Observation of torsion on bowed strings

Abstract

Research on bowed string motion focuses on transverse waves and not so much on torsional waves. These are believed to play only a minor role for stabilizing vibrations and no role for perception. Here, torsion is measured on both sides of the bow contact point for a variety of bridge-bow distances on a cello string. Electromagnetical and optical measurements correspond. Every periodic string release is preceded by a reverse torsional motion independent from bowing position or dynamics. Transverse and torsional motions are coupled and there are cases of stabilization, but also cases of perturbation or surrender. Structural and timing analyses of torsional waves suggest that the earlier concepts of differential slipping can be essentially confirmed. Other concepts cannot be confirmed, such as the Schelleng ripples, or are under question, such as the concept of subharmonics.