Resonances! Can't live with them, can't live without them! I should probably try to wrap this up.
I ran tone again today to reestablish my aural baseline. I realized that below 92dB SPL a 60Hz tone resulted in no obvious harmonics at the sweet spot. Above that level and at any frequency below about 90Hz, resonance could be distinctly heard rising in level in concert with the loudspeaker output. Just as with any LF tones in small spaces, the resonance(s) behaved like a standing wave, rising and falling in level depending on position in the room. You could feel pressure changes as you walked, but of course we expect that. It was harder to actually locate where the source of the resonance was.
Moving the experiment forward, I installed the layered rubber mats from Supply House. I drilled them at my press with no difficulty. Here you see the centers marked for drilling.
I slipped the pads over the extended blunt ends of the Revel supplied footers and returned the speakers to their marked positions. Oy! My bursitis! And yet, still with the vibes! I'll spare you the image of my confusion but I eventually realized the recessed lighting can 5 feet above the speaker was ringing. Yeah, that was surprising but gratifying. Adhesive tape (nearest to hand) fixed it. Yet to annoy more, there was still that noise, perhaps from a different direction? The other speaker is buzzing now? Finding that one of the windows was rattling out a decent imitation of a Revel loud speaker was a happy ending but underscored how hard these noises have been to track down and isolate. I shoved some matchsticks into the window frame. For now.
What did I learn? Well, I think the speaker(s) actually may have been "vibrating" at the start of this. Perhaps initially disturbing their relationship to the floor (a couple of days ago) was to good effect but then again, with rattles remaining in the room it's possible that I only thought I heard the sound coming from the speakers. But I don't (or prefer not to) think so because the first and most significant improvement came from simply tipping them over, tightening them up and returning them to their initial locations. There were no other changes but in retrospect, I think that stopped them from humming. I can't say definitively if the rubber feet are doing diddly or diddly do but it does sound lovely in here with all the sympathetic vibrations banished. I guess my rig puts out a lot of low end and my room wasn't properly rigged for the job and maybe that's the real conclusion.
I'm confident my floor is still a bit of a weak link. I can feel it moving with the music when the action gets heavy, and it has some soft spots just where they seem to do me the least good. I don't know if that's anything I can change but I am happy with the sound here regardless.
And now, for the "psycho" acoustic part, the windup and the pitch. I think the speakers may sound a bit clearer with the new feet. I can't swear to that and won't. In fact, I have no idea what really happened here except for me bubble-gumming everything that rattled. I didn't actually use bubble gum, but maybe bubble gum IS the real good stuff! What a hobby!