I wouldn't expect a notable (if any) difference timbrally since the difference, however dramatic it may appear on paper, is actually a subtle one (if listening off-axis, of course). BUT, there's one thing that always bothered me - the one about the sweet spot widening. Because as you move off the center line, you approach the on-axis sound of one of the speakers. In the "suboptimal" case the direct sounds from the left and the right speaker will be different. Could this have an impact on the image stability? That's what I would be interested in.It would be interesting to learn the outcome of a comparative blind listening test between that "suboptimal" WG and an optimized one with the proper round over (ceteris paribus).
This was the smaller one, only 23 cm (~9") wide.There has been some more results of even smaller waveguides during the recent months, based on my tools - ...
Would you consider this as a smooth enough transition? This is a waveguide of about the size of your Abbeys (12" woofer). The axial problems are also vitually gone (the graph is for 0 - 120 deg / 10). I would put this as my piece of evidence for all the points just mentioned. As for the curve C, I don't know if it is any special but a segment of an Euler spiral (or the curve corresponding to my waveguide formula) works very well as the remedy for most of the problems as you can see.
Again, this is what hapens if you change the mouth round-over from abrupt to gradual for one particular axisymmetric OS waveguide - I don't know whether the hole is eliminated, went away or diminished to neglibility, but for the best transition it is just not there anymore.