Hey i have a fi q 15 dual 2 and i have it in a ported box about 3.25 cubes tuned to 33hz and i wanna try to make a 4th order bass reflex box but i havent the slightest idea how to make one. i know its more math but i havent found a how to go on how to make the and which formulas to use to calculate the box sizes and ports. Im pretty good at car audio but i just need to get pointed in the right driection on how to make it. A local car audio installer whos a wizard with boxes is trying to teach me how to make one but he is just too busy right now to help me with my box.

You already have a 4th order bass reflex box. I don't understand you question.

I have a regular ported box. I wanna try to make a bandpass with the sealed box and the ported box in front.

No, you already have a 4th order bass reflex. The order refers to the roll-off, 4th means 24db/oct.

If you want to design a 4th order bandpass, look into the many online calculators.

I also suggest conducting a little research. There is a lot that goes into designing a proper enclosure. A good place to start would be to purchase the Loudspeaker Design Cookbook by Vance Dickason and read the first several chapters. This will shed a lot of light on what you are trying to do. You'll may get a bunch of design help on here, but if you don't understand the basics, it may do you more harm than good.

Oh ok. Ill try it out.