Schlieren visualization of ultrasonic waves is usually carried out at megahertz frequencies since it is generally realized that lower‐frequency waves are much more difficult to observe. This paper considers the factors involved in the frequency dependence of the sensitivity of an ideal diffraction‐limited schlieren system. The results indicate that relatively low‐amplitude sound waves can be visualized even at low‐kilohertz frequencies. A techique is suggested which would make the sensitivity at these low frequencies comparable to that at the higher frequencies.