Understanding Tonewoods

Watching Dana Bourgeois select the tonewoods for a future guitar is like watching a great chef gather the ingredients for the meal of a lifetime. Dana and his team flex and tap each piece to hear its inherent musical tones. They scratch the wood and inhale the pungent scent of mahogany or rosewood as the woods are cut and sanded like a sommelier evaluating the bouquet of a fresh Bordeaux or an ancient Zinfandel.

Every Bourgeois Guitars instrument benefits from the world-class knowledge and skillset we bring when choosing the woods for a guitar. But what makes one species of wood – or even different sub-species – better for building a guitar?
Fortunately, our founder, Dana Bourgeois, is recognized globally as a leading authority on tonewoods. Here, he helps break down the differences, large and small, between the various types of wood used in our guitars.

What Is A Tonewood?

Stringed instruments such as acoustic guitar, violin family instruments, mandolins and others can be built from a broad variety of woods. But over time, the luthierie (instrument-building) community has learned that some woods have a combination of features that produce a specific sound that’s desired, while also offering significant visual appeal and maintaining long-term structural stability. Certain species of trees, and even sub-species, have earned the trust of luthiers and created the sounds modern acoustic guitar buyers desire.

For back and sides, this would include the various species of rosewood, mahogany from a variety of sources, maple, koa, and more. Tops are commonly built from spruces including Sitka, Adirondack, Englemann, and others. These species have been found to have stiffness-to-weight ratios that allow them to bear the high string pressures found on a flattop guitar while vibrating freely to produce a loud, musical sound when played.

Evaluating Tonewoods

Differences between tonewoods can be as mysterious and complex as differences between people. Even within a species, no two pieces of wood are exactly alike – even from the same tree. Environmental conditions, genetics, the age of the tree, annular growth patterns, grain orientation, curing conditions, and so on all affect the tonal properties of a piece of wood. In addition, tonewoods respond differently in the hands of various guitarmakers. They can also take on different characteristics when used in different models of guitars – even those built by the same maker. And whether a particular wood sounds good or bad depends partially upon who’s doing the listening. So any attempt to sort out distinctions between tonewoods can only be offered from a relatively subjective point of view. But there are some general truths we can share.

Topwoods

Each part of the guitar seems to play a role, be it significant or subtle, in determining the tonal characteristics of the instrument. In very general terms, the top, or soundboard, seems to affect the guitar’s responsiveness, the quickness of its attack, its sustain, some of its overtone coloration, and the strength and quality of each note’s fundamental tone. Most luthiers (but not all) believe that the wood chosen for the top is the most important variable that determines the quality of tone of a finished instrument.

Spruce is the standard material for guitar soundboards. These days the most commonly used species is Sitka. Quartersawn Sitka is quite stiff along and across the grain. High stiffness, combined with the relatively light weight characteristics of most softwoods, is a recipe for high velocity of sound. A strong fundamental-to-overtone ratio gives Sitka a powerful, direct tone that is capable of retaining its clarity when played forcefully. Sitka is an excellent choice of topwood, then, for guitar players whose style demands a wide dynamic response and a robust, meaty tone.

On the other side of the balance sheet, the lack of a strong overtone component can result in a “thin” tone when played with a relatively light touch – depending, of course, upon the design of the guitar and the other woods used in its construction. The break-in period for a new Sitka guitar can also be longer than that of other spruces.

Eastern red spruce, also known as Adirondack or Appalachian spruce, was the primary topwood used by American instrument manufacturers before World War II. Its use was all but discontinued due to over-harvesting of the resource. But Adirondack has recently been reintroduced thanks to 50 years of regeneration and to the legendary status that this traditional tonewood has attained. Red spruce is relatively heavy, has a high velocity of sound, and has the highest stiffness across and along the grain of all the topwoods. Like Sitka, it has strong fundamentals, but it also exhibits a more complex overtone content. Tops made out of red spruce have the highest volume ceiling of any species, yet they also have a rich fullness of tone that retains clarity at all dynamic levels. In short, red spruce may very well be the Holy Grail of topwoods for a traditionally styled steel-string guitar.

A common alternative to Sitka and Adirondack is Engelmann spruce, another domestic western species. Engelmann is considerably lighter in color than Sitka spruce, lighter in weight, and usually less stiff. Engelmann also tends to exhibit a weaker fundamental tone, although it produces a noticeably broader and stronger overtone component. It is therefore a good choice for fingerstyle players who require a richer, more complex tone than can be obtained from most Sitka tops, particularly when the instrument is played softly.

European or silver spruce, the spruce of choice for makers of classical guitars, shares a number of characteristics with Engelmann spruce, including color, lightness of weight, harmonic complexity, and fullness at the lower end of the dynamic range. European spruce differs from Engelmann in its potentially quicker response and greater headroom.
Before leaving the spruces, I should mention bearclaw figure, or hazelficte. This delightful pattern in the grain occurs occasionally in all species of spruce.
Bearclaw, like the curl in curly maple, is a rippling of the longitudinal fibers, which divides the surface of the wood into shimmering patterns. This phenomenon only occurs in older trees that have dense, stiff grain structure and high sound velocity. Thus bearclaw is usually a reliable indicator of the better examples of tonewoods within any given species of spruce.

Another popular choice, Western red cedar ranges in color from honey brown to light chocolate. It has a quickness of sound that exceeds any of the spruces, a higher overtone content, lower fundamental content, and lower stiffness along the grain. Additionally, cedar tops require a significantly shorter break-in period than spruce tops.

Since World War II, cedar has been used extensively by makers of classical guitars. Cedar-topped guitars are characteristically lush, dark-toned, and bursting with musical flavor. They are often less powerful in projection than their spruce cousins, however, and they tend to lose clarity near the top of their dynamic range. We find cedar to be used to its best advantage in smaller- bodied guitars or with non-scalloped braces.

Redwood is similar in many ways to cedar, though is usually stiffer and heavier. These characteristics bring out stronger fundamentals, particularly in the lower range, while allowing greater dynamic range. Redwood tops perform well on small and medium sized guitars and produce a full range of overtones at higher dynamic levels.

Koa and mahogany have been used for soundboards since the 1920s, and some makers have begun to use maple recently. These hardwoods have in common a relatively low velocity of sound (as compared to softwood tops), considerable density, and a low overtone content. They therefore tend to produce a solid tone having strong midrange colorations.

Back and Sides

Besides serving to form the enclosure of the soundbox, the back and sides of the guitar also act as a sympathetic resonator whose oscillations contribute greatly to the harmonic mix.

Brazilian and East Indian rosewood have an extremely high velocity of sound and a broad range of overtones. The rosewoods, as well as their various rain forest cousins – cocobolo, kingwood, morado, and the like – produce strongly pronounced low overtones, usually the lowest resonating frequencies in the entire guitar. These lows help to create a complex bottom end, imparting an overall darkness of tone to the instrument. Strong mids and highs serve to reinforce overtones generated by the top, contributing to a fatness of tone on the upper registers. Guitars made of rosewood also have a pronounced “reverby” tone, caused by a strong, clear set of sympathetic harmonics with a delayed onset and slow decay. We’ve found that Brazilian rosewood has everything that Indian rosewood has, only more.

Mahogany and koa have relatively high velocities of sound when considered as materials for backs and sides and thus contribute much to overtone coloration. Lacking the low-end frequencies of the rosewoods and also their sustaining reverberation, these woods have an altogether different sound. Where rosewood guitars can be thought of as having a “metallic” sound, mahogany and koa guitars are better described as sounding “woody, although the harder, more dense examples of these woods such as sinker mahogany can take on some of the characteristics of the rosewoods. Between the two, koa seems to have a little more fullness in the midrange, while mahogany tends to favor the bass (to some extent) and the treble.

Maple and walnut tend to be more acoustically transparent than other tonewoods due to a low velocity of sound and a high degree of internal damping. The harder, denser examples of these woods, such as sugar maple and black walnut – particularly quartersawn examples – tend to lean slightly more toward the tonal direction of mahogany, while softer examples, such as bigleaf maple and claro walnut, tend toward greater tonal transparency.

Fretboards and Bridges

Players of electric guitars with bolt-on necks have long been hip to the fact that neck and fretboard materials can have a significant bearing on tone. Maple necks can impart a bright, poppy tone that can do much to reinforce the top end of a large-bodied guitar, while mahogany necks help push the overall palette into a warmer, more woody tonal range.

Fretboard materials also influence overall tone, although they probably act more as icing on the cake than as a layer of the cake itself. Brazilian rosewood fretboards and their denser rain forest counterparts add sparkle and ring, and Indian rosewood fretboards can help fatten up the midrange. Ebony, the traditional fingerboard material found on violins, classical guitars, and high-end steel-string guitars, has the lowest velocity of sound of all the woods commonly used in lutherie and has definite damping characteristics. This may not prove to be much of a problem for large-bodied guitars made out of red spruce or Brazilian rosewood. But it may be something to consider when choosing smaller guitars, particularly those using some of the less resonant woods for tops and backs.

Bridge materials, like fretboards, cannot make or break an instrument’s sound. But they serve to enhance or edit the tonal contributions of other materials found on the guitar. The woods discussed above – ebony, Brazilian rosewood, and Indian rosewood – contribute similar tonal qualities when they are used as bridge materials as when they are used for fretboards.

Conclusion

It is important to remember that wood species can be responsible only for certain aspects of the tone of any guitar. Equally important are the design of the guitar, the skill of the maker, and the quality of the individual pieces of wood from which the guitar is made. Species selection can, however, be a determining factor in the creation of a very special guitar or a guitar designed for a specific purpose.