A major part of this question is going to be answered in a different thread. The short of it is that I want Subwoofers that will perform at low extension with authority. Not that these aren't available on the market in various products already from many of our well known ID companies, but the desire to experiment, build and learn more goes much deeper than simple "Retail Therapy."
This, I have come to learn, is not true. Really, just look at PSA and what he (Tom?) is doing with the B&C Drivers. To be fair, I can easily be quoted as questioning the efficacy of this school of Subwoofer design. It probably wouldn't take long to find at least 10 instances of me doing so.
But the more I have looked and been willing to open my mind, the more I have seen people doing this to levels of success that, in the instance of PSA, is driving what seems to be a resurgence in his business. Even here on AH, I have seen more different people than ever post up about their experience with his Subs, and more still asking about them.
Again, this is a much bigger topic than I want to get into here and have another thread started where I intend to dig into this... but...
...As was explained to me by a California Company doing Subwoofers, what one needs to do is to understand that the T/S parameters are not necessarily limiting factors. They represent a limited system in that they apply to the Driver only. While they may give insight to how a driver will behave, they do not necessarily limit the driver from performing as one part in a larger system.
That Eminence Driver has a high Fs, as do almost all drivers in the same category (again, look at the drivers PSA is using). However, it has such a stronger motor and pole is long enough that when in a specific cabinet it can be pushing 16Hz at about 1/3 its gap while the 21" B&C or LaVoce are reaching their usable limits and pushing 2/3 their gap.
So who is right?
Again, I stress, this is largely in the name of educating myself through experimentation and practice. It has been made abundantly clear to me that the books we use to learn are also hindrances in a certain manner. Nobody is saying, "throw them out," but they don't discuss, as I've seen, how a high Bl helps stabilize the design and allows a Driver to be pushed well beyond its Fs to the point where the Xmax/Xvar/Xmech are being used to their fullest potential and where the designer can determine how much excursion is creating too much distortion for their goal and then set a limit. In the case of that NSW, I've seen models with it outperforming the LaVoce SAN214.50 and B&C 21DS115 by roughly 5-6dB at extension... and it's usually been the cabinet that limits the NSW. (I've seen a model for a box going down to 13Hz, but both the size of the cabinet and the power demand are extreme and beyond practicality.)
Where I once steadfastly would say these drivers shouldn't work like this... now, I clearly see that they can. Where once I would have flatly said no... now I am interested in understanding the how and why.
