Experimental jet velocity and edge tone investigations on a foot model of an organ pipe

Abstract

In order to investigate the physical processes involved in the build-up of the sound signal in a labial organ pipe a pipe foot model has been developed. The main important parameters, such as positions of the lower and upper lips, the wind pressure in the pipe foot, and the width of the flue, can be adjusted by means of this model. Moreover, different types of languids and pipe bodies (resonators) can be attached to the model. For the reason of corresponding to a real metal organ pipe these parts of the model are made of a typical alloy used in organ building. The reproducibility of measurements is provided by the micrometer screws applied for the adjustments. Flow and edge tone measurements are carried out with the help of this model. Velocity measurements with different flue widths show that the exit velocity of the jet corresponds to the Bernoulli-velocity and is asymmetrically contracted. At larger distances (>5 mm) the velocity distribution can be described by a Gauss-function having linearly increasing width. A mathematical relation of the centerline velocity as a function of the cut-up height L is found. The results of edge tone measurements show differences between previous studies and the present one. No frequency stages (and hysteresis phenomena) are found within the investigated pressure and cut-up range; the frequency modes of the edge tone coexist. The measured frequencies can be described by theoretical models.

Aeroacoustics of Musical Instruments

“…The pressure difference across the mouth of the instrument due to these oscillating sources drives the acoustic oscillation of the pipe. The potential flow model is furthermore used to calculate a hydrodynamic feedback at the flue exit, allowing the prediction of edge-tone oscillation (Powell 1961, Castellengo 1976, Segoufin et al 2004, Paal & Vaik 2007, Ausserlechner et al 2009. Complemented by a quasi-static flow-separation model describing the nonlinear losses by vortex shedding at the labium, the model predicts surprisingly accurately (see Figure 7) the limit-cycle oscillation amplitude for steady blowing at low Strouhal numbers Wf /U jet < 0.3 for thin jets W /h < 2 (Verge et al 1997a,b;Dequand et al 2003).…”

Roughness of organ pipe sound due to frequency comb

“…The amplification is most effective, for mouth tone frequencies that are close to the longitudinal resonances of the pipe. In case of higher cut-ups (> 5 mm) mouth tone spectra are usually similar to edge tone spectra measured by a pipe model (Ausserlechner et al, 2009). At low cut-ups the mouth tone spectra are more complex; equally spaced Rossiter-modes and other combination tones may be seen in the mouth tone spectra.…”

“…5 ("inblow" signal with a peak value of unity). In accordance with the measured profile of the air jet emerging from the flue of a metal organ pipe foot model (Ausserlechner et al, 2009) a Gaussian pulse profile is chosen. A coherent train of sine bursts is shown in the middle panel of Fig.…”

“…It may be imagined that a weak mouth tone is amplified, or a mouth tone is generated every time, when the air jet crosses the upper lip. Since the build-up of the mouth tone is very fast (Ausserlechner et al, 2009), the development of an edge tone or cavity tone burst during the crossover are possible. This mechanism could produce a periodic train of mouth tone bursts.…”

“…It may be assumed (Miklós and Angster, 2000;Ausserlechner et al, 2009) that the sound of labial organ pipes is generated in three subsequent phase.…”