Enclosure Porting, Do You Know Your Math?

Hey guys... Just found this forum and I am going to start heavy. Hopefully one of you can confirm or correct my math. my Spelling is another story!

So here it goes!

Using this equasion I have determined that a 3 inch diameter port is equivilant to aproximatley 2.65 inches square internal volume of a square port...

Ac = pi * (D/2)^2 Ac >> area of circlepi >> 3.14...D >> diameter of circleAc = (3.14) * [(3.0 in) / 2)]^2 = 7.065 For a square, the area is: As = x^2 As >> area of squarex >> length of side of a squareWhat you are looking for is "x", so that As = Ac. In other words, x^2 = Ac To find x, take the square root, so: x = sq rt (Ac) = sq rt (7.065) = 2.65 inSo, a 2.65 x 2.65 square has the same area as a circle with diameter 3.0So my question is... if I have 3 square ports that measure 2.65 inches internal diameter square... and I would like to combine the 3 ports into 1 port only what math equasion would I use? for some reason the other day when I was thinking I came up with = multiplying the one side area of the 3 ports (2.65) by 3 (representing the number of ports used) then I divided this by 2 representing the two side of the final single port... I was pretty sure I was right then, but today I can't think straight and the final measurement of 3.975 for 3 speakers that initally started off having a 3 inch circluar port of their own, just looks too small? So any help here would be greatly apreciated! Sorry for the Spelling, Math is my strong suit! BTW what is Forum Codes? and do I want them enabled?

Yes that is about what I ened up with 4.59 but you did it alot faster! Thanks for your help! Hope it works!

Here is the New Delema... Calculating the length of this port (to get 40hz) using the circular diameter of 5.12 I have gotten a couple of extreme differences depending on the site you go to... Here in th 12volt site... (  https://www.the12volt.com/caraudio/boxcalcs.asp#por ) I entered the port diameter of 5.12 the cubic measurement of the box =ing 4cfeet and the desired frequency responce of 40 hz. Here it says that the length should be 8.67257" . On this other site (  http://www.carstereo.com/help/Articles.cfm?id=31 ) using  the same numbers it gives me a significantly different port length of 4.92" So whats the Dilly... My project is a '97 Acura CL... I am Putting 3 10" subs in the rear Deck under the window and porting the box through the arm rest hole that goes all the way into the trunk! 3 HE2 RFP4210 (   http://www.autosound.no/RockfordFosgate/PDF/2003_RFP4110-4210.pdf  ) Xmas of .51 inches or 13mm, In a 4 cu. ft. box the port size has been determined to be 5.12 circular diameter or 4.59-.60 in. sq. (square port) I have figured the resinate frequency of the car to be right around 40hz using this equasion in Figure 4b ( http://www.caraudiomag.com/technical/0203cae_box2_04_zoom.jpg ) The speed at witch sound traves is converted into inches rather than feet. measurements from the box to the wall will be 84 inches. if you divide the 13560 inches by four ( to use only a 1/4 of the waveform) you get 3390 inches per second... Then you divide that by 84 and you end up with 40.3...Hz. And thus why I want to tune the box to 40hz.  Any Takers on the right answer? Don't be Scurd!