Correlation of Normal Incidence Sound Absorption Coefficient (NAC) and Random Incidence Sound Absorption Coefficient (RAC) of Polyester/Ramie Fibre Composite Materials

The acoustical properties of polyester/ramie fibre composite materials that was applied as a sound absorbing material is discussed in this paper. The aim was to determine the correlation between Normal Incidence Sound Absorption Coefficient (NAC) and Random Incidence Sound Absorption Coefficient (RAC) of the fibre composites. The acoustic measurement with Impedance Tube Kit followed the ASTM 1986 E - 1050 - 98 standard. The portion of the ramie fibre was modified with fibre length varied from 0.25 cm, 1 cm to 1.5 cm but at a constant fibre diameter. A constant volume fraction of fibre 20 % was used.The Beevers method was applied to characterize the fibre's diameter. Results indicated that the sound absorption performance of the composite fibre can reach as high as 99% at frequency of 1225 Hz at aspect ratio of 42. A correlation between NAC and RAC was presented based on a quantitative result.