SoundQubed and Square Ports

[Truk993]

I’m building a box for (3) HDS 2.112 dual 2 ohms. Box size will be 5.25 cubes total for all 3 shared. Looking for box tune 34hz. I’m doing 2 square ports 3.5”x3.5”. Calculators say I need roughly 8” port length each. This sounds kinda short, is this correct? Thanks for any input. 

[CrackFactory]

It's short because your port area is super low. You only have 24.5 sq in. I would go with at least 60 sq in if you're running them at full power.