A loudspeaker-driven clarinet for educational purpose

This paper describes a toy device, namely an electroacoustic clarinet, which was designed for educational purposes. It consists of a loudspeaker connected through a cavity to a duct drilled with several side holes. Unlike what happens in a clarinet where the emitted sound is caused by the motion of a reed and the blowing of a musician, the present system is excited by the loudspeaker through a positive feedback mechanism giving rise to self-oscillations. This feedback is achieved by placing a microphone in the cavity, and connecting it to the loudspeaker through an audio amplifier. It is shown that, by adjusting the gain of the amplifier and by opening/closing the side holes to control the pitch of the emitted sound, the system can spontaneously play all the notes of a scale. The dynamics of the system beyond the threshold of self-oscillations is also studied both experimentally and theoretically. This simple system can be easily reproduced with minimum equipment and it may have some merits for educational purpose, because its understanding requires some basic knowledge of electroacoustics, guided wave theory and nonlinear dynamics.