Port resonance fport=(1/(2*Pi))*squareroot(K/M)

K is stiffness of airspring, M is mass of moving air in port.

K=beta*Ap*Ap/Vb, there Ap is port area, and Vb is box volume and beta is a stiffness constant for air.

M=p*Ap(Lp+16/3sqrroot(Ap/Pi*Pi*Pi)) there p is air density and Lp is length of port.

If you use one port with area A and port length Lp or 2 ports with area A/2 and port length Lp, the tuning frequency should be the same