Non-invasive measurement of acoustic coupling between the clarinet bore and its player’s vocal tract

Abstract

As acoustically coupled resonators, the bore of a clarinet or other woodwind instrument and the vocal tract of the player interact in ways that affect timbre and pitch. Pitch in particular is strongly dependent on vocal tract acoustics when the bore-tract coupling is strong, such as when a tract impedance maximum is close in frequency and amplitude to a bore impedance maximum. Direct investigation of bore-tract coupling requires invasive measurement of bore and tract input acoustic pressures (or impedances), and one particular technique makes us of the ratio of these pressures (in the frequency domain, Pt/Pb) at harmonics of the reed vibration fundamental frequency. A non-invasive, model-based approach to investigating bore-tract coupling has been developed, which depends on a free-field microphone recording the sound produced by the instrument (P1), and an accelerometer placed against the skin of the neck recording skin vibrations (P2) related to intra-tract acoustic pressures. An additional, model-based calibration step is required. The ratio of these two signals (in the frequency domain, P2/P1) following calibration is qualitatively similar to the ratio Pt/Pb, and approaches quantitative identity as the model-based calibration step improves.