The vocal tract is a cavity inside our body. The production of speech is achieved through the movement of it. Such cavity can be regarded as the shape of sounds. The state of the vocal cords and the shape of the vocal tract control the size of this obstruction, thereby creating a cavity shape corresponding to the sound.
Speech sounds can be classified into consonants and vowels.
Consonants are produced by the obstruction of airflow in vocal tract. Therefore,consonants can be classified according to the position and extent of obstruction. In English, consonants are divided into 8 types according to the place of articulation from lips to velum. According to the manner,consonants can have 6 categories with different shape of gaps. Whether the vocal cords vibrate can divide consonants into voiced and voiceless sounds. In Chinese,there are Aspirated Sounds,which put out more air than voiceless sounds when pronouncing. The bending direction of the curve and the opening distance work together to show the vocal cords vibration.
In the production of vowels,the airstream is almost unobstructed. Generally,the vocal cords almost always vibrate.The location of the tongue changes the size of the space.The position of the tongue and the shape of the lips are used for vowels classification. It can also be described as Frontness, Hight and Lip rounding.