Comparison of acoustic absorption characteristics of coir and date palm fibers: experimental and analytical study of green composites

The use of natural biodegradable fibers in manufacturing of porous sound absorbers is an environmental-friendly approach employed by many researchers in the field of noise control and acoustics. The present study aimed to determine and compare the sound absorption coefficients of samples fabricated from fibers of coir and date palm by experimental and analytical methods. Experimental measurements of the sound absorption coefficients were performed in an impedance tube by modifying several parameters (thickness and air gap) of the samples. Prediction of sound absorption coefficient was determined by Delany-Bazley, Miki and Johnson-Champoux-Allard models along with differential evolution algorithm in MATLAB software and data from the experiments. The correlation between the sound absorption coefficients obtained from the experiments and the ones predicted by the existing models was examined by the Pearson correlation test. Samples from both type of fibers showed a poor and almost similar sound absorption in low-frequency range. In intermediate range (1000-3000 Hz), the sound absorption significantly increased to the maximum levels of 0.81 and 0.84 at 2000 Hz for the thickness of 40 mm. An increase in the samples thickness led to a fair agreement between values of sound absorption coefficient obtained from experimental and analytical methods. Correlation analysis showed that there was a significant and strong correlation between the outputs from the existing models and the experiments. The values approximated by Johnson-Champoux-Allard model demonstrated a better fit with the ones determined by the experimental tests.