Soundstage

Typically there is a "competition" between the desirable venue cues on the recording and the undesirable "small room signature" cues of the playback room. In this case apparently the wall behind the speakers is imposing its audible presence atop the venue cues on the recording, thereby limiting soundstage depth.

The earliest reflections are usually the one which most strongly convey "small room signature". On the other hand the later-arriving reflections are in effect the "carriers" of the reverberation tails which are on the recording, so imo we want to use absorption sparingly because early reflection energy becomes late reflection energy after a few bounces. My caution about not overdoing absorption isn’t universal, but is more likely to be applicable to systems with horn speakers, which do not start out with very much off-axis energy to begin with.

I suggest using a mirror up against the front wall to find out exactly where those reflections are coming from. With the mirror flush against the wall when you can see the edges of the horn from the sweet spot, the mirror is in the reflection zone. I suggest either re-directing that reflection energy (using large panels angled such that the reflection misses the sweet spot) OR diffusion (not sure which kind - I’m not an acoustician) OR aggressive absorption (very thick but not necessarily covering any larger area than necessary).

The wall behind the listening position will also be a source of relatively early reflections in this room, may well be worth treating in a similar manner.

I have other ideas about how to tip the "competition" in favor of the venue cues on the recording but they involve projects that I am commercially involved with.    

Duke

A soundstage which routinely "extends beyond the speakers" is a characteristic often found with wide-pattern loudspeakers in situations which result in strong early same-side-wall reflections. These reflections broaden the apparent source width (ASW), according to Floyd Toole, and are considered to be desirable by most listeners (and undesirable by some). Their downside is that they also degrade image precision and can cause coloration (according to Geddes), can degrade clarity (Griesinger), and can contribute to "small room signature", which is the imposition of your room’s acoustic signature atop the venue signature on the recording. (Note that recordings which are deliberately intended to image beyond the speakers, such as the aforementioned "Amused to Death", DO NOT rely on strong early sidewall reflections.)

Chili42 I expect that your wide room’s inherent lack of early sidewall reflections is why you aren’t experiencing the wide soundstage that you expected. I’m among the (apparent) minority who prefers the attributes which accrue to freedom from those early sidewall reflections.

In particular, if we can solve the frontwall (and possible back wall) early reflection issues, you MIGHT end up with a system where the acoustic signature on the recording tends to dominate over the acoustic signature of your room. Ime this is quite enjoyable, and can result in a "you are there" experience which varies significantly from one recording to the next, instead of a "they are here" experience whose spatial qualities are dominated by the playback room.

Imo, ime, ymmv, etc.

Duke