Abstract
This study describes and examines the acoustic properties of the 11 vowels / i, e, ɛ, a1, a2, o, ɔ, u, ɯ, ɤ1, ɤ2 / in open syllables (CV) and closed syllables, CVN (N=Nasals) and CVS (Stops), in Hanoi dialect of northern Vietnamese. The results show that (1) the vowels in open syllables (CV) are much longer than the ones in closed syllables, and in CVS syllables are the shortest; (2) the acoustic vowel space area of the vowels in CVS syllables is the smallest. On the contrary, vowels in CV form the largest one; (3) both (1) and (2) are true for the female and male speakers; (4) the key factor to distinguish the pairs of vowels [ a1, a2 ] and [ ɤ1, ɤ2 ] is vowel duration; (5) the shorter vowel duration in closed syllables will not cause target undershoot and vowel reduction, a counter example to the theory of Lindblom (1963).