1. P105 Lecture #26 visuals
18 March 2013

2. Anatomy of the Human Vocal Apparatus
Illustration from E.J. Heller, “Why you hear what you hear”

3. Vocal Tract Anatomy – Another View
Illustration from J. Sundberg,
“The Acoustics of the Singing Voice”

4. Vocal Tract Anatomy – Another View
Sound wave production starts with the larynx

5. Vocal Tract Anatomy – The Larynx
Frontal view:
View from above:
Illustrations from E.J. Heller, “Why you hear what you hear”

6. Bernoulli Effect Discovered by Daniel Bernoulli in the mid 1700’s
Essentially a consequence of conservation of energy
Statement is that pressure and flow velocity are inversely related for incompressible (approx. constant density) fluid
Mathematically: p1 + ½ r1 v12 = p2 + ½ r2 v22
(where p = pressure, r = density, v = velocity)

7. Function of the Vocal Folds
Can think of the vocal folds as a mass/spring system. Operates via Bernoulli Effect: expulsion of air from lungs  high flow through glottal opening
Low pressure
closes vocal
folds
flow stops
folds open
Repeat.
Illustration from A.H. Benade, “Fundamentals of musical acoustics”

8. Net Result: Periodic expulsion of “puffs” of air from lungs
Top: volume velocity vs time for sound production at 125 Hz (male voice); Bottom:
Power spectrum falls at 12 dB per octave
Fourier Spectrum:
From Rossing, Wheeler & Moore, The Science of Sound

9. Sound Production Summary
Expulsion of air from lungs induces vibration of vocal folds (via the Bernoulli effect).
The vocal folds open and close with a frequency dictated by anatomy (geometry) plus applied tension (contraction of muscles connecting folds with cartilage).
Give rise to periodic puff emission with fundamentals around 100 Hz (male), 200 Hz (female), 300 Hz (children). These are just the vocal fold vibration frequencies.
Thus, the vocal fold vibration frequency sets the pitch
To understand harmonic structure of speech must also take into account the filtering effect of the vocal tract  next up.