Changing the vibrational behavior of the wooden thin arched plates—The maestro violins experimental study case

From a constructive and functional point of view, the violin body is a structure with thin walls having the role of amplifying the musical sounds and consists of an arched top and back plates, the ribs and the linings with thicknesses about 100 times smaller than the overall dimensions of violin body. The present research proposes to investigate: (i) the modification of the vibrational properties of the wooden arched thin plates in different stages of violin construction: as individual plates in preparation stages, then assembled in the violin body, after the addition of the neck and finally, as finished product; (ii) the influence of the plate thickness change on their vibrational behavior. The following dynamic properties were studied: frequencies of twisting mode #1, bending mode #2, ring mode #5 in case of unattached plates, frequencies of cavity mode (A), corpus bending modes (CBR), main body resonance (B), dominant frequency (extracted using Fast Fourier analysis from the sound signal) and quality factor which corresponds to dominant frequency. The change in the dynamic behavior of the plates during the manufacture of violins was statistically investigated using Discriminant Function Analysis. The research results showed that the top (spruce wood) and back plates (maple wood) have a very different vibrational behavior from each other due to wood species features. Changing the thickness of the plates by ±0.6 mm compared to the reference thickness leads to changing the frequency response of the back plates (maple). The thinner the plates, the more obvious the difference between the top and the back plate is, in terms of the maximum frequency. The stiffening of the plates mainly affects the quality factor of the sound oscillation damping, and the addition of the neck reduces the quality factor. Dynamic rigidity and frequency in cavity mode react most quickly to changes in plate thickness.