Enhanced Low-Frequency Noise Control in Ducts through Perforated Back-Cavity Acoustic Liners

This study addresses the challenge of broadband noise control with very strong low frequency components, such as below 200Hz. We consider a duct lining with a perforated wall facing the external environment. Finite element simulation and experimental verification show that this method can significantly improve the low-frequency sound absorption, and achieve true wideband sound absorption, e.g. 100-8000Hz. The perforated wall allows extra particle velocity within the cavity, while the acoustic energy leakage through the wall to the outside is found to be insignificant in the parameter range of our interest. The method may find potential applications in HVAC system and aero engine cabin where low frequency noise is prominent.