Model experiments on the ‘‘sawari’’ mechanism: Vibrational behavior of a string with a moving boundary

Abstract

The ‘‘sawari’’ mechanism, seen in some plucked string instruments like Japanese biwa and shamisen, produces the vibration of the string with a moving boundary and results in its unique sustaining tone, whose elaborate tuning is essential in Japanese traditional music. Since a slight change of the sawari surface’s shape strongly affects the tone quality, it is important to examine the relationship between the boundary shape and the consequent vibration in reality. In this presentation, some results of model experiments on a string with the sawari mechanism are reported and discussed. By using a high-speed digital video camera and a piezo-electric pickup, the overall string motion and the local interaction between the string and the boundary surface are experimentally measured under several sawari conditions. The results are analyzed by applying image processing to video data and also time-frequency analysis to acceleration signals, then compared between basic shapes (plain and curved), widths, and shaven depths of the constraint.