What is the proper way to pronounce God’s Name in Berachot and prayers?
For one thing, it is clear that we pronounce the Divine Name of "Y-H-V-H" the same way as we pronounce the Name of "A-D-N-Y." Although these are two different Names, we pronounce them the same way because we are forbidden from reading the Name of "Y-H-V-H" as it is written. One should, however, have different intentions while reciting these two Names. When one recites "A-D-N-Y," he should have in mind that God is "Adon Kol" – the Master over everything. While reciting "Y-H-V-H," one should have in mind the concept of "Adon Kol" as well as the concept of "Haya Hove Ve’yihye" – "He was, He is, and He will be."
Returning to the issue of pronunciation, Hacham David Yosef addresses this subject in detail in his work Halacha Berura (vol. 1, p. 116). He begins by noting that the vowel underneath the first letter of the Name (the "Alef") is a "Hataf-Patah," which we generally pronounce as a short "A" sound, similar to a simple "Patah." Expert grammarians are capable of discerning between the "Hataf-Patah" and "Patah"; specifically, the "Hataf-Patah" is pronounced as a slightly shorter sound. For our purposes, however, it is accepted to pronounce the first letter of God’s Name as a short "A" sound.
The second letter of the Divine Name, "Dalet," is pronounced with the "Holam" vowel, which is a long "O" sound. Hacham David emphasizes the importance of reciting the Name slowly so as to ensure that one does not mispronounce the "Dalet" as "De," "Dee" or "Doo." If one recites the Name too quickly, he will not pronounce the "Dalet" properly, with a long "O" sound.
The final and most controversial vowel of the Divine Name is the "Kamatz" vowel underneath the "Nun." The practice among Ashkenazim is to pronounce the "Kamatz" as a short "U" sound, thus yielding "Nuh." Sepharadim, by contrast, pronounce the "Kamatz" similar to a "Patah," as a short "A" sound ("NAH"). Once again, those with proficiency in Hebrew grammar can discern the difference between a "Patah" and the Sephardic "Kamatz," as the "Kamatz" is a bit "smoother" and not as quick as the "Kamatz." It is proper, Hacham David writes, for one to study the subtle distinction between the two so he can recite the Divine Name with precision.
Hacham David presents in this context a lot of interesting source material relevant to the proper pronunciation of the "Kamatz" and the different arguments raised in favor of the customs of the Sepharadim and the Ashkenazim. Some Sepharadim brought proof from ancient poems written in rhyme, from which it clearly emerges that the "Kamatz" sound rhymes with a "Patah" sound. In any event, Hacham David concludes that everybody must pronounce the "Kamatz" – particularly when reciting the Divine Name – in accordance with his tradition. (The Steipler Gaon, an Ashkenazic Sage, went so far as to claim that if an Ashkenazi pronounces the "Kamatz" under the "Nun" in the Divine Name as a "Patah" he is not considered as having recited the Divine Name at all.)
The final letter of the Divine Name is "Yod," which is not punctuated with any vowel. Nevertheless, Hacham David writes, one must ensure to pronounce the "Y" sound at the end of the word, though of course without any vowel sound.
Finally, when reciting the Divine Name one must place the stress on the final syllable of the word (on the "NAI"). This can at times pose a challenge to Hazanim singing the prayer text, as on some occasions the melody will dictate stressing one of the earlier two syllables. Hazanim must be careful when singing the Name of God and ensure to stress the last syllable.
Summary: When reciting God’s Name, one must ensure to stress the last syllable and punctuate the word with its proper vowels, according to his family tradition. The "Alef" is pronounced with a short "A" sound; the "Dalet" is pronounced with a long "O" sound; and the "Nun," according to Sephardic custom, is pronounced with a short "A" sound. One must ensure to pronounce the "Yod" as a "Y" sound at the end of the word.