How come Horn + woofer designs are not more popular?

I think JBL M2 have too low sensitivity 92dB  for horn + 15" woofer speakers.
This fact kills they advantages over box speakers.
Yes, they should have better high and low frequencies extension compared to typical horn speakers, 
BUT
They will never sound as dynamic and alive as 97-100dB horn speakers and you can't use them with SET amplifiers.
I listen mostly jazz and classical music, and for this kind of music low mass old 15" woofers like where used in: old Altec, JBL L200, Tannoy Silver, Red suit better. 
New heavy 15" woofers more suit for rock and pop music but they don't breathing and sound more simplified on midrange. 

Speaking purely subjectively, for me speaker brands highlighted different things.  As a musician, I prefer to evaluate audio with music that doesn't rely on amplification for its realization, hence acoustic instruments.  Since I was a young teen, I've loved the way piano sounds on JBLs (I've had a Steinway grand almost since then).  I was blown away when I heard Wagner on a pair of Bozak Concert Grands.  Strings always had an unmatched warmth for me on KLH.

I've owned and loved JBLs since a teenager (over 50 years ago!), acquiring a bass reflex system with D130s alone at first, adding "potato masher" horns around 1970.  I still have them, and recently hooked in a pair of O75s.  In the early 1990s, I lucked upon a Paragon and vintage McIntosh MC240 & MC275 amps.  At first, I thought the sound impressive, but a bit harsh with weak bass.  The harshness increased as one moved closer to the horns, of course.  Subsequently, I learned that the previous owner listened at less than a moderate level (he had a cheap L Pad attached to it for convenient volume adjustment!)  I added a graphic equalizer and used it for years until I noticed that the (stiff?) 150C woofers had blossomed.  I took the equalizer offline and added a pair of JBL 2405s in parallel with the O75s.

My friends, mostly professional musicians, never failed to be impressed.  However, for me, there was yet a ways to go.  Five years ago I installed a McIntosh MEN220, "Room Perfect" component—bi-amped with an MC2105 for the low end and the MC275 for the horns and tweeters.  After running the room correction algorithm, I found that a great majority of what I had perceived as shortcomings were essentially gone.  There's nothing like live music, but this system continues to give me a thrill.

Horns can be the last loudspeaker you would ever need to buy good ones are not obsoleted as quickly or at all like nearly all conventional dynamics and estats.  They hold up well with time unlike the many others and can be easily repaired or upgraded. Horn based systems are great at producing a near real sound that the other types struggle to produce. But they are large take skill and knowledge to set up and are a bit harder to source. The best in horns is fully horn loading and most consider this just a bit to much to pull off. So many of those who claim to have heard a horn system most likely only heard hybrids not full horn loading. 

My Heresy IIIs were extremely easy to set up...you take them out of the box, put them in front of you, attach the wires...

Look how large a K Horn midrange horn has to be just to get down to 500 Hz were it crosses to a 15 inch woofer. This is one area were that ESLs have a major advantage over both horns and dynamic speakers. You can easily design a speaker that is One Way all the way down to 100 Hz as long as you can live with the size.

@mijostyn   The Classic Audio Loudspeakers model T-1 employs a machined horn that is crossed over at 250Hz. This is an easy speaker to google images. The trick to getting horns to go this low (500Hz is easy) is to use a modern surround like Kapton for the compression driver. This was solves one of the more serious issues facing old school drivers- breakups resulting from inability to deal with excursion could make older drivers somewhat painful and screechy. OTOH, crossing over a 15" woofer at only 500Hz is pretty easy- most of them can go considerably higher than that without breakups.


Admittedly the T-1 is a speaker that has been too large for my listening rooms but CAL also makes a version of the same idea that is taller rather than wider (the T-3) and that does fit. One advantage horns can have is that they can be a bit easier to place. My speakers are only 3" from the wall behind them yet they play soundstage width and depth with ease.


IMO/IME a lot of people that are down on horns really haven't been paying attention to how far horns have progressed since computer power has become so ubiquitous. Duke's loudspeakers (Audiokinesis) are also a good example of that and Duke is also a master at crossover designs that really blend seamlessly. Understanding how the horn is to be used (a PA horn is often not ideal in the home for example) can eliminate entirely that 'horn sound' to which so many audiophiles object.