Aerodynamic techniques

1. Recording air pressure and airflow

2. Setting up the assembly

3. Using the airflow equipment

4. Analyzing the data 

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.

2. Setting up the assembly 

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.

4. Analyzing the Data

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".

5. Calibrating air pressure and airflow

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. 

6. UCLA Phonetics Lab Resources for Aerodynamics

Here in the UCLA phonetics lab, we have facilities for acquiring aerodynamic data with. The lab is equipped with Rothenberg masks and small tubes for attaching the masks to the assembly. These masks can be used with either Macquirer or either of the 4-channel CSL boxes.All of the equipment for aerodynamics is located in the General Lab. 

About this page

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.