Having major issues with my room with big resonances at 50hz and other harmonics. Not helped in that the wall behind the speakers is virtually all glass (patio doors) and all walls are solid brick. Floor is wood laminate with Supercell foam insulation beneath. I do have a sub in the opposite corner which helps a bit, but what treatments should I apply to kill some of these monster peaks and dips? Note I do not have access to any corners due to the patio doors at the front and a door into my garage at the back! I am thinking limp mass bass absorbers on the back wall, but am I correct in thinking I need to address the 25Hz primarily and all the others should reduce as well? Of course 25Hz is not that 'audible' but is there any point in trying to address the 50hz without doing the 25 first?