EXPERIMENTAL INVESTIGATION ON ACOUSTIC ATTENUATOR BASED ON PERIODIC HELMHOLTZ RESONATOR WITH EMBEDDED MEMBRANE

• Main Author: Anwar, Khoerul
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/50300
• Institution: Institut Teknologi Bandung

Helmholtz resonator (HR) is widely used as an effective silencer in duct noise control applications. The HR reduces noise at its resonant frequency with a narrow attenuation frequency band. To get a wider attenuation frequency band, HR can be arranged periodically with a certain distance. The extension of bandwidth is a result of the bandgap effect that appears due to the coupling between the resonant frequency of HR and the Bragg reflection that arises from a periodic distance. In this study, an experimental investigation was carried out on the attenuation behavior of the acoustic attenuator based on periodic HR with an embedded latex membrane in each air cavity of HR, which is called the coupled membrane Helmholtz resonator (CMHR). The performance of attenuation is obtained by measuring the HR sample attached to the waveguide using the Transmission Loss (TL) parameter. Measurements were conducted in the hemi anechoic chamber, while HR and waveguide samples were developing by 3D printing technique. The results of the investigation show that the attenuation frequency bandwidth of single HR is around 120Hz while associated TL can be around 10dB. The results are in good agreement with that of analytical calculations and numerical ones. It is also found that a periodic HR consist of 5 HRs with periodic distance of 350mm can produce wider and optimum attenuation bandwidth that is around 456Hz. The presence of membrane inside air cavity of HR in CMHR system can result in addition attenuation peak at higher frequency so that overall attenuation performance improves accordingly. It is observed that attenuation of CMHR exist at around 468 Hz and 712 Hz while attention bandwidth is around 426 Hz and 22 Hz respectively. Such a behavior is affected by membrane properties particularly pre-tension applied on the membrane. Meanwhile, effects of periodic and other properties like periodic distance and membrane thickness (<0.65 mm) on the CMHR behavior are insignificant.