I don't doubt for a second that wide dispersion is universally a good thing when listening to stuff in mono, but Toole's research shows quite clearly that those differences attributed to mono almost vanishes in stereo.
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This graph shows the importance of not assuming too much when it comes to any one particular trait because one factor may not be that important when you introduce other factors. I agree completely with @andreasmaaan that we need to evaluate only high quality speakers with different dispersion to get any clear answer.
In order to do that with any relevancy to real-life situations, we also need to do that with a wider room and a smaller room to see if any preference between dispersion width is universal or situation-based.
We are in a situation where the absolute best "Toole-style" speakers almost by default will be coaxials and, because of that, the dispersion pattern in the theoretical "best" will be somewhat limited by the necessary size/shape of the coaxial drivers.
It makes no sense whatsoever to have the "perfect" speaker with regards to the preference score if it's nowhere near the top of the subjective listening evaluations due to limited dispersion.
I think this is REALLY interesting and I have a lot of questions and comments on this topic. Rather than extend the q350 thread, is there already a "coaxial and Toole" thread or should we start one? Questions about the "moving waveguide" in a coaxial - is it really a problem? Is that why it seems they limit the midrange excursion? I am sold on the coaxial concept as, in my unscientific guess, the point source design and time domain accuracy leads to some really interesting depth. Interesting that it can meet all the Toole design specs on paper but doesn't seem to make the top of perception?