Acoustical analysis on the sawari tone of Chikuzen biwa

The sawari is an instrumental mechanism of a certain class of stringed instruments so that the string touches to it repeatedly when vibrating. The Chikuzen biwa is one of Japanese plucked stringed instruments; it is equipped with a sawari which is a narrow strip of surface on the top of shirabeguchi (the nut). It is known that only a minute change in the shape of this surface results in a large difference in the quality of the resulting “sawari” tone. This paper studies the sawari tone under different grades, or strengths, of the sawari created by shaving the top surface of shirabeguchi differently with masterly craftsmanship, together with one without sawari (no shaving at all), using an excellent Chikuzen 5-stringed biwa, to compare quantitatively the effect of the degree of shaving on the resulting sound. The analysis shows the temporal development of the amplitudes of up to 24th partials for open strings under each of the above-mentioned sawari conditions. The sawari effect appears in two aspects: (1) to intensify the partials of 6th to 20th and up, and (2) to elongate their durations.