Blinds make poor diffusers unfortunately.My former house had a wall of windows that the speakers fired directly into.What worked is semi sheet curtains on tension rods next to the glass,2"white "egg crate" foam for the next layer,then blinds on the interior side.The curtains next to the glass were for aesthetic purposes only so it didn't appear to be a crack house:)If course no natural light could get through but it looked good and worked like a charm.
Please comment on your experience with Plantation shutters. Yes they look great,
but do they act as good sound diffusers over windows? Has anyone noticed they improved the sound in a room with windows? I am thinking they may do a good job when tilted, but not fully closed. Perhaps even better than 2 inch wide standard shades?