Well, they were "tuned" to
sound good with a bass guitar, kinda like old Ampegs, Fenders, Acoustics, etc. were. Those old cabs pre-date TS Parameters, which generally confounds the crop of "instant expert" self proclaimed speaker cab designers that have cropped up since WinISD became available as free ware.
Of course WinISD and to a greater extent the more sophisticated (and expensive) enclosure software are a tremendous time (and wood) saver, however in my experience their
real value lies in calculating efficient boxes for
reproducing program audio, like for home audio or sound reinforcement applications rather than for sound
producing MI boxes like bass guitar cabs, guitar cabs, etc.
A lot of the time the variations from theoretical "optimum" in MI cabs is what actually makes them
sound good when used with an instrument for sound production. For example; an SVT 810 is a
disaster according to what theory (and therefore the "internet experts") say a cab designed to optimally reproduce the sound spectrum of a bass guitar cab should respond like, but for some reason the thousands of
real professional sound folks continue to use them on pro sages across the planet.
I suppose the problem is that those folks are just too busy with recording contracts, filled stadiums and such to read internet forums, so they just don't realize that the rigs actually sound like crap...
Same goes for open backed guitar cabs, the unenlightened players like, say Joe Bonamassa, Jeff Beck, Clapton, etc. for example, obviously are completely unaware that those open backed combo's are absolutely
horrible at reproducing sound.
Imagine how much better their tone would be if they only took advice from all of the internet forum "wanna be" speaker designing gurus...
Obviously I digress. Your best bet is to try something reasonable, the 215S is a very forgiving box indeed. I have personally put a myriad of old and new speakers in my 215S cabs. My "for the time being" go to is a pair of EVM15L's, which I personally prefer over the EVM15B's and EV SRO's I've also tried in the box.
It sounds great with AlNiCo JBLs, however I pound my go to cab with a
strong 400 watt tube amp cranked up pretty good and don't really want to sacrifice one of them if I get a little too enthusiastic at a gig or something.
In the near(?) future I'm going with a real "sleeper" driver that I have
some experience with, a couple of cover band gigs; the WGS BG15C. To my ear they are tonally kind of a cross between the EVM15L and a K140, EV like power handling and mid-high extension with that rich JBLesque bottom end when loaded in a 215S. I am planning to load a pair of 215S cabs with the 16 ohm versions when I get around to it.
I figure I can bring one or both depending on the venue, without worrying about damage; they are new, inexpensive, and can take a ton of power.
The rest of my Sunn cabs will be completely relegated to Sunn head and AlNiCo JBL use, vintage duty, which as we all know ain't bad either!
