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From Trevor's Bio:
I graduated from Durham University in the UK with a Bachelor's degree in engineering followed by a PhD. I worked post-doc for a while at Cambridge University Engineering Department teaching students the complexities of applied mathematics and electromagnetism (or were they teaching me?).

I have been reading his books. The first book itself validates his engineering credential for me. I also am an engineer. I came away from reading his book with a working model of the guitar in my head that carries beyond any bracing scheme of design consideration he makes with his guitars.

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http://www.Harvestmoonguitars.com

I'm obviously missing something.

I say it's a bold statement because using curved braces is not something that's obvious to most engineers. If you look at most structures, they use straight components to connect load from one point to another point. Curved structures are often used to engineer in some weakness or flexibility (which may be desired in a guitar). I think if you took 100 hypothetical engineers who've never seen a guitar and asked them to brace it, not one of them would pick a curved brace pattern.

Again, I'm not saying he's wrong, I'm just saying that I'm not able to bridge the gap between a flexible sail reinforced with high modulus curved tapes and a guitar top that has effectively a point torque load. I'm also not able to grok how curving the braces is helping anything out. I'm sure this is borne of ignorance so please...educate me.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

What I got out of it is that what is obvious is to "put the material (braces) where the stress is..." The bridge is the primary source of stress. What is not as obvious to me is what is the optimum way to distribute the load while maximizing the desired acoustic characteristics? Heck, I wish I had a good handle on what the desired acoustic characteristics are. Straight-line bracing is fairly easy to manage but maybe not so optimum when acoustic resonance is factored in; I don't really know. But I have seen some of complications that arise when resonances become a problem with aircraft designs.

I am guessing the balance between load distribution and desired acoustic characteristics is where the curved brace comes from.

I would like to study Trevor's books, especially the first. I think it would be a good follow-on to David Hurd's "Left Brain Lutherie" and some others I have studied. I've learned a lot from the books, from plate tuning (chladni), deflection testing, and so on but I still have many more questions than answers. I am analytical by nature and training (yep, I'm an engineer too but not an ME) and am always looking for more information on how the components in the guitar interact. Hopefully next year I can afford a set.

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Steve Smith
"Music is what feelings sound like"

And I can totally buy that but, I'm having a hard time seeing how a curved brace is necessarily the most efficient way to go about it.

e.g. - looking at a typical X braced guitar, the area around the lap joint is ridiculously stiff, possibly too stiff. I've often wondered if it would make more sense from a vibrational standpoint to taper the braces so that the second moment of the whole top would be more even rather than spiking up at the lap joint. The curved braces also achieves this by avoiding a high stiffness area right at the center of the top but it also does so with a lot of mass. One could achieve a similar stiffness with an X that tapers to nothing at the center but it would be much lighter than the curved braces. Get me?

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

I see what you mean but if the X tapered to nothing at the intersection then the forward, rotational force of the bridge from string force would seem to be focused on a relatively small triangular area. By curving those ends out then the force could be distributed over a wider area? A straight X is pretty easy to build. Not sure how difficult the curved bracing would be.

I also notice that Fric has a large transverse brace in this area and I'm curious why such a large brace is needed.

I don't know enough about this to support either option, I'm just discussing because I'm curious.

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Steve Smith
"Music is what feelings sound like"

Me too! I'm an EE myself but probably should have been an ME because I rocked at the Statics and Dynamics - I got better grades in those classes than my EE stuff. Heck, I hardly ever build guitars but I do find this very interesting and I want to understand it better.

As to distribution over a wider area, yes, sort of. I think. but...When I think curve, I think spring. If you think back, remember drawing the diagrams that showed stress or shear or second moment or whatever through a section of material? A straight line is always the most efficient way to brace something. i.e. - you'll get the most bang for your mass buck but, that's not necessarily what we want as instrument makers. We need to engineer in weakness so that the thing will vibrate.

Just to illustrate a bit better:

I saw on Trevor's site this picture of his bracing: http://www.goreguitars.com.au/main/page ... acing.html

So looking at this picture, I think his intentions become a bit more clear however, toward the middle of the bridge where the braces are changing direction, the braces are mostly lined up with the grain of the top - the direction where the top is already stiffest. Why not just eliminate the brace in that spot entirely - you're then almost left with an X that tapers to nothing at the bridge.

Next, we all know that the shortest distance between to points is a line, so why not straighten out what you have left to save mass and ease production?

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

I don't what to get into engineering semantics here, but a few things need to be "straightened out".

First the loading of the top at the bridge. Not a "point load" but fairly concentrated. The things to consider are the tension behind the bridge and the compression in front of the bridge caused by the string tension. In the scheme of things, these forces are almost irrelevant compared to the torque on the top produced by the string tension acting on the top of the saddle behaving as a lever arm. The simple evidence that this is the important loading to consider is the number of guitars (e.g. old dreadnoughts) that cave in in front on the bridge and bulge behind. So the issue is about resisting the bending moment in the top, because in doing that, in most cases, you fix the tension/compression issue anyway.

Andy: We certainly have a difference in how we conceptualise things.



You might want to suggest that to the Romans or the Normans or, more recently, I K Brunel. A lot of their arched structures are "open for inspection". Falcate bracing has nothing to do with how those guys used arches, however.



Really? Lets suppose your X-braces have a typical "gabled" cross section and that this section is maintained through the lap joint. Then suppose you take a cross section through the soundboard exactly at the X, another one just above the X and a third just below. Look at the sections and what do you see? At the X there is only one brace section. At the other two sections you see two brace sections. So in rough terms, exactly at the X there is a singularity in the bracing where the stiffness reduces to approximately half the value of what it is above and below. But you can make it as stiff or as flexible as you like. Just add or remove material to taste.

If the X braces are not gabled at their intersection but remain rectangular in cross section, the bending stiffness of the assembly at the X is very similar to two separate gabled braces. So in that scenario the bending stiffness (EI) remains fairly constant down the soundboard.

Now, all that is sort of obvious to me, an experienced engineer. So maybe I should have said it's obvious to any experienced stress engineer. There are guitar books around that that will tell you different stories, but you won't find an engineering book that will tell you a different story.

Another thing to consider is the orthotropic nature of wood: it is 10 to 20 times stiffer along the grain than across. A consequence of that is that in an unbraced top virtually no load would be transferred out of the bridge's width-wise foot print. So the material outside the bridge's span is not contributing in any meaningful sense to resisting the torque on the bridge. In that sense, it's wasted material, useless you can couple it in via a bracing structure. And that's what bracing structures exist to do, from the statics point of view; they dissipate load concentrations to make more efficient use of material. And that's what X bracing does in its own way as does falcate bracing, in its own way. Fan bracing does this less efficiently, because often the bracing is more-or-less grain aligned. And you could suggest that that is why lattice bracing came along, but I let others argue that point.



Well, I don't think anyone has claimed "most efficient" for falcate bracing. But if dissipating load over the majority of the soundboard is an objective (in order to make more effective use of the material in torque restraint), it's one way to go. An alternative is a spoke type structure (which others have tried), but it's easy to end up with joints and discontinuities in material under the bridge which inevitably means adding more material (and mass) to compensate. Or, you could miss out the "hub" altogether, like Simon Mardy does (a PhD EE) and live with the resulting deflections.

There is also the dynamic consideration, lest we forget. Whilst making the top structure sufficiently stiff to withstand the string tension generated torque, it also has to be sufficiently flexible to vibrate. And that's where I think falcate bracing has a great advantage. You have all the long grain stiffness you want to resist torque, but in installing that, you don't "lock up" the structure with continuous cross-grain structural elements, like X-bracing for example, tends to do.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

So why on earth would you bring up arches to defend curved bracing when you admit it has nothing to do with it? How well does an arch hold up when you push it from the side? What about when you rotate it 90o from the load?

You made a couple of interesting points later on in your post, one that I never considered, that I would have liked to discuss but the defensive and insulting nature of your response is really disappointing and really turned me off. Behavior like that is worthy of a snake oil salesman, not a PhD trying to sell his books. It makes it obvious that you don't like anyone asking questions around your pet bracing scheme and perhaps that you don't have the chops to defend it without resorting to ad hominem attacks.

Consider me plonked from this discussion

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

Trevor, thanks for joining the discussion. Sorry you've already run up against some of us "soft" Seppos.

Andy, don't take it as defensive and insulting. It's a different culture Down Under. Watch this and you'll get a better understanding:

http://www.youtube.com/watch?v=G3EYq9PyLDY

I'm lost. Not only on the engineering aspect but the 'defensive and insulting nature' bit. Don't really see it myself.

+1

+ A N other.

Whoah there Andy,- take it easy mate!

If it was Trevor's reply your statement "Curved structures are often used to engineer in some weakness or flexibility", which upset you, sorry, I can see his point.
What immediately sprang to my mind on reading vour post was what about the egg? Try crushing one end to end between your palms - I've tried, very unsuccessfully.
Curved structures are often used to engineer in strength and lightness - like a curved car bonnet for example, with channel sections tacked on? Or Balsa pababolic braces with a CF shell?

And I don't see where "defensive and insulting nature of your response" came from - if you are ever insulted by an Aussie, you'll know all about it! - Sublty is not in the dictionary down under.

Defensive? - sorry, I missed that.
But I did see a good, brief attempt at reasoning for a different style of bracing in Trevor's post.

I'm waiting my copy's arrival, especially the construction one (maths gives me a headache, but I'll plough through that later)- the proof of the pudding is in the eating.
4 full size plans and 2 books on guitar making - all in glorious colour too, for $200 has got to be a steal!

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Sounds like some unfortunate misunderstandings above, though I think I can see each person's perspective.


This is actually correct ("often", not "always"). Some distinctions: Curved sections are very efficient to resist continuous/distributed loads (arches in compression from above, dams holding back water, cylindrical/spherical pressure vessels or the inverse: eggs in the palm of your hand), but for concentrated loads, straight members are usually preferred for least weight (e.g., beams resisting concentrated forces, bending moments, or torsion). The thumb tip and the egg shell don't get along very well; an egg with a straight internal column would be happy to resist. For concentrated loads, curved members are indeed useful to add flexibility, or define a failure mode (e.g., ~all car hoods... 'bonnets' for the UK folks... have a curved notch in the middle of their longitudinal rails so a collision causes them to buckle there rather than guillotine the driver). A curved car hood is mostly for styling, though it does resist vibrations better.

Still, I don't think this curved vs. straight *strength* debate matters a great deal for Falcate bracing for a few reasons:
- For a braced guitar top, the goal is not necessarily lots of strength, but 1) enough strength to avoid failure/warranty claims and 2) enough long-term creep stiffness to avoid an objectionably sunken top in 30 years. On #1, as Trevor said, Falcate has an advantage with its lack of butt-ish joints that can fail due to stress-concentrations and end-grain glue weakness. So, while a curve may be less weight-efficient in some respects, it avoids added reinforcements and stress hot spots. Yes, minimum weight is important for responsiveness, but...
- The composite structure of a ~1/10" top, braces, and perimeter ~foundation doesn't respond in parallel to how we are used to isolated beams and trusses responding to in-plane loads. I.e., while a curved column will buckle easily, and a curved beam will be extra heavy, the top+braces composite structure won't *necessarily* respond such that those analogies directly apply.
- If the curves are gentle as in Falcate, the bending and torsion moments accommodating to the curved braces have the top plate there to gradually drain away or feed in stress to keep the braces from going unstable and the moments well-distributed. (OK, that is admittedly a lot of hand-waving to describe something only FEA can do, but hopefully it makes sense. An alternate point is that a bending moment can't negotiate a sharply bent brace like it can a gradually bent brace.)
- Notice Trevor's inner 2 longitudinal braces -- the ones that resist a sunken top -- are basically straight from the bridge to the UTB. No extra weight there due to a curve, and maybe less weight than an X that is a full ~49 deg off the bending moment axis.

I have some other thoughts on advantages of Falcate for acoustics/responsiveness, but my insomnia is going away now.

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David Malicky

Sorry to veer off-topic, but I feel compelled to comment.

To be kind - and to hopefully display some of the subtlety you feel Aussies lack - I feel that's an unfortunate generalisation. Given that there are around 22 million Aussies, you might like to meet a few more of us before you make such sweeping statements. It's really not a big deal, but comments like yours do "press my buttons" a little.

Carry on.

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Cheers
Pete

All this is very interesting indeed, but the reality is...it won't sound like a Martin, so why bother?
(joke)

It would also seem to me that it's not that unlike an A-frame bracing or ladder bracing too. It's just that the curves act as both the verticals and the horizontals.

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

My apologies Pete, generalisation was not intended, the stereotyping" intentional" in a joking way, just trying to say the that perhaps the intended recipient was being a bit touchy.

I know many Aussies, have a lot of time for them, and have worked in and spend time in your marvellous country - any "button pressing" was unintentional.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

So technicalities aside (as I know there are many on the forum ) what effect would you suggest this pattern has on sound/tone/volume if comparing similar materials, body shape etc to taht of what might be classed as a standard X

Obviously, structural advantages/disadvantages aside, would be interesting to get opinion on this aspect from thsoe who have built a fair sample of both?

Frank - thanks for posting this as I have the same question for Trevor.

I am also interested to know if Trevor believes the Falcate bracing would offer advantages over more traditional x-brace configuration for larger guitars used for flatpicking and strumming, assuming of course the Falcate braces were made proportionally larger and stiffer to accommodate the additional stresses.

Which is why I joked about it not sounding like a Martin and mentioned ladder bracing. They all have a unique tone relative to the parent bracing scheme.

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

If it's any use, a couple of OM example soundclips can be found found on http://alanlloydguitars.wordpress.com/students/

"Kinkead shape with falcate bracing. Pictures of this guitar are shown below and it features further in the sound
clips played by Tom. The recording set up is simple, i.e. a condensor microphone plugged straight into Garageband."

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Hi Andy.

Just thought I'd write in an attempt to ease some tension here. I believe there has been a misunderstanding going right back to Trevor's initial reply to you (quoted above), that may have set you on the wrong foot to read his further replies/explanations thereafter. I don't believe he was attacking your line of questioning, or being demeaning at all. I guess this is a problem with forums - posts are open to interpretation and therefore can be unintentionally misinterpreted. I know when I write at times, I am simply posting a small fragment of a whole "conversation" I have had in my head on a given subject. You however, may not have been privy to that conversation and therefore may read my post out of context to that which I had intended it.

With that in mind, I believe Trevor's abstraction (in a very general sense) was simply - a guitars top requires most support at it's point of stress and to then dissipate that load over a broader area in a controlled manner. This I believe is what he was suggesting was "obvious to an engineer" who would look at the needs of a guitars top. He was not suggesting curved braces are the "only" or even the "best" answer; nor advocating any particular bracing style at all, but that this was the "common goal" of any bracing scheme. I believe by this comment of yours -

[/quote]

- that you read it as him basically saying "it is obvious to any real engineer that falcate bracing is the solution" - in a derogatory or "talking down to sense", which I strongly believe he was not.



Again, I think this acted as the source of inspiration if you like, to draw from in a way to interpret the guitar tops needs - not a direct or literal correlation.



So far as I've read in the books, Trevor makes no such claim. This (falcate bracing) is his design solution to a range of guitar specific related issues/considerations. It is not claimed as the only solution. In fact he says it is his experience that most bracing designs "work", to varying degrees, when constructed properly as intended by the designer. Indeed, the book comes with four full size plans of four different bracing styles (only one of which is falcate) to build with - all yielding good results when built in the holistic design approach he discusses.

However that said, he does make a good argument for falcate bracing, based on sound design principals in science/math, with the testing to back up those claims. Not many have done such rigorous research, testing and then open publication of results achieved, let alone plans to build in like, previously. Many have, on the other hand, made verbal claims before but failed to provide any sound evidence or rigorous science to support them - and if you ask how to achieve this from them, well, it's a bit of this and a bit of that... wink wink.

Having spoken with you previously Andy, I know you have some (and far more than I for that matter) experience in the field of engineering and I truly believe that you of many builders, would actually really appreciate these publications as an in depth technical study. Nothing has previously been researched, considered, theorized, tested, written and concisely condensed into just two volumes; (albeit very large ones ) to these. I think you and any luthier for that matter, would garner a lot of food for thought from them so I sincerely hope this does not put you off purchasing a set. They are not necessarily the end all be all, but will certainly provoke thinking on the way a guitar functions and how to build them with those considerations in mind. I think they will inevitably raise more questions too. It has been my experience that Trevor is in fact quite open to discussing his ideas, thoughts and conclusions with anyone who cares to raise any valid questions after reading and digesting the information. By reading them, you may find yourself with a host of material to delve further into.

Sorry for the long post and this in turn, is no attack on you Andy, nor blind support for Trevor. I just believe this whole thing got blown out of proportion by a simple misunderstanding and I'd really like to return to my rose tinted luthier glasses now! I hope you will rejoin the conversation as if you did think of a question in regard to some of the comments - I'd like to see it discussed.

Ahem... Back to regular programming now.

Finally, in an attempt to address Frank and Charlies comments -



- the sound/tone/volume produced by the resulting instrument is derived from far more than just the bracing style, it's the sum of its parts. However Trevor's guitars built addressing the many factors he discusses, are very loud compared to the "standard".

For what it is worth, here is a youtube video with a Gore and a Collings 000-42AVS -

http://www.youtube.com/user/Phydaux2000#p/u/14/nPWrzZEU2Dg

Cheers,

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Jeremy.

J.F. Custom® Guitars

www.jfcustom.com.au

Wow! Seems there’s been a bar brawl here! Thanks very much to all who helped clear up. I hope Andy recovers soon.

Back to guitars, the outstanding items seem to be those arising from Charlie, Frank and Don, basically asking what falcate bracing sounds like sounds and whether its use would benefit, say, a dreadnought.

Jeremy kindly posted the YouTube link. If you watch the video, you’ll see Rick look up warily after the first notes on the Gore guitar. He was checking that he hadn’t overloaded the input because the guitar was a lot louder, though that doesn’t really come across at YouTube compressions. Yes, I was behind the camera when that was recorded. That same guitar (different player) is also featured here http://www.goreguitars.com.au/main/page_guitars_steel_string_sound.html, played by Danny Ross. I wasn’t there when he recorded that, but he told me what set-up he used.

Lower on the same page is a recording of another falcate guitar with mass loaded sides, played by Matt Semmens. Different player, different guitar, different studio and I was there at that session. All of the above mentioned recordings were done with no EQ and no effects.

For those interested, there’s also the classical recordings. We really struggled to get those down without using compression, because the dynamic range was so wide. So if you play them, keep the volume well up and add a bit of bass, then it sounds a bit more like the real thing. I’ll have another go at the classical recordings at some stage.

My own view is that no recorded acoustic guitar sounds entirely like the really thing and it doesn’t matter who built the guitar, who played it or who recorded it. I never have a problem picking the play-back from the live, so something is always getting distorted. So at best, you only get a rough idea of the real sound from the recording.

To Charlie’s queries about flat picking and strumming: Falcate bracing (as I usually do it ) has more mids than X-bracing (as I usually do it). But remember I’m mostly making fingerpickers and mostly with falcate bracing. (In fact, I’m probably mostly making classicals this last year). With fingerpickers, I’m looking for a classical type response, even over the fretboard etc. However, strum guitars sound better to me if the mid range is scooped a bit, which is what X-bracing tends to naturally do (yes, I know that’s a generalisation but it’s the only way I can answer this type of question). The same type of scooped response seems to suit flat pickers looking for the “boom, ching” type of sound. So if you do a falcate dread (I’ve not built one) you’d probably get a louder guitar because the falcate bracing is more efficient structurally. You can get the same longitudinal torque resistance for less mass than in X-bracing. However, you’d probably want to tweak it if you want the scooped mids, by which time you might be better off sticking with the bracing native to that type of sound, as I point out in the book.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Thanks for that, Trevor.

I have ordered the books, by the way.

I really think it's interesting to see the discussion of how inventions and creativity happens.... It really does show the differences in how people's brains work.... I think the discussion between Trevor and Andy also shows that one person's explanation of how they think they got an idea can make absolutely no sense to another person.... I see that sort of thing all the time at work..... Some fellow says something like "Well, I was looking at these ants eating a flower and AH HA! I understood how the rolling mill works!!!" - and I think to myself... ??**!! But.. It works for that guy - and he gets the right ideas.....

That's the devil about trying to explain how you got an idea to someone else.... Even though the idea itself makes total sense... The path to get there usually ends up wandering around a twisty path through the weeds....

I think the other thing Trevor hasn't mentioned in this post is that his bracing scheme didn't just hatch mature and fully developed out of his mind - he did a lot of computer modelling and studying the stress/strain relationships on the guitar top.... No doubt, he built a clunker or two in there whilst working it all out.... When you look at the results of the FEA - and see the strain... At first, you probably try out conventional things and see what happens in the model... but at some point - you just go "Well... What if I did something totally weird here"....

The brace locations and shapes on the falcate bracing made total sense to me as soon as I saw it... They follow the locations where you need the extra reinforcement because of the string pull and the bridge torque... AKA where my own guitar tops would likely develop "Divots".....

Thanks

As one who is not unaccustomed to controversy, I too do not see where Trevor went astray. However, Trevor is new HERE and I think it takes time for folks to get to know each other, their mannerisms, idiosyncrasies and so on. Coming onto the board selling/promoting from the start can be a risky thing to do. Andy, I hope you will come back. I always like and respect your point of view.

OK, that said, I have a question. With the bracing going under the bridge area, how do you deal with the possibility of drilling through the bracing? Or, is this a classical top design only? If so, have you tried it with steel stringed instruments? Or are you using bridge designs that keep all of the string above the top?

Mike

Edit: Trevor, maybe buy some ad space for your book?