The electromagnetic analogy introduced in the previous chapter is used here to construct an original macroscopic theory of sound propagation, allowing for both temporal and spatial dispersion, in fluid-saturated homogeneous porous media having arbitrary microstructure—including “metamaterials”. The theory can be formulated for stationary random materials, periodic materials, and using different conceptions of the averaging operation (ensemble-average, volume-average). For simplicity, we have assumed that the structure is rigid and motionless, and the propagation occurs along a symmetry axis. The theory will have to be generalized to account for anisotropy, finite dimensions and frame deformations. In Appendix, we show that the preceding macroscopic descriptions in use in literature, leave aside spatial dispersion: this is a warning that the asymptotic two-scale homogenization method, often used to infer them, cannot be fully consistent.