Development and use of a schlieren system for sound pulse studies

Herein is described the schlieren photographic method, in which a density disturbance, such as an acoustic N wave, refracts light passing through it in such a manner that an optical image of the disturbance can be formed on a piece of film. The presentation of the method includes a theoretical description which relies on both geometrical and physical optics. Design considerations and the details of putting a system into operation are also given. The results of two investigations using the schlieren method are presented. Propagation of an acoustic pulse in a duct is modeled, and the photographs are compared with a geometrical prediction based on the method of images. The focusing of a spherical N wave is also photographed.