Asdrubali F., Pispola G.

Roller blind boxes, also know as blind boxes or roller casings, are quite popular elements in Italian buildings, as total enclosures for the roller blinds; quite frequently the boxes - made of different materials such as wood, PVC, steel plates, expanded clay - show a removable face, for reasons of access and air ventilation. Manufacturers are focusing their attention on the sound insulation performances of such components, in the framework of an overall improvement of window systems, thus better achieving the acoustic design criteria of high-quality building façades. The peculiar acoustical behaviour of the boxes, which are similar to a double panel with a large air gap, is due to the presence of apertures and leaks. An experimental and theoretical investigation was carried out to increase the sound insulation of three plastered steel blind boxes. The basic designs showed not satisfying sound insulation ratings, estimating a value for Rw equal to 31 dB by sound intensity measurements in a reverberation room. A light, sound absorbing inner lining of the casing demonstrated to be even more efficient than a traditional, denser sound insulating treatment (with expanded polystyrene), particularly when noticeable leaks were present at the access faces of the box. Suitable absorbing materials were chosen and compared such as mineralized wood fibres and polymeric foams, achieving up to 7 dB of improvement for Rw. Analyses of the frequency behaviour of the sound insulation and of the intensity maps were performed. The influence of leaks was finally estimated, demonstrating that a proper sealing could, as an optimum, lead to a further 10 dB performance rise.