Any Experienced box builders give advice plz?

[cx-7heaven 7]

I am going to build an enclosure for my 2 Havoc 18's in my 07 mazda cx-7. Each will be run off an saz-1500d, probably strapped. I have a few questions, as I suck at ported boxes.

I have calculated total gross of 12.34 cu ft. I assume this is enough for 2 Havoc 18's?

I actually want to do a "convertable" box. I want to run sealed for daily, and have a port package to run for spl. I am thinking to run with aeroports, as these will work in my mind to be easily removable. Suggestions or ideas?

I want to tune relatively low(in the 20's to 30's) for the ported part of the build. Suggestions or ideas?

Can I use a TL on my setup right now to find my resonant freq and tune the new build accordingly, or does the resonant freq change when my build changes?

Right now, I am running a single Havoc 18 sealed @ 5.69 gross~ approx 4 net. I have major flexing, but doesnt hit a meter worth a crap. Hit 139.7 legal last year. I am hoping to get a ~10db gain by going with this build, am I being unrealistic? If I posted in the wrong forum, feel free to move it, I posted here to hear from the wonderful, amazingly intelligent folks at FI/Ascendant. My main questions are with the build itself, I know a db gain is hard to estimate, but I figured approx 6db for doubling power and woofers, and another 4 for porting... or am I all screwed up?

Thanks,

Rob

Edited June 27, 2008 by cx-7heaven

[cx-7heaven 7]

This is the shape I need to use due to space restrictions. I do NOT want to fire the subs into the glass. Any ideas?

[Accordman 0]

why do you not want it firing into the glass

[cx-7heaven 7]

You see the box in my sig? My hatch flexes a lot anyway, for fun I had turned the box to fire back, and I thought it was going to shake the hatch apart! That was with 1 18 on 1500 sealed....... what do you think 2 18's on 3k ported will do?

[j_black10 0]

Have you thought about walling it?

[cx-7heaven 7]

As far as the box idea I have, it has changed a bit. That sketch will be my sealed box, and then I will build a removable extension that will be bolted to it and carry the subs and ports. What I am really looking for is a size in cu ft and port area/size whatever. I have no clue as to tuning a ported box, so if someone happens to have a good box building program out there to run the numbers with, that would be awesome. With my new plan, I can probably go as high as 20 cubes if I have to, so cu ft wont be a problem anymore( for the ported build)