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

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.

It's common ASR wisdom that "fullrange drivers are hot flaming garbage and you should be deeply embarassed to evoke them in any conversation". 

FWIW a friend of mine has been struggling with 'full range' drivers for the last 20 years. He keeps asking if I can help him out he refuses any kind of crossover or additional drivers like a tweeter. When he plays simple musical material the speakers sound world class. But if the music is more complex, particularly if there is bass and volume there's nothing for it- they lose their clarity.

He keeps trying different drivers, Lowther, PHY, Voxitive (field coil), Tangband, AER, Cube apparently expecting different results. Not happened yet...

There are true full ranges just because one hasn't experienced one doesn't mean they all require being made into a 3-way.

This statement is false, unless you can show me a driver that really in fact does 20-20Khz and not some made-up stuff like you see on a lot of websites. I've seen some that seem to have 'cracked the nut' but when you dig deeper you find things like a free air resonance that is far too high to allow it to go to 20Hz; things like that.

The other problem you have on the high end is beaminess. If you don't mind having to place your head in a vise in order to get all the highs that's fine. But quite simply, a tweeter can do that job better. If nothing else, a rear-firing or top-firing tweeter is nice to correct the off-axis response so as to maintain tonality when your head isn't in that vise.

But the biggest issue is Doppler Effect distortion. When you have the excursion required to reproduce bass notes, the higher frequencies that are made by the same driver are moving towards you and away from you with those bass notes, causing a pitch bend. If you get the excursion off of the driver, it immediately is lower distortion, resulting in a more transparent reproduction. 

So how this works out is less complex music might sound great, such as a solo voice with guitar or a string quartet. But throw some electronia with big bass in it, or a full orchestra playing at a realistic level and 'full range' drivers not supplemented by subs and the like fall right flat on their faces.

IME those drivers with whizzer cones tend to have another issue which is breakups. A breakup can be seen as a peak when you do a pink noise test, but it won't show up as an impedance peak like normal resonances do. So I find the drivers that don't have whizzer cones to have smoother response. PHY for example is pretty good at this (their driver with the best high end seems to be their new 6", which works pretty well in a quarter wave horn cab).

But even if the breakup thing is solved (which can also be solved or at least ameliorated with a crossover) the Doppler Effect thing cannot be escaped. Its very easy to hear how much better any of these drivers get when they don't have the bass to deal with.

How much volume is gained by horn loading the rear wave? Would a horn enclosure 43 x 9 x 6" inches be likely to play lower than a ported shoebox size speaker? These wouldn't be my main speakers, just an interesting addition.

@aldnorab Rear loaded quarter wave enclosures get the deepest bass response you can get out of any enclosure design. But something to keep in mind is that no 'full range' driver is really full range; all of them benefit from woofers and tweeters.

If you can keep the excursion off of the 'full range' driver it will sound better as it will have less distortion. So you can see that the quarter wave horn concept might not win you anything.

A lot of people like the idea of no crossover and with simple musical material its seems like a good idea. But if things get complicated then they don't work so well.