Illka--I used the Behringer DCX2496, but it actually doesn't have a 15 Hz HP filter. I used its lowest, 20 Hz (12 dB/octave Butterworth), setting instead but used a wide boost (bandpass filter) around 20 Hz, so effectively the filter was around 15 Hz. I couldn't have gone much lower with the DCX2496
Seaton--Hi Ilkka, Awesome results on this sub and of course the data on all the others. FYI, you can use the DCX to high pass lower than 20Hz. There are two means to get an effective lower frequency high pass filter. If you look at both 12 & 18dB/octave Bessel filters, you will see the sharper roll off is in fact a good bit lower than the nominal Fc. Addition of 1-2 PEQ's makes a lower effective XO pretty easy. The other, more straight forward option is to use a Butterworth or LR with a simple 12dB/Oct Low Shelving filter (would have to check the "Q" of the shelf to see if or LR matches best). In simple terms, you are basically applying a Linkwitz Transform to the high pass filter. Works just fine within reason. There is probably some point where the cut and boost exceed the working range of the DSP math, but I've done this in practice a few times with good results.
VAS--you can't ( as far as i can tell ) set any filter to lower than 20 hz on either DCX or DEQ however what you can do is:
1 - set SSF to 20 hz
2 - apply parametric boost at 20 hz at the same time
3 - apply CUT at around 25 hz or so
by playing with the parameters of these 3 filters you can get 2 and 3 to mostly cancel each other out above 20 hz but their net effect will be significant boost below 20 hz
this boost below 20 hz will interact with 20 hz SSF and the net result will be that the boost will largely get cancelled and SSF will shift down in frequency.
how much lower you would be able to push the SSF frequency would depend on the order of the highpass. you would be able to push a 6db/oct highpass much lower than a 48db/oct highpass.
WmAX--Well, that's actually quite easy. The DCX does not have ability to set filters below 20Hz. While this may seem to high, it's not really. You can easily extend the actual filter by for example setting high pass filter to 20Hz, 2nd order, Butterworth. Now add a single parameteric band at 20Hz in the EQ section on the unit, set to Q of 1.5 and gain of +4 dB. This will counteract and extend the roll off, giving you an effective roll off on the 13w7 of -3dB around 17Hz and -6db around 14hz, with rapid roll off after this; exactly what you want with this 10 cubic foot cabinet tuned to about 16Hz to prevent excessive excursion under this tuning frequency.
