No set blinds will have any effect below mid-frequencies and exactly where they will change from dispersing the audio to reflecting it is somewhat unpredictable. The glass is transparent to bass and reflective of HF so, in order to have a nearly equal effect across the spectrum, you need some heavy absorbtion from the low midrange up. I've used velvet drapes interlined with dacron acoustic batting. Since the coverage is adjustable, you can titrate the effect you want.
Kal
Kal