27/09/19
1) Thickness of the window. The level of insulation depends on how big is the distance between the glasses. With increasing distance between them, noise protection will be improved.
2) For double-chambers windows it is better if the distance between the glasses is different. The inner glass must be located not strictly in the middle, but closer to one of the two end glasses. Thus, the resonant frequency in air cavities are not aligned and summed together.
3) Thickness of the glass. The thicker the glass the better. In addition, if they are of different thickness, it will also affect the level of noise reduction.
4) Presence of gaps between the wall and the window profile. The gaps between the frame and the wall should be minimised because cracks reduce the level of sound proofing.
You should not ignore the possibility of balcony glazing. This will greatly reduce the noise from the street!
Choosing the glazing, we should not strive for the highest possible performance. The choice should be optimal balance of price and efficiency.