Q: Back in the day, it seemed that all new guitars came with Sitka spruce tops. Now players can choose between a great variety of tonewoods, such as Adirondack, Italian, German, and Carpathian spruces. Regardless of the top, however, guitars built by the same luthier often sound more alike than different. How fundamentally different are the woods commonly used for tops; how much do these woods contribute to tone; and how much attention should I pay to species when evaluating a guitar? —George Ramos, Corpus Christi, Texas
A: A guitar top supports a string load of roughly 160 lbs of force. To function optimally, it must be rigid enough to support string load without experiencing undue distortion, light enough to react quickly and with minimal loss of energy, yet flexible enough to accurately respond to complex and subtle vibrational forces that set it in motion. Spruce, having the highest stiffness-to-weight ratio of all woods, is the material most often used for guitar tops, as well as for most other stringed instrument soundboards.
But not all spruce is alike.
When cut to exactly the same dimensions, soundboards of the same species can have significantly different characteristics of weight, cross-grain stiffness, long-grain stiffness, and internal damping; even wood cut from the same log may have greatly varying vital characteristics. A spruce board that is sawn perfectly “on the quarter”—for example, sawn on a line from the center of the log to any edge—is stiffer, both along and across the grain, than one cut even slightly “off-quarter.” And the exact same piece of spruce can end up having different characteristics depending on how it has been cured.
Between species of spruce, characteristics can vary even more dramatically. From lightest to heaviest, common top-wood species can roughly be categorized in the following order: western red cedar (closely related to spruce), Engelmann, Italian, redwood (also closely related), Swiss, German, Sitka, Lutz (a hybrid of Engelmann and Sitka), Carpathian, Dalmatian, and Adirondack. (Mahogany and koa, also commonly used for tops, are generally heavier than most spruces.)
In general, lighter tops respond more efficiently to lighter playing styles, and more aggressive playing styles are required to bring out the full sonic potential of heavier tops.
Each species exhibits its own “average” long grain and cross grain stiffness, though as noted above, averages encompass wide variations. Stiffness corresponds roughly to weight, but as you are perhaps beginning to suspect, no firm rules apply here, either.
It should come as no surprise, then, that while different species tend to exhibit recognizable median characteristics, variation within species often creates ambiguity. To note just one example, a slightly heavy carpathian spruce top could easily be mistaken for an Adirondack top of average weight; numerous factors—accuracy of quartering, curing history, where a set was cut from the log, and so on—could also conspire to produce remarkably similar long-grain and cross-grain stiffnesses and internal damping characteristics. To further confuse the beholder, the color and overall appearance of these two species is almost identical. Equally confounding similarities also exist between other pairs of species.
To be sure, prime examples of any species tend to exhibit relatively unmistakable personalities. Without question, luthiers often deliberately select species for the explicit purpose of pushing an individual guitar in a specific sonic direction. “Purity of species,” however, is not a necessary ingredient of a great guitar. Many truly great guitars are made with tops that might be one species but could easily have been another.
Every luthier has a different building style, and more importantly, a different vision of his or her ideal guitar, ideal soundboard, and ideal materials. Because no two pieces of wood are alike, most tops, by definition, are not ideal. Luthiers often adjust “imperfect” examples to bring them closer to the elusive ideal, making lighter tops a bit thicker, stiffer tops thinner, or thinning a less responsive top around the perimeter, sometimes obfuscating species identity in the process.
When evaluating a guitar, it’s usually not possible to know why a luthier chose an individual top, or why it received specific treatment. I wouldn’t pay too much attention to species, therefore, beyond understanding that lighter species tend to favor lighter playing styles and vice versa. As always, there’s no substitute for investing time in playing a guitar that you’re interested in purchasing, and also listening to how it sounds in the hands of other players. And if you don’t know the species of a top, do yourself a favor and don’t ask until after deciding whether or not you like the guitar.