This paper explains a modification of the classical experiment of measuring the sound speed v s in free air by using measurements of time delay between two pulses of sound waves detected by two microphones in order to obtain better accuracy of measurements. We present circuits to produce and analyze 40 kHz ultrasound signals which allows not only to determine v s but also to explore the Doppler-Fizeau effect quantitatively, which is not possible with audible signals. A student group methodological approach to explore the experiment is also presented.
sound speed; Doppler effect
