The left graphic represents a standard 4 inch wall with two windows similar to what is built for residential noise reduction.
The right graphic represents the recommended 6 to 8 inch wall with two windows. Notice the angled window on the music room side of the window. Also the break in the 1x8 sill that retards transfer (fill the crack with silicone).
Be careful as the smallest width between the two windows controls how much noise is stopped, rather than the largest dimension (so if there are 8 inches at the top and 6 inches at the bottom, the 6 inch air space applies to all calculations of noise reduction and soundproofing).
Continue to Do You Need to Soundproof the Walls?