Windows are always tricky because you run into moisture and later mold problems.
Not saying that I have any real solution, but just something that I've heard others complain about after they cover their windows.
I had a cheap solution once, but it didn't include any sound absorption. I used multiple layers of dark felt, spaced out a little bit one from the next. This allowed for air to flow a little between the felt (it was pretty cheap stuff) layers, but there were enough layers that it eventually blocked all of the sunlight. You would need something a bit deeper than a regular window frame though to have a couple of inches between the layers.
Then again, I did that back in about 1996 and pretty much everything back then was either super expensive, or a bit "back woods redneck." I was young with no money, so I went with something cheap. LOL
Someone else will come along with a much better solution I am sure.
Last edited by nickbuol; 09-14-2017 at 03:01 PM.