Broadband muffler with acoustic bright and dark modes for refrigerator noise control

Abstract

In the present paper, a system composed of a two-port waveguide and two quarter wavelength tubes (QWTs) with different cross section sizes is proposed. The narrow tube performs the dark mode and the wide tube plays the bright mode. Perfect absorption can be achieved at the optimal interval between the tubes when sound waves are incident from the port close to the narrow tube. Besides first order resonance, the system with two QWTs has more high-order resonances in the concerning frequency range, which is demonstrated by simulation and verified by experiments. A strategy of resonance frequency tuning is further adopted to develop a muffler which can achieve near-perfect broadband absorption. Moreover, the straight QWTs are folded so that a compact structure is obtained. A sample of the muffler is fabricated and tested. A transmission loss (TL) of 5.2 dBA is obtained in the frequency range up to 6400 Hz. Except for the target frequency region, high-order resonances also contribute notably from 1800 to 6400 Hz. The design process is applied to a refrigerator, and noise reductions of 4.2 dBA and 2.6 dBA are achieved in the frequency range up to 6400 Hz on both sides of the compressor compartment. Due to the flexibility of the folded QWTs and distinct contributions of the high-order resonances, an extensive application of the muffler can be expected.