the studio windows are the challengers of studio sound transmission prevention.....if not constructed well ,will allow sound to pass from 1 room to another.
using 2 glasses of unequalled thickness,resonation is prevented and the huge air gap between glass dissipate the sound...bear in mind that the integrity of the glass wall structure is PARAMOUNT for success.the photo on the left is a prepared window for the vocal booth ,the right is the window between the recording room and control .this structure can be seen in its unprepped form below on some photos.