The beauty of SOVT exercises is that most of the beneficial effects occur simultaneously, without much voluntary adjustment or deliberate targeting. The system self-regulates. For example, high lung pressure produces a large vibrational amplitude, but high lung pressure with an SOVT also produces more vocal fold separation. The combined actions leave the contact stress regulated at a low value. In other words, the spreading of the vocal folds is proportional to the lung pressures produced, thereby negating the effect of excessive collision that is experienced with open-mouth phonation at high lung pressures. Wide pitch ranges can be explored with SOVT exercises without paying a high price in terms of tissue trauma.

A greater wide-narrow airway contrast for a large inventory of sound productions can be achieved by first widening the airway uniformly with a steady aerodynamic pressure. Selective narrowing can then be superimposed with specific muscle activations. Unfortunately, uniform widening of the airway with equally distributed pressure is not easily achievable with muscle activation alone because airway widening is not a frequent need in humans, other than for deep breathing during or after strenuous exercise. Hence, passive widening is accomplished by introducing a positive pressure in the upper airway with a semi-occlusion.

Acoustic and aerodynamic interaction between the airway and the sound source increases when the impedance of the airway (the pressure/flow ratio, defined in detail below) is on the same order of magnitude as the impedance of the source. For a wide-open airway at the mouth, the acoustic airway impedance is generally much lower than the source impedance, resulting in less interaction and less power transfer. If a portion of the airway is narrowed (or semi-occluded), the impedance can rise to a level closer to that of the source. This process is known as impedance matching. It increases the source-airway interaction, which leads to more power transferred from the source to the airway and ultimately from the mouth to the listener.

Methods often evolve over time, and the language to describe them becomes clearer with better conceptualization and more experimentation. As an example, we call attention to a yet unresolved issue of hyperfunction in vocalization. A narrowing of the larynx canal (epilarynx) raises the question of excessive use of constrictor muscles as a compensation for vocal fold dysfunction. It might contribute to what some describe as muscle tension dysphonia. However, narrowing the larynx canal increases the vocal tract impedance for maximum power transfer, a desired effect. This narrowing should coincide with expansion of the rest of the vocal tract and flexibility of musculature. It is yet unclear to what degree the larynx canal can be narrowed actively in such a way that unwanted ventricular or aryepiglottic vibration or tension does not take place. This is a challenge for future research and practice.

For the voicing carrier to maintain efficiency, many methods start with and often return back to SOVT methods in different contexts and in generalization for daily tasks. Diagnostically, we can rely on SOVT methods to determine a deficiency in airflow, prosody, subglottal pressure, soft tissue biomechanics, and flexibility of the laryngeal and skeletal framework. The use of masks and straws in and out of water are useful in supplementing videostroboscopic assessments with methods that reveal improved measures of phonation threshold pressure, glottal airflow, subglottal pressure, breath support, palatal strength, vocal fold stiffness, and glottal closure. Observing how deep one can submerge a straw in water and keep the bubble rate constant, or how many small straws (multiples of 3mm or less in diameter) are used to complete a full voice range profile, clarify an individual’s full vocal function and determine efficiency of the carrier. 

Cox, K.T. & Titze, I.R. (2023) Voice is FREE after SOVT. National Center for Voice and Speech.