Not to take away one bit of your post Frank as it is spot on. Here is what Jason Jones, the diffusor guru said on the matter.
Quote:
The chances that a bookshelf will be an acoustic problem are really 100%. Designing a diffuser is SO much more complicated than throwing in some random depths.
Would you buy an absorber that had specs like this:
4 Khz 0.2
2 Khz 0.4
1 Khz 1.0
500 Khz 0.2
250 Khz 0.7
125 hz 0.2
This absorber will decrease your reverberation time across the board, but very unevenly. Compared to having nothing on your walls it will sound more tolerable. It would be a fine acoustical addition to a living space especially when you have a couple of these plus couches and curtains that have different absorption qualities.
So, in a pinch if you really have no alternatives a bookshelf is better than a completely bare wall. But, it will skew what you hear.
I certainly can be an impossible perfectionist sometimes.....but couldn't you find some mineral wool or rigid fiberglass over there and wrap it in fabric. That is still pretty cheap and I would happily bless that idea (Just in case, No I don't take myself THAT seriously ).
As to the Chinese wood screen: I am not usually much into Asian art, but that really is beautiful. I can see why you would want it on the wall. Do keep it on the wall, but don't kid yourself about it's acoustic properties. Put over an absorber it might help some around 3 Khz or 4 Khz IF you already have a room that is too dead; but, that's not really your problem.
Summary:
1. Pick up some mineral wool or rigid fiberglass. If you can find it local and cover it yourself it will be cheap and acoustically very good.
2. The bookshelf is better than nothing. You can use it if you can't do #1 but it would be a delusion to think that it was more than a D grade (A-F scale) diffuser.
Jason
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GIK Acoustics
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Glenn