Wool Blankets as Room treatment

Wool blankets should work quite well.  One of the best rooms I've heard was one where the cement block walls were only covered in spots with decorative wall hangings and tapestries--no obvious and ugly room treatments were applied.  These minimalist treatments are akin to the wool blankets mentioned.

Among the worst rooms I heard--dry, sterile, lacking in life and unnaturally lacking in reverberation where custom-designed rooms where acoustic engineers/architects designed the rooms.  Maybe these rooms would work for sound engineers, but for home listeners I thought they were not good sounding.

I think that a lot of people who are serious about their systems end up over treating their rooms.  I would start small, like you are doing--treating the walls minimally with wall hangings.  It helps to have a carpet on the floor, or at least an area rug so that early floor-bounce reflections are somewhat attenuated.  Book cases, potted plants and other "normal" room objects that are placed to also break up reflections to make them more random would help too.  After that, you might consider corner bass traps--at least these can be not as ugly as other treatments (but, the bigger the trap in diameter, the better).  Another great room I heard was a very large space with modest amount of treatment (ASC corner and side wall traps).  The owner originally put in an extremely large number of such traps, but his dealer, when setting up the custom-made speakers, pulled out more than 60 of such traps.

My friend has a giant American Flag. I suggested he put 1/2" thick textured carpet pad behind it.

example, search Bed Bath and Beyond, many exist

Mohawk Home Felt Rug Pad 1/2" Inch Thick Plush Comfort Cushion - Grey - 5' x 7'

As @kijanki said above, they will only help with a very narrow range of problems.

Quite a few materials, that are thick and heavy, that we can barely blow air through, are completely transparent to entire ranges of audible frequencies. So, those ranges of frequencies, will just reflect off the wall as if the wool is not even there.

But it is possible (and probable), that absorption is not all that is needed.

Diffusion in the right places is just as, if not more, important.

I would suggest posting your question over on the DIY Audio forums, in their room acoustics forum. Many very knowledgeable people over there, with the expertise.

Wow some great suggestion here. Thank you.

One of the things I did that helped was use QUIK-TUBE® Building Forms and covered them with dimpled fleece fabric and put those in the corners. You can see them in my profile system photos.
 

Made 4 pf them for <$100