The mechanics of the soundpost in the violin

The violin soundpost, a small cylindrical rod of wood wedged between the front and back plates of the violin body, serves a crucial — if incompletely understood — role in violin acoustics. Although violin makers take great care to ensure its set-up optimises the instrument’s sound, our understanding of its mechanics and precise acoustical function is still evolving. This thesis closely examines all aspects of soundpost set-up — specifically, tightness, fit, and position — and draws on the foundations of existing research to develop a new simplified theoretical model of the soundpost that substantially improves its modelling capability. The model, in which the tightness and fit of the soundpost are modelled by axial and bending springs that couple the soundpost to the plates, has been used to carry out extensive and systematic parameter studies of the effect of soundpost coupling strength on the dynamics of the plates and on the soundpost itself. Representing a significant addition to previous modelling, a simplified model of the violin bridge is also developed and used in conjunction with our model of the violin body and soundpost. Providing for the ability to locate the driving force at each of the four strings, it illuminates questions pertaining to the ‘balance of the strings’. We examine results which demonstrate that driving at the different strings influences the magnitude of the body resonances. The radiated sound pressure generated by the model is estimated and used to assess ‘loudness’ for a given configuration of the soundpost. We conduct extensive parameter studies involving variations to the stiffness of the axial and bending springs, and to the location of the soundpost, to demonstrate the ‘optimal’ location for the soundpost at which radiated sound pressure is maximised. It is concluded that an asymmetrically placed soundpost is favourable in terms of boosting sound radiation at low frequencies, demonstrating agreement with the positioning of the soundpost in a real violin. Finally, a physical model of a simplified violin body is developed and compared to our theoretical model. The bending vibration of the soundpost is directly measured by an accelerometer, and a specially designed adjustable soundpost is used to investigate the effect of ‘tightness’ on the dynamics of the body.Engineering and Physical Sciences Research Council (EPSRC