US Patent 11668236 Acoustic liners with low-frequency sound wave attenuating features

An acoustic core includes an array of resonant cells. The array may include a plurality of coupled resonant cells respectively defining an antecedent resonant space and a subsequent resonant space, with at least one cell wall having one or more wall-apertures defining a pathway between the antecedent resonant space and the subsequent resonant space. The array may include a plurality of high-frequency resonant cells respectively defining a high-frequency resonant space and being matched with respective ones of the plurality of coupled resonant cells. A cross-sectional dimension of the one or more wall-apertures defining the pathway between the antecedent resonant space and the subsequent resonant space may be less than a cross-sectional dimension of the antecedent resonant space and/or a cross-sectional dimension of the subsequent resonant space. The array may include a plurality of partitioned resonant cells that have a partition integrally formed with at least one of a corresponding one or more cell walls and transecting the corresponding resonant space with at least one surface of the partition having an interface angle that is oblique or perpendicular relative to a plane parallel to a top face and/or a bottom face of the array of resonant cells.