Sound absorption of macro-perforated additively manufactured media

Using macro-perforations in a generic porous media may not only make the resonance frequency of a rigidly backed sound absorber lower but also its sound absorption amplitude increase. Given the rise of 3D-printing in the field of acoustic materials over the last years, it turns out of great interest to explore the possibilities of this technology on the fabrication of these absorbers. Unlike conventional fabrication processes, additive manufacturing lets design the material at the microscopic scale, thus allowing choosing the appropriate geometrical dimensions of both the macro-perforations and the micro-pores that let enhance its sound absorption. In this work, a preliminary insight into the use of additive manufacturing technology for the fabrication of macro-perforated porous media for sound absorption is reported. For this purpose, several specimens having different pore sizes and porosities in the microporous medium were produced and tested in an impedance tube. Experimental results showed an improved absorption performance for those samples having macro-perforations. Additionally, predictions through the double porosity theory together with the JCA approach using macroscopic parameters obtained by an inverse characterization procedure were compared to the absorption measurements showing a good agreement. This research suggests that the use of additive manufacturing technology may provide an excellent workbench for the optimal design of such absorbers. This work was developed in the framework of the COST Action CA15125 - DENORMS: “Designs for Noise Reducing Materials and Structures”. J. M. M-J. and L. P. M. acknowledge partial financial support from the Spanish Agencia Estatal de Investigación (AEI) and European Union (FEDER funds) through grant MAT2016-77742-C2-2-P.