View Full Version : Quick easy port calculator question!!

05-30-2010, 07:55 PM
Ok so the external dimensions of by is 34.5 x 16.5 x 16.5 so it comes to 4.3 cu ft the speaker displacement is .05 and the port disp is .25 so thats 4 ft for 2 12" p2's, This might be a little big but my question is

PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES (http://www.carstereo.com/help/Articles.cfm?id=31)

for that calculator when i type in the volume do they want total volume or do i need to subtract the port displacement. It will be tuned to 35hz and be 15x2.3 by 13.1 is what i calculated.

any advice on anything is appreciated. thanks. and its the old p2's

05-30-2010, 08:17 PM
give me a minute.

05-30-2010, 08:25 PM
you need to go by INTERNAL dimensions

05-30-2010, 08:28 PM
Ok so just internal imensions including what will be the port area? so a 4.3 cubic foot box will have a 15x2.5x13.1 inch port to be tuned to 35hz? after port and speakers it will be 4 ft cubed. is that a good size and tuning for 2 12 inch p2's the old ones?

05-30-2010, 08:34 PM
you confused me OP lol, but what the last guy said you need to go by internal dimensions as it looks like you are going by external.

05-30-2010, 09:00 PM
no im not and it doesnt matter what im going by im asking if i need to subtract the port displacment when i enter box volume into the calculator

05-30-2010, 09:04 PM
I am going to do all the work for you if you gimme a few mins that port area alone is to small for 2 p2's. I'd rather do the work for you.

05-30-2010, 09:14 PM
really thats 37.5 sq in of port. but ok that would be really cool. thanks alot.

05-30-2010, 09:48 PM
Just follow this pic from re box calculator I have already done all the hard part dealing with minimum recommended vent area and subtracting the sub displacement. So use the box volume in the figure below which is 3.597 then subtract your sub displacement if you want to check it. I already calculated it on my own so basically when you subtract your sub displacement it will slightly change your box tune and box volume. So just add .3 to the 35.173 box tune in the figure below and that will be about your real tune. Some people say RE box calculator is not accurate but it is about 99.9% accurate the user just needs to double check the figures with another box calc if needed then subtract the sub displacements.

So in simple terms just follow the port length in the diagram and you will get about a 35.5-35.9hz tune.


Yeah RF recommends 31.25 sq in of port alone for a slot ported box just for 1 of the newer p2's. The old p2 shouldn't be much different..

The 15x2.3 you had on your first post is only 34.5 sq in.

Generally 12-16 sq in per cubic foot of box is the normal guideline for subs.
IF you go by your 34.5 sq in of port that is only roughly about 9.8 sq in per cubic ft and is to small.

If you wanted to double check you can even go here where you linked before and use the FIRST formula.
PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES (http://www.carstereo.com/help/Articles.cfm?id=31)

I went by about 50 sq in of port area and it will be fine.

05-30-2010, 10:22 PM
your awesome so if i wanted one side port that was straight it would be 24.15 inches long