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FLOW PHONATION IS A TERM USED in voice therapy and voice pedagogy to describe a production that feels effortless and efficient because ample airflow is passed through the glottis when the vocal folds vibrate. Using the analogy of water flowing from a reservoir, flow phonation is similar to opening the valve to release more water if valving is too tight. Some clinicians use the term unpressing because vocal folds can easily be pressed together in an attempt to make a stronger sound, which limits airflow. With flow phonation, the implication is that more airflow produces more sound output, but every singing teacher and speech-language pathologist knows that excessive flow makes the voice breathy and weak. It is therefore a question of optimizing the airflow, not maximizing it. But what is optimal, and what is the rationale behind it?
It must first be understood that there are two components of the glottal airflow, the steady component and the nonsteady (acoustic) component. The steady component is useless for sound production, except for some turbulent airflow noise created downstream from the glottis. The acoustic component is a flow that rises and falls as the glottis opens and closes (hundreds of times per second). This rise and fall creates a pressure against the vocal tract air column, which compresses the air and sets up the acoustic wave in the vocal tract. The key question becomes: Is this vocal tract input pressure dependent on the peak acoustic flow,...