Detailed imaging - placement in space left to right is 99% due to direct sound - and the reflections mostly tend to interfere with that.
However our big brains are really good at seperating initial sounds, from their reflections... so as long as the reflections hit our ears with sufficient delay, they don't interfere with imaging. (I know, this is motherhood and apple-pie, audio 101, most of us already know this, but always good to review basics)
So important audiophile trick number 1 - keep the speakers far enough from the wall behind them, that we get the necessary delay, which allows imaging to then "work" properly....
But why bother with directional speakers - none of the directional sound goes backwards - and that is where things get more complicated... speakers aren't perfect... in a modern audio system they are the "least perfect" component...!! - some/many/most box speakers, resonate (and unless they are sealed designs... intentionally use some parts of that resonance to increase efficiency!) - there is some sound radiated to the sides and the rear from the box itself.
Many who have used panel speakers, boxless speakers (baffle speakers), or some designs such as "round" speakers (Gallo, Cabasse, a few others) - are probably very sensitive to this particular type of distortion "the sound of the box" - others who have only ever used box speakers, tend not to notice it (the joys of habituation!).
So you either have to move the reflecting surface further away (move speakers out from the wall), or ensure there is no backwards radiated sound (tricky... remember speakers are imperfect!) - or use absorbant / diffusing surfaces behind the speakers.
So much for the front wall...
Side walls have the same issues - but here we are aiming for something different (usually) - the best concert halls, have a strong radiant field, that is to say, a substantial (majority!?) part of the sound a audience member hears, is being reflected off the various walls before it hits his/her ears - and the best concert halls leverage that!
Similarly with listening rooms - you actually don't want a "dead" listening room, with no reflections (all reflections absorbed)...
How close the speaker is to side walls has an impact, how wide the speakers dispersion is, has an impact, what surfaces and/or objects are on the side walls has an impact...
So for a traditional listening room, you want diffuse reflected sound, with some delay (same as for the front) - so it doesn't mess with your imaging.
The "soundstage" as opposed to the imaging, will be primarily driven by reflected sound.
So which is better... wide dispersion or narrow - depends completely on the room and the speaker placement.
I far prefer a wide dispersion design, in a room properly set up to take advantage of it - my current speakers have tweeters with 330 degree dispersion (almost full circle!! - might as well be an omni!) - and the midranges are in spheres, and are also known for their wide dispersion (I have no measurements or specs to lean on for those)...
How things may change in the near future...
If we move from a room based reverberant soundfield, to an artificially generated soundfield (driven by many speakers in a full surround setup including heights etc...) - then optimal performance, may indeed require a focus on more directed sound (narrow dispersion) and absorbing/diffusing as much as possible of the room's own reverberant soundfield, so the desired artificial soundfield can be imposed on it.
Turning your listening room / HT into an anechoic chamber has always been seen to be a negative for stereo audio, but for fully processed surround, with true soundfield processing, it may be highly desirable.
With things like Trinnov, and Dirac SRC, combined with the soundfields that Yamaha studied in depth during the 1980's, we could be moving into a completely new era of audio in the home.
However our big brains are really good at seperating initial sounds, from their reflections... so as long as the reflections hit our ears with sufficient delay, they don't interfere with imaging. (I know, this is motherhood and apple-pie, audio 101, most of us already know this, but always good to review basics)
So important audiophile trick number 1 - keep the speakers far enough from the wall behind them, that we get the necessary delay, which allows imaging to then "work" properly....
But why bother with directional speakers - none of the directional sound goes backwards - and that is where things get more complicated... speakers aren't perfect... in a modern audio system they are the "least perfect" component...!! - some/many/most box speakers, resonate (and unless they are sealed designs... intentionally use some parts of that resonance to increase efficiency!) - there is some sound radiated to the sides and the rear from the box itself.
Many who have used panel speakers, boxless speakers (baffle speakers), or some designs such as "round" speakers (Gallo, Cabasse, a few others) - are probably very sensitive to this particular type of distortion "the sound of the box" - others who have only ever used box speakers, tend not to notice it (the joys of habituation!).
So you either have to move the reflecting surface further away (move speakers out from the wall), or ensure there is no backwards radiated sound (tricky... remember speakers are imperfect!) - or use absorbant / diffusing surfaces behind the speakers.
So much for the front wall...
Side walls have the same issues - but here we are aiming for something different (usually) - the best concert halls, have a strong radiant field, that is to say, a substantial (majority!?) part of the sound a audience member hears, is being reflected off the various walls before it hits his/her ears - and the best concert halls leverage that!
Similarly with listening rooms - you actually don't want a "dead" listening room, with no reflections (all reflections absorbed)...
How close the speaker is to side walls has an impact, how wide the speakers dispersion is, has an impact, what surfaces and/or objects are on the side walls has an impact...
So for a traditional listening room, you want diffuse reflected sound, with some delay (same as for the front) - so it doesn't mess with your imaging.
The "soundstage" as opposed to the imaging, will be primarily driven by reflected sound.
So which is better... wide dispersion or narrow - depends completely on the room and the speaker placement.
I far prefer a wide dispersion design, in a room properly set up to take advantage of it - my current speakers have tweeters with 330 degree dispersion (almost full circle!! - might as well be an omni!) - and the midranges are in spheres, and are also known for their wide dispersion (I have no measurements or specs to lean on for those)...
How things may change in the near future...
If we move from a room based reverberant soundfield, to an artificially generated soundfield (driven by many speakers in a full surround setup including heights etc...) - then optimal performance, may indeed require a focus on more directed sound (narrow dispersion) and absorbing/diffusing as much as possible of the room's own reverberant soundfield, so the desired artificial soundfield can be imposed on it.
Turning your listening room / HT into an anechoic chamber has always been seen to be a negative for stereo audio, but for fully processed surround, with true soundfield processing, it may be highly desirable.
With things like Trinnov, and Dirac SRC, combined with the soundfields that Yamaha studied in depth during the 1980's, we could be moving into a completely new era of audio in the home.
