| Summary: | A Perforated plate is used as an acoustic absorption material for compressors and acoustic barriers for roads and railways. There are many studies of the perforated plate from the aspect of the acoustic absorption. In this paper, the effect of set positions of the perforated plate on the acoustic natural frequency is considered with the TMM and the experiment. And the reason why the analytical result due to the TMM and the equation of Melling are in good agreement is clarified. From the analytical and experimental results, it is clarified that the smaller the aperture ratio becomes, the lower the acoustic natural frequency becomes with increasing of the hole length of the perforated plate. And the set position of the perforated plate can control the excitation of an acoustic specific mode. And the TMM is useful for obtaining the acoustic natural frequency, because the imaginary part of the acoustic impedance of an orifice obtained by Melling coincides with the analytical result by the TMM.
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