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I'm currently working (actively and intensively) on three new instruments (let's ignore the other three awaiting some binding and a finish for a moment, have jigs to build for the binding, and I want to finish in batches), one of them being a jumbo acoustic. Now, I'm no expert in bracing-land, but I've drawn up what I want to do with this particular guitar.

Basic specs/background: 16.5" wide, 21" long, 25.5" scale, WRC top, X-brace is going to be laminated Adi+.02" CF, the rest of the braces will likely plain 'ol Adi. Width on the X and upper transverse: 7mm, everything else: 6mm. Rectangle over the neck block will be a cutout for a fingerboard extension (floating), lines from neck block to sides represent flying buttresses (1/4" CF tube), and I'm planning on feathering the 'A' frame above the soundhole a litte.

X-brace intersection is 24.5 cm from the 14th fret (I think that's more or less standard; don't want to risk a forward shifted X on a WRC top this size), angle between the legs is around 97, 97.5 degrees. Tone bars are roughly evenly spaced along the lower X-leg. Bracing will be 'parabolic' (ie, non-scalloped), and I'm going for a sort of Lowden-esque-ish good-for-fingerstyle-and strumming vibe. Back/sides: black Walnut.

Thoughts? Look OK? Anything obviously 'wrong'? Things I should consider shifting about?

I assume there will be a bridge plate. I am no expert her but my atempts to spread the finger braces wide apart has lead to a bass domenate sound. I like to tie the finger braces into the x brace near the edges of the bridge plate. But this has such a large and long lower bout I am not sure of the outcome you will get. Structurly I see not issues.

yes, bridge plate under the bridge. Possibly even an additional 'musser' brace or 'Proulx Magic Tone Enhancer' (ie, small brace butting up against the back edge of the bridge plate.

Re: fingers: possibly add a third? I was also considering a Lowden-esque approach, with a single longer finger running down from the upper arms of the X.

the one thing I would suggest is the line of the tone bar to the finger brace . I like to place the fingerbrace along the main X's at a point that is 1/2 of the bridge plate where it contacts the main X.
I have found that this helps to handle the rotational force from the bridge.
   Having all the brace in a straight line will cause a focus or force point. The forces of the bridge are that the top is under compression from the strings up and tension from there back. The bridge will also want to roll from the force of the string pull , so keep that in mind.
   Another area of force will be the neck block. As I see you have an A frame design. This isn't a bad thing though I would splay them for a bit more of an angle. I am interested in the design and would like to hear why you decided on what you have.
Good luck
john hall
blues creek guitars

I'm not sure I understand the bit about the fingers; their location now is roughly and the 1/2 way point of where the bridge plate is going to be. Or do you mean move the tone bar down a little? I'm aslo considering a brace behind the plate to add a bit of reforcement along the back edge of the bridge plate.

The neck block will be supported by carbon fibre tube butresses, and the A-frame I plan to build fairly light/taper down and inlet them like I do the X-brace ends, since the rotational forces from the neck end should largely be compensated by the buttresses.

Basically, my thoughts were as follows:

X-brace: open a little more than my previous guitar (2 degrees), which is a little bit too 'tight', add CF to increase resilience. No forward shift to make sure the bridge and rest of lower bout is supported well. Upper face brace: tall, narrow (8mm), inlet A-braces about 1/4" tall. Tone bars: roughly even distribution over the X brace leg and midline. Fingers: one set for the bridge (midpoint) the other equidistant below it. Fair amount of surface to cover there.

It's quite 'stiff' around the bridge, but then, its a WRC top on a big guitar, so...

Mattia,

Looks a good starting point to me. As usual the proof of the pudding is in how you carve them and "voice" the whole top.

Have you considered doing the Lowden soundhole re-enforcement? This gives strength to the whole soundhole area and the pentagonal shaped piece of wood is not much heavier than the small lateral brace below the soundhole you have in your design.

_________________
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

     I was talking of the point along the line of where the bridge plate would contact the X. This off sets that line and adds more support that way.
     In a way this forms a W truss and adds stiffness without adding mass.
john hall
blues creek guitars

Dave: have you got a picture of the Lowden soundhole reinforcement handy? I'm assuming it's a spruce patch under the rosette area, gross-grained? Or something else?

John: still not quite sure what you mean, but I'll make a few sketches and post what I think you mean. Describing these things isn't always the easiest thing in the world!

I do mine cross-grained andabout the same size as the top or slightly thinner. The edges are bounded by the X brace intersection, the A frame braces and the upper bout transverse brace. Just remember to glue it on before you cut the soundhole

_________________
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

..is it a bad thing my mind is filling in a big 'S' in that patch? New soundhole/rosette design if glued on the outside, perhaps?

Anyway, thanks, may well give that one a shot! Area's a bit too big for an offcut from the top itself, but I've got plenty of bracewood billets I can saw up

Michael,

That's interesting. I like to have the top two finger braces meeting the X braces where the saddle will be. I tend to think of these braces as "sound transmission" rather than structural and, maybe wrongly, have it in my head that they help spread the saddle movements.

_________________
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

I think of them as both but if you imagine the red line as the rotational axis of the bridge you can see why this location helps resist the rotational force.



By the way having the first set of finger braces in line with the saddle as opposed t the edge of bridge plate I don't think would take anything to speak of away from the support.

Mattia. If I had been laying this out this would have been my natural intuition



The green shows an optional shallower tone bar set up but the red would have been my first attempt.

Michael: thanks, food for thought. My gut instinct is that the X on that one may be a little 'tight', but then I'm not really basing my gut instinct on a whole lot of experience building. It looks like less than 90 degrees on that one (more like 85; my drawing's 97)

Also, I just found a bracing shot of a Ryan Cathedral (roughly the same size as this design) at Bevelsnob.com (cathedral gallery, cathedral number two), which looks a lot like what I drew. I know I visited that site about a year ago, maybe more, apparently that stuck in my head! Weird...

2 finger braces are plenty per side . The diagram is correct showing the staggered brace off the tone bar. I played around with the bracing and found the wider 95 degree worked best for the sound I like.
Too tight and I think they get to tight sounding. Also you have to be careful that you don't get too close for the pins.
john

Better not tell you then that I generally have my X brace angle at 78-80 degrees

_________________
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

I am curious now. According to what I have read above, having those side fingerbraces placed as illustrated helps "handle" the rotational force of the bridge; I now have the following question; why does George Lowden seem to get away with one diagonal long side brace each side, radiating from the top sections of the X braces, as illustrated in the photograph below?



I am wanting to try a different bracing scheme myself and am finding this thread enlightening.

Dave: I'd noticed you brace quite 'tightly', yes. Just goes to show there's more than one way of doing things!

[QUOTE=Sam Price] I am curious now. According to what I have read above, having those side fingerbraces placed as illustrated helps "handle" the rotational force of the bridge; I now have the following question; why does George Lowden seem to get away with one diagonal long side brace each side, radiating from the top sections of the X braces, as illustrated in the photograph below?



I am wanting to try a different bracing scheme myself and am finding this thread enlightening.

[/QUOTE]

These two braces are resisting the rotational force



The key is the tie in to the X brace and the beefiest sction of the brace is in front of bridge resisting the rotation into it, If your fingers are behind the front of the bridge the can not aid in the resistance of the rotation.

Interesting thread guys. I'm interested in why you've come up with the
suggestions you have, and where you learned. I'm interested in learning
more about brace placement. Are you considering nodal points at all, or
are you thinking purely structuralally?

I'm thinking structure, because I don't know where the nodal points will be, not precisely. My feeling is that the way you carve and graduate the top will, in part, determine how the whole thing ends up vibrating.

I think your orginal pattern is perfectly fine the way it is. There are so many
variables as to what will cause what that you can't really say that you should
just move your finger braces here or there, or that your bridge plate needs
to be a different shape, or that you need more or less braces, or that you
need a different angle ect. Point is that the braces all work together as a
unit, sure some parts of the unit have more effect on the whole than others,
but I'd go with what you have and see how it works for you. If you don't like
what you get then start trying variations. If you do, still try some variations
and see if you can make it work for you better. My bracing pattern is
somewhat similar to yours, and I think I'm building nice sounding guitars.

_________________
John Mayes
http://www.mayesluthier.com