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With back bracing you need to decide whether you are going for a "live back" which possibly adds some harmonic complexity, or a more rigid back that plays less of a part in the tonal palate of the instrument. It is not a matter of one being better or worse - each approach has advantages and disadvantages. It is worth reading a bit about it to decide what you want to achieve with your bracing design. Start with this brief discussion of "live back" design on Trevor Gore's website, which includes a picture of his very light radial bracing:
https://goreguitars.com.au/main/page_ab ... acing.html
There is a lot more discussion of the live back concept in the Gore/Gilet books - which I strongly recommend if you don't already have them.

If you want to make a stiff/rigid back there are plenty of ways to achieve it. An X-brace style can be good for the lower bout area in a larger body guitar. Here is a SJ style one I built a few years ago, using the SJ plans available here in the OLF marketplace. If it is a small body like a parlor or 00 you are probably better with traditional ladder bracing. There is not much difference in how much wood goes into either design - so not a lot of effect on weight either way.

Attachment:

back small.jpg

Whatever you do, you are aiming for a main back resonance about 4 semitones higher than your main top resonance. But everything should start with a decision about whether you are trying to achieve a live back or a rigid back. Once you have made that decision you can think of various ways to achieve that objective. Bear in mind that pretty much every factory made guitar you have ever played has a rigid back. This is not a bad thing. It is often louder. It is certainly easier to build. And a live back becomes non-live if the player holds the instrument in the wrong way (e.g. dampens it against their belly, or plays standing up with a strap).

So - go design your own adventure, but be informed of the issues and aware of what you are actually doing. How it looks is not important. How it works is the real issue.

Author:	cablepuller1 [ Wed Aug 05, 2020 3:02 pm ]
Post subject:	Back X Bracing
Anyone use X Bracing on there backs, seems like a good weight saver and possibly easier to tune to the front? But what do I know, worth a try? Sent from my SM-A715F using Tapatalk

Author:	cablepuller1 [ Wed Aug 05, 2020 3:03 pm ]
Post subject:	Re: Back X Bracing
Seen this on Instagram looks nice and light Sent from my SM-A715F using Tapatalk

Author:	J De Rocher [ Wed Aug 05, 2020 3:51 pm ]
Post subject:	Re: Back X Bracing
The SC-13E model that Martin introduced recently has an x-braced back. Rick Davis who I learned from did x-braced backs as on option. I did an x-braced back on the guitar I built under his direction. I'm sure there others who have done it too.

Author:	Colin North [ Wed Aug 05, 2020 5:57 pm ]
Post subject:	Re: Back X Bracing
cablepuller1 wrote: Seen this on Instagram looks nice and light Sent from my SM-A715F using Tapatalk Strange intersection on the X braces, no cap no cloth patch and a space on the half lap joint. It's deliberate, probably to make for less stiffness in that area. it looks like one of Rosie Heydenrych's at Turnstone guitars, typical of her builds.

Author:	phavriluk [ Wed Aug 05, 2020 6:16 pm ]
Post subject:	Re: Back X Bracing
Just closed up a body, x-braced below the soundhole. I wanted to preserve the dome of the back, not turn the back cylindrical. It worked.

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Back X Bracing http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=53397	Page 1 of 1

Author:	Mark Mc [ Wed Aug 05, 2020 6:27 pm ]
Post subject:	Re: Back X Bracing
With back bracing you need to decide whether you are going for a "live back" which possibly adds some harmonic complexity, or a more rigid back that plays less of a part in the tonal palate of the instrument. It is not a matter of one being better or worse - each approach has advantages and disadvantages. It is worth reading a bit about it to decide what you want to achieve with your bracing design. Start with this brief discussion of "live back" design on Trevor Gore's website, which includes a picture of his very light radial bracing: https://goreguitars.com.au/main/page_ab ... acing.html There is a lot more discussion of the live back concept in the Gore/Gilet books - which I strongly recommend if you don't already have them. If you want to make a stiff/rigid back there are plenty of ways to achieve it. An X-brace style can be good for the lower bout area in a larger body guitar. Here is a SJ style one I built a few years ago, using the SJ plans available here in the OLF marketplace. If it is a small body like a parlor or 00 you are probably better with traditional ladder bracing. There is not much difference in how much wood goes into either design - so not a lot of effect on weight either way. Attachment: back small.jpg Whatever you do, you are aiming for a main back resonance about 4 semitones higher than your main top resonance. But everything should start with a decision about whether you are trying to achieve a live back or a rigid back. Once you have made that decision you can think of various ways to achieve that objective. Bear in mind that pretty much every factory made guitar you have ever played has a rigid back. This is not a bad thing. It is often louder. It is certainly easier to build. And a live back becomes non-live if the player holds the instrument in the wrong way (e.g. dampens it against their belly, or plays standing up with a strap). So - go design your own adventure, but be informed of the issues and aware of what you are actually doing. How it looks is not important. How it works is the real issue.

Author:	DennisK [ Wed Aug 05, 2020 7:17 pm ]
Post subject:	Re: Back X Bracing
In my opinion, X bracing should not be used on live backs made from dense woods. The plate must necessarily be thin in order to get the weight down, and then the large unsupported spans left by the X feel squishy. Either fill it in with a denser lattice, or smaller braces like the typical soundboard pattern, or stick with ladder bracing which is the pattern that best minimizes the distance between braces along the grain. But if you have a thick back that doesn't need much support, then a light X should hold a spherical dome better than ladder braces. Though personally I prefer cylindrical arch because I think it resists neck rotation better.

Author:	joshnothing [ Wed Aug 05, 2020 7:26 pm ]
Post subject:	Re: Back X Bracing
Michael Bashkin notably uses an x-braced back, from the photos I've seen it looks like he laminates different woods for the braces as well. I have never played one of his instruments so I can't comment on sound but it sure looks cool.

Author:	phil [ Wed Aug 05, 2020 9:47 pm ]
Post subject:	Re: Back X Bracing
My x-braced back looks very much like the pic posted by Mark mc. My motivation for the x has very little to do with tone. Given the way steel string players hold guitars I think that a "live back" is mostly wishful thinking. I consider the back to be mostly reflective. I've been using the x because it seems both lighter and more stable with humidity changes - both of which are desirable for acoustic guitars.

Author:	Clay S. [ Thu Aug 06, 2020 8:23 am ]
Post subject:	Re: Back X Bracing
On some of Torres' guitars he used "open" harmonic bars - braces only touching on the ends and in the middle. Has anyone tried that for back braces? It could possibly allow the back to move more easily with humidity changes. It might also allow the back to vibrate more which could be good or bad.

Author:	cablepuller1 [ Thu Aug 06, 2020 10:18 am ]
Post subject:	Re: Back X Bracing
Mark Mc wrote: With back bracing you need to decide whether you are going for a "live back" which possibly adds some harmonic complexity, or a more rigid back that plays less of a part in the tonal palate of the instrument. It is not a matter of one being better or worse - each approach has advantages and disadvantages. It is worth reading a bit about it to decide what you want to achieve with your bracing design. Start with this brief discussion of "live back" design on Trevor Gore's website, which includes a picture of his very light radial bracing: https://goreguitars.com.au/main/page_ab ... acing.html There is a lot more discussion of the live back concept in the Gore/Gilet books - which I strongly recommend if you don't already have them. If you want to make a stiff/rigid back there are plenty of ways to achieve it. An X-brace style can be good for the lower bout area in a larger body guitar. Here is a SJ style one I built a few years ago, using the SJ plans available here in the OLF marketplace. If it is a small body like a parlor or 00 you are probably better with traditional ladder bracing. There is not much difference in how much wood goes into either design - so not a lot of effect on weight either way. Attachment: back small.jpg Whatever you do, you are aiming for a main back resonance about 4 semitones higher than your main top resonance. But everything should start with a decision about whether you are trying to achieve a live back or a rigid back. Once you have made that decision you can think of various ways to achieve that objective. Bear in mind that pretty much every factory made guitar you have ever played has a rigid back. This is not a bad thing. It is often louder. It is certainly easier to build. And a live back becomes non-live if the player holds the instrument in the wrong way (e.g. dampens it against their belly, or plays standing up with a strap). So - go design your own adventure, but be informed of the issues and aware of what you are actually doing. How it looks is not important. How it works is the real issue. Great info thanks mark Sent from my SM-A715F using Tapatalk

Author:	Colin North [ Thu Aug 06, 2020 10:53 am ]
Post subject:	Re: Back X Bracing
Would seem to me that a double X braced back might be more effective in holding a domed shape than a single X, if that's what one was looking for.

Author:	phavriluk [ Thu Aug 06, 2020 1:51 pm ]
Post subject:	Re: Back X Bracing
My x-braced back looks very much like Mark's pictured above. I used one 'x' centered in the lower bout and 'ordinary braces from the soundhole and above thinking that the dome I wanted is roughly a slice off a big sphere and outside that rough circle I couldn't make a shape that didn't try to corrupt the dome. We'll soon see how it sounds. Maybe by the new year!

Author:	jfmckenna [ Thu Aug 06, 2020 2:34 pm ]
Post subject:	Re: Back X Bracing
I would imagine that not capping the X would create a more lively back too. It's not structural, no downward force forcing the X open so it's probably just a decision to make by the builder? IDK I've never tried it before.

Author:	Mark Mc [ Fri Aug 07, 2020 6:57 am ]
Post subject:	Re: Back X Bracing
Colin, that back looks sensational. Yes, the bracing looks great, but the timber is just superb (I assume BRW?). Regarding different back bracing, I am hoping to try a cylinder back (+/- top) for my next build. It is the style of early 20th century instruments by Vega and Howe-Orme, and modern versions by Nigel Forster and Shelley Park. Does anyone here have experience or tips for me in making such a creature? Attachment: B40787E5-23C2-48AA-AC30-B4EBD8C1A377.jpeg

Author:	Clay S. [ Fri Aug 07, 2020 8:24 am ]
Post subject:	Re: Back X Bracing
I do cylindrical arching on the octave mandolins I build. It helps create the sound I am looking for in an O.M. To make the sanding form for the sides I screw a piece of 1/8th inch plywood (underlayment) to a piece of 3/4 inch ply along the centerline. I attach sandpaper to the surface of the 1/8th inch ply. I position two sticks between the 1/8th inch ply and 3/4 ply to raise the 1/8th ply into an arch. By moving the sticks toward or away from the centerline I can change the shape of the arch. The "cylinder" is really more of a spline curve which is easier to fit the plates to. If you look at the picture you posted above you will notice it is not a true cylinder shape. On my octave mandolins I make the tail shallower than the neck end which gives a profile similar to the old citterns and increases the break angle over the bridge.

Author:	Alan Carruth [ Fri Aug 07, 2020 3:06 pm ]
Post subject:	Re: Back X Bracing
I used variations on X-bracing on backs for years. The original idea was to enlarge the area of the 'main back' resonant mode, so that it would couple more strongly with the 'main top' resonance and enhance the 'bass reflex couple' action. This was something I picked up from Fred Dickens. He used a sort of lattice, two horizontal braces and two vertical ones, with he notion that he'd have independent control over the stiffness in both directions, which would accommodate variations in the stiffness ratio of the back material itself. He got pretty good results that way. For some reason, though, I insisted on going in another direction. The stiffness ratio issue is certainly real. Hard woods in general have relatively higher cross grain stiffness than soft woods, but there's a lot of variation. It seems to me that would call for a different X angle on the back brace for each back, and it's unclear how you'd figure out what that 'should' be. At any rate,after trying several variations on the theme over the years I decided to go back to ladder bracing, and ended up with pretty much what Martin does, although I do 'tune' it using Chladni patterns. Getting the 'main back' resonance tuned to a pitch a bit higher than the 'main top' resonance does seem to help. It's not as effective when the players stands up with the guitar pressed against their belly, but not everybody plays that way. From what I can tell, the 'main back' resonance is the only back mode that actually helps the guitar to produce more sound. It does this by enhancing the 'bass reflex' action with the top and the 'main air' resonance, dropping the pitch of the 'air' mode and enhancing it's power. All the other back resonances tend to steal string energy that could be better used in the top to produce sound. The resulting 'dips' in the spectrum add tone color, so they're not a total waste, but you do want to keep them to a minimum in terms of the amount of sound they soak up. Making the back heavier seems to help: it's only dissipating energy when it's moving. Using a high-Q (low loss) material, such as a rosewood, also seems to help by minimizing the total band width of the back resonances. Of the two I'm inclined to think that added mass is better than low material damping: for one thing it's easy to mess up a low damping piece of material by bracing it wrong, ending up with a high damping structure. Clay S: That sort of rig won't give you a really cylindrical arch. It's close, but not quite on, being more curved in the middle.

Author:	Clay S. [ Fri Aug 07, 2020 6:30 pm ]
Post subject:	Re: Back X Bracing
"Clay S: That sort of rig won't give you a really cylindrical arch. It's close, but not quite on, being more curved in the middle." Hi Alan, If you read my post to the end you will see that I mentioned that. Most so called "cylindrical arching" is not truly cylindrical. Has anyone built a guitar with a "possum board" to isolate the back from one's belly similar to what some dulcimer players use? Martin came close with their "Model America" but it wasn't exactly the same thing. For those building "live backs" it might be an interesting "add on".

Author:	Bob Orr [ Fri Aug 07, 2020 4:22 am ]
Post subject:	Re: Back X Bracing
cablepuller1 wrote: Seen this on Instagram looks nice and light Sent from my SM-A715F using Tapatalk I don't think that halving joint is doing much good, looks structurally unsound.

Author:	DennisK [ Fri Aug 07, 2020 11:15 pm ]
Post subject:	Re: Back X Bracing
Alan Carruth wrote: Of the two I'm inclined to think that added mass is better than low material damping: for one thing it's easy to mess up a low damping piece of material by bracing it wrong, ending up with a high damping structure. Do you know of any specific aspects of bracing that result in higher damping without reducing overall stiffness to weight ratio of the structure? I built a rosewood top some years ago, and oddly enough it has plenty of volume but sounds terrible due to excessive power in the overtones. I'd like to try re-bracing it sometime to see if I can tame it down. Clay S. wrote: "Clay S: That sort of rig won't give you a really cylindrical arch. It's close, but not quite on, being more curved in the middle." Hi Alan, If you read my post to the end you will see that I mentioned that. Most so called "cylindrical arching" is not truly cylindrical. Yeah, cylindrical generally refers to any purely lateral arching without recurve (the pic Mark posted has major recurve). I just plane the braces by eye (with a straight line drawn on them for reference), and drag the box on flat sandpaper, tilting back and forth to give the rim a roughly cylindrical profile. Quote: Has anyone built a guitar with a "possum board" to isolate the back from one's belly similar to what some dulcimer players use? Martin came close with their "Model America" but it wasn't exactly the same thing. For those building "live backs" it might be an interesting "add on". That's generally called a double back, and I have seen a few around the net in the past. I think McKnight builds them.

Author:	Clay S. [ Fri Aug 07, 2020 11:41 pm ]
Post subject:	Re: Back X Bracing
Hi Dennis, A "double back" guitar would be slightly different. I have seen that term used for laminated backs as well as guitars that have a second internal "soundboard". In either case it would work differently than a possum board.The possum board only holds the guitar off the players body and doesn't otherwise interact with the guitar.

Author:	DennisK [ Sat Aug 08, 2020 12:38 am ]
Post subject:	Re: Back X Bracing
Clay S. wrote: Hi Dennis, A "double back" guitar would be slightly different. I have seen that term used for laminated backs as well as guitars that have a second internal "soundboard". In either case it would work differently than a possum board.The possum board only holds the guitar off the players body and doesn't otherwise interact with the guitar. So more like a temporary attachment, rather than a permanent part of the instrument? Or a permanent part, but only attached at a few points so there's plenty of airflow between the possum and actual back? I think some double back guitars have holes in the outer back for airflow, while others have holes in the internal live back. They're rare enough that there really is no standard definition yet. Laminated back is a totally different thing. But the terminology is confusing, with laminated sides being called double sides, and partially hollow composite soundboards being called double tops.

Author:	Clay S. [ Sat Aug 08, 2020 10:44 am ]
Post subject:	Re: Back X Bracing
Hi Dennis, He is a quote from a Delcamp post: "There is also much confusion, as different makers use different terms to describe the same things, and the same terms to describe different things (we like to keep the punters guessing ). So a double top guitar may be a composite top, or may have a second top somewhere between the top and the back. This may also be called a double back, which could also be a laminated back. Confused?" And yes, I was talking about a "board" that would somehow "clip" on the back edge of the guitar and hold the back off the players belly. Being removable would also be a plus. It might help the live back actually work as a live back no matter how it was played.

Author:	Alan Carruth [ Sat Aug 08, 2020 3:35 pm ]
Post subject:	Re: Back X Bracing
Clay S. Sorry: I didn't read the whole post. My bad. It's hard to say much for certain about the arch shape based on the picture that Mark Mc posted, what with the curvature of the sides and the close up shot. DennisK asked: "Do you know of any specific aspects of bracing that result in higher damping without reducing overall stiffness to weight ratio of the structure?" The main thing about bracing that seems to produce higher damping is when you mess it up. Make it 'lumpy', with lots of hard and soft spots. Thick glue lines seem to contribute, too, so use about 20 grit paper to level the inside of the top and the gluing surfaces of the braces. Then use 'Elmer's' glue. You get the general idea. No individual maker I know of is capable of work like that, but you see it in low-end factory stuff all the time. I try to avoid that sort of thing. I did see a couple of old Gibsons with ladder braced tops that had no monopole at all, at least not at any frequency I could drive the top at. You don't want to go that far; those were notably lousy guitars. The cross braces in the lower bout were right off the saw, and looked like bridge timbers. It's an example of how far you have to go to eliminate the usual modes. In a more general sense, if I wanted to end up with a low-Q top and was working with high-Q wood, I'd be thinking about how the top normally vibrates, and trying to modify that. Introducing a lot of asymmetry between the treble and bass sides, for example, might increase the damping of the monopole and cross dipole modes. Again; I'm usually trying to reduce the damping in the top, so it's not something I've given a lot of thought to. Clay S: "Has anyone built a guitar with a "possum board" to isolate the back from one's belly similar to what some dulcimer players use?" One of the apprentices in the shop I shared made a rig like that. He was playing a classical guitar standing, and wanted the free up the back. What he ended up with was very similar to the shoulder rests that violinists use; a bar that stood out from the back about an inch or so, and ran more or less diagonally across the lower bout. It was tricky to get it to clamp onto the guitars, iirc; fiddles have an overhang at the edges that keeps the clamp from sliding off and facilitates this.

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