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View Full Version : how much round port for a 4^3 for a pair of xxx 12"



plyhammer
07-12-2004, 09:53 PM
I have a pair of 12" xxx in a 4^3 box. This is all going under the rear seat of a quad cab truck so it is as big as it is going to get. I have it braced with all thread to save cubes and it is straight on 4 cubes for the pair. I am having a little problem with the porting. The subs will have to downfire with the ports facing forward but I have checked with a couple of porting calculators and have gotten different answers from them. How much port do I need.

pj_chevy03
07-13-2004, 12:36 AM
jus seal em...2 12" xxx's i'm sure would be plenty loud sealed.. question, how tall are your back seats bottom seat cuz to fit those subs downfiring that would have to be a high back seat...u gotta have room for the huge magnet and then enuff room for the excursion...this doesnt seem likely

plyhammer
07-13-2004, 06:14 AM
The subs are in the box already. I have the seat raised 5 inches to accomidate the extra room needed. Respl.com recommends 2.1 cubes per sub ported, I didn't think that I was too far off from that.

helotaxi
07-13-2004, 09:41 AM
That 2.1 was effective air volume after considering the amount of air displaced by the subs themselves (.19 cu ft each) and any port volume within the enclosure. I am running 2 3" ports for a single XXX and the port displaces around .25 cu ft. You would need roughly twice the port area that I have and thus about twice the volume. After displacements you are looking at your 4 cu ft box being only about 3 cu ft and thus needing a longer port to get a good tuning freq. You are going to be better of with a sealed setup in that amount of space.

plyhammer
07-13-2004, 09:54 AM
dang. What if the ports were external? Oh well, cant get bigger I will probably just have to seal it then. Thanks guys.

plyhammer
07-13-2004, 10:23 AM
Should I cut some of the box to make it smaller then? I would have 3.6 cubes after sub displacement (thanks heli). Will 1.8 cubes per sub be too much sealed? thanks again

helotaxi
07-13-2004, 10:53 AM
How much power are you running? It will probably sound a bit on the boomy side with that big an enclosure. If you already have it built, it can't hurt to give it a try before you cut it up to make it smaller.

helotaxi
07-13-2004, 11:28 AM
When you don't run a ton of power to it, it isn't that big a deal. With 1kw it plots at 70ish mph port velocity within the usable frequency range. I don't have any audible noise.

If your goal is SPL you need a huge amount of port area and a big box. The big box and high tune necessitate a lot of that port area. I'm in for SQ, smallish box, lower tune, lower power and smaller port area.

helotaxi
07-13-2004, 01:38 PM
I was using Win ISD (and Pro I tried them both) and they both gave me the same result. Symetry of deisgn was important for me but not nearly as important as no port noise. I fiddled with the setup for a while during the modeling stage to make sure that it wouldn't be a problem. If I had gone to a bigger box I would have had issues. I should have the 250HCCA on it @ 1 ohm this afternoon, I'll let you know what happens.

I have MSN messenger BTW. I just need to correct the setup.

plyhammer
07-13-2004, 02:56 PM
1000-1500 watt apiece.

helotaxi
07-13-2004, 04:51 PM
You'll want a smaller box.

plyhammer
07-13-2004, 10:32 PM
can I put some wood inside of the box to reduce the airspace or do I need to rip the box apart to cut out some of the space?