. It's the sort of thing where experience is needed to get the sound you're after.

After rebracing a few beaters, one interesting thing I've learned is that bracing matters much less than you'd think. Even going from ladder to X bracing doesn't fundamentally change the sound of a particular guitar. The general character remains. Sure, bracing sculpts it, but the actual top and shape of the guitar seems to matter more. I've noticed the general stiffness (or lack thereof) under the bridge has more bearing than what particular bracing system is used to achieve it.