Solar/cellular shades -acoustical treatment

My right speaker is about 5 feet(ft) from the sliding glass doors (8 ft high by 16 ft wide) and is presently covered by solar shades. I have slap echo and reverb issues in the room and this is my first reflection point. I wanted to tackle this issue first when planning my acoustical treatment.

I have been told that solar shades have an NRC of about 0.15 so I was thinking of adding a set of cellular shades which I have been told has an NRC of 0.7. However, before investing a few thousand dollars I thought of asking if anyone had any experience with cellular shades and their acoustical absorptive performance. Manufacturers have not be able to provide any test data concerning acoustical performance. Also, any thoughts on any manufacturers' product acoustically better than the other.
Before you spend a lot of money, is this a real problem you can hear the effects of, or something that you're reading about and experimenting with? Its easy to go too far and over dampen your room.

Something you can try and will be well worth the effort, is to go and get some fibreglass insulation. Not the stuff that's rolled up, but the kind that comes in rectangular pieces about the size of a picture. Most acoustic treatments are made out of fibreglass and you can use this "cheap" solution just to see if you are headed in the right direction. Actually, many people just cover the store bought fibreglass with cloth that matches the room, and just use those.
I have been playing with 4 ft x 10 ft panels of Owen Corning 800 1.5 inch rigid duct insulation for the past 4 months. When placed at first reflection point on window there is a noticeable improvement. NRC of panel is around .85, so A little better than cellular shades are supposed to be. Just can not find any test data to confirm cellular and solar shades performance and thought someone may have experience with solar and cellular for comparison.
No one out there with experience with solar vs cellular shades for acoustical properties???
Joe, I've come across both in various installations, neither one of them offers any acoustical properties worth talking about. I wouldn't spend money changing from one to the other. Treating large glass surfaces effectively is very tough, there are things that can be done but not in isolation, it has to be as part of a balanced approach to the whole space.

Hate to hear no much of a difference, but I would rather hear it before speaking the money. Thanks for the input. I guess my next step is treating the walls. Is this what you mean by a balanced approach?
I don't have data, but on the large windows that encompass one of my first reflections, cellular shades certainly tamed slap-echo in my room. With a deep windowsill, I was able to set them 4-5" away from the glass to get an even broader spectrum of energy absorbed.
What I meant was to look at the room as one space and not as separate bits. You have to look at the room as one connected space and not just treat one side without thinking about the opposite side. You need to balance both sides acoustically first, then attack the other issues.