Wood Choices
Much has been written about the choice of woods for your guitar. A quick search of the web will turn up many, often contrary opinions about the wood choice selected for a guitar especially in regards to the tonal properties of the wood. Why would there be so many conflicting opinions about the wood? Probably because wood itself can vary widely within its own species and because all of our listening experiences are somewhat subjective regarding what we think we hear. There are some things that can be measured for a particular wood species on “average” such as the woods hardness, compressive strength and modulus of elasticity or the “Q” , the amount of admittance or impedance to the energy. From our own experiences we know that striking a rosewood marimba bar will have more resonance and “Q” than striking a piece of balsa wood of the same dimensions so clearly wood is one factor in the sound.
So what does that mean in your wood selection? Pick a wood that you find ascetically pleasing, meets the structural requirements for its function and has a reputation and general agreement regarding the type of sound it is likely to produce. Discuss the merits and characteristics of your choice with your luthier and then trust the luthier to coax out the sound you are looking for.
BACK AND SIDES
Most of the sonic signature of the guitar is produced by the top or soundboard. As a result, for the back and sides there is a large variety of woods that will work. It can be almost any hard, stable wood that suits your fancy. Traditional woods of choice include Honduran Mahogany, Indian Rosewood and Curly Maple. Due to the continued world wide decline in availability of traditional back and side woods and the realization that many other varieties work as well or better, much more variety is available now. This would include Cocobolo (a type of Rosewood), Khaya (African Mahogany), Oregon Myrtle, Bloodwood, Bubinga, Bocote and the list goes on and on.
The sides add very little to the tonality of the instrument. They function to enclose the air in the soundbox. My building technique purposefully isolates the top from the back by using a heavier, high impedance kerfing at the joint of the top to sides. My experience and ears tell me that the less damping of the vibration that I allow to bleed into the sides, the greater the vibrations in the top which is the primary sound wave generator of the guitar. The back is coupled to the top via the air inside the box and it can either be a reflector or function as a live, tunable back if resonant frequencies are a problem.
The back and sides will typically be bookmatched. That is, they are adjacent pieces cut from a log and then opened as you would the pages of a book, creating mirror images of the graining and pattern on the two sides of the guitar. The wilder the grain, the more likely that they will not be an identical mirror of each other because they are a slightly different section through the log. You will often see on curly maple that even though the grain is very similar, it does not quite totally bookmatch.
I keep a fair sized amount of wood on hand that I've either bought at luthier conventions or processed from timber and can show or send photos of them.
A good source to view wood choices can be found at www.lmii.com. www.tonewood.com, www.Stewmac.com or www.hibdonhardwood.com. You will be able to view a variety of choices in all price ranges. I also usually have Oregon Myrtle, curly maple, cocobolo and Khaya (African Mahogany) in stock that I have sliced from whole pieces and can send pictures of backs currently in inventory. I generally purchase my tops/soundboards directly from a logger I met at a Guild of American Luthiers convention who lives in Alaska and searches out fallen timber and receives a forest service permit to harvest it. I like the idea of using timber that otherwise would decay and make it something beautiful. It is also usually from a very old tree with very tight growth rings and has great tap tone. A pretty good summary of many tonewoods can be found at http://tonewooddatasource.weebly.com. It is a compendium of information gathered throughout cyberspace. With that in mind, take its value as general information and not the definitive word.
TOP OR SOUNDBOARD
One of the most important decisions that affects the tone of the guitar is choice of wood for the soundboard. The soundboard is the vibrating interface that takes the energy produced in the plucked string and produces compression and rarefactions of the air over the soundboard that radiates to our ears as sound waves. Bear in mind that wood, being a natural product can vary widely in its stiffness, density and coloration even within the same tree. The thickness of the top and the bracing beneath will be controllable by the luthier to bring out the best in the top. The most common choice for a steel string soundboard is one of the spruces either Sitka from the Northwest North American continent, Englemann from the Rocky Mountains, Red (Adirondack) from the Eastern US or German (Alpine) Spruce from Europe, or Port Orford Cedar from the Northwest. Any of these are good choices.
Sitka is used on most production guitars and many custom guitars because it grows in large trees and is usually available at a reasonable price point. It is also a very good wood that is usually very stiff parallel and across the grain allowing it to be planed thinner to have less mass and more mobility but still offer good string support. It typically has a ringing tone with plenty of harmonics and works well on most guitars, cosmetically it is very nice with the better grades having very many grains per inch of grain count and a slightly off white color that ambers over time.
Englemann spruce typically comes from smaller trees and has a tendency to spiral in its growth. This means that there may be more grain runout in a piece rather than being perfectly quartersawn thereby losing some of it’s stiffness. It can usually be overcome with a thicker top or bracing for it to reach its maximum mobility. It typically is whiter than Sitka and tends to stay white longer in use.
Red (Adirondack) spruce is popular because it was used prior to WWII in some of our best sounding guitars. The manufacturers (notably Martin) used it because it was a good wood and convenient and available to the factories in Pennsylvania and Kalamazoo. Over harvesting took it almost out of production but the good news is that young trees have been growing for the last 50 years and it is commercially available in small quantities. It is denser and stiffer than the other spruces and has a more noticeable grain pattern and it is more expensive than the other spruces except Alpine. Bear in mind that the reason a lot of old Adirondack guitars sound so good is because the wood is aged not because of its species.
Alpine (German) spruce is a good top and shares many attributes of Englemann. It has not been harvested in Germany for a number of years and the current supply usually comes from the mountainous regions of Central Europe. It is often used on high end instruments and demands a premium price since it is exotic wood. I’ve been told that the folks over in Europe want to use Sitka spruce on their high end guitars because it is “exotic”.
Port Orford Cedar (really a cypress), Western Red Cedar, Mahogany and Redwood are also sometimes used for soundboard construction. Port Orford, one of my personal favorites seems to share many of the qualities of the spruces but is a little stiffer and lighter and makes a very good top wood. It was used in the past for wooden airplane spars because of its low weight to stiffness ratio.
Western Red Cedar and Redwood are mostly used on classical guitars but some steel string builders have had good success with them. They as well as the mahogany would tend to have a darker, less ringing tone than the spruces but with a lot of fundamentals.
NECK WOODS
The primary goal of the neck is to support the constant string load and provide a high impedance to the string energy so the energy is directed into the soundboard/top and not bled off into the neck. A number of woods are suitable for this purpose. The criteria for a good wood is one that is stable and not prone to warping or movement, is relatively easy to carve, sands to a glossy finish, will support the string load and is attractive. Honduran mahogany has been the neck wood of choice for many years because it meets all of this criteria but maple, Khaya, Port Orford cedar, Oregon Myrtle and some of the rosewoods have also been used with good, stable results.
FINGERBOARD, PEGHEAD AND BRIDGE
The primary goal of a fingerboard is to be dense, wear resistant, stable, able to hold a fret tang well and be attractive. Attributes of a good bridge would include, hard, able to withstand, string load, stiff, light and be attractive. Historically, the major wood of choice for fingerboards and bridges was either ebony or Indian Rosewood. In recent years other woods have been substituted with good results. This includes, cocobolo which is a type of rosewood, bloodwood, purpleheart, granadillo and the list goes on. Generally I try to match the bridge wood to the fingerboard wood. The peghead can have a number of options including bookmatching the cutoffs from the back and side sets in some cases or matching the fingerboard and bridge
