Buzzing Lips: Sound Generation in Brass Instruments

Abstract

This chapter deals with the vibrating lips as a sound source: this is a defining feature of all labrosones (brass instruments). The main processes through which the air flow generated by the player’s lungs can initiate and sustain the vibration of the lips are covered. The facial muscles which control the embouchure of a brass player are described, and the complex motion of the lips when sounding a note is illustrated by the results of experimental studies using both human players and artificial lips. Simplified descriptions of lip motion are examined, including sliding door and swinging door models, and an equation representing the lips as a single degree of freedom mechanical oscillator is derived. The application of the Bernoulli equation to the flow of air through the lip channel, taking into account flow separation and jet formation at the exit, leads to a second equation describing the relationship between the flow velocity and the pressure difference across the lips.