Re thought this design once more and finalized down to this one. It will take two 1/2" floor flanges, a 90 degree elbow, 1 18" long threaded 1/2" pipe , one 1/2" threaded stub, one speaker mount and a can of flat black paint.. One flange gets fastened to the bottom of a floor joist, the pipe gets screwed into that, then the elbow gets screwed onto the opposite end of the pipe, followed by the stub and the second flange. I will then either attach a speaker mount directly to the flange if possible or to a piece would that's attached to that 2nd flange. I should be able to do all of this for under $50.