Measured changes in the bridge mobility and radiativity of violins due to material creep following tensioning of strings
Seth Lowery, Andrew A. Piacsek · The Journal of the Acoustical Society of America · 2023
Violins have been observed to undergo a small, but measurable, deformation of the corpus after being brought into tune following a prolonged period without string tension. This behavior, which is analagous to the flexing of a bow, can be attributed to the viscoelastic properties of wood. Because of the relatively long time scale of deformation, the process is sometimes referred to as material “creep.” To assess the impact of creep on the sound of a violin, we measured the vibrational and acoustic response of multiple violins during this period of deformation. The measurement process involves tapping the bridge with a small modal impact hammer and recording the velocity response of the top plate using a laser Doppler vibrometer, as well as the far-field acoustic response in an anechoic chamber. Results show modest changes in the amplitude of the main body modes, most notably the CBR and B1- modes, and a consistent shift in the peak frequency of higher modes, over a two-day period after the strings were tuned.