SHORT FRONT OPEN-MID UNROUNDED VOWEL [ɛ]
In unstressed closed syllables, or when accompanied by the shewa/ḥatef sign, Tiberian Hebrew seghol is normally pronounced as a short ɛ-vowel, lower in the mouth than ṣere.
LONG FRONT OPEN-MID UNROUNDED VOWEL [ɛː]
In stressed and/or open syllables, seghol is pronounced as a long vowel [ɛː].
(in open or stressed syllable)
EXTRA LONG FRONT OPEN-MID UNROUNDED VOWEL [ɛːɛ]
In a final stressed closed syllable, seghol is pronounced as an extra long vowel [ɛːɛ].
(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.