LONG BACK CLOSE-MID ROUNDED VOWEL [oː]
In open syllables, Tiberian Hebrew ḥolem is normally pronounced as a long o-vowel.
EXTRA LONG BACK CLOSE-MID ROUNDED VOWEL [oːo]
In a closed syllable, ḥolem is pronounced as an extra long vowel [oːo].
(in stressed closed syllable)
SOURCES AND FURTHER READING
Khan, Geoffrey. 2020. The Tiberian Pronunciation Tradition of Biblical Hebrew. Cambridge: Cambridge and Open Book Publishers. §I.2.