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 apulmonic egressive airstream mechanism.

• = air flows out of the lungs

• Note: air flows naturally out ofthe lungs when they arecompressed

• ⇒ air always flows from areasof high pressure to low

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

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

• at which the lungs are larger than they would bealone…

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

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

• (and vice versa)

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

• This increases volume in the vertical dimension.

• Contraction of theexternal intercostalmuscles also pullsout the rib cage in thefront-back and side-to-side dimensions.

• intercostal =“between the ribs”

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

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

• Active contractionresults in:

• higher airflow

• higher intensity

• ⇒ greaterperceived stress

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

• …but speech often becomes interesting when that flowof 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 ofManus, 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 abilabial trill?

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

• Waveform = representation of the change in airpressure over time.

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

• 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 eachcycle?

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

Bernoulli Effect• In a flowing stream of particles:

• the pressure exerted by theparticles is inverselyproportional to their velocity

• Pressure = constant

velocity

• P = k / v

• ⇒ the higher the velocity, thelower the pressure

• ⇒ the lower the velocity, thehigher 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 ofmouth

outsideof 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

ΔP = (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. ΔP 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 fromlungs 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 thelarynx.

• 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 toopen and close.

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

Modal Voice

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

• In normal, or “modal” voicing, the rate of glottal trilling isconsiderably 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 thefundamental frequency (F0) of the sound.

• Let’s check it out…

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

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

• Due to Bernoulli Effect, pressure between vocal folds whenthis 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 thespeed of glottal opening and closing.

• Like tuning a violin or a guitar…

The Larynx• The larynx is a complex structure consisting ofmuscles, 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” whichconnect it tothe thyroidand arytenoidcartilages.

cricoidcartilage

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 thecricoid’s lower facet.

• The upper horns connect to the hyoid bone.

Thyroid Graphic

thyroidcartilage

cricoidcartilage

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

• The actual angle of the thyroid angle is more obtuse inwomen.

• ...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 backside, or lamina, of the cricoid cartilage.

arytenoidcartilages

cricoidcartilage

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

• The most important of these are the vocal folds.

• They live at the very top of the trachea, in betweenthe 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 theconus elasticus.

• Just abovethe true vocalfolds are the“false” (!)vocal folds,or ventricularfolds.

• The spacebetween thevocal folds isthe glottis.

Vocal Fold View #1

Vocal Fold View #2• The vocal ligamentsattach in the front tothe thyroid cartilage.

• ...and in the back tothe arytenoidcartilages.

• The glottis consistsof:

• the ligamentalglottis

• the cartilaginousglottis

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

#1: rocking #2: sliding

The Upshot• The arytenoids can thus be brought together towardsthe 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 andvoicelessness results.

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

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

• Two muscles are primarily responsible for adducting thevocal folds.

• The first is the lateral crico-arytenoid muscle.

• Note that the lateral cricoarytenoid muscles onlyadduct the ligamental glottis.

• The transverse arytenoid muscles pull together thearytenoid cartilages themselves.

• Thereby closing the cartilaginous glottis.

The Consequences• The combined forces drawing the vocal folds towardseach 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 notvoicing will occur.

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

Factor Two

• We can also change thelongitudinal tension of thevocal folds.

• I.e., tension along theirlength, between the thyroidand 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 itsconnection with the cricoid cartilage.

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

• This either stretches or relaxes the vocal folds.