Speaking of efficient speakers, apparently Tannoy made a driver for a lighthouse foghorn with a 6" coil and 500 watts of handling capacity which achieved an efficiency of 142 db at 1 metre for 1 watt input and supposedly took 2 men to lift the magnet.

AAAHH---OOOOOHHH---AAAHHHH!!!

Half of communication is listening. You can't listen with your mouth.