Harp Myth 5

About Wood

This article is the fifth in an extended series of articles addressing issues and myths surrounding traditional harps and their construction. This iteration is the first of five which deals with materials. In any stringed instrument, it is the quality of the materials which first determine what is possible. Harps speak in wood and so we begin with the structure of trees.

Foundations

Lumber is generally all heartwood. Heartwood has rings of earlywood (springwood), which is lighter in color and latewood (summerwood), which is darker. Softwoods and hardwoods are not only different families of the tree order, they are quite different on a cellular level. It is this cellular differentiation, as opposed to any relative hardness, which categorizes a wood type. Hardwoods, like maple, cherry and, surprisingly, balsa, have thick-walled, needle shaped cellular fibers which are generally about 1mm long. Softwoods, like spruce, redwood and cedar have both thin-walled tubular cells, which are 3 to 8 mm long, and thicker-walled cells. In most cases, the density of softwood is lower than that of hardwood because the overall mass of the thick-walled support fibers is much less. Luthiers often refer to the softwoods, used on instrument soundboards, as "tonewoods".

"Straight-grained" is a term meaning that the cells are parallel to the longitudinal axis of the tree/wood. "Curly-grain", as used when referring to flamed or fiddleback woods, describes wood with a grain that has longitudinal waves. Other terms like "quilted", "birdseye" and "bear claw" also refer to grain type. Lumber which is quarter-sawn is not a grain type but a way of milling and refers to the grain direction. Quarter-sawn lumber has grain which runs 45 - 90° with the face of the piece. It is a common mistake for the terms "grain" and "texture" to be confused. While "grain" describes direction, "texture" describes the size and amount of cellular variation. The most expensive soundboard blanks available are Straight-grained with a fine texture and completely consistent color.

One of the real issues in modern lutherie involves wood selection. There is, for instance, a belief that every soundboard has to look one way. Luthiers find themselves (and their customers) looking for a perfect, pale white spruce with cross silk and 25 lines of grain per inch. Diminishing spruce groves cannot support such practices. Though there is no doubt that good wood is critical, the soundboard of Stradivari's violin, The Harrison, has a knot! The Harrison is a poster child for the irreplaceable value of a skilled luthier. Master-grade quality wood should not be used to compensate for the lack of skill on the part of the builder. In terms of wood selection we join many in the stringed instrument community in expanding the definition of top quality soundboards to be more realistic. This is particularly so for defects which are strictly cosmetic. Every instrument we build has one or more cosmetic "defects" in the wood which in another time might have prevented the wood from being used. We prefer to think of these marked woods as lending character and, given a choice, we have found that our customers often prefer these woods.

Thar's Water In Them Thar Trees!

If you have ever cut your own Christmas tree down you know ... thar's water in them thar trees! Yup, there is a lot of water and getting it out is one of a luthier's real challenges. When a tree is alive, the cell cavities are filled with free water and the cell walls have water bonded into their structure. Once cut, the free water evaporates quickly. When the free water is gone and only the bonded water remains, wood is at the fiber saturation point (FSP). Wood is ready for working when it reaches the equilibrium moisture content (EMC) point, meaning that the wood and its environment are in equilibrium and the wood only loses or gains moisture in direct proportion to the gains and losses of the environment. Once wood loses enough moisture to fall below the FSP, dimensional change occurs. The amount of moisture lost and dimension effected depends directly upon the relative humidity (RH) in the environment. Therefore, the part of the country and/or the control conditions under which the wood is dried become important.

Air-drying has long been the tradition in lutherie and the greatest advantage of this slow process is that the structure of the cell walls remains intact. The disadvantage of air-drying is that it is expensive, in time, in inventory size, and in some remaining warpage losses. Commercial kiln drying, the method used for most commercially available lumber, brings the moisture content (MC) down quickly but destroys thin cell walls in the process. In recent years, some lutherie wood suppliers are using a slow, low-heat kiln process followed by reconditioning which actually dissipates more cupping and twisting stress than air drying and produces comparable wood. Once wood is dry, at its EMC, then seasoning begins. Many luthiers believe that it is the crystallization of resins, which occurs during seasoning, and the daily fluctuations in RH which may cause fibers to settle, allowing an instrument voice to develop experience.

And the moral to this myth? Stradivari built great violins with woods most would never consider using today. Guarneri built most of his famous violins from the same tree. In all fairness, yes, wood is important but it is mastery, artistry and craft that brings a voice from a plank.

 

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