Tap tones, anybody?

You heard it here first: "Tap-tuning" has been oversold. Let's put it into perspective.

When I was learning I went through what you're going through: I had HEARD about something called tap tuning and was mystified and eager to learn about it. I presumed that it held THE secret for easily-replicable world-class results. I actually thought that the alchemy of guitarmaking was somehow locked inside this arcane act of wizardry called "tuning" the top, that it was something that only the select and most sensitive few knew about, and that they weren't going to tell me, so I would somehow have to learn it myself.

Builders, alas, often do things on guitars which they really don't know WHY their doing it, but they do it because they were taught to do what the teacher did, and they're afraid if they stopped doing it, the nice sounds they usually get will go away. So they keep doing it. Then, when you ask them why they do it, they are all too happy to MAKE UP vague, fanciful, jargon-laden accounts which will leave an impression that they know exactly why they're doing it in minute detail, and by implication demonstrate that they can somehow successfully manipulate all these invisible sonic phenomena on the guitar with ease. Luthiers usually won't stop you from believing that they are wizards. This is most painfully obvious in the realm of "tap tones."

Yes, you can tap a top to derive some rudimentary information about its anatomy. What you hear does give you some feedback clues which is useful and helpful. The "tuning" part is what is so misleading to beginners. At some point (most often toward the end of the process) many builders attempt to make some final changes in the anatomy of the soundbox, which the builder believes (I've selected this word carefully:) believes is exercising some control over the final results. Both, skillful experts and deluded fools, equally, scrape here and there, tap, press, reach inside, remove a little on the back braces, on the top braces, and then at some point say THERE. It's just right.

Then there are other builders, masterful experts and deluded fools alike that DON'T. They believe that they're making all the crucial decisions in the INITIAL stages of the construction: materials selection, materials dimensioning, design: that is all they need to achieve the desired results.

My good friend and colleague, Alan Chapman is confident that he has come to appreciate the difference of fine changes in bracing heights, soundboard thickness, patterns, and has come to BELIEVE that he can goose the sound quality of a certain note, or smooth out, or sweeten, or balance, or adjust the performance of distinct notes and distinct regions of the fingerboard by subtle changes in specific areas of the soundboard. With all respect to my dear friend, Alan, I believe that this is delusional. The soundboard is responsible for the production of a very limited part of the entire guitar sound spectrum. Yet his results are terrific. So I have to swallow a good portion of my skepticism when it comes to Alan's guitars. Yet, I know of other makers whos results are equally phenomenal that do NONE of that.

That is why I say now, like I said fifteen years ago in my book, that "tuning" is something that can't be taught. But its also true that luthiers evolve idiosyncratic actions that they believe lead their guitars towards better "tone." This means that over time, each maker devises a series of actions which conform to a refined mental model that they've derived of how the guitar functions. This happens as a result of making, thinking, worrying, fussing, cursing, tossing and turning, eating and sleeping guitars for years and years. The mental model becomes more and more refined, and more and more PERSONAL. Jimmy D'Aquisto lectured that he made oval soundholes in his acoustic guitars, so the sound would "squirt further" like water from a similarly-constricted hose nozzle. The audience snickered when he said that. But nobody in the audience was getting $22,000 per guitar like he was. Snicker at that.

Heel contours--structural considerations

I decided that I wanted to individualize my guitars in several ways, and one of the areas I changed was the heel of the neck. I went to a more rounded shape, with less material at the base of the neck shaft, but larger in section [similar to Mike Doolin does on his necks].

The last 3 or 4 guitars that I used this shape on, seem to exibit an excessive action height increase after being strung up and played for several weeks. I have had to re-set the necks on 3 of them, which also required shiming of the fingerboard tongue over the soundboard to prevent a downward pitch at the 14th fret. The action itself has been restored by doing these resets, and they have needed just a tweek of the truss rod to fine tune it.
Could the lack of material under the neck shaft, where the heel block meets the shaft, be the culprit? I know that a new instrument needs time to 'settle' under tension, and the action height might rise a bit, but these occasions have been excessive; triming the saddle height would have resulted in a total loss of the saddle over the bridge!

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I don't know much about Mike Doolin, but a visit to his site shows fairly ordinary heel shapes, at least as far as the pictures there show. They look a lot like old Guild guitars and like my old partner, Michael Millard of Froggy Bottom Guitars, makes them. There are countless thousand of successful guitars made with that wide and narrow kind of heel shape. That would lead me to dismiss the notion that your heel size, mass or contour is the culprit.

Without knowing what the rest of your internal structure looks like, it would be hard to diagnose your problem. But I believe that the precise heel contour is of little importance to the rate at which the guitar distorts under tension. That is because the largest force vector of the neck acting on the body points straight into the body, just under the fingerboard. The remaining, smaller force vector is rotational--the force pulling the tip of the heel out of the guitar. So heels can be surprisingly small, even (as in some low-end Taylors) nonexistent. If my considered perception is true, then the major concentration of forces is dumped onto the soundboard, just under the fingerboard tab, in the region between the front of the box and the soundhole. That area is receiving massive compression from equal forces originating from both ends of the stretched string--from the nut and from the bridge. Those forces meet in that location. if that area yields, the box will bend, causing the string action to rise. So to counter those forces, I would pay attention to whether your structure is adequate under the fingerboard tab (including, of course, the stiffness of the fingerboard tab itself). Over-structuring that area, unfortunately, is a common ham-fisted response of many builders who recognize this problem. So the trick is finding the "minimum adequate structure"--not placing a box girder there, as some seem to want to do.

Keep in mind that I may be completely off base here, because I don't have your guitar in front of me for a valid evaluation. Your guitar design's propensity for neck rotation can be due to any of a number of other shortcomings, such as inadequate soundhole bracing (is your soundhole beginning to look like a potato chip?) or even an insufficiently arched back. Yes, the back's rigidity has an important role in the soundbox's over integrity. The entire soundbox can bend longitudinally under stress, and its rigidity is in part determined by the rigidity of the back. That rigidity is imparted by the size and arch of the back braces.

So any successful diagnosis of the architectural efficacy of your guitar design has to consider the entire guitar "holistically." It is short-sighted to assume that all your problems stem from just your heel profile.

Classic guitar soundboard arching

I have a beginners question regarding the arching of the classical soundboard as detailed in your book. The soundboard appears to be arched across the lower bout because of the arching of the lower cross strut, but there is no arching of the soundboard along the centre line from the lower end to sound hole.
I also read Roy Courtnall's book, "Making Master Guitars" where the solera is domed inward across the lower bout and along the centre line from the bottom of the lower bout up to the soundhole implying an arch across and along the soundboard.
The workboard shim you describe has a narrow section of cork all around the edge of the lower bout to accommodate and hold the arched soundboard but because the shim has cork at the bottom end of the lower bout, it implies to me that the doming is both across and down the soundboard in your method. The shim doesn't appear to be used in the soundboard arching process but is used later in the assembly process. Have I missed something important in the process? Is the soundboard arched across the lower bout only or across and along the centreline of the lower bout?

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The raised lip of the workboard shim simply raises the guitar off the flat workboard to clear the portion of the soundboard that has been arched by the lower transversal face brace. We don't want the brace to be squashed when the back is roped on. The more traditional solera is dished for the same purpose. You cannot assume or accept the "implication" that the workboard or the solera have anything to do with actually shaping the soundboard. How could it?

Having said that, I acknowledge two "schools" of thought here. One school affirms that the guitar is improved in some undetermined way by imparting a dome into the soundboard--by clamping the fan braces against the domed solera while they are being glued to the soundboard--and then curving the base of the bridge (requiring a bridge gluing-block to be arched to match). This would extend the size and extent of the dome, than doing otherwise.

The other school of thought--the one I favor--calls for simply arching the lower transverse brace and then gluing all the fan braces flat and not arching the bridge's down-face. We believe that the string's tension is going to eventually drag all those elastic elements into a final configuration of its' own. The first school, I suppose, would affirm that purposely doming the top would impart greater stiffness and resistance to the soundboard. But to the extent that the same result could not be achieved by simply increasing the cross-section of those top elements, they don't ascribe any other distinct advantage to the greater complication.

So I go with the simpler solution. And besides, great guitars can be achieved using either method. So why choose the more complicated option?

Finishing Interiors and Tuning Braces

What is your opinion about finishing the inside of the guitar body? On pianos, both sides of the soundboard are sealed with sanding sealer and lacquer thus keeping swelling from moisture to a minimum. I am inclined to do the same on the guitar body. I have heard different opinions about this subject. Mostly the theory goes: It hasn't been done in the past so why do it now. Not a very convincing argument.

Another point of interest to me as a piano tuner is tuning the tone bars to a specific frequency. We modern piano tuners almost always tune to a "tempered scale." As you probably know, this means that, except for "A440" the notes are very lightly flattened so as to be able to play the piano in any key. When I restring a piano, I check its crown and also tap it while listening for the sound of a rich kettle drum (since no strings are attached at that moment.) If I were to tune the braces to a certain pitch, I would be producing an instrument which would sound good in only one key or pitch instead of any key. So when I read about tuning the tone bars with my peterson strobe tuner, I found it interesting but not a sound musical concept. One should listen for a resonant vibration from the soundboard instead of a certain pitch so as to be able to play beautifully in any key.

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As to finishing the interior of guitars, the reason why mostly the theory goes "if it hasn't been done in the past so why do it now" is because there is no DATA for finishing the interior of guitars. Few do it, virtually nobody did it, and so there is no convincing data to persuade makers to add yet another procedure to their lengthy list--given that very few of the great patriarchs of the craft ever did it, and if you did it there would be no way to clearly determine if that it was indeed protective in some significant way--or to assuage the fear that it negatively affected the guitar in some way.

Stuart Mossman was the only serious builder I know of who finished the interior of his guitars. But he's dead, gone and all but forgotten; his instruments were quite good, but not memorable or highly prized now. And the finished insides of his guitars looked peculiar, besides. In the absence of clear evidence or a track record established by someone else that to do this is somehow good, no established build will do it. But maybe a newcomer such as yourself will to try it, utilizing the logic from another trade.

But I guarantee you. If your guitar comes out with a disappointing sound, you'll be nagged by the idea that maybe the extra finish "deadened" it. If it comes out sounding great, you may wonder how much better it might have been if you hadn't finished the interior. Or you may not. You might be able to present it as evidence that it doesn't hurt the sound much to do so. But you couldn't persuade folks that if it never cracks, it was the extra finish that guaranteed it--and not that it would have never cracked anyway. A lot of guitars never crack.

2- You're asking the wrong guy about "tuning" braces. I've advocated for years that all this "tuning" stuff for guitars was delusional nonsense, if not outright hogwash. I came to that conclusion after fathoming from my apprenticeship with a guitar acoustician that the guitar is an fantastically complex vibrational system, far more complex than any of the bowed instruments, certainly far more complex than all these folks talking about soundboard tuning--appear to grasp.

When you see the tests, like I have, those that show incontrovertibly that, for example, the headstock is the most acoustically active part of the guitar at some frequencies, and see over what an amazingly wide spectrum of frequencies the soundboard is simply silent, it drives you to conclude that all this preoccupation of tuning a certain brace or another to one note or another is just not worth the trouble.

The guitar is essentially a series of linked oscillators, or springs. Maddeningly, they all feed back into each other recursively. The strings are springs. The saddle bone is springy. The bridge is springy, the soundboard is springy, the neck is springy, and when you pluck a string, it sets all the springs dancing. And then the jostling guitar feeds energy back into the strings altering their behavior in turn. So as tantalyzing as the prospect may be, I don't believe tuning one brace to one note or another--or changing its angle by a few degrees is going to assure me the keys to world-class consistency. It will simpy generate more questions, more mysteries. And no conclusions.

Some of the confusion emerges, I suspect, from the fact that these cultural artifacts that motivate and compel us so, are called "instruments". It makes one think of an oscilloscope or a frequency generator, or some such precision scientific apparatus. The guitar is not some sort of energy-transforming device that someone invented that can be effectively tinkered with to make it more "effective" or to "optimize" it. Optimize it to achieve...what precisely? It is a cultural artifact, originally devised to satisfy the aesthetic preferences of a particular ethnic group at a particular time in history. It has been modified over the centuries to fit the evolving vagaries of culture, fashion and taste, not to somehow optimize it in some objective scientific/acoustic sense. There is no objective acoustic goal for tinkerers to reach. And if you find some kind an objective goal, you'll soon see that it, too, is a moving target.

So I've shed all that baggage, and have come to see the guitar not in terms of an acoustical problem, rather more as an architectural problem, an ergonomic problem..and an aesthetic problem. My experience is borne out daily that when these factors are well resolved and reconciled--something which is very achievable--well, the result is a product that satisfies, sometimes even enchants, skilled and discriminating players--and listeners besides.

On Scalloped Braces

Everyone seems to make such a big deal about them, but what are your thoughts on scalloped braces?

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I don't know what justification is advanced by builders who scallop their braces: I don't. Maybe you should ask them. I suppose they would reply, "Martin used them on guitars made during the 20s and 30s, and since those guitars reputedly sounded so good, presumably it must have been the scalloped braces." Sounds like lore, doesn't it?

Few people know that actually, those early guitars were originally braced for gut strings, and when decades later people swapped steel strings onto them, their tops eventually collapsed from the extra tension. But boy, they sure sounded great before they collapsed!!

The peculiar scallop shape, it seems apparent to me, must have originated as a result of an early voicing technique where (in the days when luthiers worked in factories, and were not just machine operators) builders reached inside through the soundhole with finger planes and removed material judiciously from the braces, in stages--and progressively listen to the changes after restringing, and stopped when they felt the compliance was "right."

There's nothing magic about the scallop shape itself, just that it was the result of the process of using finger planes to remove material through the soundhole. At least that's my best guess. But as it happens, that peculiar shape decades latered engendered enough lore and mystery to subsequently drive aspiring luthiers crazy trying to decipher its significance. I have been asked that same question by many of them.

Large, stiff, disappointing guitars are today "strutted" by technicians who reach inside through soundholes with finger planes to remove material from their "struts" to improve the sound. The result usually is to "hot rod" the guitar by making it sound somewhat louder and a bit deeper-voiced...while potentially hastening it's demise. The guitar survives only if the braces were way too large to start with or if the the strutting was done with great restraint. It takes an experienced eye to sense how much is too much.

The string's signal is nothing more than minute and rapid changes in tension (dynamic stress) amidst the constant background string tension (static stress). So the problem is to construct the top in a way that adequately supports the static stress without hindering the dynamic stress. It's the guitarmaker's dilemma: that the soundboard is really a trade off between structure and tone. If the brace heights are left high, the soundboard will resist the 200 lbs of steel-string tension with no problem at all, but with a price to pay insofar as the acoustical range that results: invariably a tight sound or a limited tonal response. Reducing the brace heights increases the compliance of the top to a wider range of signals coming from the strings and a more satisfactory acoustical response, but with a price to pay in its architecture. The builder is truly expert when he derives a sense of structure sufficient to dimension the top thickness and brace heights to achieve an optimum--say, minimally adequate structure.

So, the secret is not in the peculiar contour of the braces, it's in the acquired skill of the builder that senses the minimal structural requirements of the instrument and responds correctly when removing material. Note that Martin now again offers "scalloped braces"--as a marketing ploy, I suspect, because no one in the factory is graduating braces. They are likely to be using thicker, stiffer tops to hedge their bets, and make it a point to insist that low tension strings be used.

Some People Say...

A headstock thickness of 0,5", is that still safe for an acoustic steel string guitar (for strength and sound)? Or would it be advisable to add a veneer on the back of the headstock? Some people say the headstock dampens the sound when it's too flexible. Do you think that will be an issue in this case?

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Don't ask me. I haven't tested that assertion. Ask those people what evidence they have to support that assertion, or at least how they came to that conclusion. Also, how flexible, precisely, is "too flexible." Talk is cheap.

On the Significance of Soundbox Specie

I am curious what impact the different body woods has on the sound of the guitar. I have read that with mahogany one can expect a "warmer" sound. (less bright... less projection?) What I had in mind initially was something in Indian rosewood with a spruce top. (I simply have not had the pleasure to play a classical guitar made of anything else.)

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I could give you the easy, pat response that luthiers usually give their customers when answering the common question, "what is the impact of different body woods?" --with the well-worn, and ultimately meaningless words: rosewood is "clear", mahogany is "warm" and "bright," maple is "dry" and attribute more or less of one or the other quality to the specific species selected for the back and sides. But I won't do that to you, mainly because it is useless and misleading. If given ten seconds to respond, I should answer: "the sound doesn't come from the wood, it comes from the strings."

35 years making guitars has brought me to the conclusion that the guitar can physically respond to only a distinct subset or portion of the the total string's sound spectrum, creating it's own "version" of that spectrum. The guitar's effect, so to speak, on the string's sound--and thus, what we actually can hear-- is determined by among other things, it's size; it's string length; the way it is constructed; the massiveness or resilience of its neck; the thickness and hardness of the walls of its soundbox, the placement and cross sectional shape of its braces; the size and shape of its bridge, and on and on. There are so many factors impacting on the performance of the guitar--some which the luthier is aware of and can control by choice; some which are not controllable by the luthier because they are hard-wired into the guitar's culturally-determined form; and some which are beyond the perception and comprehension of the luthier. Each of these factors affects the sound, some dramatically, some slightly. The specie-name of the wood used on the back and sides plates fall into the "virtually none at all" category. The actual sample of the given specie chosen rises to the just-perceptible category. Surprising?

In other words, I could say that Indian Rosewood results in a "brighter" sound than Mahogany, but there are extremely soft samples of Indian and extremely hard samples of Mahogany that would contradict this statement--the variations between samples of the same specie are dramatic. So it may be smug and easy to talk of the "warmth of mahogany" or the "punch of rosewood" but really, they are ultimately meaningless statements.

Besides, what sound am I eliciting in your mind when I say that Indian Rosewood results in a "clearer" sound than Mahogany? Does my statement that Mahogany results in a "warmer" sound than Indian really communicate accurately to you the sound difference that I perceive in my ear? Given all the myriad known and unknown factors in any given guitar that result in it's distinctive tone, am I safe to say that the "warmer" sound that I'm perceiving is a direct result of the wood specie? Or some other solitary factor or combination of factors?

So to conclude this overlong message, I find it /not/ helpful at all to preoccupy myself or my clients about what the sound difference between two hypothetical guitars might be, one rosewood, one mahogany. That's because the perception of tone is a personal experience and not something that can be talked about, or written about. It must be experienced, it can't be described.

One thing is clear: it costs me about $20 dollars to purchase the mahogany used on a guitar, and $100 to purchase the Indian rosewood used on another; and $800 to purchase the Brazillian rosewood on yet another. And that difference will be reflected in the value of the guitar, you can be sure of that! The fact is, the cost difference biases people's perception of the guitar's sound "quality" in many people's minds (or ears). One must be very careful of falling into that trap. The perception that the Brazilian rosewood guitar is per se "better" than the Mahogany guitar, evidenced by the difference in cost, is incorrect. The Brazilian rosewood guitar is more valuable because its materials are rarer, and to some eyes, more beautiful in appearance. But one is not "better" than the other--indeed, they may be simply different, or you may not be able to perceive the difference at all. And if they are different in sound, surely there would be no way to safely say that the difference is because the specie name of the back and sides is different.

On Avoiding "Acoustical Problems" with Bridges

I'm a beginner builder of steel string guitars. I've used you wonderful book as instruction to build 3 guitars so far. I've noticed on many mass-produced as well as popular small-builder product lines, that one of the distinguishing things is the shape of the head plate and the bridge. I've done a good bit of searching the internet to find information on the pros and cons of bridge shapes/designs. I'd like to design a head and bridge that would be unique to my guitars in the future, once I get a little more experience.

Are there any general guidelines for bridge shapes to avoid acoustical problems? I notice some are very eccentric while othes (like Martin-style shapes) are very simple and straightforward. Can you advise me or point me to any infromation on this subject?

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Keep in mind that guitarmaking is an art, and not a science. Your question is like, if I change that blue area in my painting, will there be a "visual problem"?

People who like to put batman-shaped bridges on their guitar do so because after they did, they found that no acoustical "problems" resulted, so they kept doing it. It certainly is not that they calculated the precise bridge's form to produce some kind of anticipated sound. I guarantee you that no one has that power. It's more probable that the motivation was simply to make the guitar stand out.

It stands to reason, however, that if the bridge footprint is too small, there may be insufficient gluing area relative to the stress--and the bridge will be prone to eventually flying off. If it is too large, there will probably be a change, most likely a deadening, of the tone. But since you are breaking away from the traditional proportions, no one will know if that shape results in an acoustical "problem"--or has no discernible effect whatsoever--until you actually do it. Or whether it's favorable or not.

I'm reminded of someone bringing me a cheap ukelele and asked me to do something to "wake it up." It was indeed, rather reticent in its sound. I examined it, and the bridge seemed oversized. It was decidedly different from the smaller bridges that you ordinarily see on those instruments. So I took the risk and carved off some length on both sides of the bridge. Voila! The instruments sound now clearly opened up and became much more complex. The owner looked at me as if I were a wizard. And as my partner Harry always says, "never refuse an undeserved compliment."

Conversely, I also recall a Mexican Bajo Sexto that came into the shop. It had an enormous, grotesque, bat-wing bridge that covered fully a quarter of the real estate of the soundboard. Yet it had a mammoth sound, precisely the one coveted by Tex-Mex fanatics. I dared not suggest that I could improve the sound by carving material off its bridge.

So clearly, there is no magic key to world-class consistency in instrument making. The designs handed down to us by history and tradition are the sum product of the efforts of hundreds of very thoughtful and committed makers in the past who have progressively, and slowly, refined that instrument's form. So the form itself is actually the DNA for the standard sound of that instrument. If you go too far afield in your tinkering with the traditional model, you'll end up creating something...far afield. And you run the risk of it sounding "peculiar" to the listener. And be broke.

On the other hand, your tinkering may create a new paradigm, a change so drastically superior to what came before, that everybody will flatter you by stealing it. This is what happened to Antonio de Torres in Spain at about the time of our CIvil War, when he created the modern classical guitar. But be warned: this has only occurred once or twice in modern times, Torres being one and arguably, Martin's foreman taking a stab at an x-brace being the other. But it is not at all a scientific process, not a process of somehow knowing what the sound waves are going to do and then deftly harnessing them to some desired end.

Its a try it and see process, and anyone who claims that power of acoustical omniscience is either a faker or a fool. Or an X-man. Or Roger Siminoff.

On Solid Maple Soundboards

I recently saw a photograph of a very beautiful Taylor 6-string. Instead of a spruce top, this guitar had a book-end top made of quilted maple. I have always been under the impression that straight grain wood like spruce or cedar was not only structurally a necessity, but also that it gave a superior tone above other choices. Taylor, being the quality brand that it is, would certainly not make such a basic mistake to overlook the importance of these considerations. Does it mean that my understanding has been wrong altogether? And what type of tone can one expect of an instrument with such type of top? (Could it be that Taylor is merely breaking the mold and becoming innovative - like Ovation has done?)

I personally like a crisp and clear tone in a guitar - almost twangy. I have thought of cutting a saddle and a nut out of aluminum. My logic just tells me that it might give me the type of tone and clarity that I am looking for. What would your view be on this?

Many thanks for all the hours of pleasure you have given me through your book - and also your willingness to respond to my questions.

Cape Town
South Africa

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The guitar is above all other things a cultural artifact: its form is derived in great measure as a result of historic and cultural processes, from a legacy of dedicated woodworking craftsmen emulating the aesthetic preferences of their day--rather than a legacy of acoustical engineers and scientists pondering over the years how to increase its acoustical efficiency. But in modern times, another process has stepped in to dictate its development: corporate marketing.

In the guitar's cultural continuum, the guitar emerged with certain materials being prized over others. These decisions, again, were based not on acoustical or engineering principles, but on far more mundane considerations: what materials were available to builders, what materials bent the best, or were less reactive, or carved the easiest, or finished easiest, and so forth.

Now every element in the guitars form and structure has an impact, be it trivial or be it significant, on its perceived tone when played. Thus a guitar made with a perfectly straight-grained spruce top will indeed sound differently than a guitar made with a solid slab of jumbled-up-grain curly maple. So, I'm willing to bet, placed side by side and played, there will be a perceived difference. My contention is that a guitar with a quilted maple top falls outside the guitar's traditional continuum. Indeed, I'll be willing to bet that the actual decision of putting a quilted maple top on an acoustical guitar was based on a marketing rule called "product differentiation in the marketplace," and not, "how can we make the sound of this guitar louder, richer, more complex?"

Regardless, you might actually like, even prefer, the sound of the Taylor with its solid maple top. So, if you don't mind corporate marketing's impact on the guitar's historic form, then buy it. But if you think the guitar's historic form has special value, then pass it by. When is a rose a rose?

I haven't heard that quilted maple top guitar, but I would be surprised if the sound quality was not inferior in certain regards. During the 1940s, when Martin made solid mahogany tops on their acoustic guitars--during the period that Spruce was at a premium for the war effort--those guitars which I've played sounded sweet but weak. Yet some other folks--mostly inexpert players--valued them highly. So I would think the same dynamic is in force here: the stiffness to weight ratio of split spruce (it's "efficiency") is greater than any other wood, bar none. That translates to a smaller inertial load being placed on the string signal at the bridge, i.e., less damping. The consequence of less "efficient," wood like maple is that only the stronger, more energetic frequency components of the string signal will succeed in driving the denser, higher-damping top, and that many of the lower-energy signals coming from the vibrating strings will stop there and remain bound up in the string--never to be heard. But just dropping out a fraction of the string signal doesn't only change it's timbre, it changes its loudness. When you drop the sliders in an audio EQ unit, the sound source changes in character (maybe even creates an unusual new sound) and so consequently, the loudness is also reduced as you do so. Ergo, the effect is an unusual--perhaps distinctive--softer sound.

Tap Tones Ad Infitum

I just read your book (very excitedly I might add). I was wondering if it would be practical/possible/useful to post a high quality recording of sound boards in various stages of stiffness and 'just right-ness'? Being an engineer by trade, I'd love to do an objective spectral analysis as a sound board gets progressively thinner, but it turns out that the ears are probably the best spectral analyzer you can get. I take great pleasure in making things with my hands and I take great pleasure in using a guitar (at my ability, I really hesitate to say 'play'). I also love the challenge of making well fitting joinery... I am very seriously considering an attempt at making a guitar based on your book.
Of course, I assume that I would really need to mentally commit to making at least 5 or 6 before it starts coming out right, but hey... I've wasted far more money on wood in the past for projects which aren't even close in the challenge and potential reward factors. (I would need to think about what to do with all these extra guitars!!!)

Thanks (and looking forward to a video?)

Thank you for your interesting message and suggestions.

Your "recording-the-tap-tones" suggestion refers to a soundboard graduation scheme ("quenching the fundamental") that I learned from my original teachers over forty years ago and dutifully included in my Guitarmaking book when I and Jon wrote it in 1985. That was twenty three years ago. I no longer follow that graduation scheme. Clearly my priorities and techniques have evolved over twenty three years.

Your suggestion is a consequence of the fact that the text, unfortunately, can lead the reader to expect upon tapping to hear a clear distinction in the top's response before it is "just right" and at the point that it is "just right." Alas, that is not the case. Over time, I discovered that this was a traditional hallucination passed on from teacher to student over the years. We were all listening to phantoms. The underlying assumption is, that for the guitar to sound "just right," the soundboard must be "just right," i.e., that the soundboard is supreme in determining the correct spectrum of the guitar's response. My subsequent experience and studies in instrument acoustics have since shown me that it is not. But that "traditional hallucination" persists, and pervades the ongoing discussion, like noise.

Sorry to disappoint, but I have come to believe that but the difference between the sound of an ordinary guitar and an extraordinary guitar isn't discerned at a "magic moment" that happens when you're thicknessing the soundboard, or the braces for that matter. That notion reduces the guitar to an oversimplification of its dauntingly complex acoustical architecture.

More accurately, the guitar is a three-dimensional array of linked oscillators--springs attached to springs attached to springs, recursively. The loose ends of the springs are then brought back together to form multiple loops. The string is a spring, the saddle is a spring, the bridge is a spring, the sides and the back and its braces are springs; the neck is a spring, as is the fingerboard and the headstock. They are all coupled to each other, each spring with its own distinctive stiffness and length. Oh, and the air enclosed within the body is yet another spring.

When you pluck the first spring--the string--it's movement drives the entire array to jumping and dancing, attached as it is to both ends. Then, the guitar turns around--because it is vibrating--and in turn, drives the vibrating string, itself in a feedback situation. The driver drives the driven, then the driven drives the driver.

When you plane the soundboard down (or reduce the size of a brace) you are essentially decreasing the stiffness of just one of the springs in the array. Even if it was a "crucial" spring that had to be "the right" stiffness in order to optimize the whole...what would be your reference? What end result is being assured? A "beautiful" sound? What is the reference for beauty? There is no reference for beauty.

Besides, the soundboard is only able to resonate a portion of the guitar's entire sound spectrum, due to it's physical size. It is silent when the string couples to it any sound with a wave length of greater than 22 inches (the soundboard's average size). But the guitar's sound spectrum includes sounds with wavelengths of up to and over 16 feet. Indeed, the guitar cannot resonate any string frequency with a wave length of over 40 inches (the entire guitar's average size). So how does it reproduce the rest of the spectrum? Not by radiation, that is, not by sound pressure waves rising from its vibrating surfaces.

It produces sound pressures at those wave lengths by a distinct acoustical process called "point-source," which relies on the existence of a soundbox with elastic walls, a soundhole and a partially trapped volume of air inside. Its a secondary mechanism that produces all the sounds that the guitar is too small to produce by radiation. So fussing about a stroke more or less of a plane or chisel on some part of the guitar is really a very low-priority endeavor, given the scheme of things. It's very very complicated. Control is just an illusion.

In the end, the guitar doesn't create the beauty, the musician does. The best the maker can do is provide a precise, responsive and durable tool that removes as many impediments to the artists to do their art--as possible. An honorable endeavor in and of itself. Now these are objective goals that can be mastered with persistence and an evolved intuitive sense. But you'll drive yourself nuts searching for the magic stroke that will create art. The least I can do to undo my having misled you is to come clean in this way.

Can the X-brace Be Improved?

Would you agree that the "half-lap" joint on the x-brace is a weak spot, both structurally and sonically? I was thinking of making an X-brace of two pieces of curved wood rather like two letter C's back-to back, they would have a flat spot where they meet for gluing, and possibly pinning together with little hardwood dowels. (I’d like to send you a small diagram) I think this would give the x-brace strength and continuity, have you ever done anything like this?

I think you're asking the wrong person: I'm not an armchair guitar tinkerer. I'm not inclined to "improve" the guitar by imagining what may be flaws in it's traditional design and then imagining ways to remedy it. My approach is optimize the givens, not change them. But as the saying goes,"I'm a vegetarian, but I'm not going to take the meat off your plate." So you're welcome by me to go ahead and try your scheme and see for yourself.

But you make two assumptions: that the current x brace scheme needs more "strength" and that "continuity" is somehow a goal. Yet some vintage x-braced Martins I've seen dating back to the twenties have carried the string tension load for almost ninety years without distortion. And have you considered it possible that one stiff x brace and one weak x brace is precisely what makes a steel string guitar sound the way it does?

On Bending Cocobolo

Hello Master Cumpiano, greetings from Romania.

First, I will tell you, for me classical guitar is a pleasure.
I have a friend who already build 80 classical guitars. He tried now with cocobolo. But we have some problems with cocobolo. At the bending process of sides; a crack appears at one sides. I read at the others guitars makers web pages that cocobolo have a lot of oils and resins, and water can't soft the sides before bending process. If you can advise us about working with cocobolo will be very glad.

Another questions is the fresh cocobolo bend easily? (he retain a lot of water at begin, with time pass the water goes out and the wood became harder and stiffer, and I think he became more difficult to bend). If I wet the sides in warm water is useful or not? A higher temperature from bending machine is useful to bending easily or not? It is true after the drying process is almost complete the cocobolo doesn't absorb water?

I have allready read about gluing with titebond work real good. The ultimate titebond is better for gluing (Titebond Glue III Ultimate 16 oz )?

I use cocobolo frequently and yes, it is more difficult to bend due to it's oil, and it's stiffness. And occasionally it does break. That is always a danger, no one can protect you 100% from that. But the way to reduce the danger is to be consistent:

1- the temperature of the surface of your mold must be 300-325 degrees Fahrenheit (149-163 C). I don't know what temperature your light bulbs are producing. But the surface has to be 300-325 degrees F. At that temperature, the oils will come out on the surface and darken, but they can be scraped off afterwards.

2- the sides must be reduced to a consistent thickness of .080 inches. That's 2.03 mm. You need a measuring caliper instrument and an abrasive planer. And 2.03 mm is the best thickness: 2.28, or .090 inches, is too thick, it will easily break. The problem is what is the thinnest you can reduce the sides, while retaining their integrity? .080 is the thickness that works for me.

3- I would stay away from "fresh" wood, in any case. Bending fresh wood makes sense only for furniture. But when we're dealing with such thin sheets of wood, it might be easier to bend-- but when it ages, it will be all rippled and twisted. But use only well-seasoned cocobolo that is not crazy-grained, but instead straight and uniform in figure and texture.

4- Apply pressure to the wood in the mould very slowly, let the wood heat up as the pressure is applied. Leave it in the mold for 30-60 seconds before shutting off the power or turning off the gas. Don't leave it in the mold with the heat on for much longer, the wood may begin to darken. The oils on the surface will darken but that can be scraped off Let it stay tight in the mold with the heat off overnight before removing it. It will keep its shape longer. If it changes shape a little bit while it waits to be assembled, I use a hot pipe to touch it up back to the template before assembling it.

5- The difference between Titebond Original and Titebond III Ultimate is not important for guitarmakers. Titebond original is excellent and good enough. Titebond III has advantages that don't concern guitarmakers: its waterproof, you can glue it safely when the room is as cold as 11 degrees C, you can keep the joint open longer before closing it with the glue applied. All those are unnecesary for us. You can go with the Original. Unless you want to use the guitar under water!

On Pinless Steel-String Bridges

I am working on designs for a new guitar and would like to try a pinless bridge. I like the simplicity of string changes and the clean look. In your experience does this type of bridge have a marked affect on the tone of the guitar, and also is a bridge plate still necessary?

I'd definitely avoid putting a pinless bridge on a steel string guitar.

Pins anchor the strings to the bridge and soundboard and not to just to the bridge. Ball ends pulling up against the bridge patch and pins hooking into holes in the top result in a more secure mechanical connection between strings and soundboard. Having the strings end at the bridge dumps the entire load 100% onto just the bridge's small glue seam. I've just seen too many Ovation Balladeer bridges peel off their soundboards to try messing with an old, well-working tradition.

Indeed, if I were required to use a pinless bridge, I would doubtlessly use a bridge patch. Few people realize that the bridge patch also functions to stiffen the soundboard under the bridge so it's harder for the soundboard to just peel off the bridge under stress. The bridge patch protects the integrity of the bridge's glue seam besides providing a hard bearing surface for the ball ends.

But it won't stop the glue seam from failing because too much load is being directly dumped onto too small a gluing area. The bridge would probably not just peel off, it very well may pop off. But if you must use a pinless bridge, increase the size of the glueing area by increasing the size of the bridge over that of the standard pinned bridge AND make sure to include a sizeable bridge patch.