Some time ago, a speaker company starting with D... produced a set of tower speakers that was reviewed on Stereo Review (around 1993). The most notable aspect of the speakers was the streo imaging, even when standing in front of one speaker, the review said that the streo soundstage was still intact.
I understand this has to do with time domain effects, but at this time it is time domain effects and not stereo sound stage effects that I am concerned with.
I'm not sure this particular feature is as much time as dispersion, and depends on exactly what the reviewer meant by Soundstage.
There's really in my mind, two ways in which reveiwers mean this. One is the more general sense of being able to hear sounds coming from between the speakers. A second sense is that they feel they can locate the precise location of instruments in the 2D space, and maybe the 3D space between the speakers.
In the first place, it's a more general sense of knowing the bass is playing to the right of the drums. In the second it's a sense of an acoustic instrument taking up space 1 foot back and 2 feet in from the right speaker.
So, I'll assume he meant the first, general sense. This is not about having perfect time domain results as much as having wide dispersion that varies evenly with the frequency. That is, you could have a narrow speaker that you can't hear at all when close to the other, or you could have a speaker with some frequencies that at an angle are out of balance with the rest.
The Magico S1 Mk IIs are a great example of the first sense as well. Wide and even dispersion so that anywhere you sit you have a general sense of the soundstage.
There is also a great debate about what is "perfect" enough. For some, perfect means that one driver blends in perfectly with the next even if the step response is not a triangle but a series of impulses. To them (and me) what's important is the blending from one signal to the next. Here's an example.
I think in general, this would be considered a very good step response, but not time-aligned. If it were time aligned, the first pulse at the left would be gone, and the big triangle shape to the right would be better defined.
Personally, I think a great step response is a good thing, but I've heard imaging come and go with step responses not nearly as good, so I'm not sure that this particular feature is THE way to get good imaging. Maybe I need to do more listening and reading.
Best,
Erik