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UI CSD 3112 - Vibration Models

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These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. Lecture 22 Outline of Last Lecture I. Theories of Vibration II. Biomechanics a. Spring b. Dashpot c. Mass III. Mechanical Oscillation Outline of Current Lecture I. Laryngeal Vibration Models a. Single Mass Model b. Two Mass Model c. Three Mass Model d. Sixteen Mass Model II. Mechanical Oscillation a. Myoelastic Aerodynamic Theory b. Single mass model c. Three mass model Current Lecture Laryngeal Vibration Models - Laryngeal Vibration Models—Single Mass Model o simple mechanical oscillator of mass M, spring constant K (vocal fold tension), and damping b (boundary condition at vocal fold contact) o single degree of freedom model o only horizontal movement CSD 3112 1st Edition- Laryngeal Vibration Models—Two Mass Model o two degree of freedom model o vocal folds represented by two masses, capable of independent horizontal motion o two masses (bottom and top) move independently  but affect each other by “spring” connected between them (vertical phase difference) - Laryngeal Vibration Models—Three Mass Model o three degree of freedom model o vocal fold cover represented by two masses (m1 and m2), capable of independent horizontal motion o vocal fold body represented by third mass (m) - Laryngeal Vibration Models—Sixteen Mass Model o more advanced cover‐body model that simulates ....  vertical and horizontal vocal fold motion  vertical and horizontal phase difference  phonation in different registers  pathological states  etc  vertical and posterior movement of vocal folds - Mechanical Oscillation (again)—Myoelastic-Aerodynamic Theory o closed vocal folds blown apart by air pressure from lungs below o releases single puff of air o lateral movement of fold continues until elasticity and Bernoulli forces takes over to move folds back to closed position o glottis maintains “block‐like” shape during phonation o PROBLEM – too much reliance on Bernoulli forces, which cannot sustain self‐oscillation of the vocal folds (will die out) - Mechanical Oscillation (again)—Single Mass Model o now, add vocal tract air column o need (‐) pressure between folds to sustain oscillation o when folds closing, airflow begins to decrease  but air above glottis doesn’t “know” and continues to move up (inertia) o creates region just above folds where air pressure decreases  since air not coming up through the glottis as fast as it’s leaving o when folds opening, pressure against walls greater than when vocal folds together o therefore, asymmetry of driving forces (“squirts of energy”)- Mechanical Oscillation (again)—Three Mass Model o m1 and m2 allow for simulation of vertical phase difference o notice also, however, divergent and convergent glottal shapes o “0”, “+”, “‐” represent pressures relative to supraglottal pressures o glottal shape convergent during opening  facilitates high subglottal pressures that force bottom edge of vocal folds laterally  upper margins separate as result of air pressure forces and lateral pull of elastic tissue (lagging behind lower margins) o glottal shape divergent during closing  Bernoulli effect lowers transglottal pressure and creates inward pull of lower margin  upper margins again lag behind o again, asymmetry of driving forces - So… o original myoelastic‐aerodynamic theory over‐emphasizes role of Bernoulli effect o current understanding ....  aerodynamic forces (subglottal pressure and Bernoulli) work primarily on lower margins of folds (convergent and divergent shapes)  viscoelastic forces responsible for movement of upper margins o also .... original M‐A theory depended on complete glottal closure  complete closure not necessary in current


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UI CSD 3112 - Vibration Models

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