The build-up of the glazing unit matters, but noise can also pass through joints, gaps or inadequate perimeter sealing. That is why air tightness, the gaskets, the geometry of the system and the quality of installation all count.
In demanding applications, asymmetric or special laminated build-ups can be used, depending on the noise spectrum and on the aim of the project.
Acoustic performance is decided neither by the thickness of the glass nor by a single number. It is declared as Rw together with two adaptation terms: C for high frequencies and Ctr for traffic noise, which has more low frequencies — next to a main road it is Rw + Ctr that counts. In practice what works is an asymmetric composition, laminated glass with an acoustic interlayer, and a wider cavity where the profile allows it. But sound passes through the weakest point: an Rw 40 dB window next to an uninsulated roller box or an unsealed joint performs far worse.