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Acoustic Soundboard: Grading Tonewoods - Back and Sides

Acoustic Soundboard: Grading Tonewoods - Back and Sides
While grenadillo can be more prone to cracks than other wood species, it can make for stunning backs and sides.
Photo by Kimberly Dalton

There’s more to consider than tone when choosing wood for a guitar’s back and sides.

In my last column [“Grading Tonewoods: Tops,” February 2015], I wrote about choosing a top for a custom guitar. Since others and I have previously discussed the tonal qualities that distinguish various wood species, here I focus strictly on structural integrity and cosmetics. Let’s assume, then, that you’ve played a number of guitars made with many of the possible back and sides options, and have settled on a tone that suits your musical needs.

Cosmetics. When it comes to a guitar’s back and sides, cosmetics are among the main criteria. When we first pick up a guitar to admire its beauty, we immediately turn it over to look at the back. We do this even when the woods are pretty standard fare, such as Indian rosewood and mahogany, but we’re especially inclined to do so when the guitar is constructed from exotic and/or figured wood.

Even after 20 years of doing this for a living, I’m awed by the forces of nature as they relate to a beautifully figured piece of wood. Each piece is different, and its unique nature is what provides the attraction.

One thing to decide up front—especially if you intend to use an exotic species such as cocobolo, ziricote, or African blackwood—is whether you like the look of sapwood. Sapwood is the very light-colored part of the wood that usually appears in the center of a guitar’s back. Some people find it quite striking, while others don’t like the color contrast. Sapwood is usually structurally sound, but not always. It can be pithy and soft, and if that’s the case, an experienced luthier will choose not to use it.

For some species, the possibility of figuring also comes into play. Figure can consist of uneven or ribbon-like grain lines, medullary rays, or a flame/fiddleback pattern. We’re often asked if we believe that figuring changes the tone of woods, and the short answer is no. Having built many guitars side-by-side with and without figuring, I’ve never heard a difference I could attribute to the presence or lack of figuring.

We’re often asked whether we believe that figuring changes the tone of woods, and the short answer is no.

Structure. Whether or not the back and sides are quartersawn matters much less than it does for the top’s wood. In my opinion, it matters little when choosing a back, and usually only matters for the sides when they’re initially being bent to shape. (Flatsawn sides are more likely to break while being bent.) If you are unable to tell whether a set of wood is flatsawn, this is a good time to rely on your luthier’s experience.

Another thing to consider when choosing the back and sides is the likelihood of cracks occurring down the road, and how much cracks would bother you. Some people see a repaired crack as no big deal, while for others it’s the ruination of their dream guitar. For the latter group, I recommend staying away from certain species. Again, this is something to talk to your builder about, but some crack-prone woods that come to mind are ziricote, Honduran rosewood, Brazilian rosewood, and grenadillo.

As a rough generalization, the greater the density of a species, the more likely it is to crack. You can, of course, help avoid cracks by diligently using a humidifier and monitoring humidity in the places where your guitar lives. Ultimately though, cracks can occur despite your best efforts.

Durability. While it’s probably not the greatest or most exciting way to choose woods, durability comes into play as a guitar goes through its life. Woods such as mahoganies are softer, and therefore more prone to damage. When we see the guitars of out road-musician customers, the mahogany instruments are likelier to have damaged backs and sides.

I left the durability topic for last, because I think it’s the least important when choosing your back and side wood. If you are hooked on mahogany tone, then you should choose a mahogany guitar, take it out there, and play the daylights out of it!