The Lincoln’s Tube: A new apparatus for demonstrating sound standing waves

A new device for teaching the physics of sound, specifically demonstrating the wavelengths of standing sound waves, is here described. I define a “Lincoln’s Tube” as any hollow tube that uses lights (LEDs typically) to demonstrate the presence of sound standing waves. The name is chosen intentionally to recall a Ruben’s Tube or a Kundt’s Tube, which are similar apparatus that display standing sound waves in a long hollow cylinder of gas or air. In this article, a few variations of the Lincoln’s Tube approach are presented with instructions on how to build one. This new method for making sound waves visible has practical advantages over the other tubes, and the construction of one of these can be an engaging project with the potential to instruct on modern electronics and the fundamental wave properties of sound.