Strategies for Safety Thresholds of Phonation for Performers via Dosimetry

Singers are among a category of professionals, along with many other professionals, who rely on their voice for work [1]. Phonotrauma can be caused by many factors, among which the amount and intensity of vocal use are at the forefront [2]. Dosimetry metrics can assist voice professionals aim for safe amounts of voice use, but a threshold of voice use has not yet been established and recommended by researchers [3]. Understanding what dosimetry research can offer is one important step towards that goal. Furthermore, once dosimetry devices become mainstream, singers can apply the understanding of dosimetry measurements to pace vocal use and minimize vocal fatigue, vocal effort, and consequently preventing vocal injury. 

Dosimetry equipment provides three types of vocal doses: time dose (the accumulated time of vocal folds vibration), cycle dose (the number of glottal cycles; with one cycle representing the movement that occurs from the beginning of the open phase till the conclusion of the closed phase), and distance dose (the estimate of the accumulated linear distance a tissue particle covers in its repeated cyclic paths) [4]. 

Dosimetry data have been reported by many investigators [5-25] utilizing different devices and technology, and therefore each displays a slightly different metric for estimating doses. This is due to the fact that some accelerometers, such as the Sonvox VoxLog dosimeter [25], the do-it-yourself dosimeter device [26], and the KayPentax’s APM device [3, 24], for example, have slightly different sampling rates and margins of errors [3, 26]. Therefore, only an informed estimate can be made across previous dosimetry studies. 

The distance dose, measured in meters, provides the most accurate account in regard to vocal fold vibration, as its measurement is calculated from the cycle dose and an estimate of vibrational amplitude from sound pressure level (SPL) [4]. Overall, distance doses provide the distance traveled by a vocal fold tissue particle during the accumulated glottal cycles (including open and closed phases), not solely the amount of collision of the vocal folds. This concept can be compared to the total distance traveled by the foot of a runner, which accounts for the duration of impact the athlete’s foot on the ground and the path the foot off the ground. 

Previous studies have reported that, over the course of a day, human voicing typically ranged from 5% to 25% of total elapsed time, over a million cycles of vibration, and over 5,000 meters in distance traveled, which was compared to an athlete running a 5K race [25]. A singer’s vocal folds’ travel distance often surpasses those of non-singers due to the larger vocal range employed in singing when compared to speaking. High frequencies and high sound pressure levels contribute to larger distance doses, representing the cumulative load placed on vibrating tissue. For example, when high frequencies are produced with CT dominant mechanisms, the vocal folds amplitude of vibration could be smaller compared to low frequency in TA dominant register. Therefore, singing styles such as belting, which require loud and heavy vocalization, are expected to produce larger distance doses than mixed and head voice strategies [3]. 

Dosimetry studies measuring and cataloging the demands of individual Broadway roles can serve as baseline for the distance dose required for each role, which alongside self-reported measures of vocal fatigue can prove helpful in generating and recommended singing thresholds. As dosimetry devices become commercially available and mainstream, dosimetry data can serve as a vocal Fitbit for those interested in monitoring their daily and overall vocal use, especially singers performing roles that require extensive use of belting strategies, expansive vocal ranges and large amounts of time engaged in singing and dialogue during a show.

A key question for singers is in regard to the vocal folds’ recovery time. The amount of tissue vibration exposure is not easily accessed because humans don’t engage in continuous non-interrupted sound production, but include momentary vocal breaks throughout the day and when others are speaking; hence, the low time doses reported in previous studies [3, 25]. While an ideal recovery time is yet to be determined, a previous study has established a recommended speaking threshold (see Figure 1) via a retrospective analysis of vocal-fold collision stress, calculated from amplitude, frequency, and duration, generating an energy-dissipation-dose [27].

A few recommended strategies for practical application of dosimetry metrics include: 1) measuring the distance dose required for singing a specific role to obtain a baseline for the demands of the score. 2) measuring the distance dose of the overall vocal use including daily social interactions for a week to obtain a baseline of normal vocal behavior. 3) observing what the distance dose amounts to on a day when feeling vocally fatigued and comparing that week’s distance dose with previous weeks when not feeling fatigued. 4) utilizing dosimetry to evaluate ways in which to sing the same song more efficiently. For example: a singer may choose to sing the same song multiple times employing differing levels of intensity and vocal fold adduction, aiming to minimize close quotient [28-31] and subglottic pressure levels [32-37], to compare distance doses across performances. Consequently, dosimetry can assist the singer in developing pacing strategies for when to use heavier versus lighter mechanisms to preserve the voice long term when required to sing a role eight times a week. These dosimetry-combined strategies can assist singers in establishing an ideal threshold for overall voice use during seasons of increased vocal loading, preventing overuse and possibly vocal pathology. 

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A true expert in her field, Dr. Zuim’s work as a voice scientist has been recently highlighted by CBS. Credited with over 70 musical theater productions throughout her career, her work as a musical director and pianist has culminated in several awards, and her research led to findings that can impact the voice field. Her love for sound and the human voice has shaped her career as a musical director/conductor, voice scientist and expert witness. A renowned international scholar, Dr. Zuim has conducted seminars and workshops all over the world, including Israel, Japan, Taiwan, Brazil, Turkey, Greece, Canada and Australia. The knowledge of voice science and acoustics acquired during her career, combined with her passion for languages paved the way for serving as an expert witness in forensic voice analysis. Dr. Zuim served as Director of Vocal Performance at the Steinhardt School at New York University from 2016 to 2022 and was promoted to Associate Music Professor in 2022. Prior to joining the NYU faculty, Dr. Zuim served as Director of Contemporary Voice at the Frost School of Music with a secondary appointment as Lecturer of Otolaryngology at the Miller School of Medicine, University of Miami. In addition to being a multi award-winner musical director/conductor, Dr. Zuim’s credits include the iconic musical Hamilton (rehearsal pianist/vocal coach), Billy Elliot (musical director/pianist), among others.
Ana Flavia Zuim
Editor, NCVS Insights

How to Cite

Zuim, A. (2023), Strategies for Safety Thresholds of Phonation for Performers via Dosimetry. NCVS Insights, Vol 1(4), pp. 1-2. DOI: https://doi.org/10.62736/ncvs128707