EXPERIMENTAL INVESTIGATION OF THIN ABSORBER BASED ON RESONANCE SYSTEM FOR LOW FREQUENCY SOUND ABSORPTION

• Main Author: NALITA WONGSO (NIM: 23316008), ELSA
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/26919
• Institution: Institut Teknologi Bandung

<p align="justify"> For low frequency absorption, there are constraints on the conventional absorber which in principle requires ¼ wavelength of the sound energy absorbed in the system. It takes a lot of space to apply the system. In case of resonant absorber, such as Helmholtz resonator, thinner absorber can be obtained by coiling the air cavity into the planar plane, which is also know as the coiling up space system. In this study, further analysis for the coiling up space system is reviewed from the shape and geometric properties of the sample. Based on the literature studies, there are several geometric forms of the coiling up space system that is generally chosen and used, namely the form of circular, box, labyrinthine, and zigzag. This becomes interesting to evaluate the deficiencies and the advantages of each <br /> <br /> geometry to get the basic design for better development of a coiling up space system. To meet these needs, some absorption parameters are observed, such as absorption bandwidth, absorption coefficient, frequency design, channeling geometry or tortuosity, and the acoustic parameters involving characteristics impedance and complex wave number. These parameters are obtained by measurement using impedance tube with transfer function method reffering to ISO 10534-2 standard. The results obtained from theoretical studies show that the geometric form of box has the best absorption value. It is because the form produces the largest sound pressure ratio reaching 35,325. From the measurement results show that the geometric form of circular and box performs equally well, but the geometric form of box is more consistent than the other geometric forms. So far, the absorption bandwidth of all geometric forms can be said equal about 44 Hz. Based on the experimental results, the effect of the geometric properties is almost the same in the absorption coefficient of each forms. Longer coil, wider boxshaped <br /> <br /> cross-section, and panel thickness that exceed the neck thickess give a lower resonance frequency. Absorbers that have been developed have a thickness of 1.81 cm or equivalent to an average of 1 / 45.595 wavelength. For conventional absorbers of the same frequency, a thickness of 20.632 cm is equal to ¼ wavelength of the absorbed sound. In other words, the absorber developed in this <br /> <br /> study was able to reduce the thickness of the conventional absorber up to 12.2 times. To increase absorption performance, absorber is added with resistive component and perforation factor. The absorption bandwidth increased 4-fold compared to the absorber without additional resistive components and the absorption amplitude increased twice as much from each geometric shape compared with single channel absorption. <p align="justify">