Fine classical guitars traditionally are made with rosewood back and sides, spruce or cedar tops, necks of mahogany, fingerboards of ebony. This is, however, is only the beginning of a complex story. Such woods come in various varieties and grades of quality. Their behavior as tone woods also depends on how they are cut, dried, and aged.
Wood for the Top
1862 Antonio Torres papier-mâché guitar.
As Antonio Torres (1817-1892) proved over a century ago, when he made a guitar with papier-mâché back and sides, the top is critical to the guitars sound. Of the several "tone woods" available, spruce is the most widely used. There are several varieties of spruce used in building musical instruments. By far the first choice for top quality classical guitars is Alpine spruce (picea abies), commonly called German spruce. This European spruce, which comes from thinning forests in Switzerland, Germany, and the former Yugoslavia, has in recent years become increasingly hard to come by. Although Sitka or Englemann spruce from North America is inferior to European spruce for classical guitars, it is widely used to construct steel-string guitars because its slightly different fiber structure helps dampen the harsh harmonics produced by steel strings. Hokkaido spruce has been used Japanese makers in their guitars.
In the 1960s, high quality German spruce became increasingly expensive and difficult to obtain. Jose Ramirez III (1922-1995) began to explore the possibilities offered by Western red cedar (thuya plicata), commonly called Canadian cedar. Its close, straight grain, dimensional stability even under changing temperature and humidity, and tonal responsiveness made it an ideal substitute for spruce. Following Ramirez, many famous luthiers such as Ignacio Fleta (1897-1977) and Daniel Friedrich (born 1932) began building guitars with cedar tops.
Although some guitar makers are able to achieve good results with cedar, others cannot make it work for them. In my opinion, the choice between spruce and cedar (other things being equal) is a matter of taste, much like the difference between vanilla and chocolate ice cream. Cedar guitars tend to be more responsive to low-frequency resonance's, and so are often sweeter, mellower, yet guitar makers are also able use it to produce bright, clear guitars. On the whole, I find that cedar guitars have a darker tonality, and that the sound is less direct, more enveloping than spruce. The sound of a well-aged fine spruce top has an unmatched openness, clarity, directness, and edge like an arrow.
One of the raps directed at guitars with cedar tops is that unlike those of spruce they do not improve with age. The other spin, of course, is that they are responsive from the start, and one doesn't need to play them in for years to achieve the openness of aged spruce. This does not mean, of course, that a poor sounding instrument will become a good one with time. The rap against spruce is that it is much more subject to changes in humidity than is cedar. This is precisely why it is so vital that such woods be well-aged and properly dried.
From the start, the older the spruce used by the maker, the better. Spruce is a very hygroscopic wood, that is to say it tends to absorb the same degree of humidity as the surrounding air, breathing moisture in and out with changes in humidity. Wood cellulose is of two types: one which is amorphic and absorbs and returns humidity; and the other which is crystalline and does not absorb humidity. Once wood is cut, and begins to dry out returning the moisture it absorbed in its life to the air, the crystalline form begins to replace the amorphic form, reducing its tendency to absorb humidity, and increasing its rigidity and capacity to vibrate with greater amplitude. In short, as it slowly ages and dries, its tonal characteristics improve. While there are wood suppliers who guarantee the woods they provide have been aged 50 years, woods once they reach their optimum of dryness, will not improve no matter how much time passes. Air-drying is preferred by luthiers to kiln-drying methods as it allows time for chemical changes to occur which "cure" the wood. If woods are properly air dried, wood may be seasoned in as little as three to five years. Luthiers, however, may cure their tops for much longer-- often twenty to thirty years.
The quality of a top is judged by three aspects of its wood's grain: straightness, density, and medullar rays. The straightness of grain is very important in determining sound quality and timber. The wood grain should be totally straight with each grain parallel to the others. Since sound travels along these long fibers, any deviation from straight grains reduces its strength. Density is likewise important. The great the density (number of grains per cm) the finer the top. Here it is important to observe whether or not the density is uniform. Irregular spacing indicates that the wood has not been cut along the grain, and is of an inferior grade. Generally, in premium grade woods the distance between grains is less than 2 mm. One of the feature's of fine spruce tops is the presence of medullar rays, fibers which grow at right angles to the grain. While their natural function in the wood is to circulate starch and resin, they improve the tonal quality of the soundboard by providing links between the long fibers of the grain. Light medullar rays also may be found in cedar, but they are not as marked nor do they seem as important to sound as for spruce.
In recent years, some guitar factories have attempted to imitate the appearance of fine instruments by building instruments with laminated tops. Naturally, they sound like the plywood the are made from. Buyer beware. Make sure the instrument top is made of solid wood.
Woods for back and sides
Rosewood
Two types of rosewood are commonly used in classical guitars and so-called flamenco negras: Brazilian rosewood (dalberia nigra) and Indian (dalbergia latifolia) rosewood. Both woods are dense, resinous, and very handsome. Brazilian has highly figured grain, and many consider it the more beautiful of the two, but it is more brittle and difficult to work than Indian rosewood. By contrast, Indian rosewood tends to be straighter-grained, and often contains purplish streaks. Brazilian rosewood has become increasingly expensive and rare. In the mid-1960s the Brazilian government, with the aim of diverting more work to their sawmills, banned the export of logs. In 1992 dalberia nigra was declared an endangered rain forest tree, and requires a CITES permit to export. Indian rosewood, on the other hand, grows on plantation, and so remains plentiful. Indian rosewood also has the advantage of being dimensionally more stable, and of being less affected by changes in humidity and temperature than Brazilian rosewood.
Brazilain "dalbergia nigra"
Tonally these woods have slightly different characteristics. Brazilian rosewood is less fibrous, and a somewhat harder, denser wood, and so tends to reflect sound more, and thus produces a bit brighter sound than does Indian. This difference, however, can only be perceived by playing identically made instruments by the same maker. Or, to put it slightly different way, there are much greater differences in sound between makers using the same woods than between different woods by the same maker. A well made Indian rosewood guitar may be infinitely better than a fancy-expensive Brazilian rosewood guitar by a luthier of lesser talent.
Other Rosewoods
Adding to the confusion, many species of dalbergia (botanically "true" rosewoods) from Brazilian and elsewhere that are marketed as Brazilian rosewood. Slab-cut, these rosewood are very similar in appearance and tonal character to dalbergia nigra. They include dalbergia martina (Madagascar rosewood) dalbergia retusa (Cocobolo). There are a number of other woods in the dalbergia family that are also used in guitar making Dalgberia palo-escrito (Palo escrito), dalbergia cearensis (kingwood), dalbergia frutescens (Pau rosa, Jacaranda Rosa). In fact, there are literally hundreds of species of dalbergia worldwide.There are also a number of other woods from Brazil that are some times simply called “Brazilian", such as Machaerium spp. (Caviuna or Fau Ferro). Because of this confusion and hype over Brazilian rosewood, I only refer to true Dalbergia nigra as Brazilian rosewood, and if I am not sure of the species simply to call them figured rosewoods.
Laminated woods
Unlike the top, some fine makers have chosen to build guitars using laminated materials with excellent results. Jose Ramirez, for example, lines his traditional 1a model rosewood guitars with cypress. He believes that this lamination lend greater stability to the back and sides, preventing warping and twisting, and providing them with their distinctive dark sound. Henner Hagenlocher, similarly lines the sides of his guitars with cypress.
Maple
For centuries maple has been used in instrument making because its cross-grained structure allows it to be planed down to make light, but strong instruments. In the nineteenth century, it was widely used to make both fine classical and flamenco guitars. In fact, up to the 1930s, fine flamenco guitars continued to be made of maple which like cypress can be planned very thin, yet produces a somewhat fuller sound than cypress without being as mellow as rosewood. Some modern luthiers, such as Paulino Bernabé, Pedro de Miguel, and J. A. Pantoja Martin among others are again using maple to produce instruments with a sweet vivacious tone.
Cypress
The flamenco guitars are usually made with Spanish cypress, an attractive blond wood that is extremely light, and can be worked much thinner than rosewood. It is the use of thin, light cypress for the back and sides that helps give flamenco guitars their vibrant and distinctive sound. The choice of cypress over other woods, nonetheless, appears to have been a question of building affordable guitars. Few flamenco players could afford anything else, and cypress was abundant and cheap in Spain. In recent years, however, high quality cypress has become increasingly difficult to obtain.
Coral
Coral is another wood that is occasionally used to make flamenco guitars. A handsome reddish wood like cypress coral can be worked thin, to make light vibrant instruments. Harder than cypress, it produces very bright guitars. Both Pedro de Miguel and José Ruiz Pedregosa have used it to make outstanding flamenco guitars.
Mahogany
Mahogany is one of the woods widely used to make affordable guitars. While it is much cheaper than rosewood, its tone is thinner and less resonant than rosewood.
Other woods
Makers have experimented with a number of other woods as alternatives to rosewood. Paulino Bernabé, for instance, has used pear wood in the bodies of high quality classical and flamenco guitars. Paul Fisher has experimented with a Rosewood from Brazil wood, Santos Palisander, with good results In their quest to find more affordable woods guitar builders have also used sapele, an African wood in the mahogany family, sycamore from central Europe, American walnut, Koa wood from Hawaii, and Bubinga a reddish brown wood from Cameroon and Gabon.
Woods for the Neck
The wood for the neck needs to be strong and dimensionally stable or it will warp or twist under the pull of the strings with changes in temperature and humidity. The wood also should be light to maintain the balance of the guitar. Because Honduran cedar or Honduran mahogany are straight grained, and when they are properly seasoned are both light and stable, they are the woods of choice for classical and flamenco guitar necks. Even so, to prevent warping, many makers reinforce the necks of their instruments with a bar of ebony running the length of the neck, at 90 degree angle to the grain.
Woods for the Fingerboard
The fingerboard requires a wood that is very hard as the constant striking by fingers and rubbing of the strings will rapidly wear groves in softer woods. Two woods are commonly used for fingerboard: rosewood and Guinea ebony. Although rosewood is a more stable, ebony is much harder wood. As a result, ebony is universally used for fine guitars; and, rosewood only for entry level instruments.