how can I make the back wall transparent?

I think you are making matters worse by confusing what wall the OP is addressing. He really means the front wall (which is the wall behind his front speakers) People on this forum often call the walls by the wrong name. The front wall faces the listener and the rear wall or back wall is behind the listener.

If I am mistaken, I apologize. Maybe the OP can clarify, that way you are all on the same page.

Google GIK Acoustics seems you need some large bass traps behind the listening position. Give them a call I believe they can solve your problem. Good Luck

Photon,

I'm about 5 feet from the wall behind me when seated, behind me is a row of cabinets and a counter. The space above the top row of cabinets have been stuffed with insulation then the space have been sealed of with cloth creating a very nice bass trap. Its about 12" deep 24" tall and about 20 feet long.

I read the OP was wanting to treat the wall behind the speakers with something to create depth in his soundstage my reason for suggesting the RPG or similar

As alway, Good Listening

Peter

Oooops - sorry for the confusion - I meant the wall behind the speaker.

Have u looked thru the virtual systems for ideas?
In my case; room is 12 x 16 feet, speakers are 3' from wall; toe-in made a great increase in soundstage plus I'm using an equilateral triangle method. As in many of the virtual systems, I used bass traps in corners and 2 vertical DIY vertical panels on wall behind speakers; that wall then disappeared and became like a concert hall.
BUT, the panels are ugly...2 inch foam, mounted on boards that I can stow away when I have visitors. Obviously I'm not married.

"the acoustic designers I consulted seemed to feel that unless one uses massive amounts of bass trapping behind the listening position, one can't effectively ameliorate the total adverse influence of the rear wall."
I am using bass trapping panels and it works for me; in a small room you don't need massive amounts.