A silencer design and analysis of the effect of silencer perforation towards resonant frequency and insertion loss in a duct

A silencer model was designed for application to HVAC systems, specifically for noise control in ducts. The goal was to see how the perforation of the silencer affected the resonant frequency and Insertion Loss (IL), as well as analyse physical phenomena that occurred in system. The materials used were 1/2-inch PVC pipes 5 cm in length and acrylic with a thickness of 2 mm used as the silencer frame. The varied parameters were the amount of PVC pipes (percentage of silencer perforation) from 0 holes (no perforation) to 10 holes. It is concluded that perforation affects the resonant frequency through changes in acoustic mass and affects the IL through acoustic resistance. It is inconclusive whether the resonant frequencies generated affected IL. It is assumed that negative valued IL observed at lower frequencies occurred due to resonance between the sound and duct (structure-borne sound) which increased sound pressure level, or that these may be the actual resonant frequencies generated. Further research is needed to study the generation of resonant frequencies and structure-borne sound in the system, study airflow and thermal performance of a HVAC system when the silencer is applied, the transmission loss (TL) of the silencer and optimisation of the design to improve low-frequency sound attenuation.