Temporal Variations in the Acoustic Performance of Bio-Based Sound Absorbers

Sound-absorbing materials made from biomass are becoming the subject of interest for scientists who search for sustainable alternatives to conventional sound-absorbing materials. At the same time, experimental data on the time dependence of the sound-absorbing properties of such materials is rather scarce. In the current research, the time dependence of the acoustic performance of a biomass sound-absorbing material manufactured from the waste product of sweet passion fruit processing is studied. Four tests were performed under laboratory conditions over approximately 2.4 years. The normal-incidence sound absorption coefficient was measured using an impedance tube, and temporal variations were evaluated using the Acoustic Durability Index (ADI), defined as the ratio between the area under the sound absorption coefficient curve at each measurement campaign and the corresponding area at baseline. It is noted that the nature of changes in thickness and tested surfaces differed. It proves the fact that the response did not depend on time in the same way for the examined cases. The results serve as experimental proof of the alterations in the acoustic properties of the bio-absorber under investigation while being stored in the laboratory. In the case of only a few measurement procedures and one specimen per configuration, the described changes are considered descriptive and cannot be taken as evidence of any degradation processes.