本研究描述且檢視了河內越南語中十一個單元音 / i, e, ɛ, a1, a2, o, ɔ, u, ɯ, ɤ1, ɤ2 / 在不同音節中的聲學特性，所得實驗結果如下：﹝一﹞在開音節裡的單元音，其元音時長最長，而在帶有塞音韻尾的閉音節裡的元音時長為最短。﹝二﹞以聲學的元音空間面積來說，同樣地以在開音節的元音所構成的面積最大，而帶有塞音韻尾的閉音節的面積最小。﹝三﹞上述兩點結果不論對女性語者或男性語者皆成立。﹝四﹞兩對元音[ɤ1 ɤ2 ] [ a1 a2 ]其兩兩之間有顯著差異，而主要區辨關鍵在於元音時長。﹝五﹞越南語中在閉音節的元音，即使元音時長大幅縮短，卻不會有元音不到位而央化的現象，此項結果與Lindblom(1963)的預測不一致。

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).

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