Higher-order mode sound waves in an infinite rectangular straight duct can be attenuated using a thin flat partition plate inserted in the duct parallel to its axis. In this study, the performance of the single partition is examined for the (1,0) mode sound wave propagating in the duct. The effect of the partition that varies according to its length and position is confirmed by the experiment and the numerical (BEM) calculation, after the experimental and numerical models appropriately representing the (1,0) mode wave propagation in the duct were constructed. The reliability of these approaches is confirmed by comparing the experimental and calculated results that show good accordance for the sound attenuation caused by the partition. For revealing how the partition affects the sound attenuation, the calculated sound fields (sound pressure distributions) in the duct is studied. When the partition locates close to the duct wall, the effective frequency for the sound attenuation depends on the resonance of the sound in the narrow side of the partition. For the other locations of the partition, the effective frequency seems to depend on the resonance of the (1,0) mode sound in the wide side of the partition. In addition, another mechanism of sound attenuation appears when the phase difference between the (1,0) mode wave in the wide side and the plane wave in the narrow side becomes π. In the latter case, the effective frequency range tends to become wider than the former cases.
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