Measurement of speed of sound via resonant acoustic mode analysis using a smartphone

In this work, it is proposed a method to measure the speed of sound that requires a low cost apparatus. The experiment uses a semi opened PVC pipe as acoustic cavity and a free smartphone app to record and process the sound emitted by the pipe as it was filled with water at a constant rate. From the physics model that describe the system’s resonant frequencies, spectral components of the sound produced by the cavity were analyzed and a speed of sound at ${25}^{\circ }$C of $(347\pm 6)$ m/s was measured, in agreement of reported values in the literature. Due to the simplicity and accuracy of the proposed experiment, it can be implemented as an activity in physics experimental classes and classroom demonstrations.

Keywords:
Speed of sound; resonant modes; acoustic; smartphone