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There are currently more than three decades of formal research on semi-occluded vocal tract exercises (SOVTEs), as well as more user friendly sources of information such as websites, blogs, online forums, and videos. Nevertheless, questions still arise: What exactly do these exercises do? Do 1 have to use straws? Is this just a fad? These questions come up because this information needs to be framed with more attention to the why and the how. This article will attempt to survey the literature with an emphasis on bridging the gap between theoretical and clinical research and studio practice and to equip studio teachers with enough of the why and how to fine tune their use of SOVTE exercises.
Any exercise in which the vocal tract is made partially closed at or near the lips is considered an SOVTE. For centuries, hums, lip trills, tongue trills, and sustained voiced fricatives all have been a part of the voice teacher's toolbox to improve the functionality of singing. Over the past one hundred years, the speech community, led largely by Finnish practice and research, has used resonance tubes for therapeutic purposes.1 In the last few decades, Ingo Titze popularized the use of straws (paper, metal, and corn-based versions available) through numerous articles and videos (including "Vocal Straw Exercise" available on YouTube),2 and raised awareness about SOVTEs generally. As the use of SOVTEs has become more commonplace, it is important to trace what we actually know about them through theoretical models and clinical studies.
A thorough explanation of the properties of impedance is beyond the scope of this article; however, a discussion of SOVTEs requires some understanding of how the properties of impedance come into play. (The introduction to "Acoustic Impedance of an Artificially Lengthened and Constricted Vocal Tract" by Brad H. Story et al. includes helpful analogies for understanding these concepts.)3 At its most basic, impedance describes how much opposition a system encounters as it starts up.4 Titze defines acoustic impedance of the vocal tract as "a measure of the ratio of oscillating pressure to oscillating flow at the entry to the vocal tract."5 Impedance breaks down into two types: resistance, which dissipates acoustic energy, and reactance which stores acoustic energy. Reactance also breaks down into two types: compliance,...