Measurement of speed of sound in air using Lissajous curves

Lissajous figures were used to monitor the relative phase of two sinusoidal signals from a speaker-microphone system. From the phase variation due to microphone position, the wavelength was measured. We obtained wavelengths of different signals with known frequencies and determined the speed from the linear plot of wavelength and period. Our experimental value is 348.2 ± 2.4 m/s which deviates from our reference value by only 0.58 %. Our setup is suitable for speed of sound measurement in an undergraduate physics laboratory.