I have a 20ftx20ftx9ft room. While nice and spacious, the dimension causes a HUGE suckout at 40-50Hz and doesn't recover until 30Hz. I want to resize it to 20x15x9, but due to presence the room features (doors, windows, HVAC inlet, attic access), there is not good way to put up a proper permanent framing and drywall. I wonder if it is possible to line up a bunch of IKEA bookshelves and do a fake wall. They will be backed with thin backing, and likely 6 foot tall only so there will be gap on top. Will that be effective against the 40-50Hz sound waves?