The Iowa wave machines
Wave machines are a staple of demonstration lectures, and a good pair of wave machines can make the idea of transverse and longitudinal waves clearly evident to students. The demonstration apparatus collection of the University of Iowa contains examples of transverse and longitudinal wave machines that will be of interest to readers of The Physics Teacher. These machines probably date from about 1925 and may have been locally produced. You too can build them.
“The Iowa Wave Machines”, The Physics Teacher, 48, 200-201 (2010) (With Dale Stille and John D. Daffron)
The Physics Teacher