View Full Version : How many Iches²

12-18-2007, 11:29 AM
How many inches² is necessary for my port... Needed for four 12s i was looking on DD website they suggest 16 inches² per cubic foot enclosure - that seems a little big to me - since im planning on making a net 7 cubic foot enclosure. My box design i made now has 68 inches² of port. 12.5" x 5.5".

12-18-2007, 11:50 AM
More port area is better, but the problem is that with more port area, to maintain the same tuning, you have to have a longer port. A longer port, as I'm sure you realized will result in a larger box overall with no greater net volume.
From what I've observed, a port's tuning is affected by how effectively it impedes airflow.
-Of two equal length ports, the one with the smaller area will have the lower tuning.
-Of two equal area ports, the one with the greater length will have the lower tuning.

It seems then, that the best thing to do would be to make a box with small port area because you could have a shorter port while maintaining tuning, which would result in a smaller overall box.
However, the problem with a port is that too small is that the same volume of air is now going back and forth in a smaller area. (Air in a port doesn't flow in and out of the box, it stays within the port and just moves back and forward as the air is rarefied and compressed.) With a smaller area, the fluid velocity increases, [Velocity is inversely proportional to area (V=k/A).] which as it moves across the rough corners of a port can cause a noise like wind, which is called port noise.

I'd be interested to know if the fluid in the port can be treated as or is a laminar flow or not.
Ca.com members please comment.

In short, it's unwise to use less port area because you don't want to make a bigger box. Although I'm not sure how the math to that area to volume relationship works, if there even is any, I would recommend that you go with no less than 84in^2 (12in^2 per ft^3).

Brian Owens
12-18-2007, 11:57 AM
I would try to get at least 100" for (4) 12's.

If you do not have room, you can look at flared 4" aero ports. The large flares will allow for a lot less port area. You could use 4 of them 14" long for 35 Hz tuning, or 5 of them 17" long for 35 Hz tuning with your setup.



edit - I read fast and thought you were using DD subs, but you only say you read the DD site. The required port area will also depend on what subs you are using and how much power you have. A cheap sub with not much power can get away with less port area. But even if that is the case, you might as well build it right for upgrades in the future

12-18-2007, 03:23 PM
Okay well room is an issue a tad. i can squeak 81.25 inches² i think. i have to do measurements. But do you think it will be okay if i ran off 68 inches²- and brian i am not running DD i was just looking on the website for reference. I am running four pioneer premiere TS-W1207D2s.

12-18-2007, 03:26 PM
So you know how to do the exponent 2, but can't spell inches?

12-18-2007, 03:38 PM

12-18-2007, 04:50 PM
12-15^2 per cubic foot of box is pretty much the norm for a daily box, so 84^2 would be fine for a 7^3 box. Your 81^2 should be fine for daily...

12-18-2007, 05:08 PM
J31Rob thanks for the help bud.

12-18-2007, 05:08 PM
now i have to see if the box fits in my car lol:P mock up boxes ftw.

12-18-2007, 05:18 PM
This is what it would look like. the one with 81.25 inches².


12-21-2007, 03:23 AM
Am I right on that comment I made?