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Abstract: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.

The sawari is an instrumental mechanism of biwa and shamisen. Its physical structure involves a solid surface of very small size that the vibrating string touches dynamically, creating a peculiar timbre in the produced sound. This paper proposes a model of the sawari mechanism, which is a unilateral constraint on the displacement of a string, that is, a mechanism that is essentially nonlinear and time-dependent because of contact/separation phenomenon. Here, the key point of the model is the repelling force caused by the lateral elastic deformation of the string. The study is focused on the dynamic effect under an idealized problem setting so that the string vibrates at no loss of mechanical energy without any interaction with other objects such as a resonator that terminates the string in the real instrument. A numerical method is given for the computation of this problem. The numerical results show a gradual build-up of high-frequency oscillations that eventually prevail over the entire string motion. The short-term spectrum changes in a continuous way with time, maintaining a nearly harmonic structure on the fundamental frequency of the associated sawari-free problem.

The biwa is a family of Japanese lutes that have been played for more than 1000 years. This paper reports some measurements on the vibro-acoustic characteristics of several biwas of different types. The main concern is the similarity and difference of the fukuju-to-table transfer mobilities among the individual biwas. Here, the fukuju is a kind of bridge whose shape and way of installation differ distictively from those common to the majority of other lute families found in many countries in the past as well as in the present time. The measurement revealed that in most cases the fukujus have two major vibration modes, to be labeled the ‘‘twist’’ and ‘‘flap’’ modes, with the corresponding resonance frequencies in the regions of about 0.9 to 1.2 kHz and of 1.4 to 1.6 kHz, respectively, though the exact figures depend on the physical size and shape. Their resonance property takes an important roll to determine the fukuju-to-table transfer mobility as the coupled vibroacoustic system with the table. The fukuju-to-table mobilities were compared with the spectra of the corresponding plucked sounds.

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