port length question
For those of you familiar with bass box pro and/or winisd, help me out here.
The box is 2 cuft tuned to 30hz (12" rlp), 4" precision port
When I do this calculation (Lv=((8466.4*r^2)/(Vb*Fb^2))-(1.463*r) I get a number like 15.89". Winisd gives 16.28" with end correction being .614 (is that right for 2 flared ends?) And Bass box Pro gives a length of 17.35".
Which of these is correct? Or is there some other part if it I am missing? It seems as though they should all be the same length if my numbers are identical, but they obviously are not.
Also, a precision port ordered from PE is 17" in length with adding the flares and not cutting anything, correct?
Headunit: Premier DEH-P880PRS
Subs: 10" assassin in custom bandpass
Frontstage: AA 6.5" polymids, seas 27AFNC/G
Amp: Crossfire CFA 555
REFS: BoominBeast, TooLowTooGo, TrlcKed_OuT, bad84ss, mtdewelf, Dozy_production, dvrmstrng, SlickCMRick, Akizzle, Louisiana_CRX