Null at 180 Hz

I have this in my Optimizing my Beginner's System thread, but I wanted to throw this in a new thread as that thread is already huge and people may overlook it.

I've been tinkering with my system the past few days thanks to acquiring a calibrated mic (I can play with the big boys now). After a lot of adjustments recommended by Lithium (thanks, Lithium!!!) I've managed to get it sounding pretty good overall. Like lay back in the seat and enjoy the music instead of just criticizing how every bit sounds.

I do have a problem: I get a pretty big, 5 - 7 dB, dip at the 180 Hz range. I'm really not sure what to do at this point, but I'd like to address it before I start really playing with channel independent EQ for soundstaging (and learning how the heck to do that).



It exists on each of my mid woofers separately, combined, and with the sub playing.



It happens in every position I test. Fr Driver, Fr Pass, Fr Center, and really bad at Rr Center.




Lithium suggested reading up on cabin mode, which I have, but I'm not quite getting any answers that help so far.

It could easily be the woofers I'm using. 5.25, fairly low grade, they're the weak point in my system, for sure. Everything else is pretty decent.

Also, I'm in an old Jeep Wrangler that had most of the interior panels and carpet ripped out by the previous owner. I'm sitting in what's essentially a tin can. Also, the interior of this Jeep is tiny. My sub is in the "trunk", yet the distance from it to my head is shorter than the distance from my head to the right woofer, if that gives any indication.

My crossover settings are as follows:



I just changed the sub LPF to a -12 dB to see what would happen. Actually seems to improve the bass a bit subjectively.

Anyone have any thoughts/insights on this? I'm scratching my head at the moment.