The acoustics of a symmetric free reed coupled to a pipe resonator
James P. Cottingham · The Journal of the Acoustical Society of America · 2000
The Asian free-reed mouth organs employ symmetric free reeds mounted in resonating pipes, with the reed vibration strongly coupled to the pipe resonance. The sheng, the sho, and the khaen use a single pipe for each reed, constructed so that the pipe resonance frequency is fairly close to the natural frequency of the reed. The playing frequency is typically slightly above the resonant frequencies of both the reed and the pipe. The free-reed pipe with finger holes (known in China as the bawu) employs a pipe resonator of variable effective length in which both the pipe resonance and sounding frequency are normally well above the natural reed frequency, resulting in a striking change in tone quality. The operation of these instruments has been studied both experimentally and theoretically, with particular attention to the coupling of the reed vibration with the pipe resonator. Experimental measurements include both studies of reed vibration and impedance measurements of the pipes. In general, the experimental results can be shown to agree with the predictions of simple theoretical models.