Review on attenuation methods of low-frequency noise in passive silencers

Noise reduction in various industrial and building systems such as ventilation ducts, vehicles, wind tunnels, and test facilities for jet engines, automobiles, and factories has always interested engineers, especially the problematic noise reduction at low frequencies. This problem is even more important with passive silencers, which require absorbent materials and more space. Passive silencers include reactive and dissipative silencers. Among reactive silencers, Helmholtz resonators, expansion chambers, flute-like, drum-like, and plate silencers have proven effective at low frequencies. Combining some of these silencers with a dissipative silencer, called a hybrid silencer, can achieve excellent performance at a wide range of low to high frequencies. In these silencers, the reactive part reduces noise at low frequencies, and the dissipative part reduces noise at medium and high frequencies. The aim of this work, which focuses more on experimental studies, is to introduce the mentioned silencers, investigate the presented methods to improve the performance of these silencers at low frequencies, and offer the practical advantages and disadvantages of these methods.