I think it is the same tweeter in them all, it looks identical...but, there is a significant difference between how the highs of the KH120 and the KH80 and K310A sound (never used/heard 420s)...I've used them all, even in the same room...I wouldn't recommend the KH120s, they're only OK...the 80s and 310s are great though...also the 120s also seem to blow quite easily, I've installed a dozen in shops, restaurants etc. and a few have gone honky (verified by measurements), whereas i've also installed a bunch of 80s and none of them have failed...