Biomedical Engineering Reference
In-Depth Information
trachea
d
labium
A
0
a
2
airflow
bronchus
Fig. 6.2.
Schematic section of the syrinx and vocal-tract input. Airflow coming
from the lungs is modulated by labial oscillation. As a result, a diverging sound
wave is injected at the input of the vocal tract. Dashed lines indicate the region of
spherical propagation. After this region and once in the trachea (which is a very
narrow tube around 1 mm wide), the sound wave is propagated as a plane wave.
The parameter
d
is a measure of the distance between the labia and the region of
plane-wave superposition
40
0.0005
0.0004
30
0.0003
20
0.0002
10
0.0001
R
I
0
30
0
0
5
10
15
20
25
frequency (kHz)
Fig. 6.3.
Coupling between source and vocal tract. The dependence of
s
(
t
)onthe
flow and the flow derivative is mediated by the specific acoustic resistance and the
inertance
R
and
I
, respectively. The nature of the coupling (more in phase with
either the flow or its time derivative) is governed by the fundamental frequency of
the vocalization
f
of the vocalization. Note in Fig. 6.3 that the coupling is inertive at low fre-
quencies, but that it becomes resistive at high frequencies; the frequency at
which the coupling changes behavior depends on the anatomical parameter
d
and the sound velocity
c
.
An important assumption in the previous discussion is that the two valves
modulating the airflow are close to the junction of the trachea with the
