Acoustic absorber, acoustic wall and method for design and production

An acoustic absorber device, notably passive absorber, comprising:

• an enclosure delimiting a cavity opening outwardly into an inlet direction through at least one orifice passing through a front wall of a determined thickness, thereby forming a neck having a determined opening surface and a determined length, the dimensions of said enclosure and said neck being determined to together form a Helmholtz resonator for a first frequency or frequency range, called natural frequency;
• at least one mobile element, or wafer, is suspended to said enclosure by one or more mechanical connections, or suspensions, in a position partially obstructing said at least one neck, i.e. unsealed on all or part of its stroke;
• and
• the stiffness of the suspensions and the stiffness of the wafer are determined in their combination, particularly in their ratio, so that said wafer vibrates in a “piston” type resonance mode along the direction of the incident wave, at a second frequency or frequency range different from the first frequency, particularly lower, thereby achieving absorption for this second frequency or frequency range.