(2 12s) my box is 15high x 32.5wide x 25deep. (25 deep with baffle over subs) the port length is 21.5inches all together and the box has 2 1inch dowels crossed for bracing. port is 13.5 x 4.5 and i believe tuned to 36.33hz, i built a port extension (9inch) what will this make my tuning? and how much of an extension do i need to tune my box down to 32hz?