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rickm -> RE: "Guitar needs to be played" myth? (Jan. 18 2008 1:09:44)
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I posteed this on a wood carving forum I belong too and got several interesting replies. One being that the age of wood, where it was grown is certainly critical. Woods from the Mediterrrean area, grown in hotter, dryer areas, grow harder and more durable. But there is this writing as well..
wood has very different mechanical properties along different axes. Its mechanical properties are determined entirely by its cell structure. Wood is made up of long, thin cells with walls composed of the polymers cellulose, hemicellulose, and lignin. Cellulose, a carbohydrate that forms long straight chains, is the main structural component of wood. Cellulose chains usually form microfibrils, fibers consisting of groups of parallel chains held firmly together by hydrogen bonding. In wood, cellulose microfibrils lie parallel to one another in four layers, and spiral around the cell in its long direction, with different angles of spiraling in each layer. Lignin and hemicellulose, which form highly cross-linked structures, act as a “glue” that holds together the cellulose components and binds adjacent cells together. The longest dimension of each cell runs parallel to the growth of the tree trunk, in the longitudinal axis, and therefore wood has its greatest tensile strength in the longitudinal direction. As a result, wood plates must be elongated along the grain of the wood, in the direction of greatest tensile strength, in order to achieve the same types of resonant modes that are observed in an ideal square plate.
Many modern-day violin makers use visualizations of resonant modes to aid in tuning a violin’s front and back plates. During construction, modal patterns in a plate can be seen by covering the surface of the plate with a fine sand and inducing mechanical vibrations at various frequencies. As the plate resonates, the sand moves about, except at the nodes, which remain stationary. The sand collects at the nodes or is bounced away, creating much the same patterns as shown above.
Two particularly strong modes are the second and fifth harmonics of the plate, often referred to as the “X mode” and the “ring mode” for the shapes of their nodal patterns. These harmonics are the main components of a plate’s tap tone. Recently, a number of violin makers have recommended tuning each plate such that the ring mode sounds exactly an octave above the X mode, in order to mimic the efforts of early violin makers, who would have tuned the most prominent modes to exact musical intervals. While the theory is difficult to test, it seems highly plausible because tuning tap tones to musical intervals requires no specialized equipment and therefore could have been done by even the earliest violin makers. In addition, the idea parallels Renaissance ideals of mathematical perfection, which may well have guided the Italian violin makers of centuries past.
Lumber Redux: Another Look at Wood
Do violins actually improve with age? The acoustical properties of the wood used in their construction certainly change with the passage of years.
Moisture in wood absorbs vibrational energy, converting it to heat energy by evaporation. Although the wood used in violins is already dry, minute changes in water content can have dramatic effects on violin acoustics: a 1 percent decrease in moisture content reduces damping by up to 3.5 percent. The long-term improvement of acoustical response depends mainly on the degradation of hemicellulose, the component of wood that adsorbs water most readily and degrades most dramatically over time. As hemicellulose degrades, the wood’s maximum water content decreases. Even over very short periods, the sound of a frequently played violin may noticeably improve as small amounts of water evaporate from the wood.
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