Kenneth N. Stevens
Res. Lab. of Electron. and Dept. of Elec. Eng. and Comput. Sci., MIT, Cambridge, MA 02139
Several classes of speech sounds are produced by causing fluctuations in airflow in the vocal tract. This turbulence usually occurs in the vicinity of a constriction at the glottis or in the vocal tract, and results in the generation of noise sources. Teaching about these turbulence noise sources begins by introducing some basic ideas about airflow through orifices and the nature of turbulent flow, using analogies with other familiar situations in which turbulent flow occurs. Different mechanisms of sound-source generation as a consequence of turbulent flow are then considered, including fluctuating flow within an orifice, at a boundary, and in the absence of boundaries. Finally, the coupling of these sources with the vocal-tract modes is discussed, to indicate how fricatives, bursts, and other noise-like sounds are produced. Simple tubes and orifices with airflow are used to demonstrate the different mechanisms of turbulence noise generation and of noise excitation of resonators.