抄録
The experimental research on the acoustical property of Japanese bell subjected to local loading is presented. The objective of this research is to find the method adjusting the frequency of beat and the duration of remaining tone. Two Japanese bells, so called "Hansho", are used, the one is commercial one and the other is specially made without any character and figure on the surface of the bell. The measurement is carried out as follows; the bell is set in resonance by means of a vibrator controlled by oscillator, and the vibration of the bell is detected by two pick-ups, the one is directly connected to a dual syncroscope and the other through a frequency counter to the same syncroscope. The nodal lines can be determined by comparing the phase difference of the two signals. The natural frequency of the bell is measured by the frequency counter connected to the in-put side of the syncroscope. The frequency of beat and the half life of the remaining tone are obtained from the oscillogram of the bell sound recorded on sound tape. The load is applied in the following way; 1) equally distant four points below the so called "Koma-no-Tsume" hoof, especially, on the H nodal line, L one, and intermediate one of the fundamental tone, 2) a point moving on the circle of the hoof, 3) fifteen points on the bell surface, especially, on the H nodal line, L one, and intermediate one of the fundamental tone. The loading mass is varied from 50g to 200g. The following results are obtained. 1) In general, the natural frequency is lowered by loading the bell. The fundamental tone is affected by loading to the lower part of the bell, and the over tones by loading to the upper part. 2) When the loading is applied on the H nodal line (or L) of the fundamental tone, the L frequency (or H) varies remarkably larger than the H one (or L). Consequently, the beat frequency, that is, the difference between the H and L frequencies, can be controlled. 3) The character and figure scribed on the bell surface seems to affect the over tones, but hardly the fundamental one. In addition, the thinner is the wall of the hoof, the stronger the bell vibrates. 4) The above behavior takes place clearly in case of bell without charactar and figure.
