A structure which absorbs low-frequency sound comprising a perforated skin, a box having two lateral walls in the shape of a strip, that delimit between them an opening, and a bottom opposite the opening connecting the two lateral walls, the lateral walls becoming closer together with increasing distance from the opening to the bottom. The box is attached to the skin at the opening. Each lateral wall extends width-wise between the opening and the bottom. Each box has two tongues, each tongue being strip shaped, extending lengthwise over an entire box length, and width-wise between the opening and the bottom of the box. Each tongue has a first end attached along an edge of the opening and a second, free end which extends towards the bottom, becoming closer to the second end of the other tongue, where each tongue has an arcuate shape along its length.