An acoustic door assembly having 1¾″ thickness, a sound transmission class (STC) rating greater than 50, UL10C 20-minute fire rating, and constructed without sheet metal or lead. In an embodiment, the door assembly includes a frame housing a decoupled internal core sandwiched between two mass-loaded vinyl outer faces. The internal core includes a multi-layering of low-density layers for absorbing high-frequency noise, damping layers of mass-loaded vinyl for absorbing low-frequency noise, and a flame-retardant layer. The outer faces are a multi-layered assembly coupled to a frame of the door assembly and in contact communication to the internal core, the outer faces having layers of mass-loaded vinyl, plywood, high-density fiberboard, and a veneer.