(Top) Schematic representation of the grazing incidence facility used to characterise the liner sample using two sets of three microphones. The duct has a rectangular cross section of height H = 4 cm and a rotating lobe blower is used to introduce flow. (Bottom) The composite plate has been glued over 15 cavities of section 15 × 22 mm² so that there is one cantilever beam per cavity. The height of the cavities is B = 30 mm.