phonetics

In terms of length, diphthongs are similar to the long vowels described above. Perhaps the most important thing to remember about all the diphthongs is that the first part is much longer and stronger than the second part; for example, most of the diphthong ai (as in the words 'eye', 'I') consists of the a vowel, and only in about the last quarter of the diphthong does the glide to I become noticeable. As the glide to i happens, the loudness of the sound decreases. As a result, the i part is shorter and quieter. Foreign learners should, therefore, always remember that the last part of English diphthongs must not be made too strongly.