@mahlman , you have to be very careful with specs when it comes to bass. What a speaker does at 1 meter is a far cry from what it would do in a room at 3 meters. Most woofers can move fine at 20 Hz but it does not mean they are actually radiating the sound with any authority.
@phusis ,I am honored that you would spend so much time analyzing my post.
It sounds like we are on the same side of the ile. We both use computer audio and not dedicated music streamers like an Aurender. I suspect you are a PC guy and I have to admit that my computer knowledge is somewhat lacking. But, the sound cards I have heard, and I have not heard all of them did not sound as good as an Apple driving a Berkley Alpha USB. They were obviously veiled for some reason and I suspect why many dis computer audio. I would not go any other way.
My point about brains is that each brain has it's own way of interpreting it's senses. Some interpretations are better than others. Just because someone thinks a certain something sounds better does not mean it will to other people. You can only trust the opinion of other people who interpret sound the way you do. I have two such people in my life. A multitude of issues will determine sound interpretation, looks and price are the two big ones. In my world they do not count one iota other than there are certain pieces of equipment I like that I can not afford, at least for the time being.
You are quite correct. Horn loaded drivers do not have to work near as hard because they are impedance matched to the air. Very few people use subwoofer horns because they are extremely large and they tend to have their own resonance problems. Forgetting about horns everything else I said is true. Someone mentioned foam surrounds as being best. It depends on the design and intension of the driver. I will say if you see a subwoofer with a foam surround, run away. I have seen to many of them fail including the Velodynes I ran for a decade or so. One of them is now the base for a fish tank. The vast majority of sub drivers are made with butyl rubber surrounds for a reason.
Take any pair of 12" or 15" sub drivers in an appropriate sealed enclosures. Put them in a 15' X 30' room, cue up a 20 Hz test tone and turn it up to 90 dB. What you will see are cones flying in approximately a 1" blur, a little less for the 15 cone. What you will hear is your whole house rattling. This is not my local context or my opinion. If you do not know this it is because you have not built enough subwoofers. What is "local" is that I only expect dynamic drivers to make noise below 100 Hz. Most residential folded horns run up to 350 Hz. K horns used to be 500 Hz. That is not bass anymore. Middle C is 256 hz. It is well into the midrange.Then you are faced with another huge problem. A large chunk of your midrange is five feet behind the rest of your speaker. That is a 5 ms group delay! In order to make that work you will have to biamp the speaker and put a 5 ms delay on the high frequency drivers using DSP. I always wanted to try that with K horns to see what you would get. I have another local problem. I use Line source loudspeakers. In order to match their radiation characteristics I had to create a line source subwoofer array using 4 subwoofers. On a 16 foot wall 4 subwoofer horns would be a site to see. I am working on a new system with 8 subwoofers. The four 12" subs I am using right now are working too hard and on occasion I run them into their bump stops. They have a X max of 19 mm. That is a 38 mm excursion. In a 16 foot wide room. It takes a lot to make powerful sub bass, a lot more than most people think. I do not have any problem with multiple drivers. I would use larger ones but then the size of the enclosures would be prohibitive in my "local" situation.