IMPROVEMENT OF THE ACOUSTIC AND HYGROSCOPIC PROPERTIES OF WOOD BY A CHEMICAL TREATMENT AND APPLICATION TO THE VIOLIN PARTS

A chemical treatment was applied to a wood specimen and some parts of a violin. Formaldehyde cross linkings formed between hydroxyl groups of wood constituents decreased the internal friction (Q-1) of a sitka spruce specimen as much as 40% and 45% in the fiber and cross fiber directions, respectively, in the frequency range of 150-500 Hz. The degree of reduction in Q-1 was smaller at high frequencies and larger at low frequencies. The specific dynamic Young's modulus (E/gamma) at 20-degrees-C, 65% RH increased 10% in the cross fiber direction, though it hardly increased in the fiber direction within the frequency range examined. The changes of specific gravity in the air-dried state were negligibly small. The variations of acoustic properties and dimensions of the wood against humidity change were reduced markedly because of the decreases of hygroscopicity. By a sensory evaluation test, a violin having a treated bridge was judged to be more bright, sonorous, and less poor, dull, and comprehensively better than the same violin having an untreated bridge. The effect of the treatment was more pronounced when the top plate, bass bar, and sound post were treated in addition to the bridge. The variation in sound spectra and the decrease in tuned frequency of violin against humidity change diminished as a result of the treatment.