It’s practically a guarantee that most singers have used semi-occluded vocal tract (SOVT) exercises, regardless of whether they have ever heard the term. Vocalizing on a lip trill, a voiced consonant like “v” or “z,” or even on nasal consonants like “m,” “n,” and “ng” are all in the family of SOVT exercises that are ubiquitous in the voice studio.
Karin Titze Cox
It wasn’t until recent decades, however, that voice scientists started to identify what occurs when the vocal tract is semi-occluded (or partially blocked) and how that can lead to greater efficiency in vocalization. A new book published by the National Center for Voice and Speech explores the history and research that has led to our current understanding of SOVT exercises.
Voice is Free after SOVT: Semi-Occluded Vocal Tract Principles, Methods, and Training is co-authored by speech-language pathologist and vocologist Karin Titze Cox and her father, noted voice scientist Ingo R. Titze. In the interview below, they give an introduction to SOVT exercises and their potential benefits.
In simple terms, what are semi-occluded vocal tract exercises?
They are exercises that allow the sound source in the larynx to obtain maximum benefit from steady and acoustic pressures within the airway. A semi-occluded vocal tract has a narrow canal downstream from the sound source that produces a steady supra-laryngeal airway pressure, which can lead to an optimal airway configuration and optimal posturing and shaping of the vocal folds for vibration.
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Based on the research you have conducted and compiled in the book, what are the greatest benefits of SOVT exercises for singers?
Steady widening of the airways and upper separation of the vocal folds allows for tissues and muscles inside and outside of the larynx to change to an optimal posture for more efficient sound production. This prevents injurious vocal fold collision forces when wide ranges of lung pressure and pitches are used. SOVT exercises also help singers maximize the acoustic benefit they get from their instrument by allowing maximum power transfer from the source though the airway to the listener. This is accomplished with strong interaction between the vocal folds and the vocal tract. This interaction comes with steady and acoustic pressures that are built up between the larynx and the lips with a semi-occlusion.
When should they be used?
Ingo R. Titz
A short answer is that they should be used for training, warming up, cooling down, and for evaluation of capabilities throughout a vocal career. The question that is harder to answer is when they shouldn’t be used. Our book goes into depth about the implementation in the Appendix section, but if the core goal and focus is on efficient voicing in any vocal behavior, SOVT methods allow for a full range of capabilities, from high and low frequency vibration to high and low amplitude vibration (a full voice range profile). SOVT can be customized to individual needs and capabilities as outcomes are achieved. Generalization, however, depends on vocal demand and stamina. Even the best athletes need to stretch and reset from muscle fatigue, tissue wear and tear, or minor injury. Long term success in high stakes performance can be facilitated with SOVT methods targeted specifically for preservation. Vocal limitations can change over several years, but sometimes happen quickly and unexpectedly. A singer’s demand for exceptional voice use may increase and over time, and structural or tissue changes may influence efficient voicing biomechanically. As discussed above, warming up and cooling down with SOVT methods may be necessary as demand for exceptional use increases. The need to reset with SOVT methods increases as fatigue increases and any limitation can return as demand increases and age-related limitations are experienced.
Most singers are probably familiar with some SOVT exercises like lip trills, humming, and even straw phonation. Are there other, lesser-known types that singers should know about?
Vocalizing through a tube or straw into a glass or bottle of water is thoroughly described in the book, as well as the use of voiced consonants and relatively closed vowels like /u/ and /o/. There are many ways to semi-occlude the vocal tract, and many singers use multiple strategies. We would attest that if you find a vocal strategy that gives you more efficiency and ease in a high demand task, you should look for the underlying semi-occluded vocal tract resistance you could be using to accomplish it. We feature diagrams in the book for quantifying the airflow resistance and oral pressure you get from the multiple variations.
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Considering how much SOVT exercises have been studied in recent years, what aspects are still in need of further research and exploration?
The muscular control needed to selectively narrow regions in the lower pharynx and the larynx canal is not yet fully investigated. Methods often evolve over time, and the language to describe them becomes clearer with better conceptualization and more experimentation. 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.
Human vocalization is rapidly adapting to ever more electronic assistance. In this adaptation lies a dichotomy in training and care-giving. Is it more important to increase the efficiency of sound production at the larynx, or is it more important to deliver rapid and clear messages to the listener with a microphone? In amplified vocalization, the carrier of the signal (voicing) can be modulated with much variability (including unvoiced segments and distortions). Thus, the timing of voice modulations is a higher priority than the integrity and continuity of the carrier. On the other hand, if unamplified calling, shouting, or singing over long distances is the target, vocal efficiency is paramount.
