There is further bracing of the Def2 cabinet internally to make it a Def3, and some added quieting of the structure. But Def3 does not get the immense stiffening of the front baffle resulting from the inclusion of the compression-mounted Radian 850 super-tweeter. I haven't seen the internal drawings of the cabinet mods to create Def3s from Def2s.
Def4 on the other hand is a completely new internal structure, with FRDs in a mini-Griewe chamber, the structural stiffening of the front baffle by the massive Radian compression structure, and the whole speaker being mechanically anchored by the super-stiff machined-aluminum plinth to which the down-firing cast-basket 12" sub is bolted. The internal wood plates forming the Griewe load slash remaining cabinet talk and arrest booming by the tall sidewalls. The FRDs are isolated internally from the subwoofer chamber. So you have the speaker bisected into two very strong boxes within the tower, on that massive machined aluminum foundation.
Phil
Def4 on the other hand is a completely new internal structure, with FRDs in a mini-Griewe chamber, the structural stiffening of the front baffle by the massive Radian compression structure, and the whole speaker being mechanically anchored by the super-stiff machined-aluminum plinth to which the down-firing cast-basket 12" sub is bolted. The internal wood plates forming the Griewe load slash remaining cabinet talk and arrest booming by the tall sidewalls. The FRDs are isolated internally from the subwoofer chamber. So you have the speaker bisected into two very strong boxes within the tower, on that massive machined aluminum foundation.
Phil