Of course 1hz. This is so basic.
Not basic at all! As I said, most people spot check at third octave intervals. Even really good engineers often misunderstand room acoustics, so why should I have assumed you know how to measure a room?
Trying to portray me as average and lacking even elementary skills of measuring is quite childess
I don't need to portray you as anything - you do a great job all by yourself.
Anyway, back to your listening room, maybe this is in a basement and you have substantial insulation above the drop ceiling? Again, I never see a 12 dB span in a typical enclosed and untreated room that size. It's always much worse than that. If you'd like to post a few photos of your space, and a graph of the response you measured, and show where the microphone was placed, I'd be pleased to comment further.