A port are tuned to a given frequency however, the port does provide output above an below tuning with dismising returns. If chamber 1 port is tuned to 40 hz and chamber 2 port is tuned to 65 hz, will the 40hz port’s output at 65hz cancel out the 65hz tuned port at 65hz? If so, what about at 52 hz where both the ports are equally active? How close can ports be before they start working against each other? If 10% of port velocity at one port cancel the output of the other port, then that is 10% waste in output potential. It is also wasted power, heat and stress on the subwoofer driver.