...but my problem persist....

> You used 2.4 as as cabinet volume but you should have used 2.4 x
> 1728 to convert it to cubic inches. You must use the same terms
> throughout - If inches in one place then inches must be used
> everywhere. You can use feet if you wish, but then the port
> dimensions must be in feet for "Lc" and sq. feet for "Ap".

I suppose I am wrong but I cannot find where :-(
Question is : what is eqation Fre = 1/2pi * sqrt(Ap/VeLc)
calculating?

Using your values and formules from Pi white paper,
Ve = 2.45 cu ft = 4242 cu in then
Dp = 2.5" => Ap = 4.9 sq in
Lp = 2.75" => Lc = 4.872 in

Fre = 1/6.28 * sqrt (4.9/(4242*4.872) )= 0.00245 Hz :-(((

Thanks in advance,
O'Tor