Research and design of broadband muffler based on second-order Helmholtz resonators

Noise has always been a serious factor affecting people's quality of life. The most common sound-absorbing materials are porous materials, which work on the principle that sound waves entering the pores inside the material are subject to air friction and viscous resistance, thus converting sound energy into heat. Porous materials have excellent performance at medium-frequency and high-frequency sound absorption, but a large thickness is needed to control the low-frequency sound waves with large wavelengths, which limits the application of porous materials in low-frequency noise control. In recent years, acoustic artificial structures have become a research hotspot, which can realize exotic effective acoustic parameters based on periodical structure or locally resonances. Acoustic artificial structures provide a new material basis for noise control, in which Helmholtz resonator plays an important role because of its simple geometry. on second-order neck embedded Helmholtz resonators. In order to achieve low-frequency and broadband sound insulation with limited number of units and structure length, the second-order resonator is chosen as the basic structure unit, which has a stronger low-frequency noise reduction capability and has one more high-frequency transmission loss peak than a conventional Helmholtz resonator. The acoustic characteristics and insulation performance of second-order resonators are analyzed through theoretical calculation, simulation calculation and experimental test. Then, based on the theoretical model and empirical rules, a broadband muffler composed of nine second-order resonators is designed by carefully adjusting the geometry parameters of each resonator. The 3D printed resonators are installed on the side wall of a square standing wave tube for experimental measurement. In the experiment, the transmission loss curve of the muffler was measured by the two-load method. The result shows that the design muffler has good sound insulation performance in the frequency range of 267-927 Hz, with the whole transmission loss above 20 dB and the maximum sound insulation up to 60 dB. The experimental result is consistent with the calculation and simulation results. The muffler has simple structure and high practicability, which will have a wide application prospect in noise control engineering.