RicoJour wrote:

Are there storm windows on the outside? That's probably the easiest
and cheapest way to get some sound attenuation.

No, there are not, but some casual browsing suggested it was an
expensive way to accomplish what I wanted. Couple of hundred per
window is my recollection.

I googled on some weight estimates for a 1/4" sheet of glass and came
up with 52 lbs for a sheet 96 x 120, which is a lot larger than what I
plan. I'll check on the price for tempered glass, but I'm afraid it
will be prohibitive

For the windows where absolute quiet is required, I'm slowly building
some solid shutters that fit in a Z-Frame where the doors will be 1"
thick plywood. For windows where a large sound reduction isn't
required, I was looking for a quick and easy solution.