Some voicing adjustments of flue organ pipes Available to Purchase

The investigation uses a flue organ pipe designed so that mouth height Y, position of the upper lip in the air stream X, and width of the air passage are adjustable. Other dimensions can be altered with interchangeable parts. Rectangular and circular resonators of several lengths, open and stopped, are used. Speaking frequencies are 125 to 500 Hz. Speech for a supply pressure of 55‐mm water is described for the useful X,Y range in qualitative terms, and also in terms of sound‐pressure level and harmonic content. Behavior is related to resonance frequencies. Stable oscillation of longer pipes occurs in a limited X,Y range unless the first resonance frequency is some 2% lower, relative to harmonic relationship with the next few modes of vibration. As X is varied, for the speaking pipe, the second harmonic has an amplitude minimum, where the phase relative to the fundamental reverses. The acoustic pressure is proportional to mass flow rate over a range of at least 4:1 in tests involving reduction of air pressure or narrowing the passage. Threshold operating pressure for 7‐mm mouth height is 5‐mm water, in good agreement with Coltman’s flute data. Air supply energy is converted to radiation with about 0.5% efficiency for the stopped pipe.