WinISD calculates port length assuming that there are one flanged and one free end, i.e. port is mounted to the wall of the box, and another end is freely inside the box. So end correction factor is 0.732 by default. Port length in box wall is counted to port length. If you want do convert the result to different end correction, then add 0.732 times diameter of the port to calculated port length. This gives you needed acoustical length of port. Then add end correction as you like
End correction
End correction factor is analytically or empirically determined factor, how much port extends beyond its physical ends. For free end, end correction is 0.30665 times port effective diameter. For flanged end, more analytical expression is available, 4/(3·pi) ~= 0.42441 times port effective diameter. Flanged end is calculated assuming that tube terminates to infinite baffle. Which is not exactly true, but.. Following table summarizes various port configuration types and their total end correction factors (refer to above picture to various end types):
Summary of end correction values Port configuration end correction 1 end correction 2 Total end correction
Two free ends 0.30665 0.30665 0.6133
One flanged and one free end 0.42441 0.30665 0.7311
Two flanged ends 0.42441 0.42441 0.8488
Physical port length is obtained by subtracting port effective diameter multiplied by suitable end correction value from port's acoustical length.
