The Hebrew diphthong is the combination of vowels which are pronounced as a unit.
Each diphthong forms a distinct syllable.
It is worth noting that there is a difference in what is classified as a diphthong in Modern Hebrew and Biblical Hebrew.
The Modern Hebrew diphthongs patah yud  and kamats yud , for instance, are not treated grammatically as diphthongs in Biblical Hebrew where the yud is a quiescent (silent) vowel and the patah becomes a long "ai" vowel sound.
When a vav is added  the sound produced is a long "a" vowel followed by a pronounced vav. The same combination is a diphthong in Modern Hebrew.
E.g.; The Hebrew word ba-nav (his sons) is shown by its cantillation marks in the Hebrew bible to have extended the kamats vowel under the second nun to combine with the yud forming a long vowel leaving the vav to stand alone as a final consonant. While the word sounds the same as a diphthong "av" in Modern Hebrew or a long vowel "a" and a vav in Biblical Hebrew, grammatically the last syllable of the word is closed in Biblical Hebrew and open in Modern Hebrew. This difference can affect grammar rules.
Here is the word in context (Gen. 9:8) "And God spoke to Noah and to his sons with him, saying"
The diphthongs listed below are as recognised in Modern Hebrew.
Practice. ...Putting things together.
Listen to and practice these diphthong combinations. Each combination, whether open or closed, represents a syllable.
Now for some real Hebrew words
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vowels and diphthongs
Now that you have studied the Hebrew Consonants and the Vowels—it is time to put it all together with some vocabulary.