Thank you for your answer. But I still dont understand how two spreakers can create 4 times higher sound power. Does it depend on lower impedance att the crossover point so that the amplifier leaves the double power.
If we look at the graph of each drivers output. They show the SPL. If we have two drivers we should get the double of the sound power. Which is 3 db. How could it be 6 db? Maybe you can show me the math?