Mother Nature’s Sonics – Acoustic Tonewoods
By Daniel Brooks
Regardless of what kind of guitar you play, or what you play on it, the quality of sound you have at your fingertips depends on only a handful of factors. The type of guitar, the model, your choice of pickups, pedals, amps, strings and picks, and your technique itself, all of these have an immediate effect on the sounds available to you, the sonic ingredients from which you create your music. You can experiment with any or all of these as part of a lifelong quest for the sound that matches your inspiration, but you may find the search much more rewarding when you understand how much of your guitar’s tone is a direct result of the kind of wood from which it is made.
Electric and acoustic guitars both rely on the natural resonance of their wood for the quality of their tone, but each achieves their sound in significantly different ways. An electric guitar’s wooden body resonates with the strings’ vibrations to reflect, reinforce and conduct a signature pattern of frequencies, and the acoustic character of the wood has a significant influence on this aspect of the overall sound. But the electric guitar’s sound is malleable, the instrument itself is ultimately a platform for the strings and pickups to create an electric signal, which can be manipulated by effects and amp settings to alter the sound far beyond the subtle influence of the guitar’s tonewoods.
Tonewoods play a much more important role in an acoustic guitar’s volume and tone. The vibrating top and resonating body work together to serve as a natural amplifier for the strings, but also as a substantial part of the sound itself. The size, shape and construction of an acoustic guitar does play a significant role in both the tone and volume of the instrument. The laws of physics dictate that a greater mass achieves motion with a proportionally greater amount of energy, so, if all other factors are equal, a larger guitar with a larger top will project its resonant frequencies with greater volume than a smaller one, especially those lower frequencies that tend to contain more energy. For the same reason, smaller, lighter, more flexible tops will tend to reinforce the higher frequencies, creating a brighter tone. When it comes to acoustic guitars, size matters. But the kind of wood matters at least as much, if not more.
As a living, organic material, all woods are layered composites of plant cells with stiff, durable walls composed primarily of cellulose fiber and lignin. The structure, density, weight, strength and flexibility of these composites vary considerably from one species to another, and aren’t necessarily uniform among individuals of a species, or even among the various, functionally different parts of any individual tree. Each variation will absorb some frequencies, conduct and even reinforce others to create its own complex acoustic signature. These acoustic characteristics make a qualitative difference in the sound of any musical instrument they construct. Stiffer woods will sound brighter, more trebly, while denser woods will reinforce the lower bass frequencies for a deeper, darker sound.
As the strings vibrate, the tension put on the guitar’s wooden structures increases and decreases hundreds or thousands of times per second. As the top and body flex, however microscopically, in response to these changes in tension, they compress and decompress the air around the guitar to create their own sound waves. You can experiment with this by putting your hand on the top of a guitar while someone else plays it. As your hand absorbs the vibrations from the wood, two things will be immediately perceptible, you’ll be able to physically feel the music, and the vibrations lost to your hand will leave the remaining tone of the guitar relatively muffled. The vibrating wood is making a substantial part of the sound. If you are a musician, or a luthier, it matters what kind of wood your guitar is made of.
A high-quality, professional instrument will have a top made of solid wood. Many lower priced guitars will have a top and sides of laminated wood, a composite of two, three or more thin layers of cheaper wood glued together with a visually appealing veneer. Because of the glue and the conflicting acoustic properties of the layers, laminate wood rarely vibrates freely enough to create a good, open sound. You may find the occasional ply-top guitar with a sound worth buying, if the price is low-enough, but in the long run, it is worth the extra money to buy a solid top guitar. You will find ever-increasing satisfaction as the wood ages and the sound of the instrument continues to open up into a richer tone.
The most common tonewood is spruce. It is light, very strong for its weight and it conducts vibrations with high velocity for outstanding clarity and volume across a broad spectrum of frequencies, giving it a rich, balanced tone. It doesn’t add any overtones to the sound, so notes won’t necessarily bloom at lower volumes, but it will deliver all of the sound without getting in the way, even when strummed vigorously. Sitka Spruce, from Alaska, is most common, but Englemann, (or European Spruce) and Adirondack (or Eastern Red Spruce) are also well known. All three have a tight, regular grain, with a light cream color that tends to yellow slightly as it ages. Adirondack tends to be a little heavier and stiffer, and therefore slightly louder and brighter, than Sitka, which in turn is a little more so than Englemann, but each makes a fine top to any acoustic guitar intended for all-around use. Spruce continues to mature as it ages, developing its own extraordinarily harmonic tone as the decades unfold.
Cedar has long been the traditional tonewood for classical guitar tops, but it is growing in popularity for steel strung guitars, especially among fingerstyle players. Much less dense and stiff than spruce, Cedar responds nicely to less vigorous playing styles with rich overtones that lend considerable character to the fundamental notes for a warm, complex tone. With a very fine grain, a rich color that ranges from a honey brown to a red cinnamon, and a pleasant scent, Cedar has a deeply satisfying beauty to match its sound. It tends to get muddy if pushed too hard by intense strumming, so it isn’t as versatile, but it is strongly preferred by some guitarists who love its tonal quality. It matures very quickly as it ages, delivering the complex tones of an older, vintage guitar much more quickly than spruce.
Mahogany is usually used more for backs and sides, but you can find old guitars with mahogany tops nearly a hundred years old. It’s a stiff, dense, hard wood with a punchy attack and a rich, dark woody sound that lends itself well to folk, delta blues and roots music. It is also magnificently beautiful, with dark red-brown color and a short, complex and very dark grain pattern. It ages slowly, takes much longer to for its tone to bloom into maturity, but it continues to gain tonal depth with ever-increasing overtones, as anyone who has ever played an old mahogany-topped guitar will emphatically tell you. It is also ideal for back and sides where it lends substantial depth and volume.
Except for the occasional custom build, Rosewood is the most common wood used exclusively for backs and sides (and fretboards, of course). Like mahogany, it is a stiff, dense, hard wood with a high sound velocity, warm, rich overtones and powerful highs and lows that just make your guitar sound bigger. Among the most beautiful of the woods, rosewood has a rich, deep red or deep brown color with a dark dramatic grain. By far, the most common variety is East Indian Rosewood. Brazilian Rosewood has become nearly impossible to obtain, due to its rarity and the legal and financial difficulties of its trade, and has been elevated to near mythic status for its “legendary” quality of tone.
Maple is a light colored, very tight grained visual treat that is often chosen as much for its spectacular beauty as it is for its sound. It is a very heavy, dense wood with impressive sustain and virtually no overtones that lends a very bright, snappy, almost percussive sound to a guitar. Some find it ideal for live performances, especially for cutting through an ensemble with volume and clarity.
In addition to these traditional woods, some guitar makers have begun exploring alternatives, with some surprising results. Sapele can be found on an increasing number of guitars. Often referred to as African Mahogany, though it is not immediately related, Sapele has a look and sound that resembles mahogany with a bit of treble brightness. Koa is a tropical hardwood with an exotic look and all of the brightness of maple and the well-defined middle tone of mahogany. These, along with Ovangkol, Ebony, Blackwood, Cocobolo, Walnut and dozens of other exotic tonewoods will ensure that the rich variety of acoustic guitar tones will continue to be rewarding landscape ripe for exploration by the coming generations of both musicians and luthiers.