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Approaches to Stringed Instrument Voicing

Tense up a length of string between two points and pluck it, and you will discover that very little happens in the way of sound.

But connect that string to a vibrating plate, and that plate to a resonant box and all the overtones present in that vibrating string come to life. The nature of the plate (the soundboard in a guitar, uke, mandolin, etc.) and the box (the instrument’s body) will amplify the string’s sound in a general way by employing the tension of the string to (more or less efficiently) cause the soundboard to vibrate sympathetically and therefore, move (vibrate) air. The mechanism will also cause some overtones to be louder or quieter. The combination and relative strength of these overtones contribute to what is known as the instrument’s voice, it’s unique tonal character or timbre.

Voicing the guitar (or any other stringed instrument) is the process of strengthening and defining the instrument’s voice.  It’s a skill, and a set of methods, that is the unique purview of the luthier. Nothing else a luthier does is more demonstrative of his or her experience making instruments. It’s a skill, and in many cases, a talent, that is shrouded in mystique, is romanticized (rightfully) by beginners and onlookers and is the fundamental arena of the luthier’s quest for perfection.

“The soundboard is the heart of any acoustic instrument. It’s the gatekeeper to tone and a guitar’s overall lifespan. In the acoustic-guitar market, however, too much attention is given to peripheral components of the instrument, and the soundboard’s significance is too often diminished to that of hype. Think about it: Something called “the soundboard” should be the first clue that it’s the single most important component in developing the overall coupled system that will become an acoustic musical instrument” -Bryan Galloup, Premier Guitar Magazine 10/18

It might be a little frightening that there is so much emphasis on the soundboard of the instrument, but what Galloup says in the quote above is true. No amount of fancy wood, elaborate inlay, celebrity endorsements, or artistic design will rescue an instrument with an unresponsive soundboard. That guitar is destined to the display case instead of its rightful place—in a player’s hands, inspiring musical creation.

How to learn voicing is complicated by the fact that so many different esteemed builders have taken divergent paths.  I’d like to introduce you to several of the most prominent theorists, each of whom enjoys a reputation for consistently great sounding instruments. There are others who deserve mention, but I am limiting this discussion to those whom I have seen speak at conventions (Guild of American Luthiers, ASIA Symposium, Northwoods, Healdsburg Guitar Festival) and whose guitars I have had the opportunity to play and experience first-hand. I have grouped them into methodological categories, though I want to be clear that they all overlap to some degree or another.

  • Tap tuning
  • Chladni testing
  • Materials testing

 Tap Tuning

Fewer images of the luthier are more iconic than that of the instrument maker daintily pinching a soundboard at the proper resonant node, dangling it close to his or her ear and tapping it so that the wood’s innate sonic potential can be evaluated. This tapping method, called tap tuning, happens when selecting the raw soundboard material, when thicknessing, once braced, during and after carving the braces and after the top is joined to the back and sides.

Dana Bourgeois has voiced the top of every guitar to emerge from his small production shop in Maine during a long career. He enjoys a reputation for consistently exquisite sounding vintage-inspired steel strings. His technique relies solely on his hands and ears. His emphasis is on developing a variety of pitches and overtones throughout the soundboard, variety for him being the doorway to a musical sounding top. As he works the braces down, his skilled hands check the flexibility of the top and the weight.

 “It’s all a matter of working your way to that point.  Having the right weight, the right flexibility and a nice mix of overtones. …Nice and full and musical, different notes. They’re distinct. As I tap over the braces I am starting to get variety, I’m starting to get fullness…”

John Greven has crafted hundreds of guitars, also in the so-called “vintage tradition”, inspired by the sound and of iconic Martin, Gibson, and Larson Brother’s acoustics. During a discussion on voicing at the 2001 GAL convention, John shared the following:

“Everything about the guitar has some effect on both tone and responsiveness, to a greater or lesser degree. The single most important tone/power element is the top itself. Second is the brace mass and lastly the brace placement.

The essence of the great guitar over the average guitar lies in its relative level of efficiency; its ability to take the energy of the string in motion and turn it into the maximum in singing tone quality and amplification of sound. Guitars work at about 5% optimum efficiency as a mechanical device. Even a small addition of overly massive elements in the build or other impediments to the motion of the plates will reduce the efficiency and thus the output. A 1% loss in the overall efficiency of the box is actually a 20%  loss relative to the maximum possible.

Looking for the ability of the top to hold a clean ping tone and push large amounts of air. The strong fundamental should be very sonorous and substantive. Pinging (tapping) should evoke lots of top motion and a clear sense of the air moving away from the top. A top which lacks a musical quality to this fundamental note should be avoided. It is not the frequency that matters. Frequency is a function of size and thickness of the plate. The important aspect to listen for is the character and quality of the ping and the sustain.”

Mandolin maker Roger Siminoff’s approach to tap tuning is explaining in great detail in his book The Art Of Tap Tuning. No one else has devoted a whole book to this elusive topic. Of course, Siminoff’s contribution to the discussion does not define it, that is, not all will want to follow his technique, but his grasp of the basic principles is uncontroversial. And his clear explanations of sound physics, overtones, and resonance in the book are worth the price of admission.

Siminoff uses a strobe tuner and takes careful measurements of the exact pitches produced by tapping (with a small, specialized hammer in his case) on the various braces and sections of the top. He aims for specific pitches which he has come to after years of building, based on his preferences and determined by the type of instrument being built. Presumably these target pitches will be different for other builders. Still, it’s a good starting point.

Tap tuning is the process of adjusting the stiffness of individual parts of an instrument to control how each contributes to the overall tone or timbre of the instrument. To measure stiffness, the part is set in motion (by tapping or bowing) to determine the note or frequency it produces. Adjustments are then made to the stiffness of the part until the desired tuning note is reached. As a result, the tuning provides a measurement of how stiff the part is (tuning and stiffness are related) and this leads to building excellent sounding instruments that are consistent. Siminoff -The Art of Tap Tuning.

Chladni Testing

Chladni Testing is a widely used technique whose main ambassador is New Hampshire luthier Alan Carruth. LMI carries his DVD Free Plate Tuning which goes into the technique and equipment used in-depth.

In this technique, the luthier excites vibrations of the soundboard (before bracing and during the voicing process) with a speaker emitting a particular tone/pitch. Patterns will emerge in the particular material (sawdust, glitter, etc) sprinkled on the top in accordance with the vibrations. These patterns illustrate the particular resonant nodes of the top and impart other types of information to aid in the voicing process.

“‘Free’ plates give you more information than you get from the assembled instrument. The free plate patterns are very sensitive to small changes in the mass and stiffness distribution, so they’re good indicators of when you’ve got that ‘right’. Whatever ‘right’ is.

Guitars vary a lot in their structure, and different people seem to get slightly different patterns, so it’s hard to give any absolutes. You have to find out what works for you.

 

I look more at the shapes of the patterns than at the frequencies. I’ve had guitars that turned out to sound good and be strong enough with quite a wide range of frequencies, so long as the patterns looked ‘right’. However, I have made guitars that matched closely in every respect (model, wood, thickness, pattern frequencies, and so on) that differed noticeably in sound when completed, and the only difference was the ‘shapes’ of some of the free plate patterns.”

 

Another successful proponent of this approach is Mark Blanchard. Carruth reports that Blanchard “finds that if the modes on the unbraced top are poorly shaped, it will be hard to get them to look good on the braced top. In other words, the bracing only ‘fine-tunes’ the top, it does not dominate it.”

 

Materials Testing

Obviously, the emphasis on demonstrable data in Chladni testing dovetails nicely with those proponents of what I call materials testing. They are in no way exclusive of one other (and to a slightly lesser degree, this can also be said of tap tuning).

California Luthier Brian Burns was an early explainer of certain evaluations which can help a luthier select the optimum soundboard material. His formula integrates the weight, size and flexibility/deflection attributes of the top. Though his approach (and that of Bryan Galloup, here below) emphasizes the raw material, often the same techniques are employed during the voicing process as they are working with the same phenomena of pitch, resonance, stiffness and so on. Though Burn’s emphasis is on science, he clearly respects the mysterious nature of sound:

“Obviously, a great many very good guitars have been made, and are still being made, without the aid of computers and audio analysis equipment. I have a lot of respect for “intuitive” builders who have developed their sensitivities to the point that they can tell, by flexing and tapping, when a soundboard is the right thickness, or when a brace is shaved down to the right height.

I came under the influence of engineers at a tender age, and it works for me to use an engineering approach to selecting wood and voicing the instrument. This is not science as I was taught to practice it. There is neither time nor money for that. I use obsolete equipment, donated by friends, some shop built equipment and one good software program to test my wood for its acoustic properties and to check my backs and soundboards as I move through the various stages of construction.

But make no mistake ~ it’s the thrill that the player gets from playing an instrument that is the measure of the success of any method of guitar construction. I’m looking for that exciting sound and responsiveness in a guitar that makes me want to keep on playing it. It’s what master luthier Jeff Elliot calls “allure”.”

Bryan Galloup builds on the testing techniques developed by Burns and others but takes it a step further. He has developed a very detailed brand of proprietary software to ‘crunch the numbers’ (various measurements and sound data) to help guide the luthier to select the proper wood, voice the instrument and even evaluate the sound of finished instruments. His goal, besides recognizably superior sound, is the consistency of quality from instrument to instrument (a goal shared by many, of course). During the long road of developing his technique, he has made some game-changing discoveries about wood. He is no longer beholden to the long-standing traditions guiding most people’s wood choices with regards to species, grain tightness, coloration and so on. For example, in his quest for great sound and responsiveness, he no longer counts himself among those who are drawn to Adirondack Spruce as the ‘holy grail’ of soundboard woods.

“The fact is that the majority of harvested Adirondack is just too heavy to make the cut to be considered musical-grade tonewood. Unfortunately, some of these non-musical-grade examples end up making their way into the soundboard marketplace, which brings me back to my original point. The Adirondack red spruce name alone will not make a heavy piece of wood light-correct for making a good sounding guitar.

Another point to consider is that the strength-to-weight ratios of many species cross paths, making them respond identically. Sitka spruce (Picea sitchensis), for example, can fall within a wide range. I find and test sets that will perform identically in comparison to high-grade Adirondack spruce. I also see and test other sets that are light enough to be comparable to imported European tonewood.”

 The Whole Instrument

Our discussion of voicing would not be complete without a visit to the workshop of Ervin Somogyi. His instruments, like the other luthiers mentioned here, have a storied reputation for powerful tone and responsiveness that have turned him one of the most influential figures in lutherie. Proof of that can be found in the success and reputation of many of his apprentices including Michi Matsuda, Ray Kraut, Lewis Santer, Jason Kostal, Leo Buendia, Julian Gaffney, Mario Beauregard, and others. It figures that a voicing technique which is consistent and repeatable is also teachable. This is proven out with Galloup’s growing legion of students also. They include Tyler Wells, Sam Guidry, Tyler Robbins, Zach Balwinski, Maegen Wells, and Isaac Jang.

Somogyi’s pedagogical resume is long, but his website (esomogyi.com) is a good place to start, as is his book set The Responsive Guitar, available at LMI. One of his chief contributions is his imagination of the guitar as an “air pump” which is to say, a device that forces vibrations out through the medium of air. Somogyi has a unique understanding of how the top, the back, and the body cavity function as a whole to create this pumping action.

“The path of energies in the soundbox starts with the top becoming active by the strings, this activates the air mass in the body, which activates the back, which in turn activates the air mass and the top again. The sound energies bounce back and forth. Some of that sound energy is released through the sound port (soundhole) and others are bounced off the exterior surfaces (the top) -but there is a lot of bouncing around activity, and the back necessarily is involved in that….the intelligent guitar maker will try to figure out how the top and the back will function in tandem, because it’s the relationship of one to the other that will determine how successful an ‘air pump’ you’ve made….”

The back, Somogyi explains, being heavier and not in contact with the direct drive of the strings, is mostly inert. However,

“….at the right frequency relationship, a rather small amount of drive from (the soundboard) translates into a considerable increase in efficiency in driving (the back)….it’s incumbent upon the maker to determine what the resonance relationship of those plates ought to be to one another.”

Getting into Voicing

In closing, it can’t be stressed enough that the lessons to be learned in voicing come from experience, no matter which path one follows. It’s important to avoid experimenting too early. To know the end result of one’s voicing procedure, you must build within a fairly narrow range. For example, if your first three guitars were a classical, a dreadnought steel string and a parlor steel string, then any adjustments you have made to your voicing technique will get muddled in the other structural differences between these three types of guitars. So, it’s better to build three dreadnoughts (or three of any one style) and then branch from there.

Another tip—that, at the very beginning, one should not deviate much from the plan. In a factory setting, where detailed and individual voicing is not the norm, the success of the instruments relies on a solid, average platform of top thickness, bracing patterns and brace shape (which is determined by the blueprint for the instrument). The result is that if you have 20 guitars made from the same materials with the exact same top and bracing patterns, and if the design (plan) is good, then you will probably end up with something like 15 pretty good guitars and 5 awesome ones.

Your success also depends on how well, and how carefully, you listen to the voices of lots and lots of guitars. This is an advantage gained by those who have come from the repair world (Greven and Galloup, for example). They have had the opportunity to put their hands on many great vintage guitars prior to building their own. Ultimately, as you develop as a builder, you will need to listen to your client’s desires; what they want their guitar to sound like, and to develop a vocabulary and understanding during these discussions that you can take to the voicing process.

With a careful ear, broad learning, patient and incremental experimentation and if you cultivate the desire to crack into the mysteries of great guitar-craft, voicing can become one of the most satisfying and rewarding parts of lutherie.

Sources:

Galloup https://www.premierguitar.com/articles/28008-acoustic-soundboard-the-name-game

Bourgeois  https://www.youtube.com/watch?v=bNchJIfT2O8

Greven  http://www.grevenguitars.com/pdfs/VoicingtheGuitar.pdf

Siminoff https://www.lmii.com/books/3484-the-art-of-tap-tuning.html

Carruth https://www.lmii.com/videosdvds/3534-free-plate-tuning-with-alan-carruth-dvd.html

https://www.classicalguitardelcamp.com forum

Burns http://www.lessonsinlutherie.com/woodtestingandvoicing.html

Somogyi https://www.lmii.com/books/3486-the-responsive-guitar-2-volume-collection.html

https://www.youtube.com/watch?v=V-HtN_HKRHI