How much does rear horn loading add to full range driver?

Hi     @alexberger .... ideally when building a 3 way, I prefer to get a mid that handles the entire vocal range.  when you can (if your driver is good enough) you benefit greatly to keep the crossover out of the vocal range..  Even though a voice can go a bit lower and higher, overall, if you can keep a usable frequency from around 100hz and topping out at say 3000 to 4000,  You should get excellent performance.  To give you an idea,  the spoken voice is typically from around 250 to maybe 600 hz or so.  even if you had to cross as low as 2500 on top, that single driver will do a good job.....IF it has the frequency curve that fits your taste.  I hope this helps,  Tim

@alexberger    what you just described is the design philosophy of Bache audio, among others.

What do you think about using good quality 'full range' driver as a midrange in 3-way speakers. What do you prefer for midrange in high sensitive speakers - 'full range' driver or compression driver with horn? 

@alexberger In case it wasn't obvious, using a 'full range' driver as an extended midrange driver is exactly what I'm suggesting for best results.

However as soon as you do this you have an issue which is that of the crossover- the thing that so many 'full range' driver advocates detest! The issue appears to be the capacitor used to roll off the bass; it can color the sound. In the past to minimize this the woofer was often crossed in a about 500-800 Hz. My CARs at home are pretty typical of this- they cross at 500Hz. Most 15" woofers have no problem at all going that high and doing it fairly well, as anyone with Altecs can attest.

Of course this suggests that you really won't need a driver that is even 8" across. But for those that have some form of aversion to horns, this is a very viable path forward to enjoying a higher efficiency speaker and the dynamic contrasts they offer over speakers that lack efficiency.

My personal preference is a driver with no breakups in its passband! This allows it to be smoother at volume and more detailed. The compression drivers in my speakers at home use beryllium 3" diaphragms with Kapton surrounds. Their first breakup occurs at about 35KHz. So the mids of that speaker are quite good and I've seen little reason to change them out over the years.

I fairly recently heard an 8 inch Fostex driver mater to a vintage horn tweeter it was a fantastic combo but a one off design.  I've also heard and liked Charney Audio speakers.