make sure you use DAP non expanding foam. it is meant to be used for windows and doors. GREAT STUFF foam could possibly expand too much and cause your window not to operate correctly
Years ago I was big time into windows. Also was a certified Pella Cont.
Millguard and others make quiet windows.
Here's how the best are made. 2 double lites of glass seperated with a plastic sheet. Airbar [spacer ]between the 2 double glass So the glass is laminated. These are very affective and are Very heavy. Not cheap
If you can, replace the panes / sashes with double-strength laminated glass. I did this in my house, and the traffic noise was cut dramatically.
sound has a memory,if it goes through 1/8 inch glass it's pattern will change and will go through the next pane much easier.In the recording studio im building we used two different thickness of glass,so that it has to change frequency with each piece of glass the sound goes through.We also installed the glass at angles,so that some of the sound would bounce off,It travels straight through at 90' degree angles.
I am just learning about sound, This is the 3rd studio i've built,But this one is state of the art.Some big wig in nashville designed it.
I like the curtains idea. Check with music stores,about sound curtains.Most clubs the have bands with windows or smooth walls around the stage have heavy thick curtains. Good luck
I recommend an operable treatment that allows you to use it when you need it and have full view of your window when you need that. There are many sound deadening window coverings available such as a thick lined drapery or a cellular (honeycomb shade). Hunter Douglas makes a Triple cell product called "Phenomena 3" and I would recommend looking into that. Good luck.
The cheapest solution is to get some ear plugs... :p
This can be very dependent on the construction of the window, & Rockinrandy had some very relevant points. However, a method I once helped a glazier with, in Denmark, was to use Argon between the glass instead of air or vacuum. Anyone who has tried to breathe Argon can tell you, It,s heavy & soggy. (Argon is non poisnous, but heavy, & stays in the lungs- you drown more effectively than in water - Dont try this at home. If you see an apprentice in Denmark getting "wuzzy" & pale while TIG welding, you hang him upside down in a crane, & wait about 2 minutes. When he's feeling well enough to protest, you let him down gently, & send him on a long break)
Perhaps someone with your ingenuity, helped by the available knowhow of this forum can use this.
So how did this turn out? What did you do to solve your problem? What worked best for you?