ACOUSTIC PROPERTIES OF BRAZILIAN ROSEWOOD USED FOR GUITAR BACK PLATES

The acoustic properties of Brazilian rosewood (Dalbergia nigra) used f or guitar back plates were evaluated by the free-free vibration method at 20 degrees C and 65% R.H. (relative humidity). After comparing the acoustic properties with those of Indian rosewood (D. latifolia) used for the guitar back plate, German spruce (Picea abies) and western re d-cedar (Thuja plicata) used for the guitar top plate, the acoustic ch aracteristics of Brazilian rosewood were investigated from the viewpoi nt of the effects of methanol extractives. The specific gravity of Bra zilian rosewood was about 1.1, 2, and 2.5 times that of Indian rosewoo d, German spruce, and western red-cedar, respectively. The difference between Brazilian rosewood and Indian rosewood also was observed in th e value of tan delta in the longitudinal direction, and the mean value of Brazilian rosewood was less than that of Indian rosewood by 20%. I n comparison with the German spruce used for the guitar top plate, the mean value of specific dynamic Young's modulus in the longitudinal di rection was 30% less, while the values of tan delta in the longitudina l direction and in the direction perpendicular to the longitudinal dir ection were 15% and 20% less, respectively, which is opposite of the r elationship found between German spruce and maple (Acer spp.) used for the violin top plate and back plate, respectively. Due to methanol ex traction, the oven-dry weight of Brazilian rosewood was reduced by up to 30%, and the value of tan delta in the longitudinal direction as we ll as in the direction perpendicular to the longitudinal direction inc reased linearly by up to 120% with reduction in the oven-dry weight. T he acoustic properties of Brazilian rosewood are affected strongly by the methanol extractives.