1. P105 Lecture #27 visuals
20 March 2013

2. Sound production from vocal system
Three components:
Power source (lungs)
Oscillator (vocal folds  spring-mass system, driven by Bernoulli effect)
Resonator / Radiator (vocal tract and mouth  subject of today’s lecture)
Recall, periodic emission of puffs of air though glottal opening (due to vibration of vocal folds), constitutes a pressure wave with a discrete (harmonic) frequency spectrum:
fundamental is at the vocal fold vibration frequency & determines the pitch;
harmonics are down by 12 dB after each octave (factor of 2 increase in frequency). i.e., LI (n=2) = LI (n=1) – 12 dB; LI (n=4) = LI (n=2) – 12 dB, etc.
To understand harmonic structure of speech & singing must also take into account the filtering effect of the vocal tract and mouth.
This is the subject of today’s lecture.

3. 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

4. Impact of the vocal tract geometry:
Formants
Can think of the vocal tract as an air-filled pipe, closed at one end (folds) & open at the other (mouth)
Standing wave modes = “formants”
Nominally odd harmonics only:
fn = n (v / 4L), v = 343 m/s
L ~ 17.5cm  f1 ~ 500 Hz.
In practice, geometry is complex, formant frequencies influenced by tongue, jaw mouth, etc…
Illustration from J. Sundberg,
“The Acoustics of the Singing Voice”

5. How can you vary your formants?
Shape of oral cavity, mouth opening, & location of tongue are very important
For example, a constriction at a location of a formant’s pressure node will limit impact of that formant
Also, can amplify higher freq. modes with antinode at that location
from J. Sundberg, “The Acoustics of the Singing Voice”

6. Making different vowel sounds
from J. Sundberg, “The Acoustics of the Singing Voice”

7. Making different vowel sounds
from J. Sundberg, “The Acoustics of the Singing Voice”