Window Treatments to Remove reflected sound


I have a listening room with hard wood floors, two French doors beside one speaker, two more across the room and two walls full of windows. Any thoughts on the best window treatment to improve sound? I'm assuming metal blinds are just as bad as the glass and am considering cellular blinds, which seem to be made of polysester but have an air pocket in the middle. Any experience on what works best? Thanks for the input
ruhl
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A previous room had three large windows that were covered with "cellular blinds" and then the windows had heavy fabric over treatments. This proved to be very effective. You could even discern differences that resulted from opening the blinds differing amounts.
I agree with Dougmc. I have plastic 3 in. regular shutters on all windows. Turned at 45 deg., they provide good mid/high diffusion and light control to boot! Wood might work even better. (Lets, see... maple? (:-))