port length and tuning?

I have been using torres tuning calculator to find port lengths for tuning. i now see this program may be incorrect but in my search for answers i can not find any 2 programs that give the same results. how do i know if a program wants me to input net or gross volume? if the program wants the cubic footage before or after port displacement? if its taking into account end correction or if i need to factor that in myself? the calculator on here is 16 inches different from the calculator on wwww.mobileinformationlabs.com wich is also 5" different from torres wich is 6.25 inches different from winisd... this is math, plane and simple! i should not find that every God D*** calculator gives me different result. i have no idea if my current box is 34hz, 28hz or 46hz with the margin of error on these programs. I am wanting to build a 4th order but i cant even get a basic port tune correct here.   i want to know 100% how to verify that my port is indeed getting the tuning i think it is.ZX2500.1 - SP4 18"

Eclipse 34320 - dual 10" mids

Audiobahn A275HC - tweets

KX3 xover

P7800HD deck

knukonceptz wire

custom 3/8" copper plate ANL fuse

4 group 31 1150CCA batteries

You could always calculate it yourself. Lv = (23562.5*Dv^2*Np/(Fb^2*Vb))-(k*Dv) where,     Dv = port diameter (cm)     Fb = tuning frequency (Hz)     Vb = net volume (litres)     Lv = length of each port (cm)     Np = number of ports      k = end correction (normally 0.732)Support the12volt.com

49.816117" is what i get here are my numbers, does this look right? 1.463*10^7*(11.941)^2/(45^2*15310.08)]-1.463*11.941ZX2500.1 - SP4 18"

Eclipse 34320 - dual 10" mids

Audiobahn A275HC - tweets

KX3 xover

P7800HD deck

knukonceptz wire

custom 3/8" copper plate ANL fuse

4 group 31 1150CCA batteries

maybe?ZX2500.1 - SP4 18"

Eclipse 34320 - dual 10" mids

Audiobahn A275HC - tweets

KX3 xover

P7800HD deck

knukonceptz wire

custom 3/8" copper plate ANL fuse

4 group 31 1150CCA batteries

The formula requires metric input and returns a length in centimeters. That's why I posted the meaning of each term with the units required. So, if you input the other parameters in the proper units, the result will be in centimeters, not inches.Support the12volt.com