The effects of mouth adjustments on the acoustic spectra of flue organ pipes Free

The mouth height (cutup) of a flue organ pipe and the horizontal position of the upper lip relative to the axis of the jet have a great influence on both transient and steady‐state waveforms. Effects of these variables will be shown with data taken on adjustable pipes, open and closed, operating at 40 to 60 mm (water) wind supply pressure. The presentation concerns mainly (a) relative amplitudes of harmonic components in the steady signal, (b) noise components apparently created by the edgetone feedback process, and (c) multiphonic oscillation. The short pipe with highly anharmonic passive resonance frequencies is particularly discussed, because its harmonic content is due to the nonlinearity of the jet‐to‐pipe excitation described by Fletcher. Radiation from such a pipe may have second harmonic amplitude greater than 10% of fundamental amplitude, with the third harmonic much smaller. Significant characteristics of the jet‐to‐pipe excitation function are shown by the existence of a minimum of second harmonic content as the horizontal lip position is changed, and changes of the phase of the second harmonic relative to the fundamental.