Interaction of reed and resonator by sound generation in a reed organ pipe

Abstract

Interaction of reed and resonator in reed organ pipes without and with the resonator has been investigated. The wave form of the sound generated without the resonator attached is a periodic train (with the frequency of reed vibration) of decaying high frequency oscillation. The frequency of this oscillation is independent of the frequency of the reed vibration; it corresponds roughly to the fundamental acoustic resonance of the shallot. Another rather surprising phenomenon was also observed: without the pipe resonator, the reed vibration frequency, and correspondingly the sound frequency is a continuous function of the reed vibrating length, but when the resonator is added “forbidden” frequency domains occur in the vicinity of the eigenfrequencies of the resonator, and the sound frequency jumps abruptly from below to above each resonance frequency of the resonator, when the reed is shortened. This effect can be explained by the coupling between two oscillating systems, the reed and the acoustic resonator. The presented investigations result in a better understanding of the acoustical and mechanical aspects of sound generation in reed pipes, which may allow organ builders and voicers to easier pipe design and more accurate voicing to obtain the desired sound.