So I'm fixin to build a box to house an 18. I don't, however, know how to calculate my port size or to tune it. My maximum external dimensions are 35"W 30"D 17"H. I want the sub to face the ceiling of my vehicle. I don't know if thats gonna effect the port location or not. If someone could kindly walk me through the process of designing and sizing the port for my box, I'd be eternally greatful and totally post a picture log of the build process.

Thanks in advance.

Here are couple good links for ya, first one has calculators for volumes and other things, the second one has a great port calculator.

volume calculator

Port calculator

The measurements you gave come to 8.56 cu ft. This is assuming your using 3/4" MDF, you should go with 1" and possibly double up the baffle to make sure it's stiff. With an enclosure that size your going to need internal bracing too. Don't forget to subtract the sub and port displacement when your calculating your final box size too.

agree...spl blazer y does ur name sound familair

80

agree...spl blazer y does ur name sound familair

80

maybe cause we both compete at Manny's place, and I use this name in the TermPro forums too

For some reason I'm inclined to think I did this wrong. Double check if at all possible.. on the calculator found here, [http://www.reaudio.com/speaker_box/LPort_Box_Calc.html], the red numbers from top to bottom are

35

30

17

17

1

3.69

10.15

Maybe I don't understand what some of these numbers really are, I was kind of hit-and-missing with that calc.. I greatly appreciate the help guys.

if you want to do it by hand .159 x (Sq Rt of the Vent Area(in^2) x 1.84 x 10^8 /

(Enclosure Volume(in^3)(Vent Lenght(in)+.823(Sq Rt of the Vent Area(in^2)))