How to make small room sound bigger

@clearthinker - If he uses absorption, particularly deep or thick absorption behind and to the sides, it will help mask the back wall, or the lack of space from the back wall to some degree. In this or his case diffusion behind the listener is completely wasted I would imagine.

What I have suggested has worked in both a 26ft x 16ft room, and a 24ft x 15ft room with reasonable success. Both times this was used was because of entrance points and traffic into and out of the room, yes it’s a best fit compromise.
I wasn’t the clever person who came up with it, though after having actually heard it’s potential, implemented it for my own listening room. It has been working for me.

Now I am going to modify mine slightly as I do have an extra 4ft depth over the OP to try diffusion on my back wall, I’m going to need almost 6ft, the 4inches for the diffusers and 5.5ft for the effective working distance of the diffusers.

I listened again last night with a few albums, Daft Punk’s - Tron Legacy, The World of Hans Zimmer (live in concert) and the four disk set of Hans Zimmer movie scores (< that’s not the title sorry). It was not a room with the golden ratio and not perfect, but it was quite enjoyable with a decent sense of scale. I have been to venues with live orchestras and using that as a reference it truly wasn’t bad (I'm also not deluded, it will never be the same). I will say those big deep diffusers at the front work better than straight absorption ever could.

Being right up against the back wall, without diffusion there wasn’t much side reflections aimed at my ears, with speakers towed in a little, it wasn’t horrible.
The OP could move his seat all the way to the back wall and test this out for himself.

I have heard it, I do live with it, and it really can work with a bit of effort.
Failing having the room size, this has and can work the way I have suggested.

@ei001h - for goodness sakes get yourself a big thick and heavy (preferrably woolen) rug, maybe from an estate sale or used? The floor is really close to your speakers, that first reflection must be dealt with. Strictly absorption here, and not a little bit, a lot.

@rixthetrick, In this or his case diffusion behind the listener is completely wasted I would imagine. 

IMO absorption may be the preferred way to reduce the low range band levels and with direct radiated energy diffusion and absorption will be useful (needed). 

Low Freq will be the most difficult to treat and being the highest energy level the most important. As noted above placement is wide open for good results.

The Binary panels linked - look like a fine product and a quick glance at the Abfuser performance chart shows the effective range.

Congratulations on the QRD panels - well done!

@rego - Thank you. I went back to look again at the link on the abfuser, and I noticed they’d done this, very similar to what I am suggesting. However, keeping the speakers away from the side wall boundaries and placing absorption there is going to sound better, well it did for us.

@rixthetrick, lol - in the pic the L/R channels placement looks like 10-12 feet apart.

It's not easy (for me) to imagine what the sound field is like, but it does speak to the idea of the original post's inquiry of ' making room sound bigger ' which in fact treatment should do. 

What I would like to make clear is that the direct sound from the speaker is bounced off the back wall (if not effectively diffused), and then makes its way back to the diffusor behind the speakers.

Set your speakers off the front wall, through trial and error and keep them in from the left and right boundaries ( I would start with 7 foot apart)

I did suggest 7 foot apart.

yep