A method for manufacturing a noise-attenuating device comprising a facing sheet having an outer side and an inner side and a cellular core, the method comprising: bonding the facing sheet to the cellular core so that the inner side of the facing sheet faces a first side of the cellular core; and after bonding the facing sheet to the cellular core, perforating the facing sheet, characterised in that perforating the facing sheet comprises abrasive blasting the facing sheet whilst masking the outer side of the facing sheet at locations where the facing sheet is to remain imperforated; producing an abrasive blasting mask by: applying a photosensitive masking material on the outer side of the facing sheet; and selectively exposing the photosensitive masking material to light configured to activate the photosensitive masking material; and wherein selectively exposing the photosensitive masking material to light comprises projecting one or more images (50A, 50B) on the photosensitive masking material, the one or more images (50A, 50B) being configured to cause the formation of one or more holes in the photosensitive masking material in a region not overlapping the structure of the cellular core and substantially avoid the formation of holes in the photosensitive masking material in a region overlapping a structure of the cellular core. bonding the facing sheet to the cellular core so that the inner side of the facing sheet faces a first side of the cellular core; and after bonding the facing sheet to the cellular core, perforating the facing sheet, characterised in that perforating the facing sheet comprises abrasive blasting the facing sheet whilst masking the outer side of the facing sheet at locations where the facing sheet is to remain imperforated; producing an abrasive blasting mask by: applying a photosensitive masking material on the outer side of the facing sheet; and selectively exposing the photosensitive masking material to light configured to activate the photosensitive masking material; and wherein selectively exposing the photosensitive masking material to light comprises projecting one or more images (50A, 50B) on the photosensitive masking material, the one or more images (50A, 50B) being configured to cause the formation of one or more holes in the photosensitive masking material in a region not overlapping the structure of the cellular core and substantially avoid the formation of holes in the photosensitive masking material in a region overlapping a structure of the cellular core. applying a photosensitive masking material on the outer side of the facing sheet; and selectively exposing the photosensitive masking material to light configured to activate the photosensitive masking material; and wherein selectively exposing the photosensitive masking material to light comprises projecting one or more images (50A, 50B) on the photosensitive masking material, the one or more images (50A, 50B) being configured to cause the formation of one or more holes in the photosensitive masking material in a region not overlapping the structure of the cellular core and substantially avoid the formation of holes in the photosensitive masking material in a region overlapping a structure of the cellular core.