| Summary: | 碩士 === 國立屏東科技大學 === 機械工程系所 === 106 === Kalimba, also known as the thumb piano, is a kind of musical instrument. The coconut shell is dried and processed as the sound box for the speaker. The appropriate length of several steel sheets can be made and attached onto the top of the speaker. When one pulls a piece of steel sheet by thumbs, the kalimba can produce the sound amplified by the sound box. This work uses the kalmba with seven pieces of steel sheets for studying the sound generation mechanism and steel sheet vibration. The sound generation of kalimba can be postulated from the steel sheet vibration to the structure-borne sound interacted with the sound box. This work aims to investigate the kalimba play sound that may correlate to the steel sheet and sound box vibration characteristics. First, Sound Measurement (SM) program is used to capture the kalimba play sound for each steel sheet, respectively. The time response of sound can be obtained and processed to get sound spectrum. The fundamental frequency, overtone frequencies and continuity of kalimba play sound can then be determined. Finite element analysis (FEA) is also adopted to perform modal analysis and harmonic response analysis on the steel sheets, so as to get modal parameters and frequency response function (FRF). Base on the sound measurement data, the steel sheet FE model can be calibrated by adjusting material properties and equivalent to the real structure. The sound box with the air and structure interaction effect is considered and performed vibro-acoustic coupling analysis. From the modal characteristics of sound box as well as its interaction with air, one can distinguish the structural vibration modes and air-structure coupling modes. In particular, the air cavity mode will largely affect the kalimba play sound. The size of open hole of sound box is modified to show the effect of air cavity mode by FEA and verified by experiment observation. This work presents the sound measurement, steel sheet and sound box structural modal analysis, and sound box with air coupling sound field analysis as well as experimental approaches in sound and vibration measurement to study the kalimba play sound. The developed numerical and experimental methodology can also be applied to other musical instruments.
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