Phonation + Laryngeal Physiology

January 14, 2010

The Aerodynamics of Speech• Note: all sounds are created by the flow of air

• Most (but not all) speech sounds are produced by a pulmonic egressive airstream mechanism.

• = air flows out of the lungs

• Note: air flows naturally out of the lungs when they are compressed

• air always flows from areas of high pressure to low

Lung Compression• In speech, lung compression is typically a passive process.

• The linkage between the lungs and the thoracic (rib) cage tends toward an equilibrium--

• at which the lungs are larger than they would be alone…

• and the rib cage is smaller than it would be alone.

• When the linked pair is expanded beyond the equilibrium point, it will naturally contract back to it.

• (and vice versa)

Lung Expansion• The expansion of the lungs is primarily driven by the contraction of the muscles in the diaphragm.

• This increases volume in the vertical dimension.

• Contraction of the external intercostal muscles also pulls out the rib cage in the front-back and side-to-side dimensions.

• intercostal = “between the ribs”

Riding the Wave• Speech is normally produced on the passive expiration that follows an expansion of the lungs.

• Airflow may be fine-tuned by contraction of the internal intercostal muscles.

• Active contraction results in:

• higher airflow

• higher intensity

• greater perceived stress

Back to Aerodynamics• Remember: sounds are created by the flow of air

• …but speech often becomes interesting when that flow of air is interrupted.

• E.g., aerodynamic method #1: Stops

A. start air flow

B. stop air flow

C. release air flow

• Here’s an example of aerodynamic method #2.

• What kind of sound was that?

Trills• A: a Trill. A Bilabial Trill:

• Examples from Kele and Titan (spoken on the island of Manus, north of New Guinea)

Any volunteers?• Does anyone else know how to produce a bilabial trill?

• And would anyone like to demonstrate?

• How fast do your lips open and close when you make a bilabial trill?

• Let’s take a look at the waveform in Praat…

• Waveform = representation of the change in air pressure over time.

Some Terminology• Frequency is the rate at which the lips are opening and closing

• measured in Hertz (cycles per second)

• Period is the length of time between cycles

• Frequency = 1 / Period

• Some questions:

• In a bilabial trill, do we close and relax our lips on each cycle?

• When air blows the lips apart, why don’t they stay apart?

Bernoulli Effect• In a flowing stream of particles:

• the pressure exerted by the particles is inversely proportional to their velocity

• Pressure = constant

velocity

• P = k / v

• the higher the velocity, the lower the pressure

• the lower the velocity, the higher the pressure

Daniel Bernoulli

(1700-1782)

Bernoulli Examples

• Airplane wing

• Shower curtain

• Pieces of paper

• Bilabial trills!

A Trilling Schematic• Lips are closed

• adducted = brought together

• Fad = adductive force

upper lip

lower lip

inside of mouth

outside of mouth

Fad

Fad

Trilling: Stage 1• Pressure builds up inside mouth from compression of lungs

• Pin = Air Pressure inside mouth

• Outside pressure remains constant

• Pout = Air Pressure outside mouth

PinPout = k

Fad

Fad

Trilling: Stage 1• Pressure differential between inside and outside builds up

• This exerts force against the lips

PinPout = k

Fad

Fad

P = (Pin - Pout )

Trilling: Stage 2• Pressure differential blows open lips

• Air rushes from high to low pressure

PinPout = k

Fad

Fad

air

Trilling: Stage 2• The opening of the lips means:

1. P decreases slightly

2. High velocity of air flowing between lips

3. Air pressure decreases between lips (Bernoulli Effect)

PinPout = k

Fad

Fad

Pbl

Trilling: Stage 3• Lips get sucked back together

PinPout = k

Fad

Fad

Trilling: Back to Stage 1• If air is still flowing out of lungs, pressure will rise again

within mouth

• Process will repeat itself as long as air is pushed up from lungs and lips are held lightly against each other

PinPout = k

Fad

Fad

Trilling: Back to Stage 1• Air rushes through the lips in a series of short, regular

bursts

Pin

Fad

Fad

Trill Places

Phonation• Glottal trilling is known as phonation.

• It distinguishes between voiced and voiceless sounds.

• [z] vs. [s]; [v] vs. [f], etc.

• Glottal trilling is made possible by the presence of two “vocal folds” within a complicated structure known as the larynx.

• When the vocal folds are:

1. open: air passes cleanly through (= voiceless sound)

2. closed: air does not pass through (= no sound)

3. lightly brought together: vocal folds vibrate in passing air

(= voiced sound)

Voicing, Schematized

Voiceless (folds open) Voiced (folds together)

(= “abducted”) (= “adducted”)

Laryngoscopy

Source: http://homepage.mac.com/changcy/endo.htm

Voicing, in Reality

Creaky Voicing• The flow of air from the lungs forces the vocal folds to open and close.

• The slowest type of voicing is called “creaky voice.”

Modal Voice

• How fast do you think the vocal folds open and close in normal voicing?

• In normal, or “modal” voicing, the rate of glottal trilling is considerably faster.

Vocal Fold Specs• In bilabial trills, lips open and close 20-25 times a second

• In modal voicing, the glottal trill cycle recurs, on average:

• 120 times a second for men

• 220 times a second for women

• 300+ times a second for children

• For voiced speech sounds, this rate is known as the fundamental frequency (F0) of the sound.

• Let’s check it out…

Vocal Fold Specs• Air rushes through vocal folds at 20 to 50 meters per second

• = between 72 and 180 kph (45 ~ 120 mph)

• Due to Bernoulli Effect, pressure between vocal folds when this occurs is very small

• Speed of “glottal trill” cycle depends on:

• thickness of vocal folds

• tenseness of vocal folds

• length of vocal folds

Vocal Fold Specs• In men, vocal folds are 17-23 millimeters long

• In women, vocal folds are 12-17 millimeters long

• Adult male vocal folds are 2-5 millimeters thick

• Adult female vocal folds are slightly thinner

• Thicker, longer folds vibrate more slowly

• Think: violin strings vs. bass strings

• Tenseness of vocal folds can be changed to alter the speed of glottal opening and closing.

• Like tuning a violin or a guitar…

The Larynx• The larynx is a complex structure consisting of muscles, ligaments and three primary cartilages.

1. The Cricoid Cartilage• The cricoid cartilage sits on top of the trachea

• from Greek krikos “ring”

• It has “facets” which connect it to the thyroid and arytenoid cartilages.

cricoid cartilage

2. The Thyroid Cartilage• The thyroid cartilage sits on top of the cricoid cartilage.

• from the Greek thyreos “shield”

• The thyroid cartilage has horns!

• Both lower (inferior) and upper (superior) horns

• The lower horns connect with the cricoid cartilage at the cricoid’s lower facet.

• The upper horns connect to the hyoid bone.

Thyroid Graphic

thyroid cartilage

cricoid cartilage

Thyroid Angles• The two broad, flat front plates of the thyroid--the laminae--meet at the thyroid angle.

• The actual angle of the thyroid angle is more obtuse in women.

• ...so the “Adam’s Apple” juts out more in men.

3. The Arytenoid Cartilages• There are two arytenoid cartilages.

• from Greek arytaina, “ladle”

• They are small and pointy, and sit on top of the back side, or lamina, of the cricoid cartilage.

arytenoid cartilages

cricoid cartilage

The Vocal Folds• These three cartilages are connected by a variety of muscles and ligaments.

• The most important of these are the vocal folds.

• They live at the very top of the trachea, in between the cricoid and thyroid cartilages.

• The vocal folds are a combination of:

• The vocalis muscle

• The vocal ligament

• The vocal folds are enclosed in a membrane called the conus elasticus.

• Just above the true vocal folds are the “false” (!) vocal folds, or ventricular folds.

• The space between the vocal folds is the glottis.

Vocal Fold View #1

Vocal Fold View #2• The vocal ligaments attach in the front to the thyroid cartilage.

• ...and in the back to the arytenoid cartilages.

• The glottis consists of:

• the ligamental glottis

• the cartilaginous glottis

Things Start to Happen• Note that the arytenoid cartilages can be moved with respect to the cricoid cartilage in two ways.

#1: rocking #2: sliding

The Upshot• The arytenoids can thus be brought together towards the midline of the body.

• Or brought forwards, towards the front of the thyroid.

• The rocking motion thus abducts or adducts the glottis.

• The sliding motion shortens or lengthens the vocal folds.• Check out the arytenoids in action.

• When the vocal folds are abducted:

• air passes through the glottis unimpeded and voicelessness results.

• The posterior cricoarytenoid muscles are primarily responsible for separating the arytenoid cartilages.

• Voicing may occur when the vocal folds are adducted and air is flowing up through the trachea from the lungs.

• Two muscles are primarily responsible for adducting the vocal folds.

• The first is the lateral crico-arytenoid muscle.

• Note that the lateral cricoarytenoid muscles only adduct the ligamental glottis.

• The transverse arytenoid muscles pull together the arytenoid cartilages themselves.

• Thereby closing the cartilaginous glottis.

The Consequences• The combined forces drawing the vocal folds towards each other produce adductive tension in the glottis.

• Adductive tension is increased by:

• lateral cricoarytenoid muscles

• transverse arytenoid muscles

• Adductive tension is decreased by:

• posterior cricoarytenoid muscles

• Adduction vs. abduction determines whether or not voicing will occur.

• But we can do more than just adduce or abduce the vocal folds...

Factor Two

• We can also change the longitudinal tension of the vocal folds.

• I.e., tension along their length, between the thyroid and arytenoid cartilages.

• Higher tension = higher F0

• Lower tension = lower F0

• Q: How is this possible?

• A: We can rotate the thyroid cartilage up and down on its connection with the cricoid cartilage.

• ...like the visor of a knight’s helmet.

• This either stretches or relaxes the vocal folds.