The invention relates to a thin sound absorbing multi-layer assembly, which is intended, in particular, to reduce interior or exterior noise of a motor vehicle. The assembly according to the invention comprises at least three stacked layers consisting respectively of: a first layer (4) being impervious and having an area weight of between (20) to (100 g/m2); a second layer (3) having an air flow resistance of between (250) to (2500 Ns/m3) and an area weight of between (15) to (250 g/m2); a third layer (2) being an open pored, acoustic spring type layer having a thickness of between (2) to (30 mm) and an area weight of between (50) to (1000 g/m2).