Speed of Sound Calculator Using Old Earbuds

Using some simple materials and a calculator, students can easily calculate the speed of sound in air.

A pair of old earbuds

A device that can play the earbuds (like an iPad, phone, or Chromebook)

PVC pipe, around 20 cm

electrical tape

fishing weight

On one side of the PVC pipe, tape one side of the earbud so it faces into the pipe. On the other earbud, place a fishing weight.

Find an app or a website that can play a continuous tone. One can just google "tone generator", or in the case of the photo, I am using an app called Phyphox.

Play a tone that is high enough that when the lose earbud is moved up and down the tube, an interference pattern can be heard. Students can tell where the nodes and antinodes occur becuase the tone will get very quiet at points of destructive interference. When they find these points, they can measure the distance between them. A simple calculation from there (velocity=frequency x wavelength), will reveal the speed of the sound!