Nondirectional & Inaudible Bass: What Frequencies?

From personal experience my REL sub is crossed at 27Hz (so probably outputting up to 35Hz). It was directional enough that I ended up placing it between the speakers, next to the left hand speaker (since I listen to a lot of orchestral music, and that's where most of the bass comes from). The sub now blends very well with my main speakers, to the point where it is very difficult to pinpoint the subs location with your eyes closed.
I know nothing about psychoacoustics, room resonances etc, but my experience would lead me to believe that saying bass is non-directional below 100Hz is something of an over-simplification.

Sean: Please keep in mind the differences between directionality and perceived source of energy. They are distinctly different, but often confused. It does seem by your comments (left hand speaker since that's where most of the bass comes from in an orchestra) that you did experience directionality as opposed to energy source. Therefore, I would suggest that there is something other than pure bass coming from the REL. Either distortion or harmonics at much higher frequencies than 27Hz. Having heard some of the larger RELs I am surprised, but not knowing the model, it could be one of the smaller ones and could be the cause for having this occur. You really have me very curious about this, because in theory it should not exist--but we all know that "in theory" is just that--and often does happen. Could I pursuade you to use a test disc, or better sweep tones and turn off your main speakers and find out what the actual response of your sub is. I'll bet you are getting information out of it much higher than you expected.

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 :).