Aspects of the disclosure are directed to a structure comprising: a plurality of cells, a first non-permeable insert in a first cell of the plurality of cells, the first insert configured to constrict, by at least a first threshold amount, a flow of fluid in the first cell such that: acoustic power over a frequency range is attenuated by the structure by at least a second threshold amount, and a resonant frequency associated with the structure is shifted by at least a third threshold amount.