Study on the acoustic characteristics of natural date palm fibres: Experimental and theoretical approaches

The present study deals with the acoustic performance of natural fibres originated from the date palm empty fruit (DPEFB) fibres which is mainly considered as agricultural waste. The fibres were processed and fabricated to be sound absorber samples with two different densities of 100 kg/m(3) and 200 kg/m(3) and with thicknesses of 10-40 mm. The normal incidence absorption coefficients of the sound absorbers were measured using an impedance tube based on ISO 10534-2. The effects of fibre density and sample thickness are discussed. The findings reveal that for density of 100 kg/m(3) the absorption coefficient is 0.6-0.8 above 1.5 kHz for the samples with the thickness of 20 mm and 30 mm. For the thickness of 40 mm, the values even reached the value of 0.9. The values can reach 0.7-0.8 above 1 kHz for the density of 200 kg/m(3). Mathematical model using the optimized Delaney-Bazley model with Nelder-Mead simplex method is shown to successfully predict the sound absorption coefficient of the fibre samples. The Johnson-Champoux-Allard model follows the trend of the absorption coefficient, but underestimates the measured data at high frequencies above 2.5 kHz.