correct size box?

I am new to car audio and don't know much about enclosures and such. I bought 4 15 inch Rockford P1s about 3 days ago that came in a huge box. I was not able to fit into my trunk so I cut the box in half and now it fits nicely... but I still thing its too big of a sealed enclosure for these subs. I pick up low lows really nice but on higher low notes it sounds like junk. Here is a rough drawing of what the box size is--

Its 5.57 ft3 which seems huge, I was thinking of porting the box to make it sound better? Is that a good idea or how should I go about making this sound better? I have the pair hooked up to a concept 1200(rms) amp, and installed in a 97 Chrysler LHS. Thanks in advance

Well RF's website recommends atleast 1.3 cubic feet per woofer, sealed. For 4 woofers, that's 5.2.

If your box is 5.5 cubic feet, that's perfect for 4 P1's sealed. It's also appropriate for 2 P1 ported at 34 Hz.

Dumb questions:
1) When you cut the box in half, you did seal it back up properly, right? (6 sides not 5) <-- that will ruin the sound of any system
2) Have you checked the low pass filter (LPF) and bass boost (BB) settings on your amp? BB should be off, and LPF should be adjusted to your liking (80-100 Hz).

For the record,

Porting won't make it louder, unless you have the space to do it properly... and an LHS doesn't have that kind of space. Keep it sealed with a suitable amount of space.

Concept "1200 wRMS" amplifier only has 40 amps of fusing... so you're really only getting 400wRMS out of it, which is actually a good thing for 4 P1's. That being said, don't replace the fuses with big ones... you'll just catch the car on fire.

well I only have the two subs it that 5.5 box it was a full 11 cubic box before I cut it in half to make it look like the box above. Should I cut out two more spots on it and put the other two subs in that same box?

oh sorry I didn't see your stuff up top. Yes I sealed it back up after cutting it in half, but I was a bit confused as to the amp settings. I tryed to kind of play with it to see what i liked but its hard to tell. I am going to go ahead the put all four in that one 5.5 box sealed and see what I end up with, then I'll see how to tune it on the amp. Also I have two 8 inch JLs in the back. One in between the 6x9s by the back glass and one in the fold down arm rest in the backseat both of which are blown now because that's the only air space to get into the cars cab from the trunk. so now I was thinking of taking out the little 8s and putting in some ports to the trunk prob just a PVC pipe flared at the end. I will upload more pictures of everything tomorrow.

you should just start over build a new box for all 4 the you will know for sure your getting a good seal would probably sound way better

Well I got a great seal on it. I matched the 1 inch MDF that the box was made of, and used a full tube of OSI sub floor adhesive to seal it up. Doing not only the side I put on but all sides on the box. But I got really lucky I didn't cut into the box yet. I pulled to box to the back of the trunk to do some measuring and decided to listen to it like that. Turns out I should have played with the box alittle because its about twice as loud. Also I took out the two 8 inch JLs and put in PVC ports. I have been fine tuning it, which is hard to do with two ports. Cutting a half inch at a time off and its crazy loud now. I know 2 P1 15s isn't much to brag about but I am seriously thinging about going and having it tested. Just curious what kind of numbers I can hit with it tuned like this.

chrisbaldelli wrote:

Well RF's website recommends atleast 1.3 cubic feet per woofer, sealed. For 4 woofers, that's 5.2.

If your box is 5.5 cubic feet, that's perfect for 4 P1's sealed. It's also appropriate for 2 P1 ported at 34 Hz.

Dumb questions:
1) When you cut the box in half, you did seal it back up properly, right? (6 sides not 5) <-- that will ruin the sound of any system
2) Have you checked the low pass filter (LPF) and bass boost (BB) settings on your amp? BB should be off, and LPF should be adjusted to your liking (80-100 Hz).

34 Hz is kinda low isn't it? I have not changed the box at all yet I just moved it. But I think porting it and leaving only the two P1s in there for now is good. Another rookie question how do I figure out a square slot port size? that is if I'm tuning it to 34 Hz? is there a calculator online I can just enter my enclosure size and it will tell me what the port needs to be? Thanks in advance.
Oh and I still have quite a bit of room in the trunk... Really I am only about 4 inches off from being able to stick my other box of two 15s in there. I think there is about 20 inches between my back seats and the enclosure, if you think that is enough room for a slot port to help out.

34 Hz is directly from Rockford's website. LINK

Personally, I think it's about right for daily driving. For competitions, you want to tune higher (depending on the cabin's resonant frequency... which i have no clue about).

For port size calculations, CarStereo.com's calculator is pretty decent. The rule of thumb is "16 square inches of port per cubic foot of box" ... which is accurate for daily driving. Personally, 10 square inches per cubic foot is fine with low powered woofers.

For slot port length, I use the12volt.com's calculator. You can google either quite easily.

when using the12volt.com's calculator, for port size am I telling it the port size including the wood? or just the gap between the MDF?