Upright and grand piano actions dynamic performances assessments using a multibody approach

Abstract

The behavior of the highly dynamic mechanical transmission between the key and the strings of pianos remains insufficiently understood. Called action, this mechanism is essential for the instrument playability and touch. Upright and grand piano actions, although based on similar principles, present quite different behaviors. This work outlines two models, one for each action, that have been carried out using a similar multibody approach with equivalent modeling hypotheses. The models take all the moving bodies into account as well as the intermittent contacts geometry and specific force laws. In addition, experimental validation with high-speed camera have been successfully achieved. Simulations of the models allow, among others, to estimate the maximal playing frequency, to discover the bridle strap and butt spring usefulness in the upright piano, to illustrate the fast repetition capability at a halfway keystroke in the grand piano action and to virtually adjust its settings. These results help in understanding the actions functioning and capabilities, and should contribute to a useful tool for piano makers, showing the interest of the multibody modeling approach for demystifying piano actions behavior and performances.