Found in articles
ISBN 0-7190-6689-1 Hoekstra, Jarich, 12. Standard West Frisian, Munske, Horst Haider; Århammar, Hans (编), Handbook of Frisian studies, Tübingen: Max Niemeyer Verlag
Basbøll, Hans, The Phonology of Danish, 2005, ISBN 0-203-97876-5 Bishop, Nancy, A preliminary description of Kensiu (Maniq) phonology (PDF), Mon–Khmer
中前不圆唇元音
Gordeeva, Olga B.; Matthews, Benjamin, Acquisition of Scottish English Phonology: an overview, Edinburgh: QMU Speech Science Research Centre Working Papers
半閉前不圓唇元音
1017/S0025100312000102, （原始内容存档 (PDF)于2018-06-13） Sipma, Pieter, Phonology & grammar of modern West Frisian, London: Oxford University Press, 1913 Stone, Gerald
半閉後圓唇元音
Yoruba, [West African Languages Survey / Institute of African Studies], Cambridge: Cambridge University Press, 1966 Basbøll, Hans, The Phonology of Danish