The influence of mouthpiece cup shape on "brassiness"Robert W. Pyle
The degree of spectral enrichment of brass-instrument tone due to non-linear propagation in the instrument depends not only on the amplitude of the sound, but also on the maximum rate of change of the sound pressure in the mouthpiece. A skilled player has some control over the generated wave shape, but the internal contour of the mouthpiece is also very important. Judging from the sounds produced, a funnel-shaped (horn-like) mouthpiece encourages a less steep waveform than does a bowl-shaped (trumpet-like) mouthpiece. This talk will open with a review of the physics of finite-amplitude sound propagation in a flaring tube, and how this has led to the definition of a ``brassiness coefficient'' that predicts the relative degree of spectral enrichment for various brass instruments. The remainder of the talk will focus on the influence of the mouthpiece. Internal (within the mouthpiece) and external (beyond the bell) measurements of sound pressure and spectrum will be shown for a trumpet equipped with both a conventional trumpet mouthpiece and a flugelhorn mouthpiece.