Further empirical data for torsion on bowed strings.

Robert Mores,Jefferson Stafusa Elias Portela

doi:10.1371/journal.pone.0211217

Abstract

Research on bowed string motion focuses on transverse waves rather than 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. Every periodic string release is preceeded 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 while the concept of Schelleng ripples cannot be confirmed and the concept of subharmonics is under question.

Highlights

In bowed string motion transverse waves and torsional waves are excited due to the tangentially applied force at the surface of the string
Torsional vibrations are measured on both sides of the contact point for varying bowing positions on an open cello G string, and are related to the transverse motion of regular Helmholtz cycles
The structural analysis of coexisting vibrations suggests that these are mutually coupled, ready for transformation or submission while arriving at terminations or returning at the contact point. It suggests that the release action provides the main energy impulse for vibrations of both types which will decline fast, i.e. the transverse wave on the bridge side and the torsional waves on both sides

Summary

Introduction

In bowed string motion transverse waves and torsional waves are excited due to the tangentially applied force at the surface of the string. The most recent discussion concludes in the need for more elaborate friction models that could possibly be combined with the already investigated effects of a limited bow width [4]. While these models gain in fidelity, this study seeks to draw some conclusions from experiments and to revisit the relation of general observations and existing concepts. Among these concepts, which relate to torsion, are bow force limits, Schelleng ripples, subharmonics and Friedlander’s instability, limited bow hair width and differential slipping, and friction models

Objectives

Methods

Findings

Discussion

Conclusion