Beat period control of bell sound using an operational modal analysis

Abstract

Beats in the sound of a ringing bell areperiodic variations in volumethat aregenerated by a slight asymmetry of the bellstructure. However, beat periods are often too long or short due to uncontrollable elements in the bell-casting process.To optimize the beat period, beat tuning is performed after bell casting using the mode data of the bell. In the case of a large oriental bell, which is sounded by striking it witha heavy wooden hammer,mode data should be extracted only using theresponse data such as acceleration or sound pressure. In this study, we introduce abeat-tuning methodusingthe operational deflectionshape (ODS)fora large Orientalbell.Using the ODS, we extract the frequency and mode pair,which causethe beating sound,and we tunethe beatperiod of thesound througha structural modification technology.