1. Version WS 2006/7
Speech Science
Speech production II – Phonation

2. Topics Kinetic energy to acoustic energy The phonatory process
Structures of the larynx
Homework: a) Kent, Chap. 4, pp
b) Borden, Harris & Raphael, Chap. 4, pp
Deutsch: c) Pompino-Marschall, Teil II, 31-42
  d) Reetz, Kap. 3, Teil 3.2, S
Übung 3 (14 Nov): Looking at the glottal signal: Laryngography
Homework: Exercise sheet for 13th Nov).

3. Kinetic to acoustic energy
The kinetic energy of the airstream must be transformed into acoustic energy; otherwise we can‘t hear anything!
This is achieved by introducing some “disturbance“ into the uniformity of the (laminar) airflow.
The “disturbance“ can either be regular or irregular. (periodic or aperiodic)
Kinetic to acoustic energy
Reminder: Laminar flow means that the molecules (the air particles) are evenly spaced (the pressure is the same). This means they are all moving at the same speed.
If this even spacing is altered somewhere, it means that the air pressure is altered at that point. A repeated, regular alteration brings a regular pattern of pressure changes which (within a certain amplitude and frequency range) is audible.
We call a regular change of pressure a „periodic“ acoustic signal (and we shall deal with it in the sections on the acoustics of speech). If it is a completely irregular disturbance, we say that it is „aperiodic“ (Of course there can be a partially regular and partially irregular disturbance of the laminar flow.)
The vocal folds can move regularly (vibrate) in the air-stream and introduce the periodic pattern of pressure fluctuations.
But, if they are brought together a little and held stiff, so that they don‘t vibrate, then the air-stream is forced through the narrow gap and the particles become „turbulent“; the particles fluctuate in their distance to one another in a completely irregular way, and an aperiodic pattern of pressure fluctuation arises.
The first point at which the transformation of the air-stream can occur on the way from the lungs to the outside is at the larynx, when it passes between the vocal folds (through the glottis, as the gap is called)

4. The folds vibrate … P + 1/2 p U2 = constant
• because the vocal folds are close together
• because of the airflow
• and because the muscle tissue has elasticity
The folds vibrate …
… because the folds are close together. (Remember the vocal folds have been brought together, adducted, so they are either close together, leaving a narrow gap, or they are pressed lightly(?) together and have to be blown apart by the sub-glotttal air pressure, which results in a narrow gap.)
… because the airflow through the narrow glottis causes a lowering of the pressure (Bernoulli effect) dragging the flexibles surfaces of the vocal folds together.
The Bernoulli-law, which describes the reduction of pressure with increased volume-velocity through a narrow channel, is a form of the law of constant energy. It states that pressure (P) plus the square of the volume-velocity (U2) multiplied by half the air density (p) are constant
P + 1/2 p U2 = constant
… because the vocal folds are flexible and have inherent elasticity. This means that any departure from the adduction position (either being blown further apart by the air-stream or being sucked together by the Bernoulli effect) means that they try to return to the original position as soon as the force causing the departure ceases.
• = aerodynamic myo-elastic theory

5. The folds vibrate … • because the vocal folds are close together
Pressure + 1/2 density x Volume velocity2 = constant
i.e., when the airflow increases in the narrowed glottis, the pressure decreases.
The folds vibrate …
• because the vocal folds are close together
• because of the airflow
• and because the muscle tissue has elasticity
Here‘s the verbal explanation of the law of constant energy!
• = aerodynamic myo-elastic theory

6. A mechanical model • shows the elasticity of the folds
• allows the two- part movement; top and bottom
A mechanical model
The model shows how the vocal fold vibrations come about under the conditions described in the last slide.
The model only shows one side of what is a symmetrical set-up.
The inherent elasticity of the folds is shown by the two springs. Their force is dependent on the tension of the vocal folds themesleves.
The folds are close to each other for some distance vertically. This means that air-flow forces operating on the folds affect the bottom part of the folds first and then the top. The model therefore shows these two parts as separate components.
But the bottom and top are still part of the same physical unit, so a movement of the bottom will affect the top, and vice versa. This tissue link, which is flexible, is also shown by a spring force between bottom and top.
The glottal cycle can now be described in the model:
Taking the rest position (with a small gap between left and right folds as shown in the circle on the right of the diagram), the airflow causing the Bernoulli effect will first suck in the bottom part of the folds and then the top will follow (partly because of the elastic link, and partly because of the Bernoulli effect).
With the folds closed, two forces will operate to move them apart: a) the elasticity of the folds, because they are closer together than the rest position, and b) the build-up of air pressure sub-glottally.
Both forces bring the bottom aprt before the top, so the top follows again.
The forces take the opening movement beyond the rest position, so elasticity and Bernoulli bring the bottom, then the top back together, and the cycle starts again.
• with a flexible link between top and bottom
Quelle

7. The vocal folds… • have two muscular parts:
• the external (here) the internal (next) thyroarytenoid
(muscle names are given after the places where the muscles are attached)
The vocal folds
The old name was „the vocal cords“ which created a false picture of, say, two elastic bands.
In actual fact the folds are two muscles covered by tissue and mucous membrane and include tendons, which could perhaps be called „cords“.

8. The vocalis muscle…
Activating or relaxing the vocalis together with, or independent of the external thyro-arytenoid muscle ….
• is the internal thyroarytenoid
The vocalis muscle
Another (wrong) assumption is that the vocalis muscle alone constitutes the vocal folds.
The complex structure allows for extremely varied adjustments of the tension, length and thickness of the vocal folds, allowing many different modes of vibration.
… means that the vocal folds can have many different properties which affect the way they vibrate.

9. The vocal folds together and apart
• They have to be together (adducted) to vibrate for voiced sounds…. (and even more firmly together to stop things going down!)
• …and they have to be apart (abducted) to: - let us breathe freely and - produce voiceless sounds
• This mobility has nothing to do with the vocal folds themselves; it is done with the arytenoid cartilages (the posterior attachment point of the vocal folds – cf. the name of the muscles)
The vocal folds together and apart
It is probably obvious that the vocal folds are not primarily in our throats to support speech (though part of its double function was to allow cries to be produced, as in most animals.
But it is clearly also a valve, which shuts off the lungs from the outside world. That allows the thorax to be supported by a column of air (when we lift heavy objects), and it also prevents extraneous objects from entering the lungs (though the epiglottis is also there, acting as a „lid“ and preventing objects even reaching the larynx.
In the various functions, the movement together and apart of the vocal folds (called adduction and abduction from the Latin to „lead together“ and „lead apart“) are necessary.
The arytenoid cartilages, to which the posterior end of the vocal-fold muscles are attached, are able to do this.

10. The arytenoid cartilage movements
(the vocal folds together and apart)
The strange shape of the arytenoid cartilages and the way they are attached means that they can rotate on their base.
If the posterior muscles are activated (see left diagram), they pull the rear part of the cartilages together and open the front processes where the vocal-fold muscles and the ligament are attached. This abducts the vocal folds.
If the side muscles (lateralis) are activated, this rotates the arytenoid cartilages in the other direction (see right diagram), and the front processes are pushed together: The vocal folds are adducted, i.e. they are prepared for phonation.

11. The arytenoid cartilage movements
The arytenoid cartilage movements (cont.)
(the vocal folds together and apart)
The lateral (crico-arytenoid)muscles pull the back of the arytenoid catilages apart when they adduct the vocal folds unless the posterior muscles between the two cartilages are also activated to bring the back part together as well.
If they are not activated, an open triangle is formed between the cartilages, and air can escape. Because the triangle is fairly small, the air rushing through becomes turbulent (acoustic noise). This used when whispering. Therefore the space is often called the whisper triangle (see right side of previous slide).
transverse and oblique arytenoid muscles

12. Degrees of adduction a) normal adduction (“modal voice“)
b) extreme adduction (“hard/pressed voice“)
Degrees of adduction
The degree of activation of the lateral closing muscle and posterior inter-arytenoid muscles determines how closely the vocal folds are brought together (at their closest they form a strong glottal closure which prevents phonation = glottal stop).
The normal degree of adduction allows us to phonate in a relaxed way, and the voice quality is strong and resonant.
If we increase the degree of adduction, the elastic forces are exerting more pressure to keep the vocal folds closed, which means that they spring back to the closed position much harder and much more quickly in the glottal cycle. The airstream is unable to push the vocal folds so far apart.
If the degree of adduction is reduced, the elastic forces are not pushing the vocal folds together, so only the Bernoulli force brings them together, and often not completely, so that there is also some air escaping (and causing a breathy noise), even during the so-called “closed“ part of the glottal cycle.
c) weak adduction (“breathy voice“)

13. The rest of the larynx
• The arytenoid cartilages (with the thyro-arytenoid muscles attached) rest on the cricoid c.
• The thyroid cartilage (also with the thyro-aryt. muscles attached) rests on the cricoid cartilage too, standing on two legs
The rest of the larynx
We have been looking at the vocal folds themeslves, and have mentioned their attachment to the arytenoid cartilages posteriorly and the thyroid cartilage anteriorly.
We now see how these cartilages fit together in the larynx as a whole:
They both rest on the cricoid cartilage, which is the top cartilage of the trachea (wind pipe), and the only one that is not horse-shoe shaped (there is only a membrane separating the trachea from the oesophagus, which is why we can measure sub-glottal air pressure with a balloon in the oesophagus! – cf. lecture 2).
Both the arytenoid cartilages and the thyroid cartilage can move with respect to the cricoid cartilage. We have already seen how the arytenoid cartilages allow abduction and adduction of the vocal folds, and the formation or closing of the whisper triangle.
They can also slide up and down slightly on the surface of the cricoid, stretching or shortening the vocal folds.
The thyroid cartilage is less varied in its movements. It can tip forwards and back relative to the cricoid. This the effect of stretching or shortening the vocal folds (as long as the arytenoid cartilages are not sliding up and down at the same time!)
• This arrangement means that the thyroid c. can tip forwards and back …..

14. The thyroid cartilage
Movement of thyroid c. relative to the cricoid c.
The thyroid cartilage
The right side of the diagram shows how the thyroid and cricoid cartilages move in relation to each other.
The left side shows an important difference between male and female thyroid cartilages, namely the difference in the angle (120° vs 90°). This influences the relative length of the vocal folds (men‘s longer than women‘s) and the inherent voice pitch range.
Anatomically, the 90° makes the male larynx (Adam‘s apple) protrude more than the female.
Difference in angle of male and female thyroid c.

15. Stretching the vocal folds
The function of the tipping movement is shown here in more detail.

16. The whole picture
• Muscle connections between the larynx and other structures (head and thorax)
The whole picture
The larynx is a cartilage structure (not as hard as bone), and it is attached to the trachea, which is also made of cartilage.
Altogether, this means that its position is not fixed.
We can clearly feel our larynx move when we swallow, but it also moves as we speak because it is connected to the head (skull base and chin) and to the tongue (via the hyoid bone). These muscles can pull the larynx upwards.
The connections to the breastbone and collarbone can be activated to pull the larynx downwards.
The position of the larynx affects the size of the throat cavity, and with that the resonant quality of the sounds produce. (raised and lowered larynx voice are quite distinctive)