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be wrote:

Instead of defining the ULF range from the reproduced instruments, it is much smarter to do it based on the first resonance frequency of the listening room, because the frequency response of a closed room has a 12dB/oct rise in frequency response, due to the cavity effect starting approximately half a octave below the fundamental mode of the room.

Yes, I would agree BUT there is one thing. The division upon LF an ULF is purely semantic division that we invent in order to stratify out verbiage. We presume that LF is bass and ULF is not tonally auditable bass. In reality there is no such a division. A playback might have ULF channels the will set to aggressive and “modulate” a tonal output of midbass of LF channel. It also might be that a normal LF channels might not have any tonal information. Between those two polar examples there are zillion possibilities that do not comply with any rules of stratifications. So, with all out conversation there is always a give or take leverage. A playback might have some kind of a channel that goes from 100Hz and all the way down and still to be perfectly operational.

My desire to separate, at list logically bass on LF and ULF is primary derive from the fact that in most practical cases LF and ULF is need different attention. If you look at my particular case then it is obvious that only after “inventing” the separation of LF and ULF I was able to understand what I am doing with my one playback. I have no LF but midbass and ULF. It does not bother me at all but while setting the thing up it was very critical to me to get the idea that my Midbass and my Lowers Bass are different players in the auditablety game.

Generally I agree that the first room resonance along with reverberation time in the room are very big players but I feel that they might be overridden by audio methods. The crossover slope at lower frequency channel is superbly powerful tool that can do some amassing things. Unfortunately it is VERY hard, virtually impossible, to find good hard-suspended low Fs bass drivers the work with low crossovers. The low Fs drivers have cones that have to much inertia and too much freedom. Combine this driver with no enclosure air suspension (open or infinite baffle) and you have the bass driver that shaking like jelo-cake during earthquake. Put in there tone character and it is absolutely not accomplishable mixture. There was one very good 14” hard-suspended Klangfilm driver (if I am not mistaken it was 405, it was long time ago when I experimented with it) that had nice tone and worked very well with no enclosure suspension but it was 50Hz driver and below it was rapidly dying. If you want the same at 25-30Hz then good luck to find it.

If it was up to me to experiment then I would get 10 per side Altec 416/515 drivers, put them in sealed array and try to see what happen. Altec had 515B with 24Hz of Fs, I am sure it is possible to drive Fs even lower. The key is do not let them to excurt to much. If each of them moves for a few mm then it might be a good result. Where to get 20x515B drivers and to be able to much their characteristics? Do not ask and do not tell if you know where…

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