C50 was a cabinet designation, the "Olympus." It could be purchased with different components loaded, primarily the S7 (two-way) and S8 (three-way) systems. With an "R" designation (S7R, S8R,) the LE15A woofer used in both systems was supplemented with a PR15 passive radiator to tune the cabinet, so you're not seeing dual woofers, rather a woofer and a passive radiator there.Originally Posted by Bill H.
S8R is considered the more desireable, because, in addition to having the 075 ring radiator "bulllet" tweeter, it upgraded the 1" LE85 midrange compression driver to the more powerful 2" 375, much coveted by vintage collectors.
Indeed, the 4320 traces back to the C50SM, the smaller "Studio Monitor" cabinet (more like C51 "Apollo" in size,) which came loaded with either S7 or S8 ("R" would not fit) systems. It's more akin to the L200B than C50, in my view, though, having different woofer and crossover than the earlier C50SM....