Resonance-wood
Resonance wood or tonewood refers to the harmonic table of many types of musical instruments, including those of the plucked, struck and bowed string type, such as guitars, lutes, keyboard and violin family instruments. The species used is almost always Norway Spruce (Picea abies (L.)Karst), though some firs such as Abies alba have occasionally been used.
As a rule, radially cut timber is used on harmonic tables. That way, the growth rings are easily visible and the distance between each other measurable, either microscopically, or via high high resolution photos. Large amounts of tonewood have been traded over the centuries, emanating from several European mountainous areas, from the Alps towards central Europe. Dendrochronological results strongly suggest that some areas associated with large musical instrument production, such as Mittenwald and Markneukirchen, mainly used wood grown fairly locally. There is also good evidence that wood from these areas also found its way into other European countries.
Good tonewood, besides having good acoustical characteristics, often displays a fairly steady narrow or narrowing growth, with an average ring width of about 1 to 2mm, occasionally narrower, with a straight grain. Low density associated with stiffness across the grain is also a desirable attribute. Some harmonic tables also display slight ripples of the grain, known as “bear claw” or “hazel-fichte”. Some people associate this feature with high quality resonance wood, as it is found on several master instruments.
Violin fronts are most commonly made out of two “book-matched” pieces. Logs are split or cut into wedges, these wedges are again divided and jointed so as to show a symmetrical pattern on both halves. The youngest rings (which will often be narrowly spaced) will be situated in the middle of the table by the center joint. In this case, correlation analysis between the two sides will result in highly significant values. Although this is the commonest situation, many other permutations occur. Fronts made out of one single piece, fronts made out of two piece, not book matched but showing the signs of coming from a single tree, and also fronts out of two pieces of completely unrelated wood, sometimes showing no statistical or graphical correlation.