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

Did you mean the JBL M2? 

(the JBL M1 comes to mind) are horns used.  

Yes JBL M2- Sorry!.

This efficiency issue is one "spec" out of many that a designer must balance. All these performance parameters are evidence of the enormous number of trade offs in creating a complete driver/box/electronics design. So designers make their own choice ("I want a horn, that’s what I like") and balance everything to favor their choice ( it will have limited dispersion, HF narrowing, but that’s okay I’ll try and minimize it, etc). This is the way speaker design is, balancing hundreds of issues that represent hundreds of choices and all of them have resulting tradeoffs. You may want a low distortion driver but its too expensive, or the OEM manufacturer can’t build it till next year and you’ll be out of business by then. Or, the horn you want to use wont fit the box you already bought or built, or you don’t care about efficiency as amps are cheap so you want the widest bandwidth possible, ..on and on.

There is a practical science at play here, with product development controlled by economics, engineering principles, sales, marketing and a whole bunch of other factors we’ll never know about at the factory that drive those choices. In the end, the company "sells what they have" as ALL speakers are a sum of trade offs. Many of the issues debated are really arguments over someone’s clever marketing points and we as consumers take these marketing issues as gospel, as facts. Since everything is choices, it may be these performance features are important only in THIS type of design. To another design, they don’t matter. Like wide dispersion is not desirable when you are trying to throw sound over a long distance (think football stadium). But to home audio, and wide dispersion means I get to sit on both ends of the couch and hear it properly, that matters a whole lot to me.

The company I work with makes perhaps the best cone and dome drivers on the planet but their speaker cabinets are plain rectangular boxes. Some say the box is everything but in this design 2 of the 3 drivers have their own chamber and the box is not involved in the driver at all. The baffle is more or less "a holder" for position and improves output as there is acoustic gain by sealing drivers to a surface. Some say the box looks old fashioned- so to balance that we use some exotic woods and make them look like beautiful furniture. The best you can do is find a way to make some happy and others will just not see it/hear it the way you do.

These are trade offs made all the time by speaker builders and then we as purchasers and users get to choose if we agree and make the same choices. The funny part is how people, who aren’t acoustics scientists, want to insist their isn’t a choice, there is only one way to do it, and this is it! I know, I read the entire brochure! Or, I saw this demo once that showed XYZ and THAT was the truth let me tell you!   "Their" speaker maker’s choices are the only right ones, they understood it and no one else does.   A comment like this company is the only one "that really understands cabinets" is a very simple view of a very very complex business. Speaker engineering and building is HARD and because its physics, many of the choices are not flexible or open to interpretation. There is a large body of science behind all this that is available to everyone to draw on. I certainly don’t think the brand I work with has the only solution. There IS more than one way to do it and many good sounding speakers out there. Each has its own application set that it excels at and other applications that it doesn’t do well with. We have not arrived at a universal solution.

Brad

@lonemountain  If I was setting up a nearfield situation (like we use in my studio) I wouldn't use horns either; they're just too big- and how do you get the midrange and tweeter to blend? Nearfield I don't think I'd be very concerned about efficiency either.