The Hill Plasmatronic - I've been around this business for 25 years & seen most of them. The Hill is not around anymore, except used. It uses a plasma gas chamber, modulated by the audio signal as the radiating source - almost zero moving mass - driven by its own tube amp. The staging and focalization is without peer. Musicality is like triodes extended into speakers. It's meant to be used with a subwoofer, but coned units, except for Shahinians, are just not fast enough. Any Dayton Wrights still around - their perfect. But what to get for the crossover - only two choices - the older Shahinian and Audio Research units. They are the only units to have the transparency adequate to the Hill's.