The mechanisms of subharmonic tone generation in a synthetic larynx model

Abstract

The sound spectra obtained in a synthetic larynx exhibited subharmonic tones that are characteristic for diplophonia. Although the generation of subharmonics is commonly associated with asymmetrically oscillating vocal folds, the synthetic elastic vocal folds showed symmetrical oscillations. The amplitudes of the subharmonics decreased with an increasing lateral diameter of the supraglottal channel, which indicates a strong dependence of the supraglottal boundary conditions. Investigations of the supraglottal flow field revealed small cycle-to-cycle variations of the static pressure in the region of the pulsatile glottal jet as the origin of the first subharmonic tone. It is located at half the fundamental frequency of the vocal fold oscillation. A principle component analysis of the supraglottal flow field with the fully developed glottal jet revealed a large recirculation area in the second spatial eigenvector which deflected the glottal jet slightly in a perpendicular direction of the jet axis. The rotation direction of the recirculation area changed with different oscillation cycles between clockwise and counterclockwise. As both directions were uniformly distributed across all acquired oscillation cycles, a cycle-wise change can be assumed. It is concluded that acoustic subharmonics are generated by small fluctuations of the glottal jet location favored by small lateral diameters of the supraglottal channel.

Acoustic and Aerodynamic Coupling during Phonation in MRI-Based Vocal Tract Replicas

“…The results of the aerodynamical investigations show that the inclusion of the VT leads to a reduced phonation threshold pressure in combination with a decreased flow rate. This confirmed the already reported facilitation of the vocal fold oscillation by the VT [32,40].…”

“…The detected reduction of the subglottal pressure and the volume flow rate for the configurations with VT replica in comparison to the configuration without VT shows that the phonation is facilitated by the VT. The reason for the reduced oscillation thresholds between configurations with and without VT is the decrease of pressure immediately downstream of vocal folds due to the channel effect as already reported in Kniesburges et al [32,40]. Figure 5 depicts the SPL for the realistic and simplified VT replicas that were measured with the experimental setup for each subject.…”

“…The connection of the VT replicas to the excitation source was realized with a mounting adapter, as shown in Figure 3. As an excitation source, a synthetic larynx model was used that includes two synthetic vocal folds made of silicone rubber as used in other studies [32,[39][40][41]. Their geometry was derived from the M5 model as proposed by Scherer et al [42] and Thomson et al [43].…”

3D-FV-FE Aeroacoustic Larynx Model for Investigation of Functional Based Voice Disorders

“…Besides excised larynges, synthetic vocal fold models with silicone vocal folds were carried out with the focus on the glottal insufficiency (Park and Mongeau, 2008;Kirmse et al, 2010;Kniesburges et al, 2013Kniesburges et al, , 2016. Pickup and Thomson (2009) and Zhang et al (2012) investigated asymmetric vocal fold oscillations with a silicone model.…”

“…Pickup and Thomson (2009) and Zhang et al (2012) investigated asymmetric vocal fold oscillations with a silicone model. Such models can mimic specific physiological and disordered motion patterns of the vocal folds for which they have been developed for and are therefore well-established in voice science (Zhang et al, 2004;Thomson et al, 2005;Park and Mongeau, 2008;Kirmse et al, 2010;Murray and Thomson, 2012;Kniesburges et al, 2013Kniesburges et al, , 2016Van Hirtum and Pelorson, 2017;Motie-Shirazi et al, 2019;Taylor et al, 2019;Romero et al, 2020). However, both ex vivo and synthetic larynx models are restricted regarding the spatial resolution of the measuring data of fluid flow, the vocal fold dynamics, and their interaction.…”