I can understand lots of points made here. For Kr4 (Kal's) perspective, yes, he I believe he is right in his horizontal ,sideways dispersion position, relative comb-filtering, etc. Varying degrees of off-axis comb filtering apply, also, depending on crossover, relative design of speaker, driver positioning, etc, yes. Lot's come into play here.
As someone who's designed a few HT's in my time, I also try to integrated these types of speakers (or any for that matter) in a vertical arrangement, for such reasons. With a typical Dappolito designed speaker, stacked vertically, you tend to keep your wider dispersion (depending still on actual design of speaker, crossover design, and overall waterfall plot of speaker - note: even vertically arrayed, some designs still exhibit restricted horizontal dispersion, compared to others). Still, a vertically arrayed typical mid/woof surrounding a tweeter designed speaker, and similar will most always have better side-to-side dispersion characteristics than a horizontally arrayed speaker. For the most part, Kal is right here.
Most always, if you can get that speaker upright, and relatively well integrated in relation to the L/R speakers, you're gunna get better overall performance throughout your theater setup, likely.
I find issue with many options to use an otherwise full range, typical passive stereo speaker (likely with tweeter on top design) in the overall design effectiveness for a couple of reasons - especially if the overall setup of the systems is a situation where you have lots of ceiling and floor interaction reflections messing up your sound propagation from the speaker! If that's not controlled well enough, you'll be not only not adequately re-enforcing the direct sound that emits from your speaker (multiple drivers covering the same frequencies will make a stronger more dynamic re-enforcement of the sound, help eliminate of cancel out distortion), but will greatly help control ceiling to floor reflections, which need to be controlled (radically affecting dialog, detail, dynamics, imaging, and overall solidity of sound). And with your typical stereo speaker design, there's a tweeter atop a midrange, atop a bass driver. Rather than multiple drivers for stronger presentation, you are left with potentially "iffy" sound propegation subject to distortion, limited re-enforcement of the sound, and limited dynamics, comparatively, I find.
I would rather see multiple mid/woofers (as a minimum), likely multiple bass drivers, and even tweeters, depending, for the strongest sound, with lowest distortion, and most solid image from any given speaker (especially across the front) of a speaker array! It's been my experience that such dynamic piston designed speakers (not considering crossover and efficiency of speaker design) do lots of things better and more efficiently in for reproducing a dynamic, impact-full, very solid sounding presentation.
In contrast, your polite, laid-back, rather diffuse sounding speaker designs and arrangements leave much to be desired in an effective, hard hitting, solid imaging, ultra dynamic, cohesive multi-channel audio system - especially with the difficult acoustical conditions often facing home systems!
Yes, you can get otherwise descent results with some systems setup's - even in small spaces - with traditional stereo speaker designs (i.e, one tweeter and a woofer, for instance). But you really must consider the dynamic efficiency of the speakers, how hard you intend to push your system, relative size of room, and how far you are seated, proportionately, from the speakers, in relation to the boundaries - as closer proximity to your direct radiated sound will make for better sound quality. This is why THX accepts such designs for small spaces, where your dynamic needs of the speakers, and relative lack of ceiling boundary interaction with the sound is reduced. Because in such a set up, needs are reduced, you're hearing more of the direct sound being radiated from the speakers, in relation to boundary reflections from the room, etc).
Too often, you'll find people trying to use these traditional passive (even active designs like these would be more effective in a lot of ways than what we typically end up with at home) speakers in situations where there's inevitably going to be too many sonic compromises that result from improperly integrating the speakers in the system, and not working in a given application, so effectively! But, some would still swear they feel such setup's sound great! And yet the experts will still staunchly recommend otherwise. Well too each his own, I guess.
In any system given system there's bound to be compromises. And that's a fact. I find that the more you can limit such compromises, the greater you're overall results are going to be in a given system. Fail to consider or realize such compromises, and the results will speak for themselves. The more aware you are of "what's doing what" in your system, the more you can maximize and improve on the performance and effectiveness of your system, basically.
And still, the nice thing about this hobby is that you can make your recipe whatever you like! And perceived results and personal preference, options, bias's, will always vary.
Still, with all the greatly diverse speaker designs and inevitable setup variations that exist, one things for certain, and that's that results will greatly vary, depending on all the variables in play!
Lots going on in a multi-channel audio system. LOTS!
