The effect of fast trombone slide glissandi on the mechanics of artificial lips

The lips of a brass player can be modelled as a mechanical oscillator which couples with the acoustic resonances of the instrument to generate and sustain a musical note. On instruments like the modern orchestral trumpet, operation of a valve changes the length of the resonator without significantly altering the mean pressure of the air column. On a slide trombone, however, a glissando involves a telescopic change in the length of the resonator, resulting in localised changes in the mean pressure in the air column. The consequent low frequency fluctuations in mouthpiece pressure can disturb the equilibrium position of the lips, affecting their dynamic behaviour. This paper describes experimental studies in which an artificial mouth is used to investigate the infrasound mouthpiece pressure gradients generated by fast glissandi on a trombone, and their influence on the mechanics of the oscillating lips