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This study presents a novel passive noise control approach to directly suppress sound radiation from an axial-flow fan, which involves micro-perforated panels (MPP) backed by cavities and a hollow tube. Apart from the sound suppression performance in terms of insertion loss, sound quality of axial fan with a dipole nature is also investigated which serves as a significant supplementary index for assessing the noise control device. The noise suppression is achieved by the sound cancelation between sound fields from the fan of dipole nature and sound radiation from a vibrating panel via vibro-acoustic coupling and interference from the hollow tube boundaries, as well as by sound absorption in micro-perforations. A two-dimensional theoretical model, capable of dealing with strong coupling among the vibrating micro-perforated panel, sound radiation from the dipole source, and sound fields inside the cavity and the duct is developed. The theoretical results are validated by both finite element simulation and experiment. Results show that an addition of hollow tube enhances the sound suppression performance in the passband region of the MPP housing device. The findings of the current research have the potential to control ducted-fan noise effectively, to enhance the quality of products with a ducted-fan system.

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