Exactly. As Beranek derived, there is a mathematical way to express this distortion based on the underlaying physics. CD's distort by necessity. I am not aware of any such physics for piston drivers. Their distortion can be minimized to very low numbers. Besting electrostats, certainly at slightly elevated SPL.since you mentioned "reduced" my suggestion is definitely valid as well. Horns with compression drivers do definitley have less FM distortion but they have increased 2nd order harmonic distortion due to the nonlinearity of the air in the compression chamber.