As the macroscopic properties of emulsions depend essentially on the state of dispersion, its inline or online characterization forms the key to control emulsification processes. This requires particle measurement techniques with no need of sample preparation and being applicable in industrial environment. One method for the determination of particle size distributions, that principally complies with these requirements, is the ultrasonic spectroscopy. The paper is attended to reveal possible applications of the ultrasonic spectroscopy as well as its limits of applicability. This will be achieved by presenting experimental results on the precision of acoustic sensor technique as well as on the accuracy of calculation models, by showing the information content of attenuation spectra as well as the sensitivity of calculated size distributions to different material properties and by discussing the influence of emulsifying agents on the acoustical behavior of emulsions.