Contemporary Acoustic Guitar Design and Build - Review by American Lutherie

  

Contemporary Acoustic Guitar Design and Build

by Trevor Gore

with Gerard Gilet

Trevor Gore Guitars (http://www.goreguitars.com.au)

ISBN 978-0-9871174-(0-3, 1-0)

$ (Australian) 245.00 (includes shipping outside Australia)

Hard cover, 800 pages in two volumes, includes four full-size plans

reviewed by R.M. Mottola

  

[Originally published in American Lutherie # 109, Spring 2012. Copyright © 2012 by R.M. Mottola (http://LiutaioMottola.com) and the Guild of American Luthiers (http://luth.org). Reprinted here with permission.]

  

A copy of the book reviewed in the following paragraphs was provided to American Lutherie for review.  A draft of this review was sent to the author prior to publication so that any factual errors in the review could be corrected.

Let me cut right to the chase. I consider this book to represent a major milestone in lutherie “how to” publications, and for a variety of reasons any one of which would be sufficient to warrant that assessment. Although a variety of excellent books on the construction of flattop guitars is available, Contemporary Acoustic Guitar Design and Build (which for brevity I will hereafter refer to as CAGDB or simply “the book”) includes a lengthy treatise on the design of the guitar as well. The treatment is highly technically accurate, something that is rare enough in lutherie books to warrant special mention and special praise here. The design section includes substantial background information in mechanics, stringed instrument acoustics and other technical disciplines that serve as the foundation for the design effort and an understanding of how stringed instruments actually work. Although the book will have obvious appeal for technically oriented readers, it is also very accessible to non-technical readers willing to forgo some of the math. The construction part contains excellent instructions for building modern instruments in the small shop using contemporary materials and construction techniques.

The book is presented in two large volumes, one on design and the other on construction, and details how the authors design and build their guitars. It is amazingly comprehensive in scope – a simple enumeration of the topics listed in the table of contents would take much more space than I have available for this entire review. The design volume takes a broad but practical approach to the design of the guitar. The focus of the design effort is the development of a set of specifications, formulae and other “tools” that can be used in the shop during construction. The volume begins with the presentation of much background material on general issues related to guitar design, information which will be valuable to anyone attempting a guitar design effort. Roughly half of the design volume is dedicated to technical background information. Basic physics of vibrating strings, plates and bars is presented. There are good discussions of resonance and sound radiation. A good background in mechanics is provided.  The background portion finishes up with good descriptions of some basic analytical models which describe the vibration of the instrument as a whole and how the component resonances couple.

Specifically geared toward the problems of building a structure that is both strong enough to withstand static string tension loads and compliant enough to provide good acoustic output, the design volume presents derivations of equations of practical use to the builder. College level math is required to follow the derivations, but I urge readers not possessing this background to not dismiss this work on these grounds. If you can’t follow the derivations skip them – the end results are always simple algebraic equations (again, the authors’ focus is not theoretical but practical guitar making). In addition, behind these equations you will find some of the very best and most accessible explanations of the relevant mechanics and musical instrument acoustics that I have ever seen in print.

Let me point out a few examples from the many nice explanations found in this volume. On the topic of wood for the top of the guitar, the design volume points out that the great variability in mechanical properties of wood from any species of tree makes selection of top wood by species not of paramount importance. This is demonstrated in part by a very nice graphic of sound radiation coefficient of typical top species, which includes error bars indicating the variability found within each species.  This is very useful information, presented in a particularly meaningful manner. The authors opt to select top wood by testing mechanical properties on a set by set basis and describe that selection process. Again, given the practical orientation of the book, this process is not particularly time-consuming nor does it involve a lot of equipment. 

Another exemplary presentation is the treatment of a topic which I have rarely seen discussed in print in any comprehensive manner, the design of the top and bracing to support static string tension loads. The book carefully describes a standard engineering method, making use of the parallel axis theorem to derive an equivalent rigidity spec for the entire braced top structure. Because variability in brace material, orientation, and cross section affect the accuracy of this modeling, the book also describes a very simple mechanical check for optimal top rigidity on the finished guitar, looking at the change in bridge deflection angle under string tension. This latter operation is also a good example of something else the book does very well, which is presenting alternative approaches to design and construction issues, insofar as this operation could easily be used as the sole method for determining top rigidity if the builder is willing to approach this on a strictly trial and error basis.

For me a major plus in the approach taken in this volume is that it follows general engineering methods when considering the design and construction of a guitar. For those not familiar with these methods please let me offer a brief explanation. Formal engineering is a requirements-driven process. Engineers do not begin work with the proverbial clean sheet of paper but rather with a very detailed list of requirements for the thing to be designed. Collecting and prioritizing these requirements is an important part of the process. As each element of the design is considered during the engineering process it is checked against the requirements. Goodness of design is determined simply by how well the finished design meets the specified requirements.

This systematic approach is taken throughout the design volume and is applied at all levels, from the selection of materials and construction techniques to the integration of all the subassemblies that make up a guitar into a cohesive functioning instrument. Wood, glue and finishing materials are considered as engineering materials and are evaluated based on their material properties.

I have praised the technical accuracy of the information in the book, and understanding why I consider this to be so important also requires a bit of background for those that do not follow the formal research. The current state of understanding of the workings of stringed musical instruments is far from complete. Although we do have good knowledge of how instruments vibrate to produce sound, particularly in the lower frequency modes of vibration, our knowledge drops off considerably when considering the higher modes. And the farther down the “signal chain” one goes, from vibrating instrument to the human brain that perceives that vibration, the murkier things get. We really don’t know much at all about what the differences between good and really good instruments are for example. This fact can be considered in terms of our basic knowledge in the field of psychoacoustics, where, although we have good understanding of human perception of loudness and pitch, we have extremely limited knowledge of human perception of pretty much everything else. This is also reflected in the fact that musical instrument physics and psychoacoustics are not major areas of research. As such, we rely on a relatively small number of papers describing modest experiments for a large portion of our understanding. The relative dearth of hard information necessitates a careful approach to the design process. As a minimum that process should make good use of all the hard data available, and the authors of CAGDB are careful to do just that. The inverse also applies of course – anything that runs contrary to established knowledge on the workings of stringed instruments should be rejected from impacting the design. Although not a primary focus, along the way the book discusses a number of lutherie myths which fall into this category.

Considering scientific evidence in the design is important of course, but how a design proceeds in those areas where good scientific evidence is lacking is perhaps of even greater importance. The book does very well here as well, including careful analysis of some of the research literature, and takes testing and observation on the part of the authors into consideration when making design decisions. It is inevitable in this field that some design decisions are made largely by informed guessing, and here too the book shines, first by making clear that this is part of the reality of doing design work in this area, and secondly by documenting where in the presented design this was done. Only by this documentation is it possible to test and validate (or invalidate) those design decisions in the final instrument.

Two design objectives feature prominently in the volume: the optimization of monopole mobility of the top, and optimising the guitar’s ability to play evenly over the fretboard and accurately in tune. Much of the design discussion is dedicated to these topics. Design results of the first include bracing patterns considered to enhance top mobility, thick and rigid top linings intended to increase impedance at the top-to-rib juncture, and a facility for mass loading of the ribs. As a late step in the construction process described in the second volume, instruments are subjected to testing to be sure major resonances are at reasonable frequencies and do not fall directly on scale tones, and the construction is “tuned” based on those test results. The tuning involves slight alteration of resonant frequencies, and a number of the design features provide for ease and predictability in those tuning modifications. The facility provided for mass loading of the ribs for example, is a large rib reinforcement patch which includes a threaded fitting into which a bolt stacked with a varying number of weights can be fitted. Features included to help optimize intonation include both per string bridge saddle and nut end compensation, performed on a setup and string set basis.

The second volume of the set is about construction and is aimed specifically at the small shop building modern instruments with modern methods and materials. As is often the case with lutherie construction books, the authors here try to keep the tool count down for the benefit of beginners that may not have well-equipped shops. Construction descriptions using hand edge tools (planes, chisels, etc.) are common, but construction jigs for use with routers are also commonly used. This volume follows construction of four instruments, full size plans for which are included. This is an interesting collection of instruments and includes two classical guitars, a fan braced Fleta style and a lattice braced Smallman style (but without the heavy internal frame); and two steel strings, an X braced Gibson J45 style dreadnought and a laminated falcate (sickle-shaped) braced OM sized guitar. Although one could quibble with the representativeness of these choices, from the perspective of guitar construction (and in particular top construction) they represent a nice and wide variety of construction techniques and use of materials. I am most pleased to see the Smallman style instrument included here myself, which I take as yet another indication that this design is already a classic.

Certain features of these instruments and the jigs and construction techniques used to produce them are common among them. All instruments use bolt-on necks, either a straight mortise and tenon bolt-on neck with glued-down fingerboard extension or a fully removable bolt-on neck. Bodies are all built using an outside mold, and plates are all built using dished workboards and a go-bar deck for clamping. Two different styles of back bracing are described: traditional ladder bracing and a more readily tunable style that makes use of radially positioned finger braces.

The build volume begins with an in-depth discussion of tools and jigs. The construction techniques described are quite jig-intensive, in the modern style. Detailed instructions for building most jigs mentioned in the text are provided. It may be a bit unnerving for novice builders to see all this jig construction work that needs to be done before doing any work on the instrument at all, but this organization is quite logical and makes the subsequent instrument building descriptions a lot clearer. The jig building section is succeeded by a discussion of glue and gluing. As mentioned in the review of the design volume above, the authors consider glue as an engineering material, not as an object of veneration. The discussion contains good information on the material properties of various adhesives. Finishing materials are also discussed in a short section, but are not surveyed in depth. The book advocates the use of sprayed nitrocellulose lacquer and hand applied French polish.

A nice feature of the build volume is its use of photos. The build process is explained both in text and also in a running sequence of color photos which are usually grouped six per page. Although this guarantees that a referenced photo will almost never be found on the same page as its referring text, I found it a whole lot easier to follow most construction sequences by glancing through the grouped photos and their captions than if each photo were embedded in the text.

Let me point out here that there is only basic instruction in this volume on techniques of instrument decoration. The authors take a decidedly minimalist approach to decoration of their own instruments, and maintain that good books on subjects such as pearl inlay are readily available. Still, basic binding and purfling are covered, as are simple soundhole rosette treatments. Installation of pearl in both of these applications is also covered.

Since construction description is of four different instruments the text does need to provide alternate descriptions for a number of the major building steps. Probably the area where the divergence of build instructions is the greatest is in describing bracing of the tops. The Fleta style instrument is fan braced, the Gibson style X braced. Nice descriptions of bracing in these traditional styles are provided. But the Smallman style instrument is braced with a balsa and carbon fiber lattice and the small bodied steel string is braced with molded braces that also make use of carbon fiber. It is in the descriptions of these contemporary construction techniques, techniques not all that commonly known in lutherie, that the build volume really shines.

As is the case with the design volume, the build volume is too large in scope for me to even list the topics covered. But as I did above, I’d like to mention here just a few of the nice features I found. The book is written by luthiers with obvious depth of experience and this comes through strongly in even the smallest of construction details. The build instructions make very good use of cutoff material for example, using top cutoffs for back seam and soundhole reinforcement and back cutoffs for bridge plate and head plate. Glue squeeze out is removed with a snipped soda straw, a technique which I’ve instantly adopted in my own building. When chiseling a shallow mortise in the bottom of a fan brace to clear the bridge plate, the brace is held upside down in the vise and the top surface of the vise jaws is used as a depth gauge. Dished workboards are used as gluing cauls when assembling the body. The back is glued on first so that any glue squeeze out, which would be visible through the soundhole of the finished instrument, can be cleaned up before the body is closed up. These are small examples, but they are indicative of the level of detail found throughout the volume.

I found no major shortcomings in either of the volumes and even trivial gripes were few and far between. My only major disappointment was the lack of explicit instructions for the practical application of the mathematical model presented for string compensation. Although the model itself is presented in detail and represents a major focus of the authors’ designs, the book only goes as far as to suggest that this model can be put to use by the application of mathematical optimization techniques and suggests the reader research them. Mathematical optimization is a technology which is likely to be outside the background of a lot of readers and I could wish for more concrete application information. Although it is clear that a textual description (which necessarily involves computer programming in one form or another) would be daunting, it would be very useful if the compensation calculation program could be provided as adjunct material, possibly available for direct execution on the authors’ website or as a downloadable program. And while I’m making requests for adjunct material, it would be most helpful to technically oriented readers if key research on the part of the authors and used to support design their decisions could be published, preferably in a peer reviewed research journal. Absent that, even short descriptions of some of these experiments, outlining experimental methodology and sample population size, would be very useful.

In book reviews I like to provide at least a little information on presentation, writing style, and other details that impact on accessibility of the material presented, and to suggest audience groups for whom the book may be particularly valuable. Let me close with a few remarks on those subjects. The presentation here is very straight forward and as mentioned makes good and extensive use of graphics and photos. The book is formatted in a simple, clean, single-column style. The writing style is direct, conversational, often opinionated, but always clear and to the point. Chapters begin with classy full page photos of guitars or production processes. As I’ve also mentioned, complex technical topics are covered in a manner that makes them accessible to a wide audience. American readers should be aware that the authors are Australian, and the book is written in Australian English and uses SI units. As far as suggested audience groups go I can recommend this book to all lutherie audiences without reservation. To say that there is something here for everyone would be a gross understatement. The size, scope, and level of detail presented in Contemporary Acoustic Guitar Design and Build provide substantial information to anyone involved in the design and construction of acoustic guitars.

  

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