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The Steel String Guitar
Contents:
Timber treatment and seasoning
Introduction: history of the guitar
The contemporary guitar belongs to the Chordophone group of musical instruments, which are characterised by the production of sound through vibrating strings. The lineage from which these instruments descend extends back as far as ancient Greece, and back further to bowed harps, which were played as early as 3000BC in Egypt and Sumeria.
It was not until the Renaissance, during the 1600's, that the first true guitars appeared. These instruments were distinguished from others by having a waisted body shape, smooth curves, and vertical sides. Since these times the dimensions, materials used, and the music being played has changed, but the essential shape has remained.
The evolution of today's different guitars can be traced in a chronological fashion:
It can easily be seen that the guitar is a dynamic instrument, which has been changing in design and construction, and has itself changed the music that is popular today. It should therefore be no surprise that one of the modern forms of the guitar - the Flat Top Steel String Acoustic - is the most popular instrument in the world today. In terms of forestry, quality guitars are "one of the most value added things you can do with trees."
The historical origins of this guitar can be traced back to two men, Orville Gibson and CF Martin, who were responsible for the early development and differentiation from the existing European styles. Guitars built in the USA prior to this were of low quality, and were used primarily by women as a boudoir instrument. Gibson was struck by the inadequacies of American guitars as much as he was amazed at the comparative perfection of imported (usually European) violins. This gave him the idea, of using the steel strings from a mandolin to string a large, carefully fashioned guitar that he had made himself - to the construction standards he had observed in imported violins.
The result was a louder, much more resonant instrument - the American Steel Stringed guitar had been born.
Up until this paradigm, the selection of timbers in quality guitar making was simple. European Classical guitars were constructed of Rosewood - preferably Brazilian (Dalbergia nigra) or East Indian (Dalbergia latifolia), with Alpine Spruce (Picea sp.) soundboards. However, with the developing American culture came a divergence from traditional European methods. American Sitka Spruce (Picea sitchensis) was cheaper for the American producers, for obvious geographical reasons, and the development of American Steel- Stringed guitars also created a new sound. The combination of the use of new timbers, new material for the strings, and an increase in size gave rise to new design and production techniques. The European designer's problem was that animal gut strings weren't loud enough, although the tension they exerted did not create problems in the structural rigidity of the guitar, Whereas for the American steel string guitar makers, volume was inherent in their guitars, although the instruments strength was far more tested.
Considering these parameters, and other market forces which shall be discussed, the following section describes which timber species are used for different parts of the modern steel string guitar, and why.
The soundboard
American Sitka Spruce is the preferred timber for the soundboard. Aside from the geographical and historical reasons for the use of this species over Alpine Spruce, the properties of this species have now been observed to be superior to Alpine Spruce for this type of guitar. The reason for this being that the different fibre structure damps some of the extreme harmonics associated with steel string vibration. Another characteristic of this species' timber is its strongly marked rays. This gives an increased tonal resonance in the radial direction, that is, more sound is vibrating through the soundboard, as sound moves not only along the grain, but through it as well. Other properties of this timber that make it the choice for quality steel guitars are its resilient and dimensionally stable nature, and the ease with which it can be worked. Aside from anything else, Sitka Spruce is an attractive timber when cut, with a fine, even grain, which is blonde in colour.
Timber from only fully mature trees is used for the soundboard, and then only the main bole, below the first branches. The selection of each soundboard is critical to the tonal and aesthetic qualities of the finished guitar. As a result of this, there are a number of criteria that are used in its selection by luthiers:
Back and sides (the body)
East Indian and Brazilian Rosewood are still favoured for the production of steel guitar bodies. Both are dense, resinous and beautiful timbers. The Brazilian species features a highly figured grain, and is tawnier in colour, whereas the Indian species is straighter grained and often has purplish streaks. The two species are fairly interchangeable in terms of sound quality and sound maturation, although the choice has been made easy for luthiers in recent times. In the mid-60's the Brazilian Government placed an embargo on the export of unsawn rosewood logs. As a result the timber became too expensive, and luthiers could no longer control the cutting of the timber. East Indian Rosewood is now the number one choice amongst luthiers for the production of steel string guitar bodies.
Neck
Central American Mahogany (Swietenia macrophylla) is the most common choice of timber for the neck. The neck of a steel string guitar must be strong and stable, so as to resist distortion by the pull of the strings, as well as changes in temperature and humidity. Furthermore the wood must be light, to maintain the balance of the instrument in a player's hands.
Fingerboard
African Ebony (Diospyros ebenum) is the desired timber for the fingerboard. The requirement for the fingerboard is that it must be hard enough to resist the wear of a player's fingers over many years, and be reasonably stable. Ebony is an exceptionally hard timber that displays strength and durability. However, it is difficult to obtain in large quantities, and as a result, some lower quality guitars use rosewood as a less expensive substitute.
Timber treatment and seasoning
The nature of wood makes it responsive to changes in temperature and humidity. In a musical instrument such as a guitar, these tendencies can be unwanted, as the slightest change in the different wood types within each guitar lead to tonal variation - to the musician's ear warping of different parts means it is out of tune. These tendencies cannot be restrained by using larger pieces of wood, as the guitar needs to be very responsive to musical vibrations.
The first step in curtailing this problem is the cut of timber from the log. All timbers for guitar construction should be taken from boards cut as nearly as possible along the radius of the log. If a plank is cut radially to the log, so that the end grain runs straight up and down, the tendency to move will be purely along the three main axes of the plank. If on the other hand the plank is slab-cut, with the end grain running skew across the thickness of the wood, the forces exerted when it moves will twist and warp the plank. To get as much of the timber as possible in the form of radially cut planks it is quarter sawn. Unfortunately, the higher the proportion of truly radial planks the greater the wastage.
The proper seasoning of timber does more than just reducing its tendency to warp, as it ages, its strength increases and its tonal responses improve. Air drying is preferred to kiln drying, as it allows time for chemical changes which "cure" the wood. The economics of doing this means that only small luthiers can afford to air dry timber, whereas larger producers can only afford kiln drying, this is because much more time and energy is spent on each guitar by an small luthier. Some soundboards are air dried for up to thirty years. Martin Guitars (a large US steel string producer) instead take a two step approach to seasoning their timber. Kiln drying is followed by chemical seasoning to artificially recreate the effects of extended air-drying.
Construction techniques for the steel-string acoustic guitar vary widely. The highest quality guitars being made in smaller, artisan styled workshops. An Australian example of which is Maton (http://www.maton.com.au). The Maton web page gives detailed information of their alternative approach to hand making guitars, as well as the use of (often-experimental) Australian timber species. These species include Blackwood (Acacia melanoxylon) for the back and sides; Bolly Silkwood (Cryptocarya oblata) for the back, sides, and neck; and Bunya Pine (Araucaria bidwillii) for the soundboard.
Larger producers make use of their economies of scale, by specialising production in larger factories. For example, the Gibson factory in Kalamazoo, Michigan has an individual worker assigned for each step of production. The Gibson website has a tour of their Montana factory (http://www.montana.gibson.com/tour).
The future of the steel string guitar industry looks bright for both Australian and overseas producers. This is a result of supply and demand factors. From the supplier's perspective, there appears to be no immediate deficit of required materials, considering that timber is a renewable resource, and that any shortfalls in an individual species can be dealt with through substitution of another, as the Brazilian Rosewood crisis exemplifies.
Strengthening this is the current demand for guitars. The guitar is one of the most accessible musical instruments, being relatively easy to learn, and easily transportable. As well as these properties, modern music is currently dominated by "guitar music", as a glance through the recording sales charts will testify.
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Copyright 1999 The Australian National University
Author: Andrew Gilbert
URL: http://www.anu.edu.au/Forestry/woood/nwfp/guitarsteel/guitar.html