Low-sensitivity speakers — What's special about them?

That aspect @phusis "a live sound imprinting" is significant. Thanks for putting it that way. Another, good metric to judge speakers by; very useful.

@phusis 
So you say "Percieved" and that these mid and bass drivers with good extension and little cone break up are readily available.... recently I've shopped a few hundred drivers looking for such.  Please list the model numbers.  

@timlub --

So you say "Percieved" and that these mid and bass drivers with good extension and little cone break up are readily available.... recently I’ve shopped a few hundred drivers looking for such. Please list the model numbers.

Perhaps we’re addressing this matter differently by now. Initially you wrote "really good mids with any type of top end extension without cone break up is hard to find in true high sensitivity speakers," so I set out to express my impressions from a complete speaker system - not focus on a single driver. Cone break-ups can be more or less challenging depending on your design goal and overall requirements, and nothing yet has been specified into the nature of a given design to illuminate your context.

Where "true high sensitivity" goes horns seem to be dictated, and with midrange compression drivers I’d wager their upper range (clean) extension isn’t a bigger issue, if as much as their lower end limitation in a given horn. Knowing what one is dealing with here would dictate what to work around rather than against, and with horns in particular it’s not exceeding the bandwidth of each horn element to main good power response etc., so a full-range all-horn system would typically require a 4 or 5-way approach.

With true high sensitivity speakers an excellent midrange can be had via a range of designs, so why would cone break-ups be a particular issue here if the design accommodates inherent challenges? You’re addressing and calls for the existence of specific midrange (and now bass) drivers with good extension, so what’s your context, specific use and related issue?

@phusis
My original post towards this subject was dealing with what it takes to design a true high sensitivity design that is capable of audiophile use. That is why I posted a few driver spec's in that post to make sure knowledgeable people knew that I was referring to drivers. 
Yes, in general,  I was speaking of cone speakers and woofers in general.  Many may not realize that MOST cone mid range drivers are woofers that have very good top and bottom extension.  The higher in sensitivity that you shoot for,  In general, the worst the top and bottom end extension gets. 

@timlub --

Somehow I got around to base my first post only on the quoted passage by you, and not the whole post (I quoted the passage early the day before yesterday to reply, but didn’t get around to actually write it until later on, and so blissfully forgot about the rest of it).

Now taking that into account I better understand where you’re coming from, though I fail to comprehend how you apply a "true high efficiency" design with direct radiators. It appears however that this is what you believe to be the best outset to work from as opposed to horn-loading, and so presents the specific challenges laid out by you - i.e.: if a sealed bass principle is preferred (less efficient compared to a ported alignment, not to mention horn-loading) and you seek to minimize cross-over points as well, then the challenges you find yourself placed in the midst of are certainly present and understandable in the context of aiming at high efficiency.

For what it’s worth: a friend of mine has build a pair of wood replicas of the Western Electric 12a’s (fitted with a Lamar driver), and they in themselves cover from ~100Hz to a few kilohertz (sorry, can’t remember the upper frequency cut-off). Add in a horn tweeter hung down in the midst of the 12a horn and a pair of horn subs beneath them, and you have yourself a very(!) high efficiency all-horn set-up, 3-way at that, with a range potentially from 25Hz on up. Apparently several who’ve heard this setup (though with twin 15" AE units in open baffles per side for the lower range) regard it as the best they’ve ever heard, not doubt in large part due the specific frequency range of the big 12a horn driven from a relatively small and very lightweight diaphragm.