The production of voiced sounds is consequence of the interaction between the respiratory airflow, the elastic structures formed by the vocal folds and the upstream and downstream vocal tracts. This paper considers the effect of the acoustical coupling of the vocal tract on the oscillations of the vocal folds. A specific experimental set-up is used to reproduce the human phonatory system. It consists of a large pressure reservoir filled with acoustical foam which mimics the lungs, connected to a mechanical replica of the vocal folds through a straight pipe of variable length, representing the trachea. This vocal fold replica is made of latex filled with water under controlled pressure and is able to produce self-sustained oscillations at physiologically realistic values of lung (reservoir) pressure and fundamental frequency. An acoustical resonator may be connected at the exit of the replica, to mimic the downstream vocal tract. The experimental results show that both the oscillation threshold value of lung pressure and the fundamental frequency of oscillation are sensitive to the acoustical coupling, and may be characterized by a simple theoretical model based on a lumped description of the tissue mechanics, quasi-steady flow and one dimensional acoustics.
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