然而,由丹尼爾·瓊斯和約翰·C·威爾斯(英语:John C. Wells)製作的主要元音聲學分析顯示,基本上所有的不圓唇後元音(除了[ɑ]以外)在調音時都是次後元音。因此,「次閉後不圓唇元音」與「次閉次後不圓唇元音」兩者間可能沒有本質上的差異。[1]威爾斯在其著作《英語各地口音》(Accents of English)中,將這個元音轉寫為未被IPA收錄的音標⟨ω⟩。
理論上來說,它也可以在IPA中表示為⟨ʊ̜⟩(較不圓唇的[ʊ]),但因 [ʊ]在《國際音標使用指南》(Handbook of the International Phonetic Association)已經被定義為圓唇的元音(而不像[ə]與[ɐ]未指定圓唇度)[2],⟨ʊ̜⟩也可以表示稍微圓唇的[ʊ],而不一定是本文中完全不圓唇的元音。
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