Equivalent fluid approach for the acoustical finite element method: experimental validation for suspended porous absorbers

This study investigates the application of the acoustic Finite Element Method (FEM) programmed by the authors with equivalent fluid modeling to describe porous materials arranged as "acoustic clouds" in a room. A comparison was made between simulated and experimental results. For this purpose, an experiment was conducted in a small rectangular room where polyethylene terephthalate (PET) fiber boards were placed in two different configurations, both of which positioned most of the material away from the walls-resembling real-world suspended acoustic treatments. In this setup, impulse response measurements were performed in both the empty room and the room containing the porous materials, using an omnidirectional sound source and diffuse-field microphones. From the acquired signals, frequency responses were derived and subsequently compared with the numerical results to evaluate the effectiveness of the equivalent fluid model in representing the acoustic properties of the porous material. Through this comparative analysis, it was demonstrated that using the equivalent fluid model is essential for obtaining reliable results when sound-absorbing materials are positioned away from the room boundaries. Consequently, this modeling approach offers practical advantages for acoustic treatment design over other methods, such as directly assigning an acoustic impedance boundary condition to the materials' surfaces.