Influence of the bell profile of the trombone on sound reflection and radiation

One of the most striking external features of a modern trombone is its wide and rapidly flaring bell. The bore profile of this final section of the instrument influences its musical behavior in a number of different ways, since it determines both the strength of the acoustical feedback from the instrument to the lips of the player and the nature of the radiated sound field. These effects have been explored in an experimental study in which a number of trombones have been progressively modified by the removal of annular sections of the bells. Measurements of input impedance, transfer function, and directivity of radiated sound are presented, and the implications for the timbre and playability of the instruments are discussed.