Simplified models of flue instruments: Influence of mouth geometry on the sound source

Abstract

Flue instruments such as the recorder flute and the transverse flute have different mouth geometries and acoustical response. The effect of the mouth geometry is studied by considering the aeroacoustical response of a simple whistle. The labium of a transverse flute has a large edge angle (60 degrees) compared to that of a recorder flute (15 degrees). Furthermore, the ratio W/h of the mouth width W to the jet thickness h can be varied in the transverse flute (lips of the musician) while it is fixed to a value W/h approximately 4 in a recorder flute. A systematic experimental study of the steady oscillation behavior has been carried out. Results of acoustical pressure measurements and flow visualization are presented. The sharp edge of the recorder provides a sound source which is rich in harmonics at the cost of stability. The larger angle of the labium of the flute seems to be motivated by a better stability of the oscillations for thick jets but could also be motivated by a reduction of broadband turbulence noise. We propose two simplified sound source models which could be used for sound synthesis: a jet-drive model for W/h>2 and a discrete-vortex model for W/h<2.

Regime change and oscillation thresholds in recorder-like instruments

“…15 For high Strouhal numbers or thick jets, i.e., when a discrete vortices description seems more appropriate, the initialization of a new vortex at the flue exit is triggered by the change of direction (sign) of the acoustic velocity. 17 There is no simple model for predicting the receptivity. For this reason, the empirical expression for the receptivity proposed by de la Cuadra 31 based on the Schlieren visualization of a jet flowing in a transverse acoustical field is used.…”

“…16 Different models, that are based on an accurate description of the jet behavior, describe the sound generation for different blowing conditions and different window geometries. 17 However, the understanding of the different elements that contribute to the oscillation in flute-like instruments has now grown to a point where it becomes difficult to predict the influence of some specific aspects of the model on the oscillation. This difficulty arises because the system is looped and a global resolution of the equations describing and coupling the different elements is lacking.…”

Experimental investigation of coaxial side branch resonators

“…(1), which is based on the vortex sound theory, provides a general approximation for the calculation of the acoustic power. It should be noted that recent studies suggest that the flow-acoustic coupling for the cases of the narrow main duct are more accurately described by a jet-drive model (Dequand, 2003b).…”

Principles of sound production in wind instruments

“…(11), has been revealed by measurement of the deflection amplitude by hot-wire anemometry [31] and visualization [32,33]. The effects of the flue geometry [34] and the edge angle [35] on the stability of the jet deflection have been investigated in flow visualization experiments. Recently, an edgetone theory by Holger et al [36] has drawn attention as a means of analyzing the jet deflection.…”