Nondirectional & Inaudible Bass: What Frequencies?

Viridian hit it on the head. Moncrieff's research shows that bass becomes non-directional or "loads evenly" at appr 100 Hz. What allows us to precisely place the woofer or subwoofer at frequencies below that are either high levels of harmonic overtones or plain old distortion. This is one of the reasons why downloaded subs sound very different from front loaded subs. The harmonic overtones and distortion are masked to a great degree when downloading, making them harder to localize AND affecting their tonal balance or "attack" characteristics. Try listening to a sub that is downfiring and then turn it on the side so that the driver is now front firing. Other than the difference in the type of footers used, i think that you'll hear a MAJOR difference. Sean
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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.