You will probably find the replies in this near identical recent thread very helpful. (link below) If you look at the plan I sort of drew out on the screen towards the bottom, that will give you my ideas. Due to a change in hardiness, replace the japanese cedar with western arborvitae (green giant) or norway spruce. Replace all holly with sea green juniper. I'm not a fan of using slow growers like eastern arborvitae and blue spruce for privacy. Aside from that a photo of the situation will send ideas flying in your direction. Here is a link that might be useful: that near-identical recent thread I was talking about.

ROCKWOOL Called ROXUL AFB (Acoustic Fire Bats) in the States. This stuff is designed for two things. And only 2 things. Sound & Fire. It substantially reduces transmitted sound, and also is a substantial fire barrier. It withstands over 1200 degress. So it slows down the spread of a fire quite significantly. I put in Roxul or Rockwool, on a Remodel that we're finishing up. Between floors. It made a huge difference. I would also recommend getting a book on stopping sound... a whole bunch of stuff (which we didn't for the most part do...) for proper sound control - needs to be done. For example, be sure to insulate between any door jambs and the wall. Don't just let drywall cover the 'space'. Material exists to insulate heating ducts for sound... Heat ducts like to help sound bounce all over. Myron Ferguson wrote a book called 'Drywall'. His latest revision 3rd or 4th - has a section on Sound Control - since he is just learning about that... I'm not an expert, and neither is he. But if your doing a major remodel, and are concerned about Sound - now is the time. So do some research, or hire someone who knows what needs to be done. But just Roxul stuffed into the ceiling joists and between the door jambs - would help a tremendous amount. And that is easy to do for a DIY. Roxul or Rockwool is itchy - just like fiberglas - when your installing it. But it doesn't have fiberglass in it. (I think that's correct, not quite sure...) KNOW it has shredded rock, and metal slag... I really recommend it for the Sound and the increased Fire safety factor. Available at some Hardware stores. We purchased what we used from a local lumber yard. Here is a link that might be useful: Sound and Fire insulation

what area are you in??

Your experience may be correct and it woud be hard for me to disagree without knowing the exact details of what you did. If you were to compare STC or OITC ratings of manufacture of the same window , one with dissimilar glass glass package in dual pane and one with triple pane. You would see virtuallly know difference in the numbers. In most cases with a window manufacturer that produces windows for sound control you would find no triple panes offfered. The science says otherwise But if what you do works , it works. I have triple paned unitsbin my house and I know when a car drives by when I’m awake at about 200 ‘.