Box expert needed

10+ year member

I'm designing a dual slot-ported box for my single 15" Brahma and was wondering if somebody experienced could run the numbers, so to speak, and confirm these dimensions. The box will be built using 1" MDF, and the inner walls of the slot ports will be made using 3/4" MDF. The measurements I have are:

Outer Dimensions - 30"W x 17"H x 22"D

Port Dimensions - 10"W x 2.5"H x 26"L (x 2)

The main concern I have is that I may not have done the math correctly by calculating the slots as solid objects. Are they?? If they are not calculated as solid objects, then what is the proper formula to use? The formula I used was 10.75 x 3.25 x 52 = 1.05^ft, which I added to the original 3.5^ft along with the 0.24^ft displacement of the driver, +-0.10^ft for some bracing material, which gives a gross volume of 4.9^ft.

If my calculations are correct, this gives me approx. 3.5^ft net volume tuned to 26Hz (not to mention some nice bump in the trunk).

Sorry to be a PITA, but I really want to get this right the first time as this box is going to be permanently mounted in the vehicle and changes won't be easy to make once it's in place. Does everything look correct? I just want to get some confirmation by a pro before I start construction later this week.

Thanks in advance...


10+ year member

Keepin it Simple
I get a total box volume of 4.86cu'

Your ports will measure a total of 50" in length. You forgot to subtract the 1" for the face of the box. This will give you 1.01cu' of port displacement.

4.86 - 1.01 - .24 = 3.61cu'

A box with a vol. of 4.4cu', using two ports tuned to 26Hz, the ports would have to be 51" long each. So I guess that this would be out of the question.

Is there any special reason that you want to have two ports??

Try this:

Keep the box dimension that you have. (I have almost the same thing but I used 3/4".) Put the port on one side. I will be 15" tall x 3" wide x 22" long. This will give you 45sq" of port and tune it to ~30Hz.

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