Intraoral air pressure measurements should obtained using a catheter of approximately 2mm internal diameter attached to a Manophone. The end of the catheter should be sealed, but should have a number of small holes punched along a 1cm length from the seal. It should be inserted high into the oral cavity via the mouth corner: (Subject may feel impedance of lip activity). The Manophone should have a frequency response of 0-1kHz ±3dB, having a capacitance type pressure transducer. Resultant signal then should be recorded on a second FM channel of the tape recorder.
When the cross-sectional area of the constriction is large compared with the glottal opening, the pressure drop across the constriction is small, and the turbulence noise at the constriction is also small (Froma, 2000). As the constriction area becomes equal to or less than the glottal area, the intraoral pressure increases and creates a force on the articulator that forms the constriction, and this force causes a displacement of the articulator surface.
The turbulence noise at the constriction increases to a maximum when the constriction area is about one-half of the glottal area. For this constriction size, the amplitude of the turbulence noise is relatively insensitive to changes in the constriction area. For further reductions in the constriction size, the airflow decreases, and the turbulence noise decreases to zero when a complete closure is formed.
Thus there are two stable regions where the noise amplitude is relatively insensitive to the constriction area: one corresponding to a fricative consonant with the feature and one corresponding to the stop consonant. In addition, at the time of release when there is complete closure, it can be shown that there is an abrupt increase in airflow and in turbulence noise.....
