Low-frequency ultra-broadband ventilated muffler based on a resonance-labyrinthine metamaterial

We present a theoretical and experimental study of a ventilated metamaterial muffler operating at a low-frequency range. The muffler combines two Helmholtz resonance cavities with the spatial labyrinthine microstructures to achieve a large bandgap. A central hole ensures efficient air circulation. The adjustable cavity allows for precise control over the performance and bandwidth of sound insulation. By cascading multiple metamaterial units, the muffler exhibits a large transmission loss with broad bandwidth. Both simulations and experiments demonstrate transmission loss is over 10 dB in the frequency range from 230 Hz to 816 Hz. The overall dimensions of the muffler are 216 mm in length and 15 mm in diameter, much smaller than the operating wavelength. The high-efficiency sound insulation under the ventilation condition originates from local resonance with labyrinthine structures. This muffler exhibits potential for diverse applications in the field of acoustic engineering, where there is a demand for simultaneous noise reduction and ventilation.