Thanks
@svart-hvitt, didn't mean to let this slip.
The technical paper was interesting. The eradication of physical discontinuities between the tweeter and midrange must be helpful compared with earlier coaxial designs. The use of spaced outlets for the low-frequency transducer is also a clever way to extend directivity control further down into the lower midrange without spacing the woofers apart from the coaxial arrangement in the centre.
OTOT, this current generation of Genelec coaxials are higher distortion and lower SPL than their spaced designs (IIRC), so it seems these advances in their coaxial designs are improvements, but not complete solutions.
In the technical paper, I was also a bit sceptical of the multitone distortion test and the subjective evaluation that they chose to use. For the distortion test, it isn't specified which other speakers the new coaxials are compared against (presumably not Genelec's best non-coaxial designs), while in the subjective evaluation, they chose a test that was designed to emphasise the issue with spaced drivers and that in no way resembled normal use.
So I think this line of R&D is useful but am still not 100% sold on it's benefits in the widest possible range of applications.
Finally, I'm also not 100% sure I agree that the problems with vertically spaced drivers are as significant as the paper claims. This is what the paper says:
The first part of this I agree with, although this will only be a problem when the listener is not positioned on the correct vertical axis.
The second part is is absolutely correct when it comes to horizontal head movements (i.e. we move our heads from side to side to help establish ITD), but AFAIK it is incorrect when it comes to the vertical plane. Our ears are horizontally spaced, so moving our heads up and down just doesn't help us in terms of localisation. So as far as I know, we just don't do it. I may be wrong on this point, however.
I seem to recall you posted an interesting lecture or presentation on this topic at one point which I never got round to watching and then lost. Can you recall which one I'm talking about?