Curtain wall system is such a complex external envelope of the building . It is more than an enclosure but also to serve to reduce heat gain and sound proof. The evaluation of heat gain is commonly considered by the amount thermal transfer in the energy unit. Nevertheless , lesser attention is given to the acoustic consideration . Thank to my friend Dr Man and our peers Lixil who shares me one table. The airborne acoustic reduction is considered by STC value which varies as per the glass panes composition and thickness of glass. STC is to measure the degree of decibel reduction. The reduction is further related to the hertz of sound transmission. For easy communication , each composition of glass panes will be assigned the STC value. The interesting observation is that the “laminated glass” is achieving similar STC value compared to similar glass panes thickness of “insulating glass unit”. Furthermore , A 12mm thick single panes can achieve similar STC value to 6+12+6 insulating glass unit. Indeed, there are more consideration to the curtain wall acoustic including the impact-borne sound transmission caused by impact to the mullion or transom . Sometimes, the provision of the noise barrier or the provision of the balcony projecting out from the external facade can help to reflect the unwanted sound such as traffic away.