Integrated adjustable acoustic metacage for multi-frequency noise reduction

Effectively controlling the multi-frequency noise of engines while keeping air flowing is of great significance for power machines. This article presents an adjustable acoustic metacage to attenuate multi-frequency noise from diesel engines while maintaining high-flow ventilation. The metacage consists of combined reflection and ab-sorption units to achieve reverberation attenuation, with nested C-shaped unit cells forming the reflection units and microperforated panels with porous material infills forming the absorption units. The frequency of the reflection unit can be tuned by changing the relative angles of C-shaped rings. Firstly, we present a prototype of the acoustic metacage and explore the acoustic properties of the nested C-shaped unit cell. Secondly, we demonstrate the superiority of the proposed design in attenuating power machines' noise by comparing various schemes of the acoustic metacage and investigate the influence of the sound absorption coefficient of the absorption part. Finally, taking an 8 kW diesel generator as example, we optimize the metacage using the genetic algorithm and experimentally verify its performance, the insertion loss (IL) at two noise peaks reaches 13.2 dB and 18.4 dB, respectively, with an average IL of 8 dB in 100-500 Hz, while retaining a ventilated area of 25 %.