Abstract: A passive sound absorber includes a cavity opening to the outside via an input direction to form a Helmholtz resonator for a first frequency. The absorber further includes at least one moving element, or wafer, suspended or held by suspensions in a position obstructing the neck in a non-sealed manner. The relative stiffness of the suspensions and the wafer is determined so that the assembly resonates in a vibration in a “piston” movement at a second frequency different from the first frequency, achieving absorption for this second frequency or frequency range. A hybrid version includes a coil that is controlled to adjust the acoustic impedance of the absorber. An acoustic wall includes a plurality of such absorbers produced by a repetitive structure opening through perforations, each receiving such a wafer, and a method of designing and manufacturing such an absorber or wall is also provided.

Abstract: A passive sound absorber includes a cavity opening to the outside via an input direction to form a Helmholtz resonator for a first frequency. The absorber further includes at least one moving element, or wafer, suspended or held by suspensions in a position obstructing the neck in a non-sealed manner. The relative stiffness of the suspensions and the wafer is determined so that the assembly resonates in a vibration in a “piston” movement at a second frequency different from the first frequency, achieving absorption for this second frequency or frequency range. A hybrid version includes a coil that is controlled to adjust the acoustic impedance of the absorber. An acoustic wall includes a plurality of such absorbers produced by a repetitive structure opening through perforations, each receiving such a wafer, and a method of designing and manufacturing such an absorber or wall is also provided.