I want to upgrade with an extra 15" sub in a ported box.
Is 28hz about right for my purposes in the back of a blazer? I'm going after low bowel-loosing vibrations (sledge hammer to the chest effect). I think this means I want my peak in the mid-30's rather than around 40hz?
I'm playing music, not test tones, but some tracks have a lot of continuous bass! (ex: lil jon- push that n****). I have 2 lanzar 10's in sealed boxes getting ~400rms each, but they just aren't doing it for me... =).

Should sub and port face the hatch, the front, or what? Port to the rear and sub to the roof??

I'm looking at an audiopipe TXXAPX1500 ($120 shipped) and a >=1000rms@2ohm amp to drive it. I designed a box for it: 30"(tall)x18"x16.5" with like 30"-35" long zig-zag port (18"x2.5"). It's about 3.5' net volume excluding sub&port displacement.

 

32 hz would be great for you. your ears cant hear anything below that i believe. i was just at a friends house, 2 12 inch diamonds in a really nice box at 250 rms sounded amazing and loud. diamonds are garbage, but the box made them amazing. stick with back and back then you can put stuff on top of the box just in case you need the room.

 

In the past, when I've used 15 inch woofers, I've gone with sealed boxes, reason being is, a 15 inch woofer has a lot of surface area to move and they're generally slower moving than a 10 or 12, so, if the song has a lot of fast bass, it can tend to sound sloppy. With the proper box, you can get the woofers you have to be just as loud as a single 15. My brother has 2 JL Audio 10's in his Mazda and it's loud as hell.

As for positioning the sub, I'd face it backwards. My experience with stereo systems, I've had better luck facing them toward the rear of the vehicle, it seems louder

 

Interesting on the sealed for 15's. I seriously considered going with a sealed box for a new 15, and I guess I'm still contemplating it... However, my bass sometimes seems kind of muddy as it is now, so I don't feel like I'd be loosing much by adding a ported box.

As for my existing 600rms(rated) lanzars, they are pretty cheap (even compared to JL audio). The SPL rating is only 85db (low). They were a good entry level choice at the time (bought from overstock.com).

I guess I'll focus on doing better box(es) for them before I drop a bunch of green on a separate sub+amp. Right now my 10's are in cheap hack-job particle board sealed boxes (may be the reason I don't get great low-end). Perhaps I'll do a MDF ported box and see how it sounds.

I wonder if I should build a box to hold 2 drivers or two boxes to hold 1 each... *sigh*. Probably 2 boxes, right? Ported @32hz? =).

Thanks..

 

I would build 1 enclosure for both woofers. If you want to port it, it won't matter if you put a divider in it or not. Look around online at different box designs to get some ideas. When designing a box, it really boils down to your imagination. Odds are, if you can picture it, you can make it.

 

Go to a shop. Get a box built. They know what they're doing.

It's why they make money.