Diphthongs
A diphthong is a sequence of two vowel sounds “squashed” together. Diphthongs are present in the phonetic inventory of many languages, including English. The vowels we have studied so far are simple vowels, called 
monophthongs. The vowel sound in the word bite [baɪt], however, is the [a] 
vowel sound of father followed rapidly by the [ɪ] sound of fit, resulting in the 
diphthong [aɪ]. Similarly, the vowel in bout [baʊt] is [a] followed by the [ʊ] 
sound of put, resulting in [aʊ]. Another diphthong that occurs in English is 
the vowel sound in boy [bɔɪ], which is the vowel [ɔ] of bore followed by [ɪ], 
resulting in [ɔɪ]. The pronunciation of any of these diphthongs may vary from 
our description because of the diversity of English speakers.
To some extent the midvowels [e] and [o] may be diphthongized, especially 
in American English, though not in other varieties such as Irish English