開央不圓唇元音2003, 33 (1): 121–126, doi:10.1017/S0025100303001221 Ikekeonwu, Clara, Igbo, Handbook of the International Phonetic Association: 108–110, 1999, ISBN 0-521-63751-1
齿龈边近音1017/S0025100310000162, (原始内容存档 (PDF)于2019-12-16) Ikekeonwu, Clara I., Igbo, Handbook of the International Phonetic Association, Cambridge University