Advanced Physical Research

In classic acoustics one differs two areas around the acoustic source – near field and far field. There is a third area, called very near field, but it is mostly the subject of researches in the field of vibration mechanics. The near and the far field are often called Fresnel zones and Fraunhofer zone. In this work a criterion for determining the borders of Fresnel zones is proposed. The criterion is based on multiple examinations, researches and measurements of the spatial parameters and characteristics and some of the electrical parameters and characteristics of circular transducers (loudspeakers). From the presented theoretical and experimental review of the Fresnel zones one can conclude: the bigger the transducer radius, the longer the Fresnel zones; the higher the frequency, the longer the Fresnel zones; the higher the wavelength, the shorter the Fresnel zones; the higher the sound speed, the shorter the Fresnel zones.