Acoustical optimization of a roller blind box

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. The boxes quite frequently show a removable face, for reasons of access, and in some cases air ventilation vents. The peculiar acoustical behaviour of the boxes is due to the presence of apertures and leaks and for this reason manufacturers are focusing their attention on the improvement of their sound insulation performances. An experimental investigation was carried out by sound intensity measurements in a reverberation room to determine the sound insulation of various steel blind boxes. The initial design showed not satisfying sound insulation ratings. A light, sound absorbing inner lining of the casing demonstrated to be even more efficient than a traditional, denser sound insulating treatment, particularly when noticeable leaks were present at the access faces of the box. Suitable absorbing materials such as mineralized wood fibres and polymeric foams were chosen and compared achieving up to 5 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 lead up to a further 10 dB performance rise.