Pipe impedance and sound spectrum measurements of the khaen and the sheng

Abstract

Although the Asian free reed mouth organs all employ metal free reeds mounted in resonating pipes, there are significant differences among different families of these instruments. The sheng employs the free reed at the end of a closed pipe resonator with both conical and cylindrical sections. The khaen pipe has an unusual configuration for a wind instrument, with the free reed placed at approximately one-fourth the length of an open cylindrical pipe. Impedance curves have been measured for several pipes from a sheng and for artificial khaen tubes constructed from PVC pipe. These are compared with the sound spectra produced when the pipes are played. The sounding frequencies for both types of pipes are typically found to be above the natural frequency of the reed and close to, but slightly above, the frequency of the first impedance peak of the pipe. For khaen pipes constructed with the fundamental frequency of the pipe substantially below that of the reed, the sounding frequency is close to the second harmonic of the pipe. These results are consistent with those of some earlier studies as well as with theoretical considerations.