Official Luthiers Forum!

Thanks Ken, for starting this topic!

This is the kind of conversation that is essential for beginning guitar builders, like myself! I’ve
always known that there was a rhyme and reason to brace design. However, I have very little
knowledge of how each brace, tone bar, etc. has its effect on tone or the acoustical quality of a guitar.
The term, “It’s a System” as Mark and Alan have said, has helped to put the construction
of a guitar body into a whole new perspective! For me, I can liken it to the construction of a
conventionally framed house, in that, where the skeletal structure (2"X4"’s, 2"X10"’s, etc.) by
itself, is not all that strong. However, when you add sheathing (4'X8' plywood) you now have a
structure of incredible strength, that will move and breath with the whims of weather, yet retain its
original shape! Though, this is an abstract similarity, it helps me to see the “Whole Picture”! I now
can look at a guitar body, and see “A System” at work. Of course, there is still much learning
needed on my part, in understanding the relationship of braces, to the top, sides, and back! But,
this is a great start!

Also, it is refreshing to here words like, “There is no magic anything” as Alan has put it! This is
very encouraging, in that, it keeps the door open for new and innovative ideas. For now, I will not
stray to far from the established and well proven bracing methods. However, after reading Alan’s
experiment, it does invite the notion to make small changes, and see what happens!

Great Thread!

Robert

_________________
Everything has beauty, But, not everyone see's it!

What Al said about the upper bout bracing being more structural than tonal is great...with a conventionally made guitar in which the upper bout top has to be structural.   If you throw in flying buttresses from the neck block to the guitar sides in the waist that take the compression load of the neck to neck block off of the top, that part of the top no longer needs to be considered primarily structural. Suddenly it's mostly about tone...

I see the braces (OK, tone bars, if you will) as affecting the modes of nodal breakup of the top.   Given that the top "breaks up" into phase/anti phase motion at many frequencies (this is a lot of the stuff that Al studies), then by making certain areas of the top stiffer than others, you are controlling the frequencies and amplitudes of the top breakup.   The greatest effects are in the midrange with all this...just look at Chladni patterns and note the freqencies of the most prominent ones. The net effect of those in and out of phase motions is a cancellation of mid freqencies in the acoustic output of the guitar.   

This is (I believe) why the EQ settings most often used for amplified acoustic guitars with USTs is the classic "smiley curve".   That EQ curve is an attempt at duplicating the physical EQ curve that a guitar top and air chamber impose upon the guitar string signal.

Back to bracing...structural issues aside, what the braces do is to determine how the top will distort the string signal in transforming that energy into acoustical output. What you hear from a guitar IS a distortion of the string signal.   If it weren't, then all guitars of a given scale length would sound the same. The bracing determines at which frequencies and to what degree the top will vibrate to reinforce and cancel acoustic output.

Of course none of the above happens independent of the individual characteristics of the top itself without the braces, and different tops have different degrees of longitudinal to lateral stiffness. Bracing pattern changes can minimize those differences once you figure out the basic sound you're going for.

Here's a thought that's been brewing in my head lately: It seems to me that by making a second "X" behind the bridge, rather than running two "tone bars" more or less parallel to each other diagonally across that area, one should be able to create the same amount of stiffening with less mass. The lapping of the two braces where they cross (I'm assuming a "capped" joint) would seem to create more stiffness structurally, in a whole-is-greater-than-the-sum-of-its-parts kind of way. Therefore, one should be able to make those two braces substantially smaller and have the same overall stiffening result in that area. You engineers out there, please tell me if this makes sense.

(I also like the symmetry of this picture. The asymmetrical diagonal "tone bars" have never made intuitive sense to me. I know, there are tons of great sounding guitars made with that design...)

It seems to me that that the bracing of the area behind the bridge has an important structural as well as tonal role, as the stiffening there resists excessive bellying. So, in thinking about creating just the right amount of stiffening there, I'm thinking of both the structural need and the effect on tone and volume.

This line of thinking is not directly addressing the question of how the specific placement of braces affects the location of nodes; rather it is looking at it in terms of overall stiffening in a controlled way, with the goal of creating the ideal stiffness for the various areas of the top with the least amount of mass.

Thoughts?

_________________
Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

I've had a look at Steve Grimes (two hole) guitar bracing. He uses two "x" bracing as well.

_________________
A higher purpose for wood.
Rich Smith
Issaquah, WA

Todd, I don't see how you can think that so few braces as the typical Martin pattern will not force the top into very specific nodal patterns. The stiffness is broken up into patterns which are very definite.   That is much less the case, for instance, with Greg Smallman's lattice bracing which forces the top to act much more like a piston in the midrange...which is one of the reasons why those guitars project so well.   Asymmetrical bracing will cause the top to break up into different areas of dipole, etc. thus causing different amounts of phase cancellation and reinforcement at different frequencies.   That's one of the underlying truths about Kasha's bracing whether or not you go for all of it. That is creating different impedance loads in different areas of the top whether you go for the bass side/treble side stuff.   You could probably string a righty Kasha top left handed and hear little difference if it didn't have the split bridge.   

Charles Fox did a number of Dos Equis guitars as well...

Ken asked:
"are you suggesting that it is not necessarily the tone bars *or* their placement or length but rather the area of the top that is left "open" or "free" that makes the tonal differences?"

No; and I thank Mark for saying it more succinctly than than I usually do:
"..most builders believe that the double X brace doesn't work because when Gibson did it it was a failure. Yet, when Al did it, it worked great. The difference is that as a component of the Gibson "system" it was the wrong thing. However, it fit into Al's system really well."

Another way of looking at it is that Gibson had a good design idea, but, owing to limitaions of their production methods, could not realize the potential. Almost any design can work well if you know how to fine tune it, and badly if you don't.

Also, re-read Rick's post until you really understand it. Different tops sound different, in large part, because of the way the different patrts of the top move, and the braces effect that. In that sense, you could think of the bracing (very roughly) as the crossover network in a speaker system. Different values of the caps (analogous to compliance in a mechanical system) will alter the way the inductances of the speakers (analogous to mass) react to the signal, and change the output of the different components. Just as the crossover network needs to be optimized to the speakers and cabinets, so the bracing has to work with the particular top. Again, this is a very rough analogy.

So, Rick, the flying brace makes it work more like an archtop? Cool.    

Al, yes, in a way.   The deal is that with the flying buttresses and a cantilevered fingerboard, most if not all the pressure that is usually compressing the top longitudinally and pressing down in leverage through the fingerboard is transferred via the buttresses to the vertical sections of the sides below the waist where there is incredible inherent strength. Thus you can now deal with the upper bout in any way you please, and if you like, you can be done with most of the bracing on the top up there.   Note that I say, "if you like"...the point is that you are no longer forced to use the upper bout as a structural part of the guitar, so you're free to experiment.   Hell, you may decide that you prefer the tone of a blocked up upper bout, but that is now an artistic choice, not a necessity.

Actually, I have one more trick that borrows from the archtop world, and that is that I graduate my tops more than usual by sanding them from about .125" to .130" under the bridge down to about .085" or less at the edges, so the graduation is kind of archtop-like, though done on a domed flat top. This, too, helps keep the mid punch and (I think) improves the dynamic range by "feathering" out the compliance of the piston area of the top.   

I can tell you this, my guitars do not sound like Martins; they don't go "whump". What they have is a bit of archtop and SelMac overlay on top of the warmth of a flattop. They have excellent harmonic sustain, very good projection, and dynamic range that doesn't seem to quit before you just can't stand the higher action required to slam the strings harder. These are qualities I've been after, and they're almost exactly the qualities that reviewer Art Thompson wrote about in his review of one of our jumbos in the latest Guitar Player Magazine.   

I guess if there's any basic principle that I'm trying for with all this it's a controlled stiffness that is fairly high in the middle of the lower bout and then goes to looser and looser out to the edges of the guitar top.     Hmmm, kinda like an archtop...with some major differences.

Cool stuff. Great subject matter.

_________________
"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."

Great discussion !!!!

Getting back to Ken's original question....

To find out how a guitar's tone would change with the tone bars in a different position. I think one would need to actually string the guitar, play it a bit, and then move the bars to a different location.

This is not easily done on a normal guitar but it could be done if one were to build a "test" guitar and glue the tone bars on the outside of the top rather than the inside. That would make it easy to take them off and move them.

The guitar might not sound exactly the same with the bars on the outside as it would if they were glued on the inside, but I think the difference in tone noticed by moving them might still be meaningful.

And it would certainly look cool !!!

Mark

Building a test enclosure with a removable back could be useful here. If one could find a way to lock down a back and be able to easily remove it again and again....then changes could be made to the top bracing and results recorded as well. Perhaps a series of posts the same depth as linings, glued to the sides with threaded studs coming out of them, and some small plastic nuts to lock the back down to the posts. The posts would not be connected to the top, only the sides and back. This would work ideally, and could still allow the back to move as well.

_________________
"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."

like with rare earth magnets or something...

_________________
Brock Poling
Columbus, Ohio
http://www.polingguitars.com

Yeah, but rare earth magnets are problematic, in that they tend to smack together and break, but yeah, that might work too. Perhaps if they were epoxied on to the back of the back so they wouldn't move. But they would have to be small ones, that would allow you to get the back off, even using 12-20 or so of them.

_________________
"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."

Some one of these days I'm going to build a test bed guitar.   The way I build, it's easy to just rip or saw a top off and put a new one on. The neck bolts on and the fingerboard doesn't touch the top.   I could put a new top on the same back and sides set every day for a year if need be.   I don't think you can "fake" the actual glue joint around the top without adding or subtracting something necessary. Forget magnets, forget a banjo-style tension ring...they change the mass at the edges, and that is critical, I believe.

[QUOTE=Rick Turner] Forget magnets, forget a banjo-style tension ring...they change the mass at the edges, and that is critical, I believe.[/QUOTE]

Yeah, magnets doesn't seem so great, because there's more than likely going to be some buzzing. But the tone ring concept might work if done very lightly, knowing that it's going to effect the sound somewhat, so for experimentation purposes, maybe it could be valuable.

How so is the mass at the edges critical? I mean, for test purposes, for the sake of argument, you would still have the same exact structure each time, and the same top plate. The only pain in the butt will be removing the braces and putting new ones in. But replacing the top each time is problematic in that each piece is going to be different and have different tonal characterstics....
Thanks for your thoughts Rick, this is good stuff. I'm learning lots, and the wheels are spinning up in my head.

_________________
"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."

Rick Turner wrote:

"Actually, I have one more trick that borrows from the archtop world, and that is that I graduate my tops more than usual by sanding them from about .125" to .130" under the bridge down to about .085" or less at the edges, so the graduation is kind of archtop-like, though done on a domed flat top. This, too, helps keep the mid punch and (I think) improves the dynamic range by "feathering" out the compliance of the piston area of the top. "

RIck, I had a thread on here a couple of weeks ago where I have made a standard dreadnaught guitar out of Sycamore with a WRC top that I did the exact same thing to... the top was thick at the center and feathered out to almost noghting at the endges. The post on here generally got a bad review, but I can tell you now that the box is closed and sanded out, it has a response like no other guitar I have ever made. One flellow luthier that visits me on a regular basis picked it up and was looking at it and when I asked what he was looking at he said he wanted to see why this box was resonating so good just from me talking from across the shop. I now have 3 boxes sitting there almost ready for finishing, and this one stands out head and shoulders above the rest. I cant wait to get it finished so that I can play it!

As far as one guitar that you chisel off the bracesand move them to another location to see what happens, I would think that glue residues would also influence the guitar each time that the braces were removed.... maybe not enough to be a real problem though.

This thread is now getting down to the level of discussion that I had hoped for, and for a challenge to myself and others to come up with ideas that will prove to make private individual luthiers more of a difference than just making martin or gibson "copies" with different decorations.

I know there are better ways to achieve the ultimate guitar. One luthier I met from Italy had a guitar he let me play that was remarkably different than anything else I have ever played in my 35+ years of guitar playing. To this day I dont know what he did or does different than others, but there is a remarkable difference in his guitars. Unfortunately, I only got his first name, which was Tony. I would love to pick his brain a while to find out what he is doing different. I want to make guitars like that so people remember them all of their life and compare everything else they ever play to that guitar. I want to be different!

Keep the good ideas coming! I'm having a blast with this thread!

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Reguards,

Ken H

Don, point well taken. At least you'd be testing apples vs. apples, and you'd get to where you could predict ultimate results much as Al has learned to correlate free plate response with his closed up guitars.

If you believe Smallman (which to a certain extent I do) then mass and rigidity at the edges of the top matter a lot in reflecting energy back into the top rather than letting it drain down into the acoustically inefficient sides.   At least this is in the "making guitars project" department.

At this point, I'm building with a laminated bridge plate and three fan braces behind the bridge between the "X" legs. It's pretty darned symmetrical. So far, so good, and it seems pretty light weight and pretty strong in resisting top bellying. I'm probably going to stick with this for now, but I am the restless type, and I'm sure I'll try some other things.

Oh...we carve out coves in the sides of the "X" braces so they're more like tapered "I" beams.   I measured a 10% improvement in stiffness to weight ratio from doing that.   

Great thread.

I've been meaning to post this on my web site on a page titled "my most valuable guitar".

Hight tech adjustable neck, patent pending

A couple of years ago, I took an old body that, for various reasons, I had never completed.  I scabbed on a neck with the fingerboard cut off at the 14th fret.  I then cut a flap in the middle of the back and another in the side at the lower bout so I could really get inside the guitar with the strings still on.  I then proceeded to mess with every brace, including the tone bars.  I moved them around, scalloped them, tapered them, removed them, started over.  After each change, I closed the flaps and played the guitar.

Since then, I've put half a dozen test tops on that guitar with lots of different bracing patterns.  It's quick when it doesn't have to be pretty.  Based on that experience, my current view of guitar bracing is much like what Mark and others have said.  The top is a system and you can't really generalize about the effect of moving or otherwise changing a particular brace.  I've only built 40 guitars but between those and the various test body configurations, the only thing I feel like I can generalize about bracing is that, within reason and normal parameters, what happens close to the bridge makes much more difference than what happens farther from the bridge.  For instance, small changes at the bridge patch made much more difference than huge changes with the tone bars.

Another thing that was consistent for me was that adding a lateral brace of any kind or configuration (and I tried a bunch) behind the bridge patch made my guitar louder, more brash, and less warm.  I'd be surprised if that was universal to all guitars but it seems universal to mine.

It's funny because it seems that a lot of people, myself included, come into this craft interested in figuring it out with an analytical/engineering/rational approach, wanting to theorize about the function of design elements and build (literally and figuratively) on those theories.  But I'm beginning to think that, when it comes to the fine points, it's more art than science and these beasts may be too complicated to really apply universal principals to.  Again, I'm talking about the fine points.

I've seen examples of people approaching bracing radically differently and each coming up with outstanding results when, if looked at theoretically, if one scheme worked, the other shouldn't.

I've also seen examples of different people taking seemingly identical approaches and coming up with drastically different results.  I assume the die hard scientist would say that there are quantifiable reasons for all those things and I suppose they would be right.  But I think the variables are just too great from one person's guitar to the next to be able to make meaningful statements about any universal results of nuanced bracing changes.

Sure is fun though.

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http://www.chassonguitars.com

[QUOTE=Kent Chasson]

Another thing that was consistent for me was that adding a lateral brace of any kind or configuration (and I tried a bunch) behind the bridge patch made my guitar louder, more brash, and less warm.  I'd be surprised if that was universal to all guitars but it seems universal to mine.

[/QUOTE]

Thank you for your post Kent!

You have answered some questions that I hadn't even asked yet and then answered the ones I did too. I build guitars (some but not all) for the bluegrass crowd, and most of them prefer loud brash guitars, so this is something I will try for that group of buyers.

Building on your experience, I will keep in mind that the things I do closer to the bridge will affect tone more than the outward braces too.  I just knew that there had to be someone out there that had the same ideas that I did on this subject and had actually tried them. It is great to know that I'm not alone in my world of thought!

_________________
Reguards,

Ken H

Take a look at the bracing pattern that Jean Larrivee has used for years.   He's got one lateral behind the bridge right about where you'd expect the Martin belly to appear.

This thread is so unbelievably interesting.

Kent, thanks for the post! That was a great experiment. No I'm going to have to build a test body to play with. Very cool.

_________________
"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."

Sam, you are so right!

May I also add, inspirational!

Not only, am I learning important details to bracing tops, I’m realizing that I am coming up with
my own ideas for bracing patterns. All sparked off from reading posts of the very experienced
builders in this thread. Of course, only through trial and error, will those ideas be proven to have
any merit!

I should say though, that is not the most important lesson I’m getting from all this. Please correct
me if I’m wrong. I’m thinking that different bracing patterns will produce different results! I guess
that would be obvious. However, If a builder is well versed in understanding the relationship of
bracing patterns to an end result, then, that would have to be valuable to the builder/client relationship.
When a client has conveyed his/her expectations of the tonal qualities that he/she desires
from that instrument, then the builder needs to knows how to achieve those desired results.
So, the builder should have an understanding of the relationship between braces and top,
and the end result in the desired tonal qualities. Now, I know that there is much more, to producing a
desired end result for a client, but, in the context of this thread, am I on the right track?

Robert

_________________
Everything has beauty, But, not everyone see's it!

When considering questions like this I find it helpful to think about the system and its components in the most basic way and expand on that. At its most basic a top plate is a harmonic oscilator with the bridge at its center. At its most basic, a brace simply adds mass and stiffness to this system.

If the brace moves closer to the bridge, you are adding mass to the system closer to the bridge. What effect does that have... does it inhibit top movement or enhance it? Does it depend?

If the brace moves closer to the bridge, you are making the top stiffer near the bridge. What effect does that have? The angle of the brace relative to the bridge directs that stiffness. What effect does that have?

Etc etc

[QUOTE=Rick Turner] Todd, I don't see how you can think that so few braces as the typical Martin pattern will not force the top into very specific nodal patterns. The stiffness is broken up into patterns which are very definite.   Asymmetrical bracing will cause the top to break up into different areas of dipole, etc. thus causing different amounts of phase cancellation and reinforcement at different frequencies.   [/QUOTE]

Thanks for your response, Rick.

I guess I didn't make myself clear. I didn't mean to argue against your point that the braces force certain nodal patterns, or to suggest that that isn't an important thing to take into account and work with in shaping the sound. Rather, I was asking a question which has to do with a separate, but related, issue: whether a second X behind the bridge can create an appropriate amount of stiffness in that area of the top with less mass than the typical diagonal and more or less parallel "tone bars". No one has yet addressed this question; if anyone can, I'd appreciate it.

Once again, to be clear, I realize that the second X will likely result in a very different nodal pattern in addition to whether or not it gives appropriate stiffness to that area more efficiently (i.e. with less mass of bracing). The tonal result of the different nodal patterns may be something I like or not, but I know I like the idea of increasing the stiffness-to-mass ratio, so that's what I'm looking at with this question right now.

Rick, you also said:

"I guess if there's any basic principle that I'm trying for with all this it's a controlled stiffness that is fairly high in the middle of the lower bout and then goes to looser and looser out to the edges of the guitar top."

This is very similar to how I'm thinking, thanks, in large part, to what I've learned from you and other sources. I may find that more smaller braces behind the bridge, such as a number of fan braces like you're doing, give me the tone I'm after as well as the overall distribution of stiffness as you describe. Still, at this moment I'm interested in the stiffness-to-mass potential of the second X, and how that may work in a system designed with this basic principle in mind.

Clear as mud?   

_________________
Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

Rick:
Funny thing. Recently some of the folks measuring Old Master violins have found that the tops are either uniform in thickness, or thinner in the middle. I've built several uniform fiddles,and one 'reverse graduated', and one of each in archtop guitars, and they work _so_ well. However, in this case, you also have to get the arch shape and height just right. The arch has a lot to do with stiffness distribution, just like the braces on a flat top.

Kent:
I like your 'test mule'. I've gotten a lot of milage out of my 'corker', and more from another body that can use the same plug-in neck, that a student built last summer. Everybody should have one.

Mark:
'Way back when Carleen was working with Fred Saunders she built him some violas that had the bass bars on the outside of a flat top. He had a lot of fun chopping them up and playing them: you can A/B just about instantly, and learn fast. The effects seemed to be the same as they were on 'normal' instruments. In fact, on one, he used a clamp on the outside to imobilize the top and back in the same way that the soundpost would, and got the same result. So, yeah, outside 'tone bars' would probably work fine. Put them on with CA and you could test three or four configurations in an afternoon. Wash it off with acetone.

The only problem then is, what have you learned? ;)