Sound Absorbing Drapes

I had Martin Logan Reqests in about 8 ft in front of a 4x6 ft window centered I between.  I have 2 2x6 by 1:2 in thick fiberglass covered panels that I found really didn’t make much difference.  Fast forward 28 years 

I replaced them with a pair of focal Sopra 3.  Out come the panels   I found they focused the sound stage and better defined the instruments location. However they shrank the depth and I lost that alive quality.  I have ordered sheer shades  the are like fabric venicsion blinds. When rolled down they are about 2 in thick, however the fabric is thin but you can adjust the inside vane to control the light. I’m hoping to kind of get the best of both worlds. Sparkling sound will a little more focus.

I should also have stated if there was a want to not use a liner of Sheep Wool matting sandwiched within a Curtain, wool is extremely easy to dye a colour that has aesthetic attraction.

Wool dyed to a colour of choice can be used as a Wall Liner and a Curtain can be used as a additional control measure if wanted.

Note: The successful measures usually has a spacing between the structural wall inner face of the absorbent material. To make the most of a wall liner it will be best mounted on a batten frame that creates a cavity of approx' 20mm (3/4" - 1"). There is a control on the energies first pass and a improved efficiency control for the energy bounce back from the hard structural surface when a cavity is created.

Google "soundproof curtains."  There are many commercial products, such as those from 3HLinen or TheHues, that are designed to maximize sound blocking/cancellation.  There are cheaper options that are used in motels and hotels, but most of those are not that great looking.  Even if you go the DIY approach, you can study how these companies design their drapes.  Linen appears to be a popular material and multiple layers of fabric are employed.  

A related thread:

https://forum.audiogon.com/discussions/drapes-or-blinds-for-patio-door/post?postid=2863724#2863724

Typical draperies typically have a poor NRC rating.

I have a couple suggestions. This sounds like a big project that will involve hundreds of dollars and dozens of hours.

1. I highly recommend that you run Room EQ Wizard to get a baseline of where you are at before adding more treatment. The software is free and the calibrated mic is under $200.
2. Look at companies that provide sound absorbing curtains. There is a lot of detailed information about the materials and construction they use. It may give you some ideas about making your own or it may lead you to purchase a manufactured product.
3. Take the advice of @ghdprentice and experiment with heavy blankets before making curtains. Sound absorption is tricky and you may not like the result.