Official Luthiers Forum!

Thanks to Scott and Mario for the very interesting discussion. My two cents:
For the past 15 or so years I have always weighed my bridges. Ebony was
and is always heaviest (30-35 grams), Indian Rosewood (22-27 grams), and
Brazilian Rosewood (17-21 grams). Over time I began to equate the way the
guitar sounded with the type of wood used for the bridge given all other
factors relatively the same. Years ago I came to the exact same conclusion
that Mario has expressed here - I only use Brazilian Rosewood for the
bridges on my instruments unless the buyer insists on ebony. Ebony always
seems to sound more treble and almost in a harsh way as compared to the
warm tone of a brazilian bridge. It is interesting that Scott, Mario and I all
seem to come to the same conclusions regarding wood selection but from,
what appears at first glance, such different directions.

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Sylvan
http://www.wellsguitars.com

Those of you testing bridge materials: may I suggest that you add Katalox (Swartzia cubensis) to the list of materials to test for appropriateness as bridge material? I'd love to get some feedback, based on more than my gut instinct (and its ringing tone.)

Thanks,

Dennis

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Dennis Leahy
Duluth, MN, USA
7th Sense Multimedia

Hesh,

You are correct in that the stock Martin type footprint does not seem a problem, although I've never traded one of them for my bridge (and wouldn't bother). Only ones with a bigger footprint--I've seen a few in addition to the mustache--that seem to hurt the treble.

I'm not a purist about parabolas, either. More important is that the surfaces flow as smoothly together as possible.

I hope it sounds good.

Scott

Now that I have your attention, I have a question. I just received a guitar for hot-rodding, and it is the first I've seen with a capped crossing of the X brace. Would someone please give me the idea behind this, and what it is thought to accomplish? I can see an aesthetic/intellectual component to the idea, but don't understand what it does other than to add mass. It would not seem necessary, structurally.

Thanks, Scott

Funny thing building these guitars. I actually built my first guitar without capping the X brace, very recently I decided to add a cap after reading some thoughts from some very successful builders....well, I was very surprised with the results, as crude as the cap must be, it's hard to work inside that darn box after it is closed up....the guitar sounds more full, richer, louder, I know it seems hard to believe but it sure as heck was the case with mine after that little cap was added. It wasn't just my ears either I let 2 other very talented players test the guitar, before and after, both said, wow!, don't touch this guitar again it sounds great, better than before. Luck, coincidence, you got me but it sure did work.

Scott, I just looked at and sanded my bridge some more as there were slight undulations, I strung it up and played it, thought it sounded better, but my ears were shot from the sander, I'll wait a while and see what differences I can detect when things quiet down.

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Gwaltney Guitars

Capping the X-brace stiffens up the joint, as I understand it. The 'open' face of the interlocking legs form a little stress riser, and the end-grain-to-edge-grain joint is hardly the strongest there. The top 'bridges' the open end on the other side. On the reccomendation of pretty much everyone at the MIMF, I'm capping it. Prevent a potential place for traumatic cracking.

The mass, surely, is negligible? A piece of spruce that size wouldn't be even a tenth of a percentage point of the overal top weight, and in my mind, it's there for a reason. Mattia Valente38745.732037037

no postScott van Linge38749.6917013889

Because of the way the 'box' joint is cut where the X crosses it's much stiffer one way than the other. The leg that has the open part glued to the top is essentially 'bridged', so if you try to bend that leg along it's length it's fairly stiff, and, more importantly perhaps, it's pretty much the same stiffness whether it bends 'up' or 'down'. The one that has the open side facing into the box is much less stiff, and generally has different stiffness depending on the direction it's bending.

It's easy to see this diference if you look at the 'free' plate vibration modes. Without the cap they will be very asymmetric, even if the bracing is not. When you put the cap on, they will tend to 'snap in' and be much better organized. Of course, this does not show up much, if at all, on the lower order modes of the completed top that you can look at with 'glitter patterns', but it stil has got to effect the way the top vibrates.

The little patch probably doesn't weigh more than a gram or so, if that. Considering that the top assembly without the bridge will often run around 180 grams, the added weight is hardly a huge issue, IMO.

I've lost track of the number of tops I've fixed on cheap guitars where the un-capped brace split at the level of the cut due to the effects of the down force of the bridge torque, combined with a moderate blow on the top. Even the linen patch that Martin uses helps in that respect, but a slip of spruce a couple of inches long and 1/8" thinck works so much better....

That's some good science, Mario: keep it up!

Denis: I have not seen Siminoff's book, but I guess I need to. I've been measuring the forces the string puts on the bridge, and I can tell you that most of the time the transverse force that pushes the top 'in-and-out' can be much greater than the tension change that torques the bridge. Also, of course, we build tops to resist torqueing, at least at low frequencies. So it's hard to see how the torquewise motion could possibly be greater than the in-and-out loudspeaker sort.

This is backed up by an experiment I did in which I used an electrical driver, sort of a 'pickup in reverse', to drive a string. By setting it up right you can make the string go in any direction you want. When the string moves 'vertically', toward and away from the top, the sound is very much louder than it is when the string moves 'horizontally', across the top. Since horizontal motion drives only the torquewise movement of the bridge, while vertical drives both the in-and-out and torquwise, I conclude that we're going to get more out of the guitar by maximising the vertical motion of the top. This, in fact, is the way most successful brace systems are designed.

The little patch probably doesn't weigh more than a gram or so,

Well, let's see...

Mine are an inch long, 1/4" wide. That's 0.25 sq.in. times 1/8", which gives us 0.03125 cubic inch volume.

Sitka spruce weighs an average of 28 lbs/cu.ft.

1728 cubic inches in a cubic foot.

28 lbs devided by 1728 gives 0.0162 pounds per cubic inch.

Multiply the slip of spruce by the weight:

0.03125 times 0.0162 gives 0.0005062 pounds os spruce.

converted to grams, it is 0.2296

Just a little over 1/4 gram.

BUT WAIT! there's more!

I shave mine down to feather into the brace at each end(must eliminate stress risers, right?), and that effectivel takes half the mass off again.

So, mine weigh in at a hair over 1/8th of a gram! Since everyone surely shaves theirs down, also, even if yours is 2 inches long, it still weighs less around 1/4 gram.

BUT WAIT! There's still more....

I have enough lightweight and soft Engelmann spruce to make all my spruce slips for the rest of my life. In fact, I've cut up a top that was too weak to use as a top, and have jars of these slips ready... And since Engelmann weighs less than Sitka, mine must come in at less than 1/8th gram.



See, a little math never hurt nobody, and facts are always so much more interesting than hunches....

Y'all may now resume discussing lumpy bridges....

Ahem! It feels like we're in Harvard here !

[QUOTE=Alan Carruth] Denis: I have not seen Siminoff's book, but I guess I need to. I've been measuring the forces the string puts on the bridge, and I can tell you that most of the time the transverse force that pushes the top 'in-and-out' can be much greater than the tension change that torques the bridge. Also, of course, we build tops to resist torqueing, at least at low frequencies. So it's hard to see how the torquewise motion could possibly be greater than the in-and-out loudspeaker sort.

This is backed up by an experiment I did in which I used an electrical driver, sort of a 'pickup in reverse', to drive a string. By setting it up right you can make the string go in any direction you want. When the string moves 'vertically', toward and away from the top, the sound is very much louder than it is when the string moves 'horizontally', across the top. Since horizontal motion drives only the torquewise movement of the bridge, while vertical drives both the in-and-out and torquwise, I conclude that we're going to get more out of the guitar by maximising the vertical motion of the top. This, in fact, is the way most successful brace systems are designed. [/QUOTE]
Hi Alan,

The first attempt at bracing my guitar was somewhat similar to a speaker cone: a full circular brace about 8" in diameter, and a set of radial braces emanating from a point at the center of the saddle that were long enough to intersect the circular brace. I was thinking about the piston motion of the top. I know Siminoff is a guru to some and a nut to others (no offense, Roger), but he showed a setup in his book that measured the movement of the bridge when the string is plucked. It was primarily a fore and aft rocking motion, and not a piston. Could be flawed science, or an experiment that by design measured the wrong forces (a self-fulfilling prophecy), or maybe not applicable to my design by virtue of where he anchored his strings and how he braced his top. Nonetheless, I scrapped my piston design and started sketching a rocking design, the result shown above.

If that particular sonic bracing scheme has poor results, in my thinking, the sky's the limit with what could be done in terms of engineering soundboard braces (almost) solely to promote balanced tone, volume, and sustain, when the structural tasks are handled by other braces.

If you look at the structural bracing scheme I've come up with, and include the "tunnel bridge" that removes the shear force from the bridge (leaving torque force as the major structural force that has to be dealt with at the bridge/bridge patch area...

...now, for the sonic braces imagine a typical Martin X-brace pattern, or a double X-brace, or whatever you can think of. Only now, you can shave and whittle like crazy on those braces, because they aren't having to perform the task of managing the string force.)

Perhaps Mr. Martin was a true genius, or the luckiest inventor of all time, having designed a bracing scheme perfectly optimized for sound and structure simultaneously. My hunch is, (with all due respect), the X-brace scheme can be vastly improved upon if you take the structural task out of the equation.

Sorry that was long-winded. Have I converted you? Can I hear an "Amen!"? Well, I didn't think so, and rightly so. This is a pile of theories at this point. But, I'm getting closer to at least constructing one of these. I'm intrigued by your experiments in soundboard and bridge movement, and maybe the next one of these guitars will sport a "piston-optimized" set of sonic braces.

Dennis

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Dennis Leahy
Duluth, MN, USA
7th Sense Multimedia

Hesh you are a genius by just being able to work in your environment and i'm not kidding at all here, i probably have 2 or 3 times the size of shop you have and i get pretty mixed up when there is more than 2 extension cords plugged in. But hey, i'm slowly gettin' there, so maybe i'll install a bathroom in my shop when i'm more organized, like you

Serge

This is for classical's, but something else to 'think about'. The Gilbert Bridge

http://schrammguitars.com/gilbertbridge.html

CrowDuck

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Chris Nielsen
Soquel, CA.

Scott,
Bryan lives on a ranch outside of Greenville in northeastern New Mexico, not too far from Clayton. From everyone I have heard from who sent their guitars to him, he does superb work.
He has a web site. Obvious Google.Jimmie D38746.3578472222

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Scott van Linge38749.6937962963

Was waiting for some time to read the whole thing.

Awesome thread.

Scott, Thanks so much for all the great theory - can't wait to sand my bridge.

Mario, Great info as usual. Have been revisiting your site to check all your great work.

Greg, As a beginner builder I would LOVE to see some pics of your current bridge shape.

Dennis, I think your design is very interesting. I do not have enough experience to discuss actual tonal/brace theory but if I understand your design, won't the back of the bridge have a lot of upwards tension created from the angle back to the string attachment point? How is that area of the strings held down? It looks like the strings pass through some sort of 'hold down' area and it seems a little odd to my inexperienced eye to have any upwards tension on that area of the bridge. Could be wrong and will look forward to any pics and real world data.

Thanks again to all for the great info.

Sponge brain soaking up info

Larry

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Thank You and Best To All

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Scott van Linge38749.6865046296

Scott,

It's unfortunate that you did not complete your scientific training, because I bet you would make a good scientist. For now, though, you don't seem to appreciate how important it is to distinguish between what you truly know versus what you _believe_ that you know. As Mario offered so thoughtfully (very nice Mario!), no one doubts that you hear the changes you hear when you alter a guitar's structure. Rather, it is the mechanisms by which you claim the changes occur that seem dubious.

I am not suggesting that your mechanisms have no merit (concentric rings, parabolas, smooth rather than sharp edges, energy release, and so on); I suggest only that you offer us no objective way to really evaluate them other than your own experience or that of a client who can hardly be considered objective. Sure, removing mass from the structure of a guitar will make changes to a guitar's sound, no one doubts that.

If you really want to convert the informed (rather than those that are willing to buy the newest tonic), then you need to support your claims or be dismissed. Your choice. So consider providing some reliable, objective form of evidence. I suggest this as necessary because your mechanistic explanations seem to have little foundation. Again, not the results that you hear, but the potential explantions (i.e., hypotheses) you have suggested for why those results occur.

Again, I remain open-minded, but you have to play the effective game that scientists play if you want to be taken seriously. Evangelicalism simply has no place.

It's worked this way for generations. New ideas are suggested and are almost always challenged. Those that are well supported can withstand those challenges and might even change our view of how the world works. Those with no support just fade away. Take your pick! The scientific method is the most reliable approach for explaining nature ever invented, and so far, it works more reliably than any alternatives.


http://en.wikipedia.org/wiki/Science#Scientific_method

The view once was that the world was flat AND had a hard stop that one would fall off from. Someone thought differently

Ah, good analogy! 'Ol Christopher also had to prove it before he was taken seriously. Had he not proven it, he would not have gone down in the history books as the one who proved it, right? Right!

That's all we're saying; do some good testing to see if the -thinking- behind the results is sound. Nobody disputes the results; we all know enough to know that if we make a lighter bridge, or lighten an already too-heavy bridge, it results in a much brighter tone. Nobody disputes that. We'd just like to see the reasoning behind the curvy thinking justified.

Whenever an idea is thought out and steps taken to prove or disprove it, new ideas and methods arise from it. In this case, Scott may indeed find that his ideas holds up to good, well-planned, and well executed testing, which would lead to new thinking about all of what we do. He would be forever acknoledged as the father of the modern whatever.
On the other hand, he may learn that the shape isn't as important as he thought, and that the mass is what is causing the results. This would again lead to more recognition for him, and also a lot more work and income. People are more apt to have their guitars worked-on and hot-rodded if the guitar still looks like it did, or at least nearly as it did.

An e-mail from a happy client who plays his guitar directly through an under-saddle pickup, in church, is not science and tells no one anything. There's many an awful sounding acoustic guitar that sounds just great through its pickup....

I agree totally with you Hesh, to me, no one here has to prove anything that is new, if i feel like experimenting on those new ideas, i will or i won't depending on the degree of confidence i have towards what is put forward, if i really wanted justification for what one considered progress, i would either try it myself or get invited by the founder of such a theory, to see it first hand!

I love this place for all the open minded folks that make it such a special place, and i also think that we're all here because we have a gift that very few have, a passion that brings magic in our lives and into those of non-initiated to lutherie, we can take ourselves seriously but in the end, the result has to do more with the goal in mind of producing nice sound out of that box and i'm pretty sure that every single one of you great folks have experimented what i did when you strung up that first instrument, i.e. magic, you thought WOW, i can do it and it probably humbled you like no other experience before. My only wish is to keep that in mind, that it is a gift and my only responsibility is to appreciate it and share the joy with others!

In the end, it' all good!Now, excuse me, i'll run and hide in me shop!

Regards

Serge Serge Poirier38746.5789699074

I'll take some pictures of the bridge as it sits today, after all of the sanding. I'll tell you the thing is about as small as I would dare go with it, it will be interesting to see if this thing holds together.

Greg

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Gwaltney Guitars

[QUOTE=LarryH]
... if I understand your design, won't the back of the bridge have a lot of upwards tension created from the angle back to the string attachment point? How is that area of the strings held down? It looks like the strings pass through some sort of 'hold down' area and it seems a little odd to my inexperienced eye to have any upwards tension on that area of the bridge.
Larry[/QUOTE]
Hi Larry,

Think of it as a pinless bridge. I'm thinking it will have roughly the same amount of torque force as a pinless bridge, and no shear force. In other words, if a pinless bridge can stay on (and resist the 180 pounds of shear force), then it should be easy for my bridge to stay on. The torque force does have to be dealt with, though, or it will belly like a Buddha.

Dennis

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Dennis Leahy
Duluth, MN, USA
7th Sense Multimedia