So I've done a bit of work on these speakers. First off, I've put back the original mid-range driver. The reason it sounded muddy & unclear is because it was fading out intermittently. The Italian made Faital Pro replacement mid-range was too efficient (97db @ 1 meter) for the other drivers and it was over-powering on certain music genres, so I had a look at the original mid-range and repaired the short. Sounds fine now. It is a bright & crisp mid and is now properly balanced with regards to the other drivers.
I managed to get my hands on another woofer produced by JVC, it was actually in a Pioneer speaker. Got these all Japanese made woofers for nothing. So I pulled the JVC passive radiator and mounted the second 12" woofer in parallel. Overall speaker impedance dropped from 8 ohms to between 4 & 6 ohms, still fine for my amp. I also replaced the tweeter a few times with a Jensen, JBL, an old Tannoy and an AR tweeter - all were very good but their volume was too low on account of their low efficiency rating. So I chose this 105db @ 1 meter Piezo tweeter. My top-end hearing isn't what it used to be, so this one worked out much better. I field tested them with jazz, some classical, hip-hop, house, Paul Oakenfold techno and some 80s rock. They handled them all no probs.
These Franken-speakers are now the perfect speakers for my den. Mid-range is smooth and not peaky, mid definition is good too - but not as good as the Faital Pro mid. May hunt for another mid going forward. Highs are dynamic & crisp without being harsh. Harsh is always something I'm trying to avoid. The previous JVC tweeters sounded boxy and closed, these new tweeters are open and much less directional - speakers sound similar when I walk around the room.
Not sure what I've made these into, whether they are still semi-passive rad or are now semi-sealed is tough to say - there is no port and certainly no lack of bass. The math says there is enough volume in the cabinet to support a sealed or semi-sealed design, but my ears were the final verdict. I'm glad I ignored the math and just used my ears. The whole idea of this was to get that bass I was after, modern designs w/ 6/5" woofers just don't do it for me unless there's a sub attached and I didn't want that in this application. They now have excellent bass, much smoother and more well rounded on the bottom end, nothing quite like dual 12" woofers. I feel the extra sound dispersion is from just having 2 extra drivers to produce more sound projection, so more bass, more perceived volume.
Just in case I was polishing a turd, I invited a couple of audio snobs over and after a good laugh at my creation, they enjoyed the sound and especially the deep bass. They liked the Faital Pro mids better though, I'll work on that.