NOVELTY - The sound absorber has a micro-perforated plate (2) defining part of the air duct. The plate can form one or more side walls of the air duct (1) which has a rectangular section. An integral wall of the duct can be perforated. The plate can alternatively be mounted inside the air duct. USE - For glazing i.e. double glazing panels in building walls. ADVANTAGE - Allows Does not require use of sound absorbing fibers. DESCRIPTION OF DRAWING(S) - Drawing shows sketch view of duct and plate Duct wall 1 Perforated plate 2