Dayton RS75-4 Midrange Speaker Adapter

Adapter for fitting a Dayton Audio RS75-4 midrange driver to the front-door and rear-deck speaker enclosures of BMW E31 840 and 850 models. The creator supplies STL, 3MF and Fusion 360 source geometry and physically demonstrates the adapter loose and fitted in the factory enclosures; mounting holes require drilling after printing. This adapts aftermarket hardware rather than reproducing a BMW component, so no speaker-box parent number is assigned. Verify cone, grille, wiring and fastener clearance before reassembly.