Let me start by apologizing for the length of this post. "I have made this longer than usual because I have not had time to make it shorter." Blaise Pascal I recently converted some of my 90-year-old basement into a one room project studio. It started by moving one four-foot section of wall to make a more convenient jam space, and moving one outlet on that wall. This led to moving the outlet on the wall. The scope of the project quickly escalated into replacing most of the electrical in the house and adding additional circuits (a lot of the house was still on knob and tube wiring), building walls, reading a dozen books, significant acoustic treatment, and a lot of time and money spent. Let's just say I've caught the bug in the last year. I can post details if anyone is interested. Anyway, I ran an analysis of the room using RoomEQ Wizard today, performed at the mix position about a third of the way into the room. I'm generally pleased with the results, the low end of which is posted below. They're a significant improvement over the bare concrete walls they once were. The room is now flat enough for my needs, except for a null of about 17 dB at 59 Hz that I can't explain. This corresponds with what I hear in mix translation. Things tend to translate well, except the kick, which tends to explode when listening to the mix elsewhere. The room is 15' x 25' x 7'3" to the unfinished floor joists stuffed with fiberglass (7'10" to the subfloor above). From my limited understanding, I would think that a null that deep would correspond to a prominent axial mode. Dimensionally, though it's nowhere close to an axial mode. Only a tangential mode gets close to 59 Hz. Is it possible that a tangential mode could create a null 17 dB deep? Does anyone have any ideas on what might be causing this? I'm grasping at straws. As far as treatment, I have triangular bass traps 2' thick straddling the front corners from floor to ceiling, and a dozen 2" 703 panels spaced 2" from the walls. The third corner is also straddled with 703 backed with fiberglass batts. Which leads to the last corner... The biggest irregularity in the room is the HVAC. The furnace with all its sends/returns are in one corner of the room, so I'm imagining that somehow acting as a Helmholtzish resonator and sucking out the 59 Hz. A stretch? I can post post pictures/make a drawing of the room, or anything else that helps. Thanks for reading my ramblings, and I appreciate any advice.