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.