Feedback excitation mechanism in organ pipes

A feedback theory on the organ pipe sounding mechanism was established for small amplitude oscillations. Lateral displacement of the jet at the edge is amplified to produce the driving current, part of which is fed back to the jet. The self-sustained oscillation is realized if amplification and feedback functions combine to unity in the feedback loop. Numerical calculation clarified that (1) phase shift due to the lip-to-edge transit time of the jet has physical significance, and its range for sound production extends roughly between π/2 and 3π/2, (2) feedback oscillation must be maintained by the decrease of phase shift with ascending frequency, (3) “octave jump” occurs and the phase shift is doubled for such high speeds as exceed the allowable limit, and (4) oscillations take place at the antiresonance of the current-driven parallel system. Experimental results on four models made by authors encourage our feedback excitation theory.