- "A straw man...-Wikipedia
My apologies, I forgot nobody has a sense of humor anymore. I thought it obvious the word "bookshelf" was a bit tongue and cheek, especially since I included "small towers" with them in the very next sentence. Though I wish you'd spent more time addressing the technical aspects of the discussion.
Since I agree JBL left some sensitivity on the table by tuning the box lower than would be optimum for sub-only use, I'll give you that with a higher tune on the box and a 12" the overall end result wouldn't be hugely compromised output-wise, but that's a judgement call. And since their target customers wouldn't buy them since they'd sound like garbage without a sub, it's hard for us to say the 15" is "wasted" for output capability as it allows the sensitivity/output of a higher tuned 12" but also sounds OK without a sub which is needed for their target customers.
A 10", 8"? No. It's a completely different speaker by then. Been there, done that. Pick pretty much any line of high sensitivity pro audio woofers, from the same brand in the same line with the same intended purpose, and go down the line in size from 15 to 12 to 10 to 8" and you see a significant hit in efficiency and power handling with each size reduction. And when you properly design a box for each of them in order to maintain as much of that efficiency as possible, you generally end up with a smaller box with a higher tune and a lower output capability.
Remember to properly integrate with a sub at 80 Hz you need meaningful output well below that, so at some point this becomes an issue if you let the box tuning get too high--and yes, that does become an issue with the smaller high sensitivity woofers.
I've built a pair of very similar speakers (in concept) with a very high efficiency 8" pro woofer and a "full sized" waveguide (for that driver size) as you can see in my avatar. And yes, they're fantastic speakers given how much was (not) spent on them. I'm not sure it can be done much better from the standpoint of efficiency/output/directivity.
But they are what they are. They're a little speaker (yes, I'd call them "bookshelf sized"), a very sensitive high output speaker
for their size, but a little speaker in the end. They certainly aren't mid-bass monsters (though if mounted in a baffle wall would be fine
for their size), and while output would be adequate for use as an LCR in a small room, personally I'd choose a larger speaker for a medium and especially larger room. When compared with my "big" speakers, there just really is no comparison at output levels needed for a large room. The bigger speakers are just a much better tool for the job.
A 12", 10", or even 8" pro audio mid bass of substance can deliver vast impact or slam above 80 Hz, to the point where the home audio listener runs out of the room with hands over ears.
I guess you've never experienced a half way decent home theater.... One needs to be very careful generalizing about how much SPL "home audio listeners" need. On this site we have people reading from closet-sized dorm rooms to giant mansions and everything in between. People who listen to dynamic content (largely orchestral recordings and movies) who want a realistic experience will have much different output requirements than those who don't. So, to leave personal SPL tolerances out of it, one can look to some industry standards for guidance.
Dolby specs 105 dB at 2/3 the length of the room for each of the LCR by themselves. Not peak, but sustained for 2 hours...with 3 dB amp headroom in reserve. Is that a higher bar than most people
need for "good sound?" Probably, but it's not for me to tell them that. It's a pretty important bar that gives us one point of reference. I'm certainly not going to tell somebody there is nothing to be gained by going bigger from a system that can't even come close to it. And personally, I find listening to classical music at a level where the "quiet parts" approach the noise floor of the room enough you're left with a crappy SNR just isn't much fun.
All that's only addressing dynamics/output capability. You completely ignored directivity. A speaker that can control the directivity 500-700 Hz lower than another is a completely different speaker at any output level. Without judging whether it's right or wrong, if the user wants directivity control to the lower frequencies with this design, a smaller speaker simply doesn't give it to him as others have addressed above.
As I stated before, the 4367 certainly isn't a perfect speaker. But it does do some things many other speakers don't, or at least don't do as well. For those who are looking for those things, there are a whole lot of worse choices.