An Experimental Study of the Acoustic Field of a Line Source Coincident with the Focal Line of a Parabolic-Cylinder Reflector.

Abstract : The acoustic radiation patterns from acoustically soft parabolic reflectors driven by a line source coincident with the focal lines of the reflectors were measured in the NRL Acoustic Research Tank Facility to verify a mathematical model of an ideal parabolic-cylinder reflector. Data taken in the near and far fields of the reflectors at various frequencies between 10 kHz and 40 kHz were plotted together with the theoretically predicted radiation patterns. Agreement is good between theory and experiment. The experiment was performed with a shallow reflector (4.0-inch focal length and 28.3-inch aperture) and with a deep reflector (2.0-inch focal length and 28.4-inch aperture), and all measurements were made in the median planes of the reflectors. Emphasis was placed on careful construction of the parabolic reflectors and precision alignment of the line source. Error analyses were performed to determine the parabolicness of the reflectors and the effect on the radiation pattern of a slight misalignment of the line source. To illustrate the use of the mathematical model as a design tool, curves were plotted showing the reflector performance characteristics as a function of the reflector parameters. (Author)