THE SPEECH ORGANS AND THEIR FUNCTIONS
Speech is produced in the throat, mouth and nasal passage, but there are no “speech organs” as such, strictly speaking; all of the organs used in speech have other, and perhaps more fundamental, purpose involving eating and breathing. Nevertheless the term is familiar and meaninful in the contex of articulatory phonetics, and will be used here. The speech organs are shown in a diagram, a cross-section of the head and throat.
The lungs, diaphragm, chest muscles and windpipe also act in the production of speech, but they will not be discussed in detail as their function is more or less automatic.
Speech is produced by causing a column of enclosed air to víbrate. It is the same prosses, basically, as the production of sound by a wind instrument in music. Air is forced under pressure from the lungs trough the windpipe (trachea), to the voice box (larnyx), a structure that sits on top of the windpipe and contains the vocal cords, as they are called. (These are not cords at all, really, and would be more properly named band sor membranes). The vocal cords have the capability of closing off entirely the opening (glottis) and can hold considerable air pressure (as when a person coughs or strains to lift a heave weight). They can also assume other positions. They may be wide open, allowing the air to pass unimpeded. Or they may be closed almost but not quite completely, so that the scaping air, forced through the narrow opening between them causes them to víbrate like the reed in a musical instrument. This vibration makes tthe all-important vocal tone. known technically as voice, without which speech would be impossible. Speech sounds that have this tone as part of their makeup are called voiced., and those without it are called unvoiced or voiceless. Varying the amount of tensión on the vocal cords causes the vocal tone to vary in quality and in number of cycles per second; in other words, the timbre and pitch of the tone can be changed voluntarily, within limits. by the speakers.
The air stream issuing from the larynx w ith or without voice, can now be modified in many ways; that is, we are at the stage of articulation. Almost all the parts of the throat and lower head that are accesible to the air stream can take part in articulation. For discussion purposes, we can divide these parts into three groups; resonating cavities, ariticulators, and points of articulation.
The size, the shape, and the material composition of the vessel enclosing a vibrating air column all have important effects on the quality of the sound that comes from it. There are quite a few spaces in the speech tract that effect sounds by their resonating qualities; in acousting terms, their reinforce (amplify) certain frecuencies and and suppress or weaken (dampen) others. In addition to te sinuses and other spaces in the head, which function passively and without the control of the speaker, the resonating cavities involved in speech production are these: the pharnyx, the space formed by the root of the tongue and the walls of the throat, which affects the sound by its shape but is not actively used in English; the nose, which adds its quite distinctive quality to the sounds if the air is allowed to pass through it whether or not the mouth is involved at the same time; and finally, the mouth, the most important of all because it contains a number of highly mobile organs and can assume a tremendous number of different shapes.
These are movile organs that can be brough close to, or into contact withi, various locations in the speech tract (known as points of articulation) so as to stop or impede the free passage of the air stream. The manner of articulation is determined by the kind of closure or near closure that is made, as well as its manner of release. The articulators are the lips, especially the lower one; the tongue, usually divided into four parts; tip, front, middle, and back; the uvula; and, to an extent, the jaw, through its role is minor (it is posible to speak quite clearly with the jaws clenched, as ventriloquist do).
POINTS OF ARTICULATION
These are fixed locations againts which the movile articulators operate in order to produce speech sounds: the teeth, the gums, the alveolar ridge, the various parts of the palate (sometimes called “hard” palate to distinguish it from the “soft” palate or velum), the velum, the walls of the pharynx and the glotis.