subsonic level?

Hey guys i was wondering which way would be best to run my current sub set up.

I have an H labs in line subsonic filter, which i am running at 30hz and i am not sure if that is the correct level to run it at? how many hz should the amp be set at? i have 2 12inch kicker L7s in 38hz tuned boxes. I am using a JBL BP1200.1 @ 1ohm to push them.

Suggestions?

You have boxes tuned at 38 Hz.  Drivers unload under the box tuning frequency, so the safe thing to do is use a 24 db/oct subsonic filter set at just under the box tuning freq., IMO.  Your filter should be set a bit higher at about 35 - 36 Hz.  Although there is very little music information in that range, there could be bursts of noise or some subsonic harmonics in the low 30's, which would cause the subwoofers to flap out of control.  The higher filter should clean up your sound.

Here's a good read:  http://www.clubknowledge.com/Car_Audio_FAQ/?t29

If you can't adjust the filter (I'm not familiar with it at all) then keep it at 30 Hz and don't go below that.  (Sorry to disagree with tcss whom I learn much from!)  I would want it closer, though, to the Fb.  A good thing to do is to run a series of tests using recorded test tones in that range of freqs and try to ascertain exactly what freq your boxes are tuned at (see the linked article on what to look for in cone movement).  It may be the case that the boxes are actually tuned a bit higher than what you think (I don't know)...in which case you would look for a higher freq filter.

24 db/oct is best, but a lot of filters are set at 18 db/oct which would be better to use than a 12 db/oct.