confused about port area, tuning, length

So the further into building a box I'm getting the more confused I get. With the specs I have from a manufacturer a 1.95 vented box should have a port area of 25sq in and a length of 17.75 for tuning at 40hz. I was making some adjustments and thought it maybe easier to use a round port since I have 2 3" port kits. I read somewhere that I would not change the length of the port to keep the same tuning and if I use a larger area port I would need to use a longer length to keep said tuning. Yet every calc I use has the 3" port anywhere from 3.88-3.91 in length wit the same tuning. So what am I missing? There area of a 3" port is 28.27" Should I just build it to the specs I get from the calcs and forget the 17.75" length? Thanks Isk99' Dakota ex cab

IN PROGRESS: Premier P980BT, Alpine 1.1000, 4.150, 2.150, Oz Audio 380CS, ME12.4, Infinity 652.7i

220amp alt, big 3, Red Top

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area of two 3 inch round ports is a TINY 14.14 sq inches of port area...NOT 28.27 sq inches. where did you get 28.27 sq inches??

Arghhhh. I used diameter instead of radius. Thanks for pointing that out, it shows me right there in winisd too. I'm still somewhat confused. The specs I was given were for my truck, I went and dug up more info from their website and it says Box Volume    1.5 Fb            40 F3            34 Round Port    4 x 10.5 Diameter / Length Square Port   12.56 x 10.5 Area / Length Using the 4" port and the specs using winisd are pretty close, Fb is off by .92hz or the port length should be .62" longer. So I should be okay using a single 3" at 5.71 since this is what I get with winisd? Everything else looks like it would work. This is all with a 1.5cf box. Isk99' Dakota ex cab

IN PROGRESS: Premier P980BT, Alpine 1.1000, 4.150, 2.150, Oz Audio 380CS, ME12.4, Infinity 652.7i

220amp alt, big 3, Red Top

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Yeah, I even thought maybe I should keep this in the thread I had about the enclosure since this seemed to be a separate topic but it's kinda steering in the same direction... Oz Audio ME12.4 Alpine PDX 1.1000 SQL, hip hop w/ quality I've been using winisd but I'm having a major problem with it. No matter what I do this sub will not model out well, it won't even take the specs without an error message. I realized that a 3" port is going to have more port noise but even the specs from OZ are 170ft/sec w/ a 4", keep in mind I can get jack to model out. Part of this whole problem is I have is conflicting specs from Oz. The manual and the tech dept have different values for the t/s parameters. With the specs out of the manual I have a 7db peak at 56hz. So really I need some help from somebody who HAS ME12's so I can know what they did for modeling. Isk99' Dakota ex cab

IN PROGRESS: Premier P980BT, Alpine 1.1000, 4.150, 2.150, Oz Audio 380CS, ME12.4, Infinity 652.7i

220amp alt, big 3, Red Top

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