Nondirectional & Inaudible Bass: What Frequencies?

Bass may go non-directional at 100-125 Hz (equal power in all directions), but that does not mean we CAN'T tell where it is coming from. In that case, the answer to your question is that the room does have some effect and that psycoacoustics are taking over at that point.

The audible cut off may vary from person to person, just as it does at higher frequency's. However, sound presure on the skin, the movement of hairs all over the body and the vibrations felt through the floor, chair etc... all take over at even lower frequencies. Your brain combines all of this audible and inaudible information to figure out what is going on. With that said, the lowest frequency in which you can DETECT it's source is probably lower than you think.

Sdcampbell make some good points, however I disagree with the time duration comment. Longer may be more difficult to detect, as the sound waves and their respective decays are colliding and overlaping each other all over the room. A short duration sound is much less confusing to the brain. We hear the initial sound and it's decay with nothing else to fool us.

I also disagree with the lack of low frequency info on home theater software. The LFE might not have much below 25Hz, but the amount of bass in classical music on a movie soundtrack is the same as what is found on 2ch. If you think about it, 80% of most movie soundtracks is actually music.

There are two issues about this. One is directionality, such as hearing a distinct sound coming from a source, vs perceived energy source. Thus GS has a point about the distance between the ears (except it should be 1/8 of a wavelength and your head can't move for that to really be true). My own listening says we lose directionality at a fairly high level, perhaps as high as 100 to 150 Hz, but we lose energy source perception somewhere between 40 and 60 Hz. Now there are many things that change these subjectively perceived values. For example, distortion in the subwoofer will translate into harmonics at higher frequencies, thus we may perceive directionality of a subwoofer that is crossed over at 60 Hz.

Room and placement of a subwoofer absolutely have an effect on this. There are multiple ways the room plays a significant role, from reinforcing bass frequencies (thus reducing total distortion) to positions at certain (say 1/4 wavelength) places that can create nulls and quickly give us clues as to where something is (at least generally).

One thing that makes a huge difference is multiple subs (as has been stated). This allows a flatter frequency response through the room, less work for each sub (thus less distortion), and two sources that make picking out where the sound is coming from very difficult.

Hope that helps.

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
>