The AWS 90 AC.SI is a window system for buildings in areas with high levels of noise pollution. The perpetual dilemma in such cases is whether the windows should be kept closed for sound insulation, or whether to tolerate the noise in order to ventilate, and this acoustic window presents a practical solution. In the sound insulation tilt position, air from the outside is directed over the pre-assembled ventilation cassettes installed in the top blind frame. This way the sound is muffled and noise distraction reduced drastically by up to 34 dB, depending on the type.