I need help for a port length

[Virtue]

Hi, hopefully someone with a box program can help me out. I have one Focal Utopia 38Wx (15") sub and I would like to make a sound quality, ported box. I have my box already made. It has a total internal volume of 3.475 cu f. I have already cut a hole for (1), 4" port. This internal volume does not include my sub (cause I don't know how much room this sub takes up) and port volume. What port length do I need for a sound quality box?
Thanks!

I can make the box smaller if need be...
Sub Specs:

Sd: 855.3 cm2
Xmax: 9 mm
Fs: 35.0 Hz
Qes: 0.51
Qms: 6.19
Qts: 0.47
Vas: 122.2 l
Re: 3.6 Ohms
Mms: 174.0 g
Bl: 16.4 T.m
Le: 2.85 mH

[Virtue]

Really, no one can help me out? Pleeeeeease anyone?

[Mr. Wild]

According to the owners manual youre going to need two 4inch diameter ports for your box. One six inch diameter port would do the trick too. Lenght of ports should be 12 inches (each).

Personally I would use shorter ports, maybe 9 to 10 inches to get the tuning frequency a bit higher.

[stipud]

Including polyfill. Boosted end shows 12db/oct rise at 50Hz, approximating cabin gain.

Red: 15" long port
Orange: 12"
Yellow: 9"
Green: 6"

I think 9" looks pretty good.

However, I think Mr. Wild may be correct about using two ports. The vent velocity of a 4" port gets pretty bad from 20-40Hz (see shaded area), even on only 500w! The 15" port would almost work, but you wouldn't be able to take full advantage of its extended infrasonics

[Virtue]

Sweet, thanks for the graph. It helps with the visual and decision making. I am making home speakers. Once I get a back for the cabinets I'll show some pictures. The coils and caps were freekin expensive, especially when I have a 5 way set up...