View Full Version : Port queation

11-27-2006, 10:44 AM
Im going to stop being lazy and start on my box for my 15 XXX. I was thinking of doing 4 cu feet tuned to 28hz. I need to do a square or round port, because i dont have enought room in my trunk to get it in. Unfortuantly, i have no idea how to figure out how long to make the port or big.

My box is 4.16 ft^3.

I used this calcualtor http://www.carstereo.com/help2/Articles.cfm?id=31 But i dont undstand my answer.

for my min diamter i got 10.9 inches and 93.26 for area.

So does this mean i need a tube 10.9 in diamter and how ever long to get an area for 93.25 inches?

11-27-2006, 11:35 AM
Try this site as well http://www.the12volt.com/caraudio/boxcalcs.asp

When you go from round to slot or square it gets a little tricky. For example what is a 6 inch round port equivalent to on a slot port. You have to be able to figure out the port area of both to be able to compare apples to apples. The formula for area of a round port is pie (3.14) x's radius (R) squared. So for a six inch port this woud be : 3.14 x's (3) squared= 3.14 x 9= 27 or 28 inches roughly. So for a slot port to be the same it would need roughly the same area so a port that is 2 inches by 14 inches would be 28 inches of port area so these ports would be close to the same area. But remember that perfectly square ports and round ports are a little more effecient that the long slender ports because the drag of the air having to pass over all of the woods surface area on the solt ports causes the air to move slower than the air through the round ports.
The easiest way IMO to get the largest amount of port area in a box is to use the slot port like this one....


11-27-2006, 04:30 PM
alright, that helps alot. I never knew how they compared to each other. Thanks

11-27-2006, 04:33 PM
You can get away with using less port area on an aero port since it flows air better than a slot port. I do all my calculations by hand. I just don't like how every calculator out there always seems to give me a different answer. Look up all the equations and do it by hand. I'm very math inclined so I find it easier.

11-27-2006, 04:54 PM
can you throw some of the equations this way? Im pretty decent at math, so i can probably figure them out.

11-27-2006, 06:28 PM
they will be confusing as hell in computer type...but I'll look and edit this post with what I find...


the one I use is Fb=.159 x (Av x 1.84x10^8)/(Vb[Lv+.823sqrt{Av}])

Fb=Tuning frequency, Av=port area, Vb=volume of the box in CUBIC INCHES. I find this one easier than solving for R and what not. If you want to use multiple ports, divide your net volume by the number of ports and use your answer as your Vb. Then number crunch.

11-27-2006, 06:37 PM
Here you go:

11-27-2006, 06:46 PM
Here you go:

****...I thought it was on JL's site but wasnt sure...that link explains everything for designing ports. From how to figure length to multiple ports to port bending and end correction...

11-27-2006, 10:53 PM
wow thanks alot. The crazy part is i actually understand the mess of numbers.

So if i want a specific frequency, i just set it equel to what ever i need to know, and out comes the number. Right? Like i know i want it to be tuned to 28hz so i plug that in, the size of my box, and then what ever other constant i want.

11-28-2006, 11:03 AM
Alright, iv been playing around with this but i cant decided where to start. I know i want frequency of 28 so i got that. and i have a box of 7200 inches^3. But i cant decided to put in length or area,

11-28-2006, 04:53 PM
Alright, iv been playing around with this but i cant decided where to start. I know i want frequency of 28 so i got that. and i have a box of 7200 inches^3. But i cant decided to put in length or area,

Area should be one of your givens and port length is what your solving for. Decide what dimensions for your port you want, whether it be 12"x4" or a 4" round port and from that, derive your port area. Unfortunately, the equations doesn't express port length in its truest terms; as a function of port area and net volume...