<p>This study investigates the influence of voids on the acoustoelastic effect in solid materials, combining both theoretical and numerical approaches. An analytical model based on rules of mixture and the nonlinear elastic Murnaghan model is developed to describe the influence of the voids. Numerical simulations are conducted using ABAQUS/Explicit, where the voids are randomly distributed within the material, and both longitudinal and Rayleigh wave propagation are analysed. The results show that the second- and third-order elastic constants exhibit a nonlinear dependence on void density, with the third-order constants being more sensitive to changes in porosity than the second-order elastic constants. While the acoustoelastic constant remains nearly unchanged for low void densities, the propagation velocity of longitudinal and Rayleigh waves decreases with increasing void density, primarily due to the reduction in the second-order elastic constants. The analytical expressions show good agreement to the observed numerical simulations.</p>