Given the socio-environmental costs of traditional noise control measures, the transition to sustainable acoustic solutions is a fundamental commitment. In this context, the valorization of locally sourced granular waste offers a promising avenue for improving acoustic conditions in indoor areas. The aim of the present study is to increase the absorption coefficients of a granular-based absorber. Two types of recycled materials were adopted: Expanded Glass beads and Perlite in a range of diameters fixed from 0.25 to 5 mm. The properties of granular mixtures were determined using a semi-empirical approach combining direct and inverse characterization methods. The results show the influence of physical properties, particle shape, and size, as well as binder ratios on the sound absorption performance. They also reveal that mixtures containing a major proportion of large particles tend to exhibit resonant sound absorption behavior compared to samples with higher concentrations of small granules. For an optimized absorption performance, an innovative design approach inspired by acoustic black holes is proposed. This technology has already been numerically verified by simulating the role of decreasing hole profiles in improving the acoustic absorption coefficient of conventional materials. Used on our eco-friendly granular absorber, this technology allows a significant improvement in its sound absorption coefficient over a wide frequency band. It would therefore be appropriate to test its experimental applicability to produce an effective, eco-friendly granular absorbent.