Guitars

Table of contents:

Wood stability

Wood used for the back and sides

Wood used for the top (soundboard)

Basic theory of guitar construction

Fig. 1: A "birdseye" maple electric guitar

Source: http://home.pacbell.net/tyrswood/guit3.html

Background to wood use in guitar construction

Guitars are constructed from exotic, precious woods gathered from distant places - for example; Rosewood (Dalbergia sp.) from Brazil or East India, Spruce (Picea sp.) from Central Europe or the American and Canadian Northwest, and Mahogany (Swietenia sp.) from Central America (Sloane 1975). These are some of the main woods that have been used in guitar making since the early 1900s. Other woods, such as Morado (Machaerium scleroxylon), Cherry Koa (Acacia koa), Maple (Acer sp.), Larch (Larix sp.), Western Red Cedar (Thuja plicata), Blackwood (Acacia melanoxylon), along with a number of other woods, are also used in today's guitars (Wyza 1999). Rosewood-veneered plywood is also available for backs and sides of guitars, although plywood guitars are disappointing, which is partly due to the general cheapness of their manufacture (Sloane 1975). The sound tones in plywood guitars can be improved if the wood is two-ply rather than three-ply, which would reduce the rigidity and permit manual tapering or thinning if necessary (Sloane 1975). Soundboards are made of spruce; an even-grained, resonant wood that combines exceptional strength with lightness (Turnbull 1974).

For generations in the past, forests of the Tyrol, Dalmatia, Bohemia and Rumania provided the spruce for guitar manufacture. Now the spruce used from these forests has been largely exhausted, and imported spruce is difficult to find and expensive (Sloane 1975). Sitka spruce is a large tree growing in the American north-west, western Canada, and Alaska. Its strength to weight ratio is lower than that of European spruce, but in all other respects it is a perfectly satisfactory replacement (Wheeler 1974). Fingerboards are made of ebony or rosewood. Ebony is always preferred on guitars of high quality because of its durability and lack of grain, and also due to the elegant contrast it makes with nickel-silver frets (Sloane 1975). Soundboard struts and bracing are usually made of straight-grained, clear spruce, the stiffer the better. Honduras Mahogany is used for the cross struts on a rosewood back, Sitka spruce or maple on a maple back (Turnbull 1974).

Wood stability

Dampness is the enemy of all stringed instruments, particularly the guitar. If moisture gets into wood, the wood swells (Wheeler 1974). In a drier environment the moisture leaves the wood and the wood shrinks to its former size. A guitar can tolerate these changes if they are gradual and not extreme (Wheeler 1974). Ideally, a guitar should be built in an atmosphere containing less moisture than the atmosphere in which it will most commonly be used because swelling (the absorption of atmospheric moisture) is a less serious hazard than shrinkage (Sloane 1975).

Physical and tonal properties of some woods used in guitars

The following list of woods is a guide, and does not nearly cover all the woods used in guitar manufacture:

Wood used for the back and sides

Brazilian Rosewood (Dalbergia nigra)

Brazilian Rosewood is scarce, and hence many commercial guitar manufacturers have switched to Indian Rosewood - it is unlikely that manufacturers will switch back to using Brazilian Rosewood (Sloane 1975). Sometimes referred to as "Jacaranda", several factors have made Brazilian Rosewood the ideal wood to use in guitar manufacture. Due to its exceptional strength and density, yet thinness without sacrificing rigidity, along with a high resin content, Brazilian Rosewood has a superior resistance to decay and warp (Wheeler 1974). Its lustrous, dark-grained beauty is a prized asset in an instrument where visual appearance is an important consideration. Brazilian Rosewood ranges in colour from pale red-brown to deep chocolate. The grain is often wild, with pores that can be large or small (Sloane 1975).

Fig. 2: Brazilian Rosewood image

Source: http://bumpy.braille.uwo.ca/~charles/woods.html

Indian Rosewood (Dalbergia latifolia)

Indian Rosewood has a grain that is more uniform and its colour ranges from pale grey-brown to deep red-brown or sepia with a vaguely purple haze (Sloane 1975). Its grain is generally more open-pored than Brazilian Rosewood and its lustre is duller. Indian Rosewood is resinous, stable and generally more consistent in grain than other rosewood species. It is extremely resonant producing a deep warm projective bass response that accentuates on large bodied guitars (Peckham 1994).

Mahogany (Swietenia macrophylla)

Mahogany is a heavy wood, which is considered to be porous. There are two types of mahogany - Honduras (Brazilian) and African (Marks 1999). The most common is Honduras and it has a golden brown appearance. African, on the other hand, comes in more of a reddish brown colour. Mahogany is consistently clear and light in weight, and yields a strong sustained sound with an emphasis on clear bright trebles (Turnbull 1974). The wood is easy to machine and finish, possessing both a spiral and interlocking grain pattern, making it an exceptionally stable wood (Wyza 1999).

European Flamed Maple (Acer campestre)

European Flamed Maple naturally occurs in Germany (Marks 1999). In some rare individual maple trees there is a characteristic alternating soft and hard rippling appearance that runs perpendicular to the grain, that is sometimes referred to as curly, flamed, tiger shaped, or "Fiddleback" maple (Peckham 1994). This particular species of European maple is very hard in texture and reflective, producing a loud, powerful projective sound. The uniquely textured "Birdseye" maple displays characteristics and tonal properties similar to European Flamed Maple. Maple is a strong, heavy wood that is light in colour, and can be used for both the neck and the body of guitars. Maple finishes well and can be steamed and bent. Maple also has very densely aggregated pores, a feature that simplifies finishing (Wyza 1999).

Cherry Koa (Acacia koa)

Koa is an expensive hardwood that naturally occurs in Hawaii and has a golden brown to dark red colour with dark streaks and a lustrous sheen. Sometimes known as "flamed" Koa, the wood occasionally develops a curly or flamed appearance. Koa is considered to be porous. It has a bass response that is slightly less than that of rosewood and a treble response that is slightly less than that of mahogany. This results in a very equally balanced instrument (Peckham 1994).

Fig. 3: Cherry or "flamed" Koa image

Morado (Machaerium scleroxylon)

Morado occurs naturally in Bolivia. Also known as Bolivian or Santos "rosewood", Morado ranges in colour from a light violet brown to reddish brown with occasional olive and black streaks (Peckham 1994). It is finer in texture than most rosewood species, and is a close visual substitute for Indian Rosewood, having very similar tonal properties.

Blackwood (Acacia melanoxylon)

Blackwood is excellent for back and sides sets. It is light ochre in appearance to dark with reddish brown streaks. This species occurs naturally in Australia from Tasmania to Queensland, and is used for guitar manufacture by the Maton guitar company. Blackwood prefers drainage areas (e.g. gullies) and high rainfall, taking about 90 years to grow to a utilisable size, by which time it is often 'piped' or rotted in the core and almost at the end of its life cycle. The grain is usually straight though sometimes figured or 'flamed', especially the buttresses or stumps of the tree (Hindman 1998). Blackwood is a relatively stable, strong hardwood, that has been experimented with in the construction of guitar necks with excellent results. This timber is beginning to be highly valued abroad as it is almost identical to the Hawaiian species Cherry Koa (Acacia koa) used in traditional luthier construction (Hindman 1998).

Wood used for the top (soundboard)

Sitka Spruce (Picea sitchensis)

Sitka spruce naturally occurs in Canada's north-west and Alaska. It has a consistent quality in the grain, being straight and uniform, is durable and long lasting, with good tensile strength (Wyza 1999). Tonally, Sitka spruce is extremely vibrant, providing an ideal medium for transmission of sound on any size of stringed instrument (Peckham 1994).

Fig. 4: Sitka Spruce image

Englemann Spruce (Picea engelmannii)

Englemann spruce naturally occurs in the USA. It is prized for its similarity in colour to European (German) White spruce, as well as its extreme lightness in weight. This produces a slightly louder and more projective or "open" sound than Sitka spruce (Peckham 1994). Englemann spruce grows in high altitudes in the Rocky Mountains and the Pacific Cascades, and is considerably more limited in supply than Sitka spruce (Marks 1999).

Western Larch (Larix occidentalis)

Western Larch naturally occurs in the USA. It has clearly marked annual rings and a fine uniform texture. Larch is harder and stronger than most conifers, including spruce (Wyza 1999). It has a close visual resemblance to Sitka Spruce and due to its increased stiffness, it is an appropriate choice for scalloped braced models, yielding a projective and crisp response (Marks 1999).

Western Red Cedar (Thuja plicata)

Western Red Cedar naturally occurs in the USA. It has long been utilised as a soundboard material by classical guitar makers for its vibrancy and clarity of sound. It is extremely light in weight compared to spruce and the tonal result is generally a slightly louder, more open response (Marks 1999). It is a poor choice of wood for steel-string guitar construction, because of its low inherent strength - a misdirected pick will abrade and scar this soft-fibre wood (Sloane 1975).

Basic theory of guitar construction

The volume of sound produced by a guitar depends mainly on the volume of air enclosed by the resonating sound cavity or box (Sloane 1975). Large, deep boxes tend to produce a louder sound and give a deeper bass response than small, shallow boxes, which tend to produce a greater treble sound and hence suffer a proportional loss in volume or loudness (Peckham 1994). In the traditional construction of a classic guitar, great importance is attached to the character and wood use of soundboard bracing (Sloane 1975). Bracing patterns are designed to promote the flow of sound vibrations across the diaphragm like the effect of a stone dropped in the centre of a pond; concentric circles of sound vibrations ripple out from the bridge, meeting less and less resistance as they reach the diaphragm perimeter (Turnbull 1974). A properly constructed guitar has a vibrant, well-braced body and a soundboard especially designed to vibrate. A top that does not vibrate produces a muffled, insubstantial sound (Sloane 1975). A guitar constructed with thin back and sides tends to have a louder sound than a guitar made of thicker wood. However, a thin guitar also produces disturbing overtones and excessive noise unless securely and strategically braced (Wyza 1999). Hence, the guitar maker's basic job then, is to build a sound box enclosing an adequate volume of air within walls thin enough to ensure sufficient loudness, yet stable enough to prevent harmonic difficulties and with a top that will flex properly to lend body and presence to the sound (Sloane 1975). It is therefore essential that suitable wood types are used for the various components of guitars, such as the soundboard, back and sides, neck etc., as different wood types have varying densities. The wood types used should suit the function of the component, in order to achieve a good resonance, and so that the guitar is durable and will last for a long period of time.

Fig. 5: A 10-string classical guitar made from Honduras Mahogany, German Spruce and African Ebony

REFERENCES

Hindman, C. (1998). Maton: Australian timbers. http://www.maton.com.au/timber/index.html

Marks, T. (1999). Wood FAQ. http://www.netmagic.net/~tmk/faq/woodfaq.htm#1_1

Peckham, C. (1994). RMMGA frequently asked questions. http://www.guitarnotes.com/rmmga/documents/rmmgafaq.shtml#resources

Sloane, I. (1975). Steel-string guitar construction. Dutton-Sunrise Inc., New York.

Tauber, C. (1999). Maker of guitars and lutes. http://www.braille.uwo.ca/~charles/index.html

Turnbull, H. (1974). The Guitar. B.T. Batsford Ltd., London.

Wheeler, T. (1974). The Guitar Book. Harper & Row, New York.

Wisner,. J. (1998). Tyrson's wood. http://home.pacbell.net/tyrswood/guit3.html

Wyza, B. (1999). Guitar builders FAQ. http://members.aol.com/wyza/gtrfaq24.pdf

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Copyright 1999 The Australian National University

Author: Robert Priddle

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Date last Modified: 21.10.99

URL: http://www.anu.edu.au/Forestry/wood/nwfp/guitar/Guitars2.html