how can I make the back wall transparent?

Thank for all the feedback - seems I got a few things to try :-)

The speakers are Gershman Acoustic Sonograms - which are very forgiving and very transparent.

I'm very fortunate in that I have not experienced many of the problems others have re: traps and reflected sound - I did have an echo behind the speakers, but a couple of tall panels fixed that.

I tried hanging some material behind the speakers, which helped a little with reflected sound, so maybe something thicker like a rug might be more effective ?

The speakers are of the standard forward firing drivers type, so I assume that if there is some reflected sound coming from the wall behind them, then it would be first be coming from the wall behind the listener?

The speakers do have quite a wide dispersion angle, but not enough to reflect off of the wall behind them.

If I were to look into some kind of deflection panel, which direction should I aim the deflected sound?- up, down, outwards, inwards ?

Would the deflectors need to be the height of the room?

In one hi-fi store I visit, they have "scatter reflection panels" which are long strips of wood at 45 degrees to the wall - can anyone vouch for the effectiveness of something like this?

Many thanks

The only way really is to use speakers that are bi-directional, like Magnepan planars for example, or omnidirectional. Front ported or acoustic suspension speaker designs, ie those where most or all sound is emitted from the front, will be most problematic.

Then it is a matter of getting enough distance between speakers and rear wall for proper timing of spatial queues (usually a few feet minimum) along with a good balance level between the direct and reflected sound that reaches your ears. That is determined mainly by distance from wall and db level of rear emitted sound, ie that reflected off rear wall. More distance to rear wall will require higher db of reflected sound to produce illusion of extending past rear wall. That is why bidirectional or omni speakers tend to do this best.

Again, I think Mapman means "front" wall. I'm in the "room sound" camp (although perhaps alone) where the furniture, rugs, bookcases, me, etc., provide plenty of ambience control. I do have my listening "sweet spot" 4 feet or so from the back wall (behind me...in case we're still not clear on that), and the main speakers about 3 feet from the front wall with a sub tucked behind one of them. Done. The side walls/glass doors are well away from all this and besides, I like some "room sound"...there are bumpy standing waves here and there but not in my listening spot so I don't care. I have a glass coffee table in front of that spot and put a couple of throw pillows on it when doing "active listening" (love that concept), so I'm not a complete philistine.

...by replacing a sheet rock with glass

YEs, I mean wall behind speakers opposite from listening position, which is the one in front of you when listening facing speakers.

You can use room acoustics or fight them. Both are valid approaches. Each might have a better chance of success depending on magnitude and nature of room acoustics. All rooms have a unique sound and best to first assess it then use it and tweak accordingly as needed IMHO.