Vibration mode of Guzheng soundboard with composite structure

  Objective  The structure of the Guzheng soundboard is one of the important factors affecting its vibration performance. The sound quality and tone color of the soundboards with different structures will be different. So far few scholars have studied the vibration and sound characteristics of the common structure of the composite Guzheng soundboard.

  Method  In this study, two modal analysis methods were used to investigate the acoustic vibration performance of the composite soundboard. The experimental modal analysis method was used to analyze the collected excitation signal and the vibration response signal using digital signal processing technology. After data conversion, the frequency response function of the system was obtained, and then the resonance frequencies of each order and the corresponding modal shapes were obtained. Through using computational modal analysis, a three-dimensional model of the composite soundboard was established, discreting it by finite element method, then the resonance frequencies of each order and the corresponding mode shapes were calculated by approximate method.

  Result  The experimental modal results showed that the (0, n) and (1, n) orders could be identified and they were mostly concentrated in (0, n). The (1, 4), (1, 6), (1, 7) and (1, 10) order were composite vibrations that bending along grain and perpendicular grain directions, and they were more difficult to identify. The modal shapes of the composite soundboard corresponding to each order frequency were clear and easy to identify. Compared with the experimental results, the computational modal analysis could identify all orders in the selected order range, and the modal shapes were more uniform and ideal. However, it was difficult to identify individual orders in the experimental modal analysis. The results of computational modal analysis showed significant linear correlation with the experimental modal results, and the correlation coefficient was 0.9996.

  Conclusion  From the results of modal analysis, the modal shapes of the composite soundboard corresponding to each order frequency are easier and more clear to identify than the whole soundboard, and the vibration frequency is also higher. In terms of wood utilization, the composite soundboard is more conducive to saving wood resources than making the whole soundboard. Through the comprehensive comparison of the two kinds of modal analysis results, it is verified that the computational modal analysis is feasible to apply to the vibration modal analysis of the Guzheng soundboard.