Predicting the effect of microstructural variations in porous sound absorbers on their sound absorption performance using the perturbation method

Noise reduction is one of the most important issues in various industries. Quantifying the variation in acoustic properties is an essential task to improve the quality of products. Porous sound-absorbing materials are commonly applied to reduce noise. Variations in the microstructure of porous materials have a significant impact on variations of sound absorption coefficient. Experimental methods have been used to predict manufacturing variability of sound-absorbing porous materials. However, they take a lot of time and cost. In this study, a perturbation method is applied to predict variations of sound absorption coefficient of sound-absorbing porous materials combined with the homogenization method based on an asymptotic expansion. Properties of microstructure of a sound-absorbing porous material, such as fiber diameter and cell size, are assumed to follow normal distribution and identify the expectation and variance from the observation of microscopic images obtained by scanning electron microscope. Calculated variability of sound absorption coefficient is compared with measured variability and they agree well in the frequency range of interest.