My question is not so simple as it seems to be. First of all, it relates to choice of the range between close modal frequencies, because modal frequencies distribution defines the smoothness of AFC (SPL curve) and as a result, the timbre of the room music. If we have mf close to each other, the resonance probability for such a room dimensions grows. Second, we don't talk about any person. We assume, that HT or any other kind of control stereo room is intended for persons with sharp "musical" ears. For this kind of person, I mean, we can define minimal distance between two close frequencies. I never met anybody, who can resolve the difference in 1 Hz between two frequencies.
To my practice, it begins from 20 Hz with interval 3 Hz up to 80 Hz and than 4 Hz to 150 Hz. But unfortunately I never know any investigations in this theme. :-(