Ervin Somogyi

September 22, 2012

Q: Recently I bought your books & DVD and I found one sentence particularly interesting: you mentioned that if a guitar with a normal flat back had an arched top, its dynamics would be unique. Can you please reveal from your experiences in which direction the sound will change, compared to that of a normal flat/domed top?

A: It’s an interesting question, and to my knowledge no one has yet made a guitar like this. Mario Beauregard of Quebec, on the other hand, has been making something truly new: nylon string guitars with arched backs and flat tops.

The arching of a plate stiffens it: it improves its stiffness-to-weight ratio. And, acoustically, it raises the plate’s pitch: its vibrational behaviors are shifted toward high-frequency signal — such as the violin has. A small highly domed plate is not likely to have a good monopole — that is, a good low end. Also, the greater the arch, the shorter the sustain is likely to be.

Cellos have a low end, and they have violin-like arched plates — but they are huge compared to a guitar. So part of what we are discussing is the SIZE of the plate, in addition to its doming vs. flatness. But it would be difficult to play a cello-sized guitar.

There’s another factor too: what wood the arched plate is made of. Traditionally, all arched-plated instruments (violins, violas, cellos, standing basses, and jazz guitars) have used spruces and maples — spruces for the tops, maples for the backs. Maple does not have much sustain compared with some of the woods used in guitars, especially Brazilian rosewood (although, in my experience of the maples, Eastern rock maple has the most, Western broadleaf maple has the least, and European maple — which is a sycamore — has some). Therefore, if we’re talking about a guitar with an arched spruce top and a flat maple back, it would likely have a sound characterized by a quick attack and a quick decay: bright, brisk, zingy, sharp, and not much sustain.

Sustain is not a factor in arched-plate and bowed instruments. They don’t need natural sustain: they will make sound as long as the player continues to scrape his bow over the strings. In the guitar on the other hand, because it is a plucked rather than a bowed instrument, the sound stops as soon as the strings do — just as happens with the banjo, lute, koto, ukulele, mandolin, dulcimer, harp, or harpsichord. [NOTE: the harp and the harpsichord are both excited by plucking action; the piano is excited by hammering action.]

It’s not likely that these traditions had such acoustic considerations behind them. The science of acoustics didn’t yet exist, and early European makers would of course have used the woods available to them — in this case the European alpine spruces and maples. They were a long way from having access to imported exotics from the New World. Also, in those days, the cost of labor was cheap and the cost of materials was high, so a thick plate of an imported exotic wood (that you’d carve down into an arched surface, and in the process wasting much of the wood) would have been quite expensive, compared to a thin plate of the same wood such as would eventually be used on guitars.

December 18, 2011

Q: In my limited experience with classical guitars there seems to be a need to have a more flexible top on the bass side and a more stiff top on the treble side, giving the warm and low sound on the bass and more sustain on the treble, as well as preventing the percussive anvil sort of trebles . The flamencos seem to have a somewhat less flexible bass and a flexible treble side, which gives them a somewhat percussive sound with rapid decay in sound. This is at least consistent in the examples I have and have had the opportunity to play. 

If one were to attempt to make a classical guitar as stated above would a change in top thickness to accommodate the additional stiffness required on the treble side be in order, or would changing or stiffening the bracing on that side be a better option than making a guitar with a top that is not of uniform thickness? 

So…essentially, bracing or thickness or both?

– – – – – – – – – – – – – – – – – – – – – – – – – –

A: Your question addresses the primary issue of whether it is desirable to design a plate that relies on symmetrical design, or an asymmetrical one, for optimal functioning. The matter is clouded by the fact that some remarkably good guitars of both types have been made. Also, some pretty unimpressive guitars of both designs have been made. So there’s no clear winner, and I’m not convinced that the mere fact of symmetrical or asymmetrical construction is the most important consideration. I mean, if it were, one of these designs would produce consistently better results than the other.

As I read your question, I am translating it (to myself) into language that I am most comfortable with. So my answer might put a different spin on things than you’re used to. Let’s see if this makes sense to you.

To my knowledge, flamenco guitars achieve their characteristic sound by having looser, more flexible tops in general than classic guitars. Specifically, they are so loose that the monopole (the base) is discharged quickly — thus giving those instruments the characteristic traditional “dry” sound without a lot of sustained presence; their sound is more percussive. Usually, if one believes in asymmetrical construction, the treble side is made a bit stiffer than the bass side. In any event, compared to classic guitars, flamenco guitars have a more prominent cross-dipole. They are “looser” in that mode, in which the top moves side-to-side across the centerline and the bridge teeter-totters with one wing going up as the other goes down, and back. You can get a sense of this looseness by simply pressing down on one of those tops with your thumb: you will probably feel them “give’ fairly easily. You can also test for cross-dipole compliance by lightly putting one or two fingers of one hand on one wing of the bridge and lightly tap on the other wing with your other hand. You should feel a definite and instantaneous displacement as the bridge see-saws relatively freely. Classic guitars will be built less loosely, and will accordingly have less mechanical “give”. Neither one of these designs is “good” or “bad”, by the way; they are simply different — and different for a reason.

To my knowledge, these characteristics of flexibility and movement in a guitar top are best achieved by careful BUT SYMMETRICAL calibration of the plate — and I do not try to build any mechanical or dimensional asymmetry into my own guitar tops. But I acknowledge that other makers of successful guitars use dimensionally asymmetrical faces, so I’m inclined to believe that the motions of the cross-dipole (or any other mode) apply to a variety of architectures. At that point, the issue becomes that of basic calibrating so that one is “in the ballpark” and doesn’t overbuild or underbuild. I go into several detailed discussions of this concern in various chapters of my book The Responsive Guitar. You’ll undoubtedly find some of my ideas from there worth at least thinking about.

Your question addresses the question of whether it’s appropriate to add or subtract bracing in order to accommodate to changees in top thickness — as a matter of making material stiffnesses — and hence vibrational action — be consistent. The matter of achieving a balance between stiffness and/or looseness through top thickness vs. bracing mass is central to lutherie. And in this balancing act, there are two factors that inform my thinking.

First, in the traditional approach, if one were to make part of the top thinner, one would indeed want to “compensate” for it by making the bracing a little stiffer. This is assuming that the maker’s goal is to have AN EVEN GRADIENT OF MECHANICAL AND VIBRATIONAL STIFFNESS FROM THE BRIDGE TO THE PERIMETER, IN ALL DIRECTIONS. This is certainly my goal. In purely practical terms, this is surprisingly tricky to do until you begin to understand what you’re doing and have some practice at it; after that, it’s surprisingly easy. So an experienced hand and eye are really useful to have. I should add that, incidentally and technically, the gradient that I visualize in my work is only even in the sense that there are no lumps or irregularities of localized stiffness between the center and the perimeter; but it is not the same slope on all axes, in the sense of being identical. The longitudinal gradient is stiffer than the lateral gradient.

Be all that as it may, the second factor is, I think, just as important. It’s also interesting, subtle, and elegant — and obvious. So much so that it took me years to see it. It’s the “water running downhill” principle; you know: that water will find a way to run downhill regardless of trees, rocks, or irregularities of slope or terrain — because that’s the nature of water. In fact, such downhill movement of water cannot be prevented short of putting up a barrier or obstacle that exceeds the power of gravity over water.

Interestingly, sound energy is the same, except that instead of running downhill it wants to radiate off a guitar top — with all the freedom of water running downhill. It’s the nature of sound energy to dissipate into its surrounding medium, be it air or water. If we think of sound energy as seeking its easiest path “out”, as water wants to find the easiest path “down”, then it’s a short step to seeing physical unevenness in a guitar top as being analogous to unevenness in downhill terrain. And unless any of this unevenness is significantly huge, both water and sound will continue to flow and radiate. Tweaking any of the minor irregularities of slope, terrain, or structure will by no means stop any of the flow or radiation; they’ll find a way to get from here to there.

Let’s take a look at how this might work in a guitar. Let’s assume that you have a dimensionally asymmetrical plate, as you described above. And let’s further assume that the structure — irregularities and all — is “in the ballpark” as far as not undermining the monopole, cross-dipole, and long dipole. Or, saying the same thing with different words, that the irregularities are such that they allow the capacity of the plate to engage in these modes without messing any of them up). The top will flex and bend and seesaw and vibrate just as all the theories, diagrams and Chladni patterns suggest. The question then becomes: what makes you assume that such a top and its vibrational modes have to function symmetrically around the guitar’s centerline? Or that the various vibrating quadrants and subsection of the face will map out as being active with elegant evenness, symmetry, and consistency? I mean, no one expects water to flow downhill over a natural terrain in a straight, even, consistent, and predictably regular line, do they?

Your question cites differential side-to-side construction. This is the axis of the cross-dipole, which is (in theory) a see-sawing action around the centerline. If we were to imagine two kids on a playground see-sawing up and down on a teeter-totter, that device will be pivoting on its center point as a matter of the manufacturer’s design. But, suppose one of the kids is heavier than the other one? That would introduce an irregularity into the flow of their play. The manufacturer of the teeter-totter wouldn’t care about that, of ocurse; only the kids would. And to anyone to whom the kids’ fun was important, they could compensate for this disparity in mass (in the “playing field” or “gradient”) of that teeter-totter by simply adjusting the fulcrum point to a somewhat off-center position. Then, being better balanced, the kids could see-saw happily and without strain: same mass, same energy, same frequency, easier and more harmonious oscill.ation.

This is close to my sense of how the guitar works. To repeat, using other words: if there is sufficient unevenness in the top because of any design idea of the maker, and the design variable isn’t so huge as to throw a monkey wrench into the natural functioning of the guitar, then that “uneven” top will accommodate to the needs of the energy flow of that irregular structure all by itself. It’ll adjust, within some limits (of the natural capacity for flexibility of its woods), and perhaps wind up fulcruming, say, 1/16″ off the centerline. It can do that because the guitar lacks a fixed fulcrum in the way that a teeter-totter has one. Therefore, the vibrating quadrants of the top may be a little bit lopsided or asymmetrical in actual movement, etc.. But, as far as dissipation of strings’ energy is concerned, nothing has been prevented; it’s simply found its way out via an alternate path from what “the manufacturer’s blueprint” might have suggested.

This doesn’t fully answer your question yet, but my answer required me to have sketched in this background before addressing it specifically. This background, to repeat once more, is that tonewood that has been worked to more or less optimal dimensions has a certain innate flexibility of vibratory potential. There are no fixed fulcrums or vibrational nodes. And it may not matter that you’ve made an irregular plate — as long as you have not made it so uneven that you’ve pushed the plate past some limit of being able to perform its principal vibrational tasks.

So, to sum up: my answer to you is in four parts:

First, that yes, if you make a top thinner on one wing, which necessarily weakens it, then there’s a logic to adding bracing stiffness to it to make up for that weakening. I believe that one should aim toward at least some standard of evenness of physical/mechanical/tonal gradient if one’s goal is to make better and more reliable guitars.

Second: I believe that these maneuvers work most effectively if the top and braces are “in the ballpark” as far as optimal mass and stiffness are concerned — rather than the system being overbuilt as is often the case. Or underbuilt, if you’ve gone too far in thinning. If you’re overbuilding, then the thinning and bracing work that you are considering might be nullified or overshadowed by the fact that the structure is still too stiff. Or maybe the part that you’ve thinned will work fine, but the part that y ou haven’t thinned will be inhibited. But you won’t get 100% cooperation from such a top.

Third, you will probably produce minimally uneven tops no matter what you do; guitars in the real world always have something or other that’s not optimal.

Fourth, as with the example of water cited above, and if your gradient is not too unevenly made to begin with, then what you’ve constructed or misconstructed probably won’t matter. Or at least it won’t matter very much within the context of the flexibility of vibrational potential that the top has. The top will bend itself (sorry about the pun) to work in any way it can, to release its load of sound energy. It’ll modulate itself physically and vibrationally. As I said above, the vibrationally active areas of the top may functionally be a little bit asymmetrical, things may be a bit off-center, vibrational patterns might not be quite mirror-image, etc. But this is no big deal: the top plate has the capacity to function at least a little bit like that in order for the system — as it is physically constructed, with its unevenness and irregularities — to engage in an adequate monopole, cross-dipole, and long dipole. Finally, the sound will get out, sometimes because of, and sometimes in spite of, and sometimes without being much bothered one way or the other by, the work you’ve done. And I think this is where a bit of the magic comes in.

I hope this makes some sense.

December 18, 2011

Q: If the soundhole is not in the traditional location at the end of the fretboard, is there a better bracing pattern than the X-brace, in your experience? 

A: The soundhole is where it is, as a matter of tradition rather than critical thought: it’s always been put there. One might put this in terms of history trumping dynamics. History and tradition notwithstanding, the guitar soundhole has a tonal role to play, and I devote an entire chapter of The Responsive Guitar to the mechanical and dynamic functions of the soundhole with respect to brace location.

As far as the mechanical dynamics go, the soundhole in the Spanish guitar is outside of the main vibrating area of the face; it’s isolated from it by a massive brace that acts like a dam, and the comparatively delicate fan bracing on the other side of it does its work without being affected by exactly where, above that dam, the soundhole is. In the steel string guitar, instead, the soundhole is inside the main vibrating area of the face. It represents a mechanical perforation of that plate — and it necessarily weakens it. Imagine a drum head (a vibrating diaphragm) with a great big hole in it, and you’ll be able to grasp one of the principal bad dynamic ideas in the steel string guitar.

As far as bracing placement is concerned, my opinion is that the acoustical work of the bracing is more important than the specific location of the soundhole, and that these shouldn’t be in conflict with one another; therefore, I think there’s more to be said for moving the soundhole “out of the way” than moving the bracing around. Those kinds of judgments depend, of course, on understanding the functions and possibilities of various bracing systems. You don’t just want to move stuff around randomly.

Speaking of tradition vs. critical thought, the Kasha guitars (with the innovative Kasha bracing) were the first ones to focus on the bracing layout first and the soundhole placement second — in spite of how oddball those guitars looked. I give the Kasha people credit for understanding about putting the soundhole in a place where it helps rather than hinders. The soundhole’s dynamic function is to act as a port (as per the discoveries of 18th century Dutch scientist Christian Huygens, which I go into in my book), and as such doesn’t HAVE to be in any particular location. I recommend reading my book if you haven’t already.

Whether or not one moves the soundhole, it’s useful to have an idea of what each bracing layout can do, in terms of its mechanical and vibrational possibilities. Or impossibilities. There’s a logic to each bracing pattern and each one can be tweaked and altered in many ways — some subtly, some radically. And, as I said, part of the challenge is to not put the soundhole where it’ll create a problem. Either way, we’d have to understand how these factors interact before going on to talk about “better” or “worse”… because there are many ways to spoil the efficacy of any blueprint pattern and there are many ways to “get it right”.

But, let’s get back to your question about “X” bracing and soundhole location. The virtue of “X” bracing is that it ties the face together so as to create the possibility of a dominant monopole motion. Now, it won’t work nearly optimally well if the bracing/top are overbuilt and too stiff, or if the plate isn’t properly or consistently tapered, etc., and your job is to learn to do an INFORMED balancing act. Plus, the soundhole is right in the middle of this, sort of like interrupted ceiling beams that are holding up a roof that itself has a great big hole in it.

If you can get comfortable with the idea of relocating the soundhole to somewhere else then you do have to think about what to do with its area of topwood that is newly available as vibrating diaphragm. I mean, you’re creating an empty space bigger than any other empty space on that braced top. You could close the “X” brace up a bit… but that would necessarily open up the bass and treble quadrants, and you’d have to figure out if you were comfortable with that. As I said, it’s all a balancing act. If you didn’t want to mess with the balancing act then you might think about installing one or more finger braces into that space, to tie it into the rest of the bracing. I don’t have a better specific answer for you than this.

My unspecific answer is to think of what your changes might signify in terms of the main modal movements of the top: the monopole, the cross-dipole, and the long-dipole. Mainly, “X” bracing is a recipe for bringing out the monopole; it ties everything together. Fan bracing is a recipe for facilitating cross-dipole; there’s nothing there to prevent or inhibit that mode. Ladder bracing is a recipe for emphasizing long-dipole; it destroys the monopole and the cross-dipole.

So, if you were thinking of closing in the angle of the “X”, you would be justified in suspecting that this will facilitate more cross-dipole: the legs of the “X” would be stiffening the plate in a different way, as a function of their new orientation. So, the equation might look like: (Take away soundhole) + (closing in the “X”) = (more cross dipole). A second equation might be: (remove soundhole and add a bit more topwood) + (leave “X” the same) = (maybe a bit more monopole). Another equation might be: (remove soundhole) + (enlarge the space by spreading the “X” legs out) + (make new bracing accommodations to reinforce this larger space) = (?).

My point is that if you can accept that there’s some actually useful information contained in technical jargon such as “monopole”, “cross-dipole”, and “long-dipole” (which are simply formal words for some basic concepts of top vibration, and hence sound) then I think you can begin to have really interesting ideas about how to problem-solve your next guitar project, and make it better.

November 3, 2011

The guitar is about many things: craftsmanship, commerce, history, tradition, entertainment, science, wood and gut and a few other things, physics, acoustics, skill, artistry in design and ornamentation, music, marketing and merchandising, magic, etc. Mostly, the guitar is supposed to be about sound. But that thing is the hardest of all the things on this list to pin down and get a measure of.

Sound is air molecules hitting and exciting our ear drums, pure and simple. But there’s no magic at all in this objective description. The magic in musical sound all happens subjectively, in the brain and in how it’s able (through innate ability, training, and acculturation) to processes the neural impulses being sent in from the ear. In this regard sound is very much like food and wine, where the magic happens in one’s own mouth, tongue, palate, nose, eyes, as well as in one’s brain. While many of us report that we “like” this or that sound or wine or food — the fact is that many of us hold these preferences because we’ve learned that we should have them, without ever knowing whether we have any authentic preferences that are different. So when it comes to guitar sound, I’m big on listening and really paying attention. And I recommend it to everyone.

Guitar sound is complex. Good sound is, by definition, sound that pleases the listener — whether he understands anything about the sound or not. A guitar can have any combination or quality of: bass, treble, midrange, resonance, timbre, definition, sustain, projection, dynamic range, warmth, volume, percussiveness, tonal bloom, note shape, harmonics, sweetness, clarity (or lack of it), tonal rise and decay time, cutting power, spareness, evenness of response, brittleness, directionality, separation, brilliance, dryness of tone, tinnyness, tonal darkness or lightness, and/or cleanness of tone. So, unless you have a really sophisticated and practiced ear, it won’t work to evaluate a guitar’s sound by listening to someone play a whole piece of music on it. That amount of information overwhelms the average ear within the first eight or ten bars of the song.

However, there is a way of coming to grips with sound that I stumbled on a few years ago. It is so simple that no one ever thinks of it: that is, really listening to the simplest sounds the guitar can make — and doing it in a quiet place. It’s very much like tasting food or sipping a wine; one does it slowly and without distractions, in order to get a reliable sense of their flavors, textures, sweetness, spicyness, and overall pleasingness. Let me explain what I mean, and my own method; it’ll help you next time you are shopping for a guitar to buy.

What I do (among other things) is to sit down, tune the guitar, and just play a chord. I play it slowly so that I can hear each note separately. And I listen until the sound dies away. I do this more than once. A simple chord can give one a lot of information, especially if one takes one’s time at this. It can also be useful to listen to a second guitar, to compare against. The thing is: the voice of the guitar is the voice of the guitar regardless of what’s being played. But playing a chord, or a few notes, will give you all the information that playing an entire song can give you — without your senses being clogged by any player’s flashy technique. Not that one shouldn’t play whole pieces; but I suggest playing sound-bytes first.

Here’s a checklist for what you can usefully listen for in a six-note chord. If you cannot hear each note [at least somewhat] distinctly, the solution is to keep on listening and learn how to focus your ear. In saying “focus” I mean just that: train your ear to focus on one quality of sound at a time — exactly as you focus on one person’s voice at at time at a well-attended cocktail party. Unless you’re playing a really bad guitar, I guarantee you: the information is all right there. The things to notice are whether or not, or how much, there is of any or all of the following.

1. A chord will emerge from the guitar either quickly or slowly;
2. notice whether any part of the sound dies off sooner, or lingers longer, than another. This is basic information that you won’t get if someone is playing whole songs;
3. listen for basic volume and presence;
4. a chord will emerge from the guitar either quickly or slowly;
5. listen for some degree of separation: that is, you may be able to hear each note. Or not: the sound may be fuzzy or cloudy and lack focus;
6. pay attention to the quality of sound — that is, whether it’s warm, sweet, tinny, rich, live, fundamental, shallow, breathy, open, held back, and/or has lots of overtones;
7. is there compliance of response? That is, do you have to push the guitar or does it respond easily to your touch;
8. listen to whether the sound is bass-heavy or treble heavy, or well balanced;
9. and whether the strength/presence of each string is even;
10. and whether there are any wolf tones (i.e., problematically louder or quieter notes)
11. and whether the guitar really plays in tune or not;
12. and whether the sound is good close-up, and/or from across the room (you’ll need a playing/listening partner for this);
13. and whether the guitar sounds different depending on whether you’re listening from in front of it or from off to the side. Some guitars will astonish you with how narrow their area of projection is;
14. and whether or not the guitar has good dynamic range; that is, whether can you get different quality of sound from playing very softly, softly, medium, harder, and/or really hard;
15. if you repeat these exercises with different chords up and down the neck you’ll get a sense of how evenly (or not) the guitar plays on the whole fingerboard;
16. be on the lookout for tonal bloom; that is, whether the sound comes out immediately at full volume or whether it integrates and gets louder before it begins to wane;
17. finally, you get to notice and decide whether and how much you like or dislike any of these qualities of tonal response in the guitar you’re playing.All the information is in the soundbox. You just need to know how to listen without having your ear get overwhelmed. And in addition to all these things, you can get a sense whether the guitar is easy or difficult to play; this has nothing to do with sound; it’s about how well the string action, scale length, string spacing, and shape of neck are adapted to your hand.

November 3, 2011

Q: Assuming you’re looking for a back to work in tandem with the top, as opposed to a reflective back, should the back also be thinned till it “relaxes”, as you do on your guitars?

A: Ummmmm… this is a really interesting topic that very few people have done any thinking about — and most of the ones that have are classic guitar makers, not steel string guitar makers.

The matter is too complicated for me to write fully about in this format, especially as I have written about exactly this kind of thing in my book. Have you read my book’s chapter on the functions of the guitar back? If you haven’t, it’ll be useful for you to do so. Mainly, my answer is based in the proposition that the job of the guitar top is to generate an optimal mix of monopole, cross dipole, and long dipole signal… which gets converted into sound a bit further on down the line. The back has a different function — although, frankly, almost no one that I know of has ever considered making a back that might have a purposely dominant monopole, cross dipole, long dipole, or whatever.\

The back has not been studied like that. And one indicator of this circumstance is that while guitar tops have been made with all kinds of variants of “X” bracing, double-X bracing, fan bracing, lattice bracing, ladder bracing, Kasha bracing, radial bracing, and even the most oddball experimental bracing, over the years… 99.99% of all guitar backs have been made with three of four parallel braces since the back was invented. Period. So our information about the possibilities of the back is limited to one model of bracing that has been done over and over and over and over again. I show some experimental back-bracing ideas on page 91 of my book The Responsive Guitar; take a look at them.

Also, consider that it doesn’t matter how the back is constructed if it is not allowed to be active. For instance, Bluegrass guitars are played with the guitar’s back resting against the player’s body. These backs are significantly damped out. That is, they are prevented from participating in the dances of the frequencies. Would it matter to that kind of guitar that the back has been thinned to the relaxation point? Not at all. That back isn’t expected to do anything. The technique of playing the typical bluegrass guitar (standing up, strap around shoulder, guitar resting against player’s body) does not concern itself with the back’s doing anything in particular except maybe acting as a reflecting surface and otherwise keeping the dust out. And, as I say in my book, (at the risk of becoming unpopular): the use of a highly resonant and expensive wood on the back of a guitar that has no use for a functioning back is to waste the wood.

But aside from all this, to get back to your question, the short answer is “yes”. My prejudice is to make the back more flexible than other makers typically do. The reason for making both the top and the back flexible to begin with is that everything else you do to them does nothing but stiffen them up. You brace them, dome and stress them, and attach the perimeters to the guitar rims. Pretty soon, you’ve got something that you’ve (perhaps inadvertently) made really too stiff.

But too stiff for whom? For you? Maybe; or maybe not. For me? No, I don’t really care. For the strings and their work? Yes: they care.

I first got onto this idea, years ago, from an interview with David Rubio in [long-since disappeared] Guitar And Lute Magazine. Rubio recommended thinning the free (unclamped and unbraced) top until it had no tap tone of its own. If it still had an identifiable tap tone, it would be introduced into the guitar’s structure and responsiveness. But if one introduces a “tone-neutral” top (or back) into the system one could then build an appropriate tap tone back into it by bracing it, attaching it to the guitar, and bridging and stringing it. The basic equation is: if you start out with this, and then add that and something else, you wind up with this + that + something else = something greater than what you might think you have..

November 3, 2011

Q: Do you use the same X amount of flexibility for all your guitar tops? Is there any reason to have a different, Z, level of flexibility when you use woods of different species? 

A: I certainly try to for the same level of stiffness in every guitar top I make, regardless of species of wood used, for reasons of consistency of sound and musical responsiveness.

However, it’s not quite a simple yes-no. The thing is, if you’re going to build a guitar that’s slightly bigger or smaller than the last one you made, then you’ll need to factor some accommodations into your measurements.

A bigger guitar top is weaker than a small one of the same absolute mechanical stiffness (i.e., the same mechanical stiffness is asked to cover a larger span or area), and will have to be left thicker to compensate for that weakening. And vice-versa. For example, imagine standing on a plank that serves as a bridge to cross a 5-foot wide creek, and a longer but otherwise identical plank spanning a 10-foot wide creek. The latter will sag more when you stand on it. Your weight is the same, just as the guitar’s string tensions are the same. The resistance over the span needs to be adjusted, however, if you want the sag to be the same amount.

That “sag”, in the guitar, goes to vibrating-plate motion, which has everything to do with sound. You probably don’t care how much sag there is in a simple footbridge, but in the guitar the ‘sag amount’ corresponds to how much or how little the guitar face can move and flex in order to produce sound. There’s a direct correlation, as sound is nothing but excited air molecules. Finally, we’re (you’re?) trying to build guitars that are optimally permeable and receptive to the strings’ energy level and budget. Assuming the use of standard strings of a standard scale — which goes to the energy budget — this implies the same (or at least comparable) optimal amount of structure.

October 16, 2011

Q: Obviously, your method [of working tops to stiffness than to target dimension] is going to lead to different thicknesses for every piece of wood of a certain species to get the same flexibility. I am curious, though, if you find that different species have to be worked to a different degree of flexibility? For example, say you thin your steel string Sitka tops to have X amount of flexibility with a Y weight on them. Do you use the same X amount of flexibility when you are using Engelmann or Cedar, as well, or do you find that you need to develop a Z amount of flexibility for a different species? Thanks.

A: You’re correct that in theory no two pieces of topwood will wind up being exactly the same thickness if one follows my method. That is, we’re looking to achieve a consistent level of RESISTANCE, and different woods will have different proportions and densities of xylene, cellulose, and fiber with which to achieve that level of resistance.

This level of resistance isn’t some theoretical number that’s gotten by formula — although it can be gotten that way. The level of resistance is organic to the guitar: it is set by the top’s need to work with the strings’ pull, modulated by the kind of sound (character, sustain, overtones, etc.) that you might be after. And that’s all. Various gauges of strings, of various scale lengths, exert a certain amount of pull which, when excited, provide the motive force and energy budget. This is, of course, affected by things like how hard the player plays, bridge height and torque, etc. I don’t think any of this is exactly new information to anyone who’s been paying attention.

If the top is too resistant to the strings’ pull, then the mechanical response of the guitar is hampered. It is compressed into (i.e., limited to) regions of high-frequency/low amplitude activity/signal. You might or might not like that sound, but it will be a limited sound. If the top is too wimpy and flexible then it MIGHT have to rely on the bracing to restore its dynamic balance to a higher level of stiffness and hence response. The bracing will reinforce, or undermine, or overpower, what the top itself is able to do. It’s a partnership.

Steel strings on a guitar exert a pull of around 180 pounds. Nylon strings exert a pull of nearly 100 pounds. Let’s say that the strings on your guitar exert 125 pounds of pull and torque when tuned to pitch. I’m just grabbing a number here. Now consider: it really doesn’t matter whether your guitar has a Sitka spruce top, an Engelmann top, a redwood top, a European or Lutz spruce top, a cedar top, a koa top, a mahogany top, or a plywood top. That top is, in every case, going to be driven by 125 pounds of string pull/drive/torque. We’re assuming everything else being equal here: guitar size, soundhole size, bridge height, etc.

The question is: why would you put a top with any different stiffness (than that needed to deal with a 125 pound pull and torque) on your guitar? Put it another way: if string gauge were like octane in gasoline (i.e., a measure of its ‘oomph’) and top stiffness were like tire pressure (a certain ease or hardness in car maneuverability), then regardless of what octane gasoline you fill your car’s tank with, why would you change the tire pressure every time you gassed up?

Now, there are different things than mere stiffness going on. There’s also internal damping and mass. Different woods WILL behave a bit differently, at identical stiffnesses, when excited by strings, because of these other factors. Some woods will suck the strings’ energies up pretty quickly and damp their motions. Some will be vitreous and live and allow the strings to remain excited for longer. Some will be internally brittle. Some will be internally tough and ropey. Some will be very dense; others will be like Styrofoam, etc. You get the idea. So there’s a lot to be said for familiarizing one’s self with the average tonal potential of different woods, as well as which woods tend to be more consistent in qualities and which species have a wider, less consistent, range of qualities depending on which plank or log you’re working with. The main thing is to work with woods that have the least energy loss possible. You want the energy to go into the air (sound) and not into the woods and materials of the guitar.

If you’ve ever been to a lumber yard you’ll have noticed that some planks of a given wood are dense and heavy while other planks right next to them are not. Such things affect a guitar’s behaviors, and need to be factored into your calculations — if only to the extent of your using the same selections of woods on the guitars that you make. You may or may not have a clue as to what difference any characteristic that you’re aware of might make, but it’s smart to not throw uncontrolled variables into your work if you can help it.

Having said that, EVERY guitar will produce a monopole, a cross-dipole, a long-dipole, and whatever other mode of motion you think is important enough to consider. If you don’t know about these, please stop reading this right now and read up on these fundamental vibrational modes of a guitar top: they’re critical. Every guitar has SOME mix of these modes, and every guitar has a fixed energy budget with which to excite these — depending on how the maker has knowingly or ignorantly designed his system to ALLOW, FACILITATE, INHIBIT, SUPPORT or PREVENT certain movements of the top.

October 3, 2011

I’ve completed a new and unusual classic guitar: it’s got a koi fish carved into the top. You can see what this looks like in the accompanying photographs.

I like to make an extraordinarily decorated guitar from time to time, but when I do so I limit the ornamentation to the upper bout, which is acoustically not very important, or other non-acoustically critical parts of the instrument. The lower bout of the face (the area around the bridge) is acoustically critical and I won’t mess with that. I want those instruments to have as full a sound as anything else that I make.

This is a beautiful guitar. One of my witty friends took one look at it and commented that it ought to be great for playing scales. Ho ho ho.

October 1, 2011

I have a DVD out; it’s a lecture I gave on the topic of Voicing the Guitar which I delivered at the Healdsburg Guitar Festival in 2009. It’s engendered both positive and negative comments. The negative ones generally have to do with the fact that I don’t reveal my specific methods for voicing the guitar — or at least not enough of them for anyone to usefully copy.

From the outset, that DVD was intended to have a dual purpose. First, I sought to give an overview of the principles of voicing the guitar — for which work I’m fairly well known — to people who are interested in the guitar but don’t yet know much about its actual ins and outs. Second, as the Healdsburg Guitar Festival happened shortly after the publication of my two-volume work The Responsive Guitar and Making The Responsive Guitar, the DVD was put out as a way of letting people know what these books are all about and how enormously informative they are. I mean, these books took me eight years to write: the one-hour lecture took a few days to plan out and prepare for.

My experience of lectures has been, on the whole, uninspiring. I’ve sat through a zillion boring ones in my life and I wanted to at least enliven mine with helpful signage, props, and visual aids. Otherwise I threw in every important thing about the workings of the guitar that I could think of short of the kitchen sink, and organized it into an hour-long presentation. These relevant concepts are:

1. the guitar as an air pump
2. monocoque engineering vs. structural engineering (i.e., the guitar as a monocoque)
3. the monopole and the cross- and long dipoles as the principal vibrating modes of the guitar
4. the Cube Rule of materials stiffness
5. stiffness-to-weight-ratios
6. the different tonal functions of steel string vs. classic guitars
7. the usefulness of tap tones as a guide to structure
8. the Acoustic Gradient of the top
9. the different strategies for organizing modal movement represented by “X”, ladder, lattice, and fan bracing
10. mechanical impedance
11. the acoustic functions of the guitar back
12. the guitar top and back as harmonic oscillators
13. structural coupling / connectedness / disconnectedness in bracing and structure
14. differential rates of energy use or discharge as a function of structure, and
15. a realistic representation, via a constructed-to-scale bracing-stiffness diorama, of ACTUAL stiffnesses of various structural members and braces.

 

My lecture was not intended to be an exposition of specific techniques of carving braces — which is what most people think “voicing” is. The whole point of it was to let people know that the shaping of braces is part of a package that involves a whole lot more than that.

Such considerations have not stopped others from putting out instructional DVDs that focus on the kinds of mechanical shaping and assembly operations which can be carried out serially and without reference to how the various parts combine and interact. However, Voicing work is precisely about how the different components interact dynamically. Therefore, it requires actual Thinking, Consideration, Judgment, Experience, Tracking, and Presence of Mind. It’s a bit like playing chess. Yet many people think of Voicing more as working a slot machine — and hoping that there’s a secret technique for how to pull the handle correctly to win. I don’t think there is a secret technique; instead, a specific skill set is needed. I voice each one of my guitars personally, slowly and attentively in a process that stretches out over a day and a half or two every time, and involves all the factors I listed above. It’s not any kind of quick formulaic slam-dunk.

I stopped short of showing the audience my own specific methods of profiling braces, and I erred when, in responding to an audience member’s question, I said that people would have to take my class to find out what I actually do in shaping my guitar tops’ braces. I think I blew it on that one. If I had it to do over again I would not have said that glib and flip sounding sentence — and I unfortunately didn’t think to point out that my bracing is described and illustrated at length in my books (although, if I’d had, I might have come across as being even more of a shill for them). I would have explained instead that I did not wish to do so for two reasons. First, what I do is the end result of decades of learning, experimenting, and making some really bad sounding guitars. So it’s understandable that I’d feel proprietary about the specific ways in which I’ve achieved my results: I feel they are mine to share, but I don’t do that indiscriminately in public forums. Second, to simply show what my guitars’ innards look like, mechanically, and without explaining what thinking and design variables this work entails, is bad teaching.

So, instead, I spent the hour describing the factors and variables that inform my own voicing work. While I use these principles, I don’t feel that I own them. I more or less slowly and painstakingly discovered them where Nature had left them lying around in plain sight for anyone to find. If anything, I am indebted to them for helping me to do my work successfully: they have allowed me to arrive at better methods, thinking about, and approaches to lutherie. Mainly, they are more useful than any description of any specific mechanical technique can be — in spite of the fact that today’s emphasis in teaching is to focus on specific techniques rather than on understanding how something works. My attitude is based in the fact that the principles cost me years of work and time to learn. The specific techniques, on the other hand, are easy to learn and do: glue this, cut here, profile in this way, shave that down, taper it, tuck this into that, etc.

The factors of Voicing that I outlined in my lecture lend themselves to many ways of being used and implemented to achieve a wide variety of better results in guitar making — just as different specific ingredients can be combined in many ways to make a meal. I described these factors in non-scientific everyday language because I wanted to make them accessible and easily comprehensible. I tried to give the audience a good foundation, or starter kit, toward their being able to achieve better results — instead of spoon-feeding them rote methods. All in all, I did my best to give the audience the kind of starter kit that was nowhere available when I was starting out, and as far as I know it is still not available to luthiers from any source other than my writings. There are engineering and physics texts that cover this same material, but these are generally scientific exposition written by engineers and physicists for other engineers and physicists. Get a hold of Richard Mark French’s book “Engineering the Guitar: theory and practice”, and you’ll see what I mean. It’s a fine book, but not all that easy for the layman to read.

My presentation wasn’t intended to be a strip show where I reveal everything, nor a tease in which I hold information back. I was attempting to deliver pertinent information. It’s ironic that some people feel shortchanged by my not having given them specific information about WHAT MY CURRENT BRACING LOOKS LIKE — even though my lecture includes an explanation of what every known bracing pattern does or doesn’t do. I am of the opinion that if I’d shown the audience “my secret bracing patterns”, everybody would have immediately forgotten everything I’d said and gone home and started to copy what they’d seen me do as faithfully as they could — without putting any effort at all into understanding how the things I’d discussed participate in the making of sound. I think that’s really lousy teaching; it reduces complex relationships to lowest-common-denominator factoids.

The principal subtext of my lecture is that (1) most guitars made today are waaaay overbuilt, and (2) comparatively small amounts of wood added to or taken away from certain key points of the top-as-vibrating-diaphragm make huge differences. My “secret bracing patterns” don’t look all that much different from most other guitar bracing — and various ones I’ve used are shown in my books.

I say “various ones” because my building style has always evolved and continues to evolve. What I’d be showing this year is merely what I’m doing this year. It’s different than what I was doing five years ago and different from what I’ll be doing five years from now. Same principles, different applications. I am aware that the world has changed a lot during my professional lifetime and that people want information simplified and they want it quickly. But I really can’t provide genuinely useful information in recipe form and still feel I’ve done a good job. Trust me: I’m not getting rich off DVD sales.

I’ve heard complaints that my DVD was made mostly as an adjunct toward promoting my books. Well no, not mostly — although there is some truth in it. The fact is that the books are unquestionably more informative than any one-hour presentation can ever be. Nonetheless, in both efforts I’m concerned with getting people to think and make discoveries for themselves based on a reliable map that I’d provided.

On a different track, I might say the following to someone who had approached me with these concerns: I don’t know you personally but, if I may ask: did you really not find anything useful in the DVD? Did it seem to you that I talked for an hour and said nothing important? And, for that matter, do you expect to learn anything more pertinent about any skilled hands-on and ears-on activity from watching any DVD? I’d think that the stiffness-diorama example alone is an eye-opening GENERAL concept that applies to any guitar making effort. Such dioramas are structural features in every guitar that’s ever been made and which is the strings’ job to drive and make work (or work against, in many instances); and shaving and profiling braces is meaningless outside of this context.

Finally, EVERY guitar will have it’s own slightly different and specific diorama-configuration of wood, graining, thickness, bracing, areas of greater or lesser stiffness and looseness that are necessarily part of a mechanical and tonal gradient. This is another essential concept that’s mighty useful to have regardless of how big, small, thin, thick, floppy, stiff, tapered, braced, etc., a guitar top might be; in fact, without it, any effort at shaping braces is as hit-or-miss as pulling the lever of a slot machine and hoping for a good result .

August 8, 2011

I do as much writing for website guitar discussion forums as I can, in addition to answering questions that people email me personally. I can’t really keep up with this demand very well, especially as so many of the questions are duplicates and I wind up giving the same answers over and over again. So I thought that I could eliminate a lot of this repetition by posting some of the questions I’ve gotten, along with my answers. Here’s one such:

Q: In The Responsive Guitar book you go to great lengths to discuss importance of and your method for top “stiffness testing”. I realize you would not want to divulge the optimum number you look to achieve for your guitars. Could you give us a range of numbers that you see from you experience that a new builder could use as a starting point?

A: Yours is a good question. To my mind it’s not so much a question of there being a “right number” or “right quantity”, as finding a method that delivers that information in a way that the brain can take meaningfully. In our culture, weights and measurements and statistics are how such information is most easily taken in and digested.

In other times and other places, however, the same information was transmitted differently, using different language and different tools. But it was the same information. One alternative method that I learned (from master luthier Jose Romanillos, who is certainly a traditionalist in the school of Spanish guitar making) is the following:

Take your joined top plate and start to thin it. It doesn’t matter if you do this with a plane or with a power sander. It is only necessary that you thin evenly, and not leave the plate full of lumps and low spots. Flex it from time to time to get a sense of its stiffness along the grain. Stiffness along the grain is considered the most critical indicator of where you want to wind up, as opposed to strength across the grain or diagonally to it.

You’ll notice that the plate is stiff, of course. How stiff? Well, stiff enough so that when you are pressing your thumbs against one side while holding onto other side with your fingers, and are bending the plate by pushing it with your thumbs, you will find that the spot that your thumbs rest against will be resistant. It will be resistant to the extent that if you keep on pushing so as to bend the plate, it will crimp at the points where your thumbs are. That is, you will induce a bend at those points that is different from the bend that the wood will take between those points.

That tells you that the wood isn’t ready to bend evenly yet. Keep on removing wood. By the way, if you’ve read my chapter on the Cube Rule you’ll understand that removing seemingly small amounts of wood will make a huge difference in the wood’s measured stiffness. So don’t hack a lot of wood off too quickly: go slowly and methodically.

Keep flexing the wood and removing wood. There will come a point at which the wood will “relax” in your hands and, when you press on the long axis with your thumbs, the board will begin to make an even arc along its entire length. It’s not fighting you.

That’s your starting point. No fancy equipment other than your hands and fingers, and a bit of sense of the wood, is needed.

You can of course keep on removing wood, and you can do so until you’ve reached a threshold on the other side and rendered the wood too wimpy to be useful on a guitar. (At the extreme, you can imagine how relaxed and unresistant a paper-thin slice of wood would be, right?) Your next twenty years can be happily spent exploring the range between these two extremes — which define a range of thickness that’s probably on the order of 1/16 of an inch. It’s pretty amazing what a few thousandths of an inch can do — and that’s not even considering the possibilities of selective tapering, bracing, and thinning!