When the voice is not being used, muscles move these cartilages outward and hold the vocal cords against the sides of the larynx so that breathing is not obstructed. When one starts to speak, sing, grunt, or shout, the ends of the vocal cords connected to the cartilages are brought across the larynx, so that they partly obstruct it. As air is forced through, the cords vibrate, producing sound waves, the voice. In speaking, the size and shape of the mouth and pharynx are varied as the sound goes through, by means of muscles of the mouth, throat, and tongue. Consonants are formed by controlled interruptions of exhaled air.
Volume depends on the effort made in forcing air through the vocal cords.
The pitch of the voice depends on the amount of tension placed on the vocal cords, and on the length and thickness of the cords. Children's and women's vocal cords are short, giving them higher-pitched voices. A man's are longer and thicker and his voice is deeper. Bones in the head and chest also contribute to the quality of a voice. By long training in the use of the voice, singers are able to alter and control the mouth, throat, and chest cavities to produce a wide range of harmonics or overtones.