Application of a Helmholtz structure for low frequency noise reduction

In this work, we numerically investigate the existence of low-frequency band gaps in the Helmholtz resonance structure. Finite element method is utilized to calculate the band structure and transmission spectrum. Three band gaps and two neighboring partial band gaps are found from 0 to 4000 Hz. Geometrical parameters which may affect the band gap width or positions such as the inlet width and length are analyzed. Results indicate that the first band gap will become wider and higher with the increase of the inlet width of the resonators. However, variation trend of the first band gap is completely opposite when inlet length becomes longer. Calculated transmission spectrum validates the band structure well. This designed and calculated structure has potential application in the low-frequency noise reduction. (C) 2015 Institute of Noise Control Engineering.