Phonation part 2 and 3 speech acoustics

• Myoelastic-aerodynamic theory

• First postulated by Muller, later by van den Berg

• The elasticity of the vocal folds allows them to be set into vibration by aerodynamic forces, specifically by the Bernoulli effect.

Theory of voice production

• Pressure exerted by a fluid on a surface decreases as the velocity of the fluid across the surface increases

• Effect gives an airplane its lift

Bernoulli Effect

Minimal sublottal pressure for phonation

usually between 3 to 5 cmH2O

Phonation Threshold Pressure

the precise moment the vocal folds transition from an open position to sustained vibration

Phonation onset

simultaneous exhalation and adduction of vocal folds

Simultaneous onset (gentle)

airflow begins before adduction

Breathy onset (aspirate)

firm closure before airflow - explosive

Glottal Attack

Duration from onset of voice to steady state amplitude

Vocal rise time

Breathy Voice

Longest

force per unit area

Stress

length of change of tissue in the direction of force

strain

greater tension on tissue

Greater force

Do vocal folds react in a linear fashion?

No

the lowest and typically loudest frequency produced by a vibrating object or periodic wave

fundamental frequency

primary function is to lengthen, thin, and tense the vocal folds, which increases vocal pitch during speech and singing

Cricothyroid muscle

forms the main body of the vocal fold and shortens and relaxes the vocal cords to lower pitch

thyroarytenoid muscle

the air pressure that builds up in the trachea directly beneath the closed or closing vocal folds (the glottis), providing the fundamental aerodynamic energy required to make

Subglottal pressure

Longer, thicker vocal fold =

deeper voice

tendency to increase vocal intensity within high ambient noise levels

Lombard effect

the sound of your own voice or actions that your brain hears and uses in real time to monitor and control movement

Auditory feedback

when the flexible outer layer of the vocal folds vibrates while the inner muscle remains relatively still or loosely engaged

occurs during soft, quiet phonation or high-pitched vocal production

cover-dominant vibration

a mode of vocal fold vibration where both the flexible outer layer (the cover) and the underlying muscle (the body) of the vocal folds vibrate together to produce sound

Body Plus Cover Vibration

• Subglottal pressure

• Vocal fold closure

• Increasing subglottal pressure causes a larger amplitude of the mucosal wave – large

volume of air speeding through the glottis

• If you increase intensity by 8- 12 dB SPL you double subglottal pressure

• Pressure during speech ranges from 3.8 to 20 cmH20

Control of Intensity

why do Men have greater intensity than women

b/c of larger vocal tract and greater lung capacity

the study of how vocal fold living tissues stretch, bend, and respond to physical forces during speech and singing

Biomechanics

What is the first step in the biomechanics of phonation?

The vocal folds approximate (move toward each other).

What happens to the thoracic cavity during phonation?

The thoracic cavity compresses.

What happens to lung pressure below the glottis?

Subglottal/lung pressure increases.

What does airflow encounter when the vocal folds are closed?

Resistance from the closed vocal folds.

What causes the vocal folds to move laterally and the glottis to open?

Increased subglottal pressure pushes the vocal folds laterally.

Which part of the vocal folds separates first?

The lower margin separates first.

What happens to the upper margin when the lower margin separates?

The upper margin remains closed temporarily.

What shape does the glottis take as the lower margin separates first?

A triangle shape called a convergent-shaped glottis.

What does a convergent-shaped glottis create?

High subglottal pressure.

What happens when maximal opening of the vocal folds occurs?

Airflow begins.

What happens to pressure across the vocal folds after airflow begins?

There is a pressure drop across the vocal folds.

What happens to airflow after the pressure drops?

Airflow is drawn upward through the vocal folds.

What shape does the glottis move toward after maximal opening?

An inverted triangle called a divergent-shaped glottis.

What effect occurs as the glottis becomes divergent-shaped?

The Bernoulli effect occurs.

What happens to pressure during the Bernoulli effect?

Pressure lowers, causing the vocal folds to pull inward.

Do the vocal folds completely open during the vibratory cycle?

No, the vocal folds do not completely open.

What pressure relationship is necessary for airflow to occur?

Subglottal pressure must be greater than supraglottal pressure.

What is the pressure difference that drives airflow called?

Driving pressure.

What happens with every cycle of vocal fold movement?

There is excitation of the supraglottal air mass, creating a pulse.

What two types of pressure changes are produced by vocal fold vibration?

Compressions and rarefactions.

What does glottal closure lead to?

Excitation of the air in the vocal tract.

What causes the vocal folds to pull back inward after opening?

The Bernoulli effect, which lowers pressure between the vocal folds.

What is the sequence of glottal shapes during the cycle?

Convergent → maximal opening → divergent → closure.

What must be greater than supraglottal pressure for airflow to occur?

Subglottal pressure.

What is the convergent-shaped glottis?

A triangular-shaped glottis that occurs as the lower vocal fold margin separates first.

What is the divergent-shaped glottis?

An inverted triangular-shaped glottis that occurs as the vocal folds move toward closure.

What is the Bernoulli effect in vocal fold vibration?

As airflow moves through the glottis, pressure decreases, helping pull the vocal folds back toward each other.

What happens when the vocal folds close?

They excite the air in the vocal tract, producing pressure pulses including compressions and rarefactions.

the measure of the friction and force that air must overcome as it passes through the larynx, or voice box

Laryngeal airway resistance

What is glottal resistance?

Resistance to airflow through the glottis; it is related to the ratio of pressure to airflow.

How does vocal fold position affect glottal resistance?

More closure = higher resistance and less airflow; more opening = lower resistance and more airflow.

Why is glottal resistance difficult to measure?

The vocal folds are constantly vibrating and changing their degree of closure, so resistance changes throughout the cycle.

What happens to airflow during vowel production?

Airflow is relatively unrestricted through the vocal tract.

During vowel production, what is supraglottal pressure approximately equal to?

Atmospheric pressure.