Kumarika Subhakarn และ Suraporn Konthong. (2013) The Common vocal problems in western classical vocal performance encountered by Thai students of Mahidol University at The Pre-College and undergraduate level. Mahidol University:ม.ป.ท.Kumarika Subhakarn และ Suraporn Konthong. 2013. The Common vocal problems in western classical vocal performance encountered by Thai students of Mahidol University at The Pre-College and undergraduate level. ม.ป.ท.:Mahidol University;Kumarika Subhakarn และ Suraporn Konthong. The Common vocal problems in western classical vocal performance encountered by Thai students of Mahidol University at The Pre-College and undergraduate level. ม.ป.ท.:Mahidol University, 2013. Print.