The Influence of Geometrical and Mechanical Input Parameters on Theoretical Models of Phonation

Abstract

The influence of initial aperture and mechanical properties on the onset pressure thresholds and oscillation frequencies is experimentally assessed on ad eformable vocal fold replica in case of strong and weak acoustical coupling. The mechanical replica enables to vary the initial aperture while mechanical properties are maintained and therefore to mimic abduction and adduction gestures of human phonation. Depending on initial conditions (geometrical, mechanical and acoustical)one or twooscillation regions are experimentally found for which important differences are observed for both oscillation onset pressure thresholds and oscillation frequencies. Measured onset pressure thresholds are used to validate the outcome of at heoretical model of phonation using a reduced mechanical model. The applied coupling stiffness in the theoretical model is estimated from the measured frequencyresponse instead of imposed by an 'ad-hoc' criterion. The variations in coupling stiffness result in aq ualitative agreement between predicted and measured values for all assessed experimental conditions. In addition, the Yo ung'smodulus of the replica is qualitatively estimated to be within the range observed 'in-vivo'. PACS no. 43.70.Bk, 43.70.Jt 291 ACTA ACUSTICA UNITED WITH ACUSTICA Cisonni et al.:T heoretical models of phonation Vol. 97 (2011)since recent modelling studies point out its importance [19,20]. Next, particular attention is givent ot he estimation of model parameters from experimental observations. Finally,theoretical predictions are validated on adeformable replica.

Influence of glottal cross-section shape on phonation onset

“…Each of the vocal folds is modeled as a reduced spring-mass-damper system with 2 degrees of freedom driven by the pressure difference, DP ¼ P u À P d , across the masses as illustrated in Fig. 2, 25 where subscripts u and d refer to upstream (u) and downstream (d) of the glottis, respectively. The applied models for glottal airflow, vocal folds mechanics, and acoustic interaction with a downstream and upstream pipe, representing the trachea upstream from the glottis and the vocal tract downstream from the glottis, are severe simplifications of the fluid-structure interaction in the larynx during human voiced sound production.…”

“…Acoustical coupling between the vocal folds and a uniform upstream tube with length L u representing the trachea and/or a uniform downstream tube with length L d representing the vocal tract is important when the acoustical resonance frequencies of the pipe and the vocal fold resonance frequencies are close. 25,26 The acoustic set of equations for frequencies up to and around the first vocal tract resonance frequency 5,27 is given as…”

“…Besides the constriction degree and the cross-section shape the other model parameters are taken constant with values taken from Ref. 25 and correspond to a configuration for which auto-oscillation was experimentally observed. Concretely, the following values are used: Geometry Fig.…”

“…1. In order to provide a fair comparison with the quasi-one-dimensional model approach width w is fixed regardless of the cross-section shape to w ¼ 20 mm, which is within the range observed on human speakers (15 up to 25 mm 9,15 ) and mechanical glottal replicas (20 up to 25 mm 8,25 ). All cross-FIG.…”

The influence of glottal cross-section shape on theoretical flow models

“…3 Resulting non-dimensional numbers (Mach number, Reynolds number, Strouhal number, and mean aspect ratio) allow one to treat the glottal flow as incompressible, laminar, inviscid, quasi-steady, and one-dimensional. Nevertheless, experimental validation of theoretical flow models on rigid [4][5][6] and deformable 7,8 glottal replicas tends to show that viscous effects due to boundary layer development cannot be neglected. Therefore, the one-dimensional model approach is extended to a quasi-one-dimensional model accounting for viscous flow effects based on the assumption of a quasi-onedimensional flow in a rectangular glottal area with fixed length.…”