The aeroacoustic mechanisms in human voice production are complex coupled processes that are still not fully understood. In this article, a hybrid numerical approach to analyzing sound generation in human voice production is presented. First, the fluid flow problem is solved using a parallel finite-volume computational fluid dynamics (CFD) solver on a fine computational mesh covering the larynx. The CFD simulations are run for four geometrical configurations: both with and without false vocal folds, and with fixed convergent or convergent-divergent motion of the medial vocal fold surface. Then the aeroacoustic sources and propagation of sound waves are calculated using Lighthill's analogy or acoustic perturbation equations on a coarse mesh covering the larynx, vocal tract, and radiation region near the mouth. Aeroacoustic sound sources are investigated in the time and frequency domains to determine their precise origin and correlation with the flow field. The problem of acoustic wave propagation from the larynx and vocal tract into the free field is solved using the finite-element method. Two different vocal-tract shapes are considered and modeled according to MRI vocal-tract data of the vowels /i/ and /u/. The spectra of the radiated sound evaluated from acoustic simulations show good agreement with formant frequencies known from human subjects.
- MeSH
- akustika * MeSH
- hlas * MeSH
- hlasové řasy fyziologie MeSH
- larynx fyziologie MeSH
- lidé MeSH
- vzduch * MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Impact stress (the impact force divided by the contact area of the vocal folds) has been suspected to be the main traumatizing mechanism in voice production, and the main cause of vocal fold nodules. However, there are also other factors, such as the repetitive acceleration and deceleration, which may traumatize the vocal fold tissues. Using an aeroelastic model of voice production, the present study quantifies the acceleration and impact stress values in relation to lung pressure, fundamental frequency (F0) and prephonatory glottal half-width. Both impact stress and acceleration were found to increase with lung pressure. Compared to impact stress, acceleration was less dependent on prephonatory glottal width and, thus, on voice production type. Maximum acceleration values were about 5-10 times greater for high F0 (approx. 400 Hz) compared to low F0 (approx. 100 Hz), whereas maximum impact stress remained nearly unchanged. This suggests that acceleration, i.e. the inertia forces, may present at high F0 a greater load for the vocal folds, and in addition to the collision forces may contribute to the fact that females develop vocal fold nodules and other vocal fold traumas more frequently than males. Copyright 2009 S. Karger AG, Basel.
- MeSH
- akustika řeči MeSH
- biologické modely MeSH
- fonace fyziologie MeSH
- glottis fyziologie MeSH
- lidé MeSH
- plíce fyziologie MeSH
- počítačová simulace MeSH
- pohlavní dimorfismus MeSH
- tlak vzduchu MeSH
- Check Tag
- lidé MeSH
- mužské pohlaví MeSH
- ženské pohlaví MeSH
- Publikační typ
- práce podpořená grantem MeSH
- srovnávací studie MeSH
Current models of the vocal folds derive their shape from approximate information rather than from exactly measured data. The objective of this study was to obtain detailed measurements on the geometry of human vocal folds and the glottal channel in phonatory position. A non-destructive casting methodology was developed to capture the vocal fold shape from excised human larynges on both medial and superior surfaces. Two female larynges, each in two different phonatory configurations corresponding to low and high fundamental frequency of the vocal fold vibrations, were measured. A coordinate measuring machine was used to digitize the casts yielding 3D computer models of the vocal fold shape. The coronal sections were located in the models, extracted and fitted by piecewise-defined cubic functions allowing a mathematical expression of the 2D shape of the glottal channel. Left-right differences between the cross-sectional shapes of the vocal folds were found in both the larynges.
- MeSH
- biologické modely MeSH
- biomechanika MeSH
- financování organizované MeSH
- glottis anatomie a histologie fyziologie MeSH
- hlas fyziologie MeSH
- hlasové řasy anatomie a histologie fyziologie MeSH
- lidé MeSH
- senioři MeSH
- zobrazování trojrozměrné statistika a číselné údaje MeSH
- Check Tag
- lidé MeSH
- mužské pohlaví MeSH
- senioři MeSH
- ženské pohlaví MeSH
The maximum impact stress at the contact of the vocal folds achieved during the oscillation cycle was estimated in phonation using an aeroelastic model of voice production. Relations of impact stress to the lung pressure, fundamental frequency of self-oscillations, prephonatory glottal width, sound pressure level generated at the end of the glottis and vibration amplitude of the vocal folds were studied. Using the fundamental frequency, prephonatory glottal width, lung pressure and airflow rate values found in normal speech, maximum impact stress values of 2-3 kPa were obtained. The results fall well within the limits reported for excised canine larynges and human subjects. Impact stress increased with lung pressure almost linearly after the phonation threshold but reached a plateau when the limit of maximum glottal opening was reached. When the fundamental frequency and lung pressure were kept constant, impact stress appears to fit closely with a parabolic function of prephonatory glottal half-width.
- MeSH
- financování organizované MeSH
- fonace fyziologie MeSH
- hlasové řasy patofyziologie MeSH
- lidé MeSH
- modely anatomické MeSH
- numerická analýza pomocí počítače MeSH
- plicní ventilace fyziologie MeSH
- počítačová simulace MeSH
- poruchy hlasu patofyziologie MeSH
- řeč fyziologie MeSH
- vibrace MeSH
- zvuková spektrografie MeSH
- Check Tag
- lidé MeSH
