Ron Scherer

The membranous contact quotient (MCQ) is introduced as a measure of dynamic glottal competence. It is defined as the ratio of the membranous contact glottis (the anterior-posterior length of contact between the two membranous vocal folds) and the membranous vocal fold length. An elliptical approximation to the vocal fold contour during phonation was used to predict MCQ values as a function of vocal process gap (adduction), maximum glottal width, and membranous glottal length. MCQ is highly dependent on the vocal process gap and the maximum glottal width, but not on vocal fold length. Five excised larynges were used to obtain MCQ data for a wide range of vocal process gaps and maximum glottal widths. Predicted and measured MCQ values had a correlation of 0.93, with an average absolute difference of 9.6% (SD = 10.5%). The model is better at higher values of MCQ. The theory for MCQ is also expressed as a function of vocal process gap and subglottal pressure to suggest production control potential. The MCQ measure is obtainable with the use of stroboscopy and appears to be a potentially useful clinical measure.

The goal of this essay is to emphasize the correspondence among interactive phonatory variables, complementary assessment measures, and voice problems. An additional related goal is to suggest that we pay close attention to figures and expressions that interrelate phonatory variables, for they can be strong guides to our therapeutic thinking. Acoustic and aerodynamic factors are the focus here. This essay is not historical per se, but rather interrelational.

ABSTRACT Pursuing a deep interest in understanding the complexities of human sound production, particularly singing, Ingo Titze received his Ph.D. in Physics under the tutelage of Bill Strong at Brigham Young University in 1972. His dissertation on computational modeling of vocal fold vibration launched a career in research and teaching that has had a profound influence on the field of voice and speech science. Although his research alone is prodigious, Ingo Titze created an academic family that stretches far and wide. This presentation will trace the careers and research of the many students and scientists that were trained by Ingo Titze or influenced by his training.

Air pressure associated with airflow from the lungs drives the vocal folds into oscillation and allows the air to exit the glottis as a turbulent jet, even though laminar flow may enter the glottis from the trachea. The separation of the turbulence from the deterministic portion of the glottal jet was investigated in the excised canine larynx model. The present study is methodological in that the main goal was to examine three methods of obtaining reasonable representations of both the deterministic signal and the residual turbulence portion: (a) smoothing, (b) wavelet denoising, and (c) ensemble averaging. Ensemble averaging resulted in a deterministic signal that disregarded gross cyclic alterations while exaggerating the turbulence intensity. Wavelet denoising can perform an excellent analysis and synthesis of the glottal velocity, but was problematic in determining which levels of analysis to choose to represent both the deterministic and turbulence appropriately. Smoothing appeared to be the most appropriate for phonation velocities because it preserved gross cyclic variations important to perturbations and modulations, while extracting turbulence at what appears to be reasonable levels.

Velocity distributions within three models of the human larynx, namely, a rigid plexiglas model, an excised canine larynx, and a computational model are investigated with experimental and theoretical analyses. A plexiglas wind tunnel with interchangeable glottal constrictions was used as a two-dimensional steady-flow model to measure velocity and pressure for various glottal shapes. A canine excised larynx was used as a prototype pulsatile flow model to study pressure and velocity variations during phonation. Results of the plexiglas modelling indicated a parabolic laminar velocity profiles upstream of the glottal constriction and turbulent and asymmetric velocity profile downstream of the glottal constriction. The time-averaged velocities of the excised larynx had similarities with the plexiglas model results, and instabilities and asymmetries were also demonstrated by the computational method.

Studies in airflow during speech production typically use a pneumotachographic mask system to measure expired airflows. Accurate measures of airflow using the Glottal Enterprises MSIF-2 aerodynamic system require a complete seal of the mask rim to the face. Literature frequently cites mask rim leaks as causing flow measure inaccuracies, but quantitative studies of inaccuracies are needed. Prior work (May & Scherer, in press) provided a general empirical equation relating mask rim leak flow, the cross sectional area of the rim leak, and upstream airflow. The current empirical bench research extends this DC flow work to an AC flow situation as in the case of vibrato and/or tremor using 3 and 6 Hz, 2 leak areas, 50 and 200 cm3/s peak-to-peak variations, and an upstream flow of 200 cm3/s. Results: smaller leak area, higher AC frequency, and higher AC airflow extent resulted in the lowest mask rim leak airflow.Studies in airflow during speech production typically use a pneumotachographic mask system to measure expired airflows. Accurate measures of airflow using the Glottal Enterprises MSIF-2 aerodynamic system require a complete seal of the mask rim to the face. Literature frequently cites mask rim leaks as causing flow measure inaccuracies, but quantitative studies of inaccuracies are needed. Prior work (May & Scherer, in press) provided a general empirical equation relating mask rim leak flow, the cross sectional area of the rim leak, and upstream airflow. The current empirical bench research extends this DC flow work to an AC flow situation as in the case of vibrato and/or tremor using 3 and 6 Hz, 2 leak areas, 50 and 200 cm3/s peak-to-peak variations, and an upstream flow of 200 cm3/s. Results: smaller leak area, higher AC frequency, and higher AC airflow extent resulted in the lowest mask rim leak airflow.

The goal of this essay is to emphasize the correspondence among interactive phonatory variables, complementary assessment measures, and voice problems. An additional related goal is to suggest that we pay close attention to figures and expressions that interrelate phonatory variables, for they can be strong guides to our therapeutic thinking. Acoustic and aerodynamic factors are the focus here. This essay is not historical per se, but rather interrelational.

Pulsatile flow in an excised canine larynx was investigated with simultaneous recordings of air velocity, subglottal pressure, volume flow rate, and the signal from an electro-glottograph (EGG) for various conditions of phonation. Canine larynges were mounted on a pseudotrachea and sustained oscillations were established and maintained with sutures attached to cartilages to mimic the function of laryngeal muscles. The pitch and amplitude of the oscillations were controlled by varying the airflow, and by adjusting glottal adduction and vocal-fold elongation. Measurements with hot-wire probes suggest that subglottal inlet flow to the larynx is pulsatile but mostly laminar, while the exiting jet is non-uniform and turbulent. In the typical ranges of flow rate, subglottal pressure, and oscillation frequencies, the Reynolds number based on the mean glottal velocity and glottal hydraulic diameter varied between 1600 to 7000, the Strouhal number based on the same parameters varied between ...

The purpose of the study was to better understand the pressure-flow behavior of a self-oscillating vocal fold model at various stages of the glottal cycle. An established self-oscillating vocal fold model was extended to include the false vocal folds (FVFs) and was used to study time-dependent pressure and velocity distributions through the larynx (including the true vocal folds [TVFs] and FVFs). Vocal fold vibration was modeled with a finite element method, laryngeal flow was simulated with the solution of unsteady Navier-Stokes equations, and the acoustics of the vocal tract was modeled with a wave reflection method. The results demonstrate realistic phonatory behaviors and therefore may be considered as a pedagogical tool for showing detailed aerodynamic, kinematic, and acoustic characteristics. The TVFs self-oscillated regularly with reasonable amplitude and mucosal waves. There were large pressure gradients in the glottal region. The centerline velocity was highest during glott...