The invention regards an acoustic liner which comprises: a facing sheet that comprises holes, the facing sheet having a porosity and a facing sheet thickness, a backing sheet, and a plurality of cells arranged between the facing sheet and the backing sheet, the cells having a cell depth and each cell defining a cavity. A plurality of internal necks are provided that extend from the inner side of the facing sheet towards the backing sheet, each internal neck being located around a hole of the facing sheet, thereby extending the longitudinal length of the hole. The invention further regards a gas turbine engine with such acoustic liner.