Park, Mun Hum

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Park, Mun Hum
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Park, Munhum
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Email
munhum.pa@kmitl.ac.th

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    Item type:Publication,
    The presence of Helmholtz resonance modulates the modes of circular membrane
    (2020-08-23)
    Toboonchuay, Kajornpop
    ;
    Park, Munhum
    A Helmholtz resonator with a circular membrane is a structure that represents a number of real-life systems: For example, kettledrum with hole, the instrument body of Asian spike fiddles (e.g. Thai Saw-u and Cambodian Tro-u), and some acoustic energy harvesters. In the current study, two coupled equations governing the motions of the membrane and that of the air mass in the sound hole were established and solved based on simple assumptions. It was shown that the resonance frequencies corresponding to the circular modes of the membrane were shifted in the presence of the Helmholtz resonator. Furthermore, an additional circular mode could be observed at the frequency lower than the Helmholtz resonance frequency. To validate the theoretical prediction, an experiment was conducted by using a 3D-printed drum, where the frequency response was measured with an impact hammer and a laser doppler vibrometer. It was found that both the additional resonance and the shift in the existing membrane modes could be observed, which agree well with the predicted values.
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    Helmholtz resonator coupled with circular membrane
    (2024-05-15)
    Park, Munhum
    ;
    Toboonchuay, Kajornpop
    ;
    Rattanangkul, Pairoj
    The Helmholtz resonator is an old yet highly versatile model of various structures. The conventional form of this resonator with rigid surfaces has been extensively studied, and its characteristics are well understood. In many cases, however, the resonator consists of flexible surfaces that readily respond to the changes in the cavity volume, where recent examples include the base structures for acoustic metamaterials and energy harvesters. In the past, several models, including the two-degree-of-freedom lumped-element models, have been proposed to describe the acousto-mechanical coupling within the membrane-coupled Helmholtz resonator (MCH). However, the predictive scope of the previous models was limited only up to the first two modes of vibration, or they were relatively complicated to implement, offering little insight into the relationship between model parameters and output. In this study, a classic model of the circular membrane fitted to an air-tight cavity was modified and extended to predict the resonance characteristics of the MCH. By solving the equations that describe the transverse wave on the membrane and the motion of the equivalent air mass in the port, a conditioning formula was derived, with which the resonance frequencies could be estimated not only at the first two but also at higher modes of vibration. Moreover, the model was found to provide a unified framework for understanding the resonance characteristics and modal patterns of the three related systems: The circular membrane, the circular membrane with air-tight cavity, and the MCH. When validated in a measurement, the proposed model could reasonably predict the resonance frequencies up to the fifth mode of vibration, above 1.5 kHz, where the prediction accuracy was either comparable to or higher than some previous models.