N. V. Tatsenko introduction to theoretical phonetics of english

Figure 2.3 - The Lungs



From the lungs through the wind-pipe the air-stream passes to the upper stages of the vocal tract. First of all, it passes to the larynx containing the vocal cords (folds).
The Larynx. The larynx is colloquially known as the voice box. It is a box-like small structure situated in the front of the throat where there is a protuberance. For this reason, the larynx is popularly called Adam’s apple. This casing is formed of cartilages and muscles. It protects as well as houses the trachea (also known as windpipe, oesophagus, esophagus) and the vocal folds (formerly they were called vocal cords). Over the larynx is a flap called the epiglottis that closes off the trachea when we swallow. When the epiglottis is folded back out of the way, the parts of the larynx that are involved in speech production can be seen (see fig. 2.4):


Figure 2.4 - The Larynx



The Vocal Folds. They are two thin sheets of tissue that stretch in a V-shaped fashion like a pair of lips placed horizontally from front to back. They are joined in the front but can be separated at the back. When the vocal cords are stretched tight and close together, they vibrate rapidly - more than 100 times per second - and the sound that comes out is louder. When the vocal cords are more relaxed, the sound that comes out is quieter, like a whisper. The vocal cords also affect the pitch of the sounds we produce. Pitch is a measure of how high or low the voice is at a particular point in time; that is, high or low in the sense that a musical note is high or low; it doesn’t mean a high or low volume or loudness. When the vocal cords are stretched out longer, the sound has a lower pitch; when they are shorter, the sound has a higher pitch. The opening between the vocal cords is known as the glottis. The glottis is considered to be in open state when the folds are apart, and when the folds are pressed together the glottis is considered to be in close state.
The function of the vocal folds consists in their role as a vibrator set in motion by the air-stream sent by the lungs. When the glottis is tightly closed and the air is sent up below it the so-called glottal stop is produced. It often occurs in English when it reinforces or even replaces [p], [t], or [k] or even when it precedes the energetic articulation of vowel sounds. The most important speech function of the vocal folds is their role in the production of voice. The effect of voice is achieved when the vocal cords are brought together and vibrate when subjected to the pressure of air passing from the lungs. This vibration is caused by compressed air forcing an opening of the glottis and the following reduced air-pressure permitting the vocal cords to come together again.
The height of the speaking voice depends on the frequency of the vibrations. The more frequently the vocal cords vibrate the higher the pitch is. The typical speaking voice of a woman is higher than that of a man because the vocal cords of a woman vibrate more frequently. We are able to vary the rate of the vibration thus producing modifications of the pitch component of intonation. More than that, we are able to modify the size of the puff of air which escapes at each vibration of the vocal cords, that is we can alter the amplitude of the vibration which causes changes of the loudness of the sound heard by the listener (see fig. 2.5):





Above the vocal cords, in the vocal tract itself, are several parts that move in various ways to change the size and shape of the open part of the vocal tract and produce all the sounds of English, or any other language. These are called the articulators.
From the larynx the air-stream passes to supraglottal cavities, that is to the pharynx, the mouth and the nasal cavities. The shapes of these cavities modify the note produced in the larynx thus giving rise to particular speech sounds.