The effect of thickness and surface roughness on the absorption coefficient (α) of Aluminum (Al)

Noise is an essential factor in determining various interior elements and machinery, especially those made of metal. The noise level generated by metal is caused by the low level of sound attenuation factor, known as the absorption coefficient (alpha, α) of the metal. Aluminum (Al) metal has the characteristics of corrosion resistance, lightweight, attractive color, and ease of form, so it is popular as a material for various households, machinery, and industrial machinery. This study explains the effect of surface roughness (0.05, 0.12, and 0.15 Ra) and thickness (2, 4, and 6 mm) of Al specimens on the measurement values of absorption coefficient (α). The measurements result show that the average value of α is relatively stable by variations in surface roughness and thickness within the low to medium frequency range (200-800 Hz). Although in general there are increased α values for the high-frequency ranges (1000-1200 Hz), the lowest average of α value occurs in the specimen with the highest surface roughness of Ra 25. Thus, even though the variation in thickness has no significant effect on the α value, the higher surface roughness of Al will reduce the value of the absorption coefficient (α) resulting in higher noise generated.