Im going to make my first box that will use a port. The problem im stumped on is, when you do a right degree angle, how do you figure the port length then? Say the letter " L " is the port shape i need and total length needed is 10 inches. At the part that bends how do i figure it out or is the bend nul and void and the straight parts is all i need to do to equal 10" Any info will be greatfull

 

Technically you measure down the middle of the bend. If the vent uses the wall of the cabinet be sure to do the end correction too.

Or ignore both, they will likely cancel each other out or you will get a box tuned 1-2hz higher or lower than you planned. minor.