P105 Lecture #26 visuals

18 March 2013

Anatomy of the Human Vocal Apparatus

Illustration from E.J. Heller, “Why you hear what you hear”

Vocal Tract Anatomy – Another View

Illustration from J. Sundberg, “The Acoustics of the Singing Voice”

Vocal Tract Anatomy – Another View

• Sound wave production starts with the larynx

Vocal Tract Anatomy – The Larynx

Illustrations from E.J. Heller, “Why you hear what you hear”

View from above:Frontal view:

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 v2

2

(where p = pressure, r = density, v = velocity)

Function of the Vocal Folds

Illustration from A.H. Benade, “Fundamentals of musical acoustics”

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 openRepeat.

Net Result: Periodic expulsion of “puffs” of air from lungs

From Rossing, Wheeler & Moore, The Science of Sound

Top: volume velocity vs time for sound production at 125 Hz (male voice); Bottom:Power spectrum falls at 12 dB per octave

Fourier Spectrum:

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.