Vibratory and acoustic characteristics of automatically performing bell

An automatically performing bell system, which informs the specified time with music, has many types of bell configuration and arrangement. The first requirement for the bell system is to tune the fundamental resonance frequencies of each bell to an equal temperament of scale. Finite Element Method (FEM) was applied to determine the natural frequencies and mode shapes of the axisymmetric bell. Experimental evaluation was also carried out to examine the accuracy of the FEM calculation. Moreover, measured result showed the existence of the two orthogonal modes of which frequency difference was very small. This frequency difference generates the beat sound of the bell, which is desired to be reduced in playing music. The optimal circumferential impact point is investigated to minimize the beat sound. Boundary Element Method (BEM) was applied to investigate the acoustic radiation properties of bell eigen modes. Based on this result, bell was approximated by the point sound source with specific radiation directivity and the reflection and absorption at the wall and ground are taken into account. The waveform of sound pressure radiated from the vibrating bell is simulated by use of this point sound source and transient response of the bell eigen mode. Calculated sound waveform was compared with the detailed BEM analysis to confirm the accuracy of this method.