2 C2 threatcon-2 15's...box design help (port advice)

[Jordan Guess]

Im usually okay with designing my own boxes but this one is throwing me for a loop on getting the right port. So as stated, using the two 15's on a American Bass VFL 4480.1 @ 2 ohms (roughly 1k rms each) in a VW Mk4 Golf. MAX dimensions Im working with here are Height=27in. Width=35in. Bottom Depth=24in. Top depth=18in. Woofer displacment is .28 cu ft for both subs...netting me around 9.37 cu ft. Im not sure if i should go slot, square, or aero port...no matter what i try putting in, it doesnt seem like i can get a good design with proper port area per foot and tuning and box volume. Im hoping to land anywhere in the 30-34hz range if possible and ive been told that these subs like to be a little on the smaller side of 15" boxes, thanks in advanced for your help!

[CleanSierra]

2 6" aeros would work. For the airspace after the displacement of the ports themselves, I'm guessing around 8.5-8.7 cubes, and a tuning of 32 Hz, they would only need to be around 13" long. That might be where I started if it were me.

I don't think I'd go with a square or slot port since the box will have that angle. You could try the square port but it will eat up a little more airspace than the aero option.

[Jordan Guess]

2 6" aeros would work. For the airspace after the displacement of the ports themselves, I'm guessing around 8.5-8.7 cubes, and a tuning of 32 Hz, they would only need to be around 13" long. That might be where I started if it were me.

I don't think I'd go with a square or slot port since the box will have that angle. You could try the square port but it will eat up a little more airspace than the aero option.

yea that back angle is whats really killing me on the slot design...how much port area per foot is recommended with two 6" aeros would you say?

also, thanks for the input!

edit: put in the two aeros at 13" long...gave me 6.4 port per foot and a 56.52 port area total on torres...seems a little low but i could be wrong...hence my previous question xD

[CleanSierra]

I wouldn't focus on port area per foot. One 6" port PER sub should be sufficient to avoid port noise and operate as intended.

If you want the answer though, around. 6.4-6.5" per foot. This isn't like an ideal amount of port but two 6" ports for those 15s should work out fine. Unless you want to pretty much double the length(which would eat into the net volume) and use 8" ports instead.

[Jordan Guess]

I wouldn't focus on port area per foot. One 6" port PER sub should be sufficient to avoid port noise and operate as intended.

gotcha. definitely aero tho? or could I use straight pvc (i know its less efficient) but just getting as much info on this as i can.

[CleanSierra]

You could use PVC for sure. I would DEFINITELY flare the outside piece of wood with a,45° roundover bit and the inside ban be die with heating and the dog bowl trick. You could also do a piece of MDF butted against the inner port openings and flare them with a router too. The flaring is a very crucial part of eliminating the port velocity and turbulence issues to avoid noise.

[Jordan Guess]

You could use PVC for sure. I would DEFINITELY flare the outside piece of wood with a,45° roundover bit and the inside ban be die with heating and the dog bowl trick. You could also do a piece of MDF butted against the inner port openings and flare them with a router too. The flaring is a very crucial part of eliminating the port velocity and turbulence issues to avoid noise.

Ill probably just use the heater and dog bowl trick...im no good with a router. Although I could always find someone to make the flares and ide buy em and attach em to the pvc...or find someone with some precision 6"ers. Torres final specs with two aeros at 13" length gives me 29.82 hz and 8.92 net volume...thats before bracing though which ill probably use all-thread...then ide be guessing around 30ish hz. Thanks for all your help CleanSierra, if you got any other clever ideas please feel free to let me know.

[CleanSierra]

I was roughly estimating the displacement. You can shorten then up to get the tuning you want. Or perhaps try adding an additional 6"er and see what you can come up with.

[Jordan Guess]

3 6"aeros at 18" long gives me 10.09 port area per foot with a total of 84.78 port area net volume of 8.41 cu ft. tuned to 32.58hz....any longer of tubing and im getting within 6" of the back of the box...do you think that will benefit me more than just two? im giving these subs about 400 watts rms over what they are rated each so i dont know if its going to be better to have more or less port to box volume ratio?