The sounds we make when speaking are produced through muscles contractions. Humans have a very large and complex set of muscles that can produce and modify the air flow coming from lungs, transforming it in different sounds of speech. In order to understand how this air flow is transformed in sounds of speech it is necessary to understand what parts of the vocal tract influence the way we produce the sounds of speech.
Below is a graphical representation of these vocal tract parts (often called articulators) and a short description of them. It represents the human head (section seen from the side) and it should be familiar for those who were involved in the study of these articulators.
The soft plate it is also called velum and it is placed in a key position that allows the air to go through your mouth and through your nose. In speech, the soft plate (velum) is often in a raised position that doesn’t allow the air to go through your nose. The soft plate (velum) can be touched by the tongue. For example when we make the sounds /k/ and /g/ the tongue touches the soft plate (velum) and the sounds produced in these conditions are called velar sounds.
The lips are very important in speech. They produce a large number of sounds. In rounded shape the lips produce vowels like /u:/. In contact with the teeth the lips produce sounds like /f/ or /v/ (these sounds are called labiodental sounds). Pressed together the lips produce sounds like /p/ or /b/ (these sounds are called bilabial sounds).
If you look in the mirror with your mouth open then you can see the back of your larynx. It is just a tube which begins just above the larynx. It is about 8 cm long.
The alveolar ridge is placed just behind the top front teeth as it is shown in the image above. Sounds produced here (the tongue touching the alveolar ridge) are called alveolar sounds. For example the sounds /t/ and /d/ are produced by the alveolar ridge.
The tongue is in contact to the teeth (especially the upper side teeth) for many speech sounds. These sounds are called dental sounds.
Have you ever asked yourself why some sounds are called vowels and others are called consonants? These two words, vowels and consonants, are very familiar for any learner of English but most of them don’t know what they mean.
Specialists consider vowels to be sounds in which there is no obstruction to the flow of air from the larynx to the lips. The others (where there is obstruction to the flow of air) are called consonants.
Looking at the back of patience’ mouth a doctor asks the patience to make the sound “ah”. In this way there will be an unobstructed view for the doctor. But, if we make a sound like /s/ or /d/ we make it impossible for the air to pass through the mouth. These kinds of sounds (such as /s/ and /d/) are considered consonants.
However, if we say that the difference between vowels and consonants is a difference in the way that they are produced, there will be some cases of disagreement. This is something that can not be avoided.
It is possible to look at vowels and consonants in a different way. The most important difference is not the way they are made but their different distribution.
Let’s consider the sound /h/ at the beginning of an English word. What sound can follow this /h/? All the sounds that can follow /h/ sound are considered vowels (such as /e/ sound in the word “hen”). I can’t think of any consonant sound that can follow the beginning sound /h/.
Let’s consider the beginning sound /bi/. Most of the sounds that can follow /bi/ are consonants (as in the words “bill”, “bid”, “big” etc.). I can’t think of any cases where a vowel sound can follow /bi/. However, looking at vowels and consonants this way creates many other interesting theoretical problems and everything will be more difficult and confuse.