Room Acoustics - Best way to cover a glass door?


My small room (about 12x12) has a glass door (leading to a balcony) on the right side, between the speakers and the listening seats.  I have stand mounted mini-monitors and tube electronics.  I listen to acoustic jazz, blues and rock, with lots of female vocalists. Bass is not important to me; I live for soundstage, imaging and sweet midrange.

I am looking for a simple (and inexpensive) way to cover the door.  I plan to install hooks or curtain rod on the wall above it, and hanging some sort of material/curtain.  I am wondering if there is anyone with experience and recommendations on what material I should use.  I have been considering:

-something light- a simple sheet or cotton cloth from the fabric store.
-something medium- a fuzzy blanket or perhaps cloth of fleece, denim, corduroy,
-something heavy - room darkening curtains, possibly plastic lined
-Multiple layers of material?
-Free hanging or fixed on the bottom?
-Or what about blinds- vertical, horizontal, thin, wide, fabric wood.

I figure I will end up trying a couple things (ideally just 2), but any advice on where to start would be appreciated. Especially along the lines of "xyz is a really stupid idea" or "start with this". 

I am an engineer, so I tend to want to understand why something will work rather than just snake oil, but, ultimately it is all about the ears.

THANKS,

Bill



meiatflask
Go to GIK Acoustics and look at the free standing acoustic panel. It's 60"H by 24"W so it should cover most of the door. Simply move it into place when you listen.
http://www.gikacoustics.com/product/freestand-acoustic-panel-gobo/

My front door which has 6 panes of glass is in my listening room.  I put a curtain rod above the door with some light curtains.  Took care of the problem.