Effect of Perforated Aluminum on the Sound Absorption Ability of Calotropis gigantea Fiber Material

An excellent example of plant-based fiber used for noise reduction is Calotropis gigantean (CG). This research aimed to determine the sound absorption coefficient (SAC) value and sound reduction ability of the CG fiber. The fiber was coated with 0.3 mm thick aluminum and perforated with 1, 1.5, and 2.5 mm diameters. Furthermore, Bruel & Kjaer’s Type 4206 impedance tube with a diameter of 100 mm and a thickness of 10 mm was used as the model for the test sample. The sample, which weighed 50 g, was hot pressed in a mold for 10 min at 200 °C, and the test was conducted following the ISO 10534–2 transfer function method using an impedance tube at a frequency of 1/1 octave. The results showed that the test sample without aluminum coating can reduce the SAC by 0.05–0.1 (5–10%) compared to those coated with perforated aluminum. This is because the aluminum surface area is larger than the total hole area that transmits sound to the test sample, so more sound is reflected. Lastly, the uncoated sample’s noise reduction coefficient (NRC) value was larger than that of the coated sample and reduced the overall noise by 28%. This proved that the aluminum hole's diameter affects the noise reduction coefficient. The coated sample can be categorized into two classes, class D for uncoated samples and class E for aluminum coated.