I am going to attempt to create my own door assembly (frame, door, etc) for my soundproofing project and am looking for very dense, heavy wood. The first wood that comes to mind is oak, but I suspect that will be incredibly expensive. However, if that's really the only wood that would do the job then I guess I'd be willing to pay for it. I prefer types of wood that are typically readily available through retailers like Lowe's, Home Depot, and the like.
Note that is a separate inquiry from door sweeps and other add-ons. This is solely about the door and frame itself.