This article was aimed to examine tonal system of northeastern Thai dialect of Suwannakhuha District, Nong Bua Lam Phu Province. The researcher collected data from 8 sub-districts from an informant in each sub-district, totaling 8 persons. The analysis of tonal system was conducted based on the concept of tone box of Gedney (1972) to investigate tone splits and coalescences by listening and word lists of Akharawatthanakun (2003) was used to study phonetic features of tones with acoustic method by transforming fundamental frequency from Hertz to semitone. The findings reveal that tonal system of northeastern Thai dialect in Suwannakhuha District, Nong Bua Lam Phu Province could be categorized by tonemes into 2 groups. The 1st group included 5 tonemes and was found in 6 sub-districts: Ban Khok Sub-district, Dong Mafai Sub-district, Na Dan Sub-district, Na Si Sub-district, Boonthan Sub-district and Suwannakhuha Sub-district. The characteristics of tonal splits and coalescences in column A were divided into 3 sub- groups including 1) A123-4, 2) A1-234 and 3) A12-34. The second group consisting 6 tonemes was found in 2 sub-districts: Kud Phueng Sub-district and Na Dee Sub-district with only form of tone splits and coalescences in column A which was A1-23-4.
Tonal variation, Thai dialect, dialectology, sociolinguistics