In recent years, the only place I have seen "passive radiators" at use is in some of the "small box" high-powered sub-woofers. Since many of the speakers in these subs can be 10" and smaller, I gather the passive radiators are there to be engaged by the air that is bouncing around in the cabinet along with the "active" speaker(directly connected to the internal amp) just to emphasize additional bass.
More drivers and higher-powered amps in these cubes make them usually significantly more expensive than a regular larger box sub.
