The measured vocal tract impedance for clarinet performance and its role in sound production.
Teresa D. Wilson · The Journal of the Acoustical Society of America · 1996
The role of the vocal tract in clarinet performance has been investigated by examining the vocal tract impedance, Zu. Theory predicts that Zu peaks aligned with harmonics of the pitch frequency stabilize the oscillation. The vocal tract impedance was measured directly with a one-microphone technique and indirectly from a calculation using the continuity of flow equation pu/Zu+pd/Zd=0, where pu and pd are the mouth and mouthpiece pressures and Zd is the instrument impedance. The continuity equation was verified for single tones and then used to examine the role of the vocal tract in a variety of musical situations. In orchestral excerpts, the performer tends to align resonances with the first and/or second harmonics, and there is some dependence on the musical context. For multiphonics, the performer creates a resonance that supports an oscillation at a linear combination of the audible pitch frequencies. For tones played with pitchbend, induced by slacking the jaw muscles, the playing frequency is controlled by the frequency of a large-amplitude vocal tract resonance, for which ‖Zu‖≊100–400 CGS ohms. Zu changes only slightly when clarion tones are played without the register key, suggesting that other variables are involved.