The atomization of liquids by means of low frequency ultrasonic atomizers results from unstable surface waves generated on the free surface of a thin liquid film. These unstable waves are obtained from the tuning of the amplitude and the frequency of an imposed oscillation. The thin liquid film develops as the liquid spreads over the atomizing surface of the atomizer. This paper focuses on a systematic experimental analysis of the sprays produced by this type of atomizers. The thickness of the liquid film is measured. Its effects on the drop diameter are studied as are the effects of both the liquid's physical properties and the ultrasonic atomizer's characteristics. The relationship between the mean drop diameter and the surface wave wavelength is accurately determined. A mathematical approach based on the Maximum Entropy Formalism is successfully applied to theoretically determine the drop size distribution of the spray.