No abstract

The Doppler effect is a common principle in all types of waves when sources and receivers have a relative motion. In acoustics, there are scenarios where sound sources rotate and produce the Doppler effect. These scenarios include sound produced by a speaker with a rotating horn and by the rotational motion of helicopter blades and airplane propellers. In this study, we experimentally measure the frequency shift due to a rotating sound source. A buzzer (2.8 KHz) is set to rotate at a fixed radius (75 cm) with the rotational velocity (60 rpm) controlled by a stepper motor. The radiated sound signals are recorded by a microphone at different locations. Spectrograms of the recorded signals display a shift from the buzzer’s original frequency. The shift oscillates with the period of the source rotation. We characterize the dependence of the shift on the position of the microphone. A formula for the shift is derived and is used to compare with the measurements. Our measurements and analyses gain insight into the Doppler effect due to a rotating source.