Speaker power consumption quadruples when producing sound with double amplitude.
Two speakers consume two times the energy of single speaker.
Two speakers playing signal in phase double the sound amplitude.
If all these statements are correct,it means two speakers will produce same sound amplitude as single speaker with half the power consumption.That seems impossible becose if single speaker had more than 50% efficiency,it will create more energy than it consumes thus violating laws about conservation of energy.
Maybe it have to do with fact that double velocity is quadruple energy and sound a amplitude is related to volume of displaced air so two speakers can move same amount of air,but with half the particle velocity so the total energy is half ( 1/4 for single speaker,half total for two )
What are your thought? Is it really possible that two speakers need half the power to produce same sound amplitude? Is there something that I am missing that would prevent violating the laws of energy?