The four English approximant sounds (the l sound, r sound, w sound and y sound) are created by constricting the vocal tract slightly, but not so much that the air becomes turbulent as it passes through.
Closely related to the r sound are the four r-controlled vowels: schwa+r, ar sound, or sound, and air sound. The schwa+r is essentially a syllabic r (the r sound creates a syllable); the other three r-controlled vowels are a combination of a vowel sound and an r sound.
Note: There are other options besides the primary ones described above for creating the r sound and the l sound. Refer to the specific lessons for these sounds to view the options.
Semi-vowels: w sound and y sound
The w sound and y sound are called semi-vowels because, although the vocal tract is relatively unrestricted during the formation of both of these sounds, they are not syllabic (meaning they do not force a syllable to occur). Another vowel-like quality of these two sounds is that two-sound vowels (also called diphthongs) include a sound that is nearly identical to a w sound or y sound in their pronunciation. American English two-sound vowels include the following: long a, long i, long o, long u, oi sound, and ow sound.
Syllabic consonants: l sound and schwa+r
A syllabic consonant is a consonant sound that becomes the base sound of a syllable. While schwa+r is always syllabic and can occur on either a stressed or unstressed syllable, it is only possible to have a syllabic l on an unstressed syllable.
Voiced and unvoiced sounds
Although approximants are voiced, when they occur after unvoiced stops (the k sound, t sound, and p sound), as in the words crash, play, and twin, the approximant begins as an unvoiced sound and the vocal cords begin to vibrate during the production of the sound. Non-native speakers who have difficulty with these types of consonant clusters often accidentally add an additional voiced sound after the stop and before the approximant. Learning to delay voicing avoids the possibility of an accidental vowel sound (and the accompanying unwanted syllable).