Nondirectional & Inaudible Bass: What Frequencies?

I think the theory might hold up better in an anchoenic chamber than in real listening rooms. Bass frequencies can excite all kinds of resonances in real rooms the que the listener back to the source of the added vibrations, the bass.

I think that theoretical calculations may be helpful, but eventually, each particular setup will have its own characteristics, depending on room size, the components, placement, and even the furniture (and so on). In my experience, the importance of bass directionality increases proportionally with room size. Using test tones, in my smallish living room, I could not identify the source below 70 Hz or so. Again, with test tones, the very lowest limit where I could hear a signal was 20 Hz, but this can vary from person to person and the equipment also makes a difference. At 16 Hz, I could clearly see the woofer's cone moving, and feel some physical air pressure, but no sound (at least for me). I think with real music these low frequencies are seldom "audible" per se, what they most often do is to "round up" or to "fill" the sound of the instruments (complementary harmonics? I'm not sure).
Anyway, this is just MY experience from the period when I was concerned with these questions spending hours with measurements and tinkering. Lately I just try to enjoy the music :).

Different theory. My room is 15 x 25 feet with high ceilings. Instead of stereo subs, I am crossing everything over at 100hz and have 1 sub in the front and 1 in the rear. With a lot of furnishings in the room, the bass just wasn't even throughout the room.
What subs: pair of Nelson-Reeds with Janis 1/a sub amp-crossover and an energy.

This discussion also presupposes that the output of a sub is nonexistant above the crossover frequency. But, with a 24db crossover at 100 cycles the thing is only down 24 db at 200 cycles and 48db at 400 cycles. This is certainly audible.

Viridian, excellent point!