Those 19-21 composite look nice, but I had very bad luck, so far, 3 drivers dead and only 2 survived, seems they are too fragile, they also don't really fit mx500 shells, they seem to be slightly more shallow, a wee bit less then 15.4mm wide
Had to sand the lip off the mx500 shells, but even then, I can't Close the shells or else they break the voice coil leads, I also noticed the leads are glued really tight to the ring the holds the diaphragm, so if you press hard to closed the shell, the ring seems to flex and breaks the leads
I don't know why they have done this, other drivers don't, guess it's some genius way to make us buy more
For now, though I know they sound good, I think I will pass.
Decided to invest in some closes back cans
Srh840 is looking good