1.
Recording air pressure and airflow
3.
Using the airflow equipment
5.
Calibrating
air pressure and airflow
6.
UCLA Phonetics Lab Resources for Aerodynamics
1.
Recording air pressure and airflow
The
UCLA Phonetics Lab has equipment that enables one to record the airflow
from the mouth and nose. In addition, it can record the pressure of the
air in the front of the mouth and in the pharynx. The system is illustrated
in Figure 1. It consists of a small box (bottom left of the picture) connected
to a laptop or desktop computer (bottom right), and an assembly with oral
and nasal masks and pressure tubes held by the speaker, together with a
microphone that records the sound.
Figure 1. The system for
recording air pressure and air flow described in the text
The mask for capturing
the oral airflow fits around the mouth and below the jaw. The nasal airflow
mask is fastened over the nose by a band that goes around the head. Both
masks are joined to the assembly by small tubes.
Some notes on connecting
the assembly:
Make
sure the tubes for pressure and flow are placed over the corresponding
pressure and flow ports.
The
nasal mask has only one tube.This should be placed over the flow port.(There
is no nasal pressure to be measured).
3.
Using the airflow equipment
Recording the airflow:
While
talking, press the masks firmly against the face, making sure that there
are no leaks.
To
record the pressure of the air in the mouth, hold a small tube between
the lips while speaking. (If the tube is small enough it will not interfere
too much with speaking).
The
pressure of the air behind a velar closure one can be measured using a
small tube passed through the nose, with its open end in the pharynx.However,
this will not be discussed here.
Tips
for recording :
When
recording air pressure in the mouth, it is important to keep the tubes
free of saliva. The tubes should be blown clear at frequent intervals.
If
you want to record the changes in pressure and flow that occur as a result
of the vibrations of the vocal folds, you will need to use tubes with an
internal diameter of at least 2 mm.
Figure 2 has three records
made of"He paid the price ", with the emphasis on the second
word.
The
top line (Audio) is the record produced by the microphone. It represents
a rather distorted sound, as the voice was muffled by the mask. The only
information it gives us is that there are four syllables, and that the
third one, "the", is the weakest.
The
second line (Oral flow) shows the bursts of air that occur when the lips
open for each of the aspirated stops.
The
third line (Oral pressure) shows the increase in the pressure of the air
in the mouth for each of the aspirated stops. It also show the variations
in pressure associated with the voicing. (In making these records the tip
of the tube inserted between the lips must have been behind the alveolar
ridge, as the record shows that the pressure in the mouth increases for
[d] at end of "paid" and for the fricative in "the").
Figure 2. Audio, oral
flow and pressure records during the sentence "He paid the
price".
The scales, like those
in figure 2,allow us to measure the airflow and pressure data so that we
can quantify the differences between sentences.
Flow is measured in terms
of the volume of air that passes a given point in a second. (We normally
speak of the airflow through the lips or the nose, although we are really
measuring the volume of air that passes across the mesh in the mask). The
units are milliliters per second (ml/s). Calibrating the rate of flow requires
the apparatus shown in figure 3. A fan produces a steady airstream that
flows through the mask and then on through a special flow calibration tube
containing a ball that is blown higher in the tube as the flow is increased.
Figure
3. A system for calibrating airflow.
Pressure is measured in
terms of the force required to raise or lower the height of a column of
water by a certain amount. This corresponds to how much effort you would
have to use to blow bubbles out of a tube immersed in water as shown in
figure 4. This technique can be used to calibrate a pressure measurement
system as shown in the figure.The figure shows a force being exerted to
produce bubbles at the end of a tube 12.5 cm below the surface, a pressure
of 12.5 cm H2O.
 |
Figure
4. A simple system for measuring pressure.
Calibration measurements
can be made more accurately by using a U-tube as shown in figure 5. When
the tap is open, the tube can be filled with water to the zero level, with
the water level reaching the same height in both branches. The figure shows
what happens when the tap is closed and pressure is applied by pushing
the syringe down. In this case the level has gone up by 5 cm on the one
side and gone down by 5 cm on the other side, so that the pressure being
applied is 10 cm H2O.
Figure
5. Using a U-tube to calibrate pressure.
The
information on this page has been adapted from the forthcoming Analyzing
phonetic data: An
introduction to fieldwork
andinstrumental phonetics by Peter
Ladefoged.
This
page was created by Rebecca Brown and Christina Esposito.