Square Port addition

Ok, I still am having a hard time with this square port conversion or addition of another sub.  Ok, let say you have 1 10in sub and port dimensions are (square) 2.5x5x12.5,  Now I know the length stays the same but, lets say I want to add two more subs how do I determin the length and width of the port for the additional subs?

Thanks

You can separate each sub into its own chamber and each one will have a port at exactly the size of the first one.  Or, you can start getting aquainted with a box-building program and use it for your designs.  WinISD Pro and Unibox are two free ones that I use.

BTW, the length of a port only "stays the same" if you are converting round to square or vise versa.  When you add subs to a common chamber, all dimensions will change to get the same tuning frequency and control port noise.