Trytone, I am not sure I can help other than to offer my sympathy. I have been working on my room since last October, and although I have made a good bit of progress, I have a fairly high level of frustration at this point. I have spent some money, and done a lot of work, and am at the point where everything I try results in improvement in one area at the expense of another. I have dealt with two different reputable companies, and they are both quite reluctant to offer anything definitive in terms of systematic diagnostics. I've been told it is very difficult to do better than plus or minus 5 dB without having a custom built room. After several months of work and spending about 2K in treatments, I'm still seeing plus or minus 9dB and having some ringing issues below 50 Hz.
With respect to your 50 Hz null, you eliminated speaker boundary problems in that you moved the speakers and it did not shift the frequency of the null. I use the REW software, and I plugged your room dimensions and speaker and chair locations into the room simulator. It does not predict a null at 50Hz. You have changed most of your equipment recently, which seems to rule out your stereo system.This is weird. Can you use your Omnimic program to send a single frequency continuous tone? I was thinking it might be worth sending a 50 Hz tone through your system and seeing if you perceive a null from your chair. If you hear an obvious audible reduces volume vs 40 and 60 Hz tones, you know it is real and not some sort of software measurement glitch.
One other possibility. It is possible that something in your room has a resonant frequency at 50 Hz. If, for instance, the flooring were selectively absorbing 50 Hz, it might well result in a general reduction of that frequency around the room. I read somewhere that 1/2 plywood tends to absorb at 70 Hz, and I am seeing a dip in my room centered at about 68 that seems to resist my efforts to mitigate. Perhaps others can comment who have plywood sub flooring in their rooms.
With respect to your 50 Hz null, you eliminated speaker boundary problems in that you moved the speakers and it did not shift the frequency of the null. I use the REW software, and I plugged your room dimensions and speaker and chair locations into the room simulator. It does not predict a null at 50Hz. You have changed most of your equipment recently, which seems to rule out your stereo system.This is weird. Can you use your Omnimic program to send a single frequency continuous tone? I was thinking it might be worth sending a 50 Hz tone through your system and seeing if you perceive a null from your chair. If you hear an obvious audible reduces volume vs 40 and 60 Hz tones, you know it is real and not some sort of software measurement glitch.
One other possibility. It is possible that something in your room has a resonant frequency at 50 Hz. If, for instance, the flooring were selectively absorbing 50 Hz, it might well result in a general reduction of that frequency around the room. I read somewhere that 1/2 plywood tends to absorb at 70 Hz, and I am seeing a dip in my room centered at about 68 that seems to resist my efforts to mitigate. Perhaps others can comment who have plywood sub flooring in their rooms.