Noise attenuation performance improvement by adding Helmholtz resonators on the periodic ducted Helmholtz resonator system

The transmission loss achieved by a periodic ducted HR system is depended on the structure and the number of HRs. However, the number of HRs is restricted by the available space in longitudinal direction of the duct. Moreover, such system will occupy a large space and may have some spare space in the transverse direction of the duct. By adding HRs on the available space in the transverse direction, a modified ducted HR system is therefore proposed. The wave propagation in the periodic ducted HR system and the modified HR system are investigated theoretically and numerically. The transfer matrix method is developed to conduct the investigation. The predicted theoretical results fit well with the Finite Element Method (FEM) simulation results. The results indicate that both the noise attenuation band and peak amplitude are increased by adding HRs on arbitrary side of the cross-section of the duct. The proposed modified ducted HR system can improve the noise attenuation performance and fully utilize the available space, and it is practical to be used in an actual ventilation ductwork system.