All sounds can be classified into two classes. They are obstruents and sonorants. All obstruents are consonants, but sonorants consist of both vowels and consonants.
The class of obstruents includes plosives, fricatives and affricates. All vowels are sonorants but nasals, liquids and approximants also belong to the class of sonorants. Nasals and liquids are consonants with more acoustic energy than obstruents.
Obstruents are often voiceless, but sonorants are usually voiced. Obstruents are sounds which are formed by obstructing airflow. This is not the case with sonorants, which have greater airflow through the oral cavity and thereby resonate.
The two largest classes of speech sounds are obstruents and sonorants. All vowels belong to the class of sonorants. Most consonants belong to the class of obstruents, but consonants such as nasals and liquids are sonorants.