building a sub box

Two actually. Ive got this idea, but im having trouble with the actual creation. here is a really rough mock up i made out of some very flimsy cardboard..... trust me my actual skills are better than this.  This box is being designed for an MTX Thunder 9512-44.... I hope :) Here are the problems I'm having. 1.) How do I figure out the size/shape of the hole that needs to be cut to slide the tube into, in the angled portion of the box. The tube is coming out straight, not angled, and needs to be perfect. 2.) How do I cut the tube itself to the proper angle, cutting a tube isn't easy, and how do I mark the cut line on the tube? 3.) I want to vent this box into my cars cab (1996 Mercury Cougar) by putting the vents up through the back deck, but if I come straight out of the box, the vents will be very very short, and not really able to be tuned to any particular frequency, So I may need to bring them off of the larger tubes that the sub is mounted into.... how then would I tune this port since it likely wouldn't be able to come straight off the tube, it would need to be bent or elbowed or something. Right now my main concern is the mounting of the larger tube that the sub will mount into. So any help with that would be greatly appreciated.

if your box is roughly that size you do not have enough room to have a ported enclosure

thats pretty much the exact same size as my box. 16.5 x 16.5 x 6.25 x 14h The vent wouldnt actually be inside the box..... could i not make a vent that goes into the box, and then sticks out of the box. The vent would be coming up through my back deck in the car, porting the bass into the cab. What would be the effect of just running a tube off of the box into the car.... what would happen to my sound/speaker?

Don't port into the vehicle cabin unless you want to create a bandpass one-note system.  If you build your system like that then the predmonate sound you hear will be the port, not the speaker.Support the12volt.com

really.... Thats a shame, since there are already holes in my back deck covered by material, i could have very easily run vents up through them. I wanted to not only vent the box but gets some of that butt kicking sound pressure inside the actual car itself. Can i still achieve this? Since there are already holes in the back deck, it would have been kind of a cool effect when the speakers were "in" it would have been pressurizing the cab with the vents and excess pressure would have went back into the trunk through the existing holes. When the speakers were "out" it would have been sending that sweet sound pressure through the existing holes, with the excess pressure going into the vents. I dont know if that makes sense, I just really like good tight sounding bass that kicks you in the chest. The boxes will be about 1.5 Ft3, I dont know if i mentioned it but i was designing the boxes based on MTX Thunder 9500's, although they wont be the first speakers going into the boxes (I just found out they were about $700 ea) should i vent the boxes at all? Im also going for something that looks really cool too, but sound is more important.

Your theory about how ports might function through your parcel shelf is, well, wrong.  Just build a proper enclosure for the speaker(s) you plan to use.  If the MTX wants a ported system, build that.  Always design and build for the speaker first, then make it fit into the car, then worry about making it look cool but only after it is properly designed.Support the12volt.com

ya, when i re-read that, it does make me come across as just another one of those idiots who wants to stick a sub in a box and all of a sudden im so cool.... Anyway, that was mroe or less just a thought as i could imagine the air/pressure being moved through the car. I do actually have a rough idea of what a port is for, and I wasnt designing the box just so i could vent it into my cars cab. The specs for the T9512 say 1.0Ft3 for a sealed box and 1.75Ft3 for a vented box, tuned to 34Hz. My original plan is for a sealed box, but i got thinking, the speakers are in the trunk, and yes I will hear/feel the bass, but it would seem that it wouldn't sound as good in the car since the bass is in the trunk..... you wouldnt get the real feel of the bass, maybe it would be a little muffled?? Im not all too clear on this really. I thought that if i built a vented box with the specs stated in the speakers spec sheet, I would have a vented box and just be able to run the vents up into the cab of the car. The boxes themselves are directly below the rear deck and only about 1" or so away from it. I just figured it would be easy to take my vented box, designed properly, and just vent it into the cab. no? I totally get what your saying, and thats what Ive been doing. I picked a speaker, and now im designing a box based on the speakers specs. that also happens to look fairly good (i think.... the end result will tell lol) but also meets the requirements. Its measured to fit in the trunk, but once its all built and assembled I need someway to make it look like its supposed to be there, and not some half-assed job that some fool did in his backyard in 5 mins with no research.... i swear im not one of "them" I see a lot of systems in cars, and guys acting all macho with their killer systems that happen to be nothing more than a sub they know nothing about, stuck into a box that was mass produced at a factory with no consideration for the speaker/sound, and half of the time the boxes arent even securely mounted. I dont know whats with these people and how they can act so obnoxious about something they not only didn't do themselves, but they know nothing about. anyway, ive rambled enough. Any suggestions for this project? Ive got the materials they are already marked and cut, i just need to assemble it for the most part.... then save $$$ for the speakers :)