SOVTs and the MT!


Alex Davies 

I’ve always been intrigued by training methods that are considered unorthodox.

So, when I first started seeing singers use SOVTE (semi-occluded vocal tract exercises) to warm-up and train their voices, I was hooked! After researching SOVTEs as part of my Masters in Vocal Pedagogy, I discovered some of the many benefits and interesting ways we can utilise SOVT exercises by personalising the training for each individual student.

For this singing method, more research is needed as scientific underpinnings of SOVTE benefits have been emerging over the last two decades – which for us Pedagogues, is VERY exciting!  

So why am I interested in the benefits for Music Theatre students?

Music Theatre (MT) students tend to require athletic ability, or durability, for professional MTs to sustain prolonged cord collision because of the extreme vocal qualities needed.

For an MT singer, the vocal demands of the 21st century are leading away from “classical” or “traditional” MT, there is a great level of athletic ability and versatility required from a professional MT performing eight shows a week across many music styles, most often with high vocal intensity[i].

In a 2014 study, Green et al[i] found four primary categories within Broadway musical theatre audition listings for a range of high-low paying jobs listed for a demographic of mixed-gendered young performers (aged 18-24) between six months:

Pop/Rock (25%),

Contemporary (30%),

Traditional (40%) and

Legit (5%).

Freeman, Green, Sargent [ii] discovered, from 24 Broadway shows in April 2014, that Belt dominated the Leading Female role listings by 85%: Belt (62%), Belt/Mix (23%), and non-Belt (15%). Things may have changed again in the last 8 years.

So, when it comes to SOVTEs where do we start?

SOVTEs have been a very popular method for voice rehabilitation and therapy, and classical singing.

Early mentions of Traditional SOVTEs dated between 1960 to 1999 emerged in voice pedagogy such as:

  • covering the mouth with one hand (Aderhold),
  • Straw (Sovijärvi),
  • Y-Buzz and nasal consonants,
  • Lip-trills (Linklater),
  • “Standing Wave” exercise (Coffin), Humming,
  • Bilabial Voiced Fricative (Laukkaenen),
  • Nasal Consonants, Lip-trills, Tongue-trills and Raspberries (Nix).

While Resonant Voice Therapy and nasal consonants (Verdonlini), Flow Resistant Straws (Titze), and Titze’s SOVT Voice Training and Therapy rational were developed in the early 21st century.

This early explorations of SOVTEs contributed to training and warmups cross the country.

Have you ever used any of these methods?

What is an SOVTE?

Semi-Occluded Vocal Tract means that the vocal tract (the space between the vocal cords and lips where sound travels, amplifies and resonates) is partially closed in some form.

A Semi-Occluded Vocal Tract Exercise is the premise of economy-oriented voice training which is used as a vocal warm-up or technique exercise that occludes (closes) part of the vocal tract and increases supraglottal pressure (pressure above the vocal cords).

These exercises can vary in type of occlusion and can be at the front/back of the mouth or extended outside the vocal tract. For instance, exercises such singing using the shape /ŋ/ (as in sing) occludes at the back of the mouth with the tongue, or using hand-over-mouth extends the vocal tract outside the lip.

Vocal tools such as straws, vocal tubes, and mouth masks also extend outside the mouth and have become another commodity in the Music Theatre industry of recent years.

Straw and tube phonation, hand-over-mouth and cup phonation differ from a lot of SOVTEs because the vocal tract is extended outside the lip. Stirring and drinking straws, Finnish glass “resonance tubes” and LaxVox silicone tubes differ greatly as they can be of different diameters and lengths and used in the air or submerged under different amounts of water which create different levels of resistance. See below for some of my favourite SOVTE TOOLS!!!


CREDIT – Isabel Cooke McKay


CREDIT – Oren Border / Vocal Process


CREDIT – The Voice Straw

So why do MTs LOVE these vocal methods?

From my research, I found it was hypothesised that the supraglottal pressure SOVTEs facilitate can mimic a mixed register[i] which may be favourable to an MT singer for the durability of phonation (production of sound) and less vocal cord collision.

SOVTEs can also be quite effective for Belt. When talking about SOVT benefits, Cordeiro et al say “probably the difference becomes more evident during high-intensity voice production (fortissimo)”[ii].



SOVTEs will have a range of benefits but the benefits will vary depending on which exercise is used and what the singer needs at the time.


  • Aerodynamic energy can be defined as a transfer of the glottal airflow to vocal fold tissue and drives airflow through the vocal tract.
  • Acoustic energy is described as sound waves (vibrations) disrupting energy by traveling through matter (tissue and air)

SOVTEs can improve the aerodynamic and acoustic energy, therefore the output-to-cost (OCR) benefits the phonation threshold pressure.

Supraglottal pressure can mediate the usually greater subglottal pressure lowering the intraoral pressure (between the vocal cords) with the upper portion of the vocal cords spread apart equivalent to supraglottal pressure.

The folds adopt a rectangular glottis shape. High sound pressure level (SPL) phonation with low vocal loading increases vocal fold vibration “massage effect”, contributing to lessened cord collision/stress/trauma on vocal organs[i]. This allows for tension reduction and promotes a more resonant voice quality. SOVTEs will have a range of benefits but the benefits will vary depending on which exercise is used and what the singer needs at the time.


If used correctly, SOVTE may help a singer develop a range of benefits:

  • Breathing mechanisms – airflow improvements (aerodynamic energy) and increase maximum flow declination (MFDR)
  • A more resonant voice quality/timbre/character (acoustic energy)
  • Phonation Threshold Pressure (PTP) lowered
  • Combatting adduction – stabilize vocal fold’s coming together reducing vocal fold collision/stress/trauma
  • Vocal fold oscillation cycle – reinforce the full phasing of the vocal cords
  • Vocal economy with the lengthening of the vocal tract
  • Assisting with register changes
  • Extending vocal range
  • Pitching issues
  • The singer’s perceived effort
  • Sensory awareness – vibrations
  • Preventing vocal injury

Further benefits of SOVTEs may also be found by combining SOVTs[i]. Last year, Manternach, Maxfield, Manternach conducted a 30 participant MT study on four different SOVTEs (humming/lip trill/drinking straw phonation/stirring straw phonation).

This study looked at both acoustic and perceptual analysis with the aim to discover a correlation between the two which could better equip teachers with SOVTE recommendations.

They suggest that SOVTEs may need to change depending on the individual and hey can bring vocal awareness to the singer. The perceived effort may be another indicator of SOVTE prescription[ii].

Further research is needed for the carryover to the “vocal norm” looking at natural phonation methods combined with SOVT, and what effect SOVTEs have in a long-term study with live subjects.

This could discover trends in SOVTE benefits that may assist in training customisation. The singer’s perceptual results may also be useful to consider. More detailed demographics of age, voice types, and abilities are definitely needed to find trends.

Studies would benefit from cross-examining a larger quantity of exercises, looking at SOVTE combinations, and looking at how to perform exercises correctly to create an inclusive program. More research is also needed on the SOVTE effects on professional MTs.

List of SOVTEs (so far) …

I have started to put together an SOVTE table (which I am sure will change over time). I have use both Titze’s SOVTE Rational and Andrade’s Steady and Fluctuating groups. Titze identified a ‘most artificial to most natural’ rationale of some SOVTEs through his research which could be a good way to determine part of an individual development plan (IDP) for a singer. I have used the rational in the table below and extended it slightly. The aim, to transition the benefits of artificial phonation (production of sound) to the most natural form of singing, using the lyrics.

Titze’s Resistance Rational: Most artificial to most natural:

  1. Highly resistant (small diameter) stirring straw
  2. Less resistant (larger diameter) drinking straw
  3. Bilabial or labiodental voice fricative
  4. Lip or Tongue Trill
  5. Nasal consonants
  6. Vowel /u/ and /i/
  7. Natural singing with resistance (**added**)

I have also used Andrade’s Steady and Fluctuating groups:

The first is the ‘Steady’ group which has a single source of vibration such as humming /m/ or /n/, straw phonation and hand-over-mouth.

The second is the ‘Fluctuating’ group which introduces a second source of vibration which amplifies the “massage effect” for example at the lips, tongue, or additionally LaxVox.

SOVTE Description Group – Single or double vibration Titze Resistance Rational
Bilabial Voiced Fricatives /v/ or /z/ sound Fluctuating 3
Cups Placing a cup over the mouth to extend occlusion outside the vocal tract Steady 7
Hand-Over-Mouth Hands covering the mouth creating an occlusion out of the mouth Steady 7
Hand-Over Mouth with a Tongue-Trill A combination of Hand-Over-Mouth and the Tongue-Trill Steady & Fluctuating 4
Humming Phonating on /m/ or /n/ Steady 5


Soft silicone tube – length 25mm and diameter 4mm Fluctuating 2
Lip Trills Occlusion at the lips Fluctuating 4
Puffa Fish Mimicry of straw phonation without the straw adding puffy cheeks for back pressure Steady 1 and 2
Raspberries (linguolabial) An occlusion at the lip with the tongue between the lips Fluctuating 4
Sirening Phonating on /ŋ/ Steady 5
“Standing Wave” exercise Vowel sung then cover the mouth (hand-over-mouth) Steady 6
Straw Phonation Using Straw or Tubes in the air or under different depths of water Fluctuating 1 and 2
Tongue Trills An occlusion inside the mouth using the tongue on the hard palate Fluctuating 4
Vowels – /o/ and /u/ Traditional vowels used in speech and singing Steady 6
Water-Resistance Ventilation Mask A mask with a tube into water allowing for speech/singing to occur while maintaining resistance Steady 7


/j/ sound Fluctuating 3


How to put the SOVT into practice…

SOVTEs can be used over a variety of vocal exercises/patterns, and also working on your repertoire. To use SOVTEs correctly, it is best that you speak to your coach who can make sure you are choosing the right exercises and performing them correctly.

Top Tips:

  • Hold your nose to check all the air is flowing through the mouth/straw
  • If using a straw, make sure the lips seal around the straw so no air escapes at the side of the mouth
  • Relax your face, neck, and shoulders
  • Breath through your mouth as you would regularly
  • Short and regular sessions of SOVTEs are best

SOVTEs can be performed incorrectly:

When it came to looking at developing and independent development practice for my students, I found research suggested that one SOVTE may suit one person more than another as they render different outcomes depending on the exercise combined with additional variables associated with the singer[i].

It also suggested that the same singer may need different SOVTEs during the course of their training.

Titze (2006) says, sensory changes in a singer may influence results as they feel the sounds in the facial tissues and experience heightened supraglottic pressure. SOVTEs are not successful for every singer and could have a damaging result if not performed correctly.

Therefore, it is important to take this into consideration when recommending and teaching SOVTE. As Keltz and McHenry argued:

“This study revealed that these strategies are not universally successful, and clinicians should recommend them only after assessing their effectiveness for their clients. Another consideration is the importance of teaching proper SOVT technique, so it is done correctly without added tension. Even blowing bubbles into a cup of water with phonation can be done poorly, in some cases yielding counterproductive results.”[ii]

Long term effects of SOVTEs

According to Titze[i] the effects of semi-occlusion at the lips are efficient when transitioning to a nonoccluded vocal tract acting as “muscle memory” for the singer. first live study on Lip-trills.

Gaskill, and Erickson found untrained singers tended to have a larger change which could have occurred because trained singers have experience with SOVTEs[ii]. The varied results between the two groups suggest that SOVT training could have long-term effects as the trained singers had a baseline closer to the concluding results.

SOVTE Tool Recommendations:

What next?

We are at the infant stage of our physiological understandings of SOVTEs and that to me is incredibly exciting!

At the beginning of my research project, I thought I may conclude by being closer to developing a training program to maximise the potential of economy-oriented voice training, however, a ‘Pandora’s box’ surrounding SOVTE has emerged which I’m excited to get stuck into.

The BIG takeaways:

  • SOVTEs need to be chosen with care
  • SOVTEs are hypothesised to facilitate a mixed register
  • Water-resistant ventilation may be a way to bridge the gap between artificial and natural phonation while benefiting from the effects of SOVT still
  • There is potential to mix SOVTEs as a training method, but beneficial combinations need to be studied
  • Evidence suggests that a tailored program should be recommended to the singer; the SOVTE could accordingly require alteration during a training program
  • Evidence suggests that SOVTEs may have long-term effects

If you are an MT performer who is looking for a valuable and efficient training method which utilises time during practice, I would recommend speaking to your coach about experimenting with some the SOVTEs above.

We also use this technique extensively in the Vocal Gym – our daily live class available on the Membership.

They have a multitude of benefits occurring simultaneously while also helping to prevent injury, looking after your vocal health!

Alex is a Sing Space recommended coach and her profile can be found HERE.


Get in touch today to join our community at The Sing Space.

[1] Melton, J. (2007) Singing in musical theatre: the training of singers and actors. New York, N.Y: Allworth Press.

[1] Green, K. et al. (2014) ‘Trends in Musical Theatre Voice: An Analysis of Audition Requirements for Singers’, Journal of voice, 28(3), pp. 324–327.

[1] Freeman, W, Green, K, Sargent, P. (2015) ‘Deciphering vocal demands for today’s Broadway leading ladies’, Journal of singing, 71(4), pp. 491–495.

[1] Titze, I.R. (2006) ‘Voice Training and Therapy with a Semi-Occluded Vocal Tract Rationale and Scientific Underpinnings.’ Journal of Speech, Language and Hearing Research, 48, pp. 448-449.

[1] Cordeiro, G.F. et al. (2012) ‘Comparative analysis of the closed quotient for lip and tongue trills in relation to the sustained vowel /ε/’, Journal of Voice, 26(1), pp. e17-e22

[1] Titze, I. (2018) ‘Major Benefits of Semi-Occluded Vocal Tract Exercises’, Journal of Singing, 74(3), pp.311-312.

[1] Andrade, P.A. et al. (2016) ‘The Flow and Pressure Relationships in Different Tubes Commonly Used for Semi-occluded Vocal Tract Exercises’, Journal of Voice, 30(1), pp.36-41.

[1] Manternach, B, Maxfield, L, Manternach, J.N. (2021) ‘Effects of Varied Semi-Occluded Vocal Tract Exercises on Acoustic and Perceptual Measures of Music Theatre Singers: A Pilot Study’, Voice and Speech Review, 15(1), pp. 40-50.

[1] Dargin, T.C, DeLaunay, A, Searl, J. (2015) ‘Semioccluded Vocal Tract Exercises: Changes in Laryngeal and Pharyngeal Activity During Stroboscopy’ Journal of voice, 30(3), pp377.e1–377.e9.

[1] Keltz, A, and McHenry, M. (2020) ‘Steam and/or Semi-occluded Vocal Tract Exercise as Morning Vocal Warm-up Strategy’, Journal of voice: official journal of the Voice Foundation, 15/04/22, DOI: