In-Vitro and Numerical Investigations of the Influence of a Vocal-Tract Resonance on Lip Auto-Oscillations in Trombone Performance

International audienceControlling the acoustic impedance of the upstream airways in brass instrument performance may bean important factor influencing the efficiency of the sound production process. Because of the complexcharacteristics of the lip-valve oscillator, the conditions under which a vocal-tract resonance may be favorableto the sustain of lip auto-oscillations are not easy to determine. In order to investigate this aspect ofbrass performance, an experimental method based on an active control approach is applied to an artificialtrombone player system in order to simulate the influence of a vocal-tract resonance at the playing frequency.By varying the amplitude and phase characteristics of this upstream impedance load, we investigatethe acoustical influence of this resonance on lip vibrations and on the acoustic pressure generated in theinstrument. The observations reveal that variations of the phase difference between the downstream andupstream impedance induce significant variations of the playing frequency. An optimal phase tuning pointcharacterized by a maximum of downstream acoustic pressure at the input of the instrument, and uncorrelatedto a maximum of downstream input impedance, is identified. These experimental results are comparedwith numerical simulations, both of which produce similar findings. The optimal tuning point appears tobe partly related to the displacement of the playing frequency close to a mechanical resonance of the lips.This induces a greater “efficiency" of the lip-valve system, hence maximizing the acoustic flow generatedinto the instrument while other control parameters (quasi-static mouth pressure, lip tension) are maintainedconstant. In addition to an exploration of acoustical influence of the vocal tract, this experimental methodhence offers promising perspectives for the study of artificial lips under playing conditions