It’s impossible for us to see a sound wave, we can only hear its effect on us. When thinking about or working on room acoustics we imagine how sound waves might be traveling within the room.  A ripple tank is a way to see waves moving and from this experience get better at visualizing sound waves moving in rooms. 

For his Master’s Thesis back in 1975, our president Art Noxon was assigned the task of developing and building a ripple tank which would visualize the acoustical concepts introduced in the graduate level textbook: Fundamentals of Acoustics by Kinsler and Frey.  In so doing, he developed the unusual ability to “see” sound waves in his imagination.  Here are some excerpts from his thesis.

Seeing Waves

The ripple tank is an optical device by which the ripple wave action of a transparent liquid becomes visible via shadows and bright spots cast upon a viewing screen. See figure 1.

Light is passed through a glass bottomed pan and is refracted by the sloping water surfaces of the ripple wave, leaving a shadow directly above on the viewing screen. The wave peaks and troughs have a flat surface and impinging light is not refracted but passes directly through to create bright spots on the screen.

Making Waves

A pneumatic wave drive was developed, shown in figure 2, which provides a clean frequency response from 1 to 40 Hz. The driver is a hollow chamber whose open end is set just below the surface of the water, thereby entrapping a quantity of air. As the air pressure is varied, it raises or lowers the water level inside the chamber which changes the local water level just outside the walls of the chamber, creating ripples.