18" AA mayhem in Ford Ranger Box designs

[pioneerpoundingspl]

Alright So ive just ordered my sub and now have to come up with a box. Ive always used Re Audio's box calculator has always worked good for the boxes ive made. Heres what Dimensions ive got to work with. I can make the box 47" long by 27" in height. As well as 18" depth. Ive seen on other posts of people that have put 18" in these little extended cabs and what seemed to be the only option is to have the bottom 18" and the top say 15" then have the sub facing the back of my seats with a slot port behind the passenger or something like that. Anyways using the box Calculator I came up with this.

Box width- 47 "

Box height- 25"

box top depth- 15"

box bottom depth- 18"

wood thickness- 0.75

square port width- 5"

square port length 1-10.75

square port length 2- 10"

total port length- 29"

square port diameter-12.231

square port area-117.5

square port volume internal-3407.5

square port volume displaced-3422.5

box volume-7.301

tuned frequency 33.8

Now i would loooove to get this thing tuned to 30hz. But im sorta stumped at the moment on how to get it any lower. All help is appreciated any suggestions would be great as well

[OrionStang]

How does a square port have a diameter. Download Torres box calculator.

[pioneerpoundingspl]

Idn man I just took that info off the site. Alright ill give it a go