This paper aims to analyze the acoustic characteristics of initial consonant voicing perturbation of the fundamental frequency of oral vowels and nasal vowels of Ban Doi Pwo Karen. Three age groups of informants were selected: over-sixty years old (>60), middle aged (35-45), and under-twenty years old (<20). The acoustic analysis method was employed to analyze the mean vowel duration (msec), mean vowel amplitude (dB), and mean vowel fundamental frequency (Hz). The results show that voiceless initial consonants tend to cause a lower fundamental frequency than that of the voiced initial consonants. This has excited controversy concerning the tonogenesis theory of initial voicing perturbation on vowels. However, it was later found that the vowels followed by voiceless initial consonants were breathy and it was the voice register of vowels that caused the low fundamental frequency values. In contrast to other studies, the nasal vowels were not always higher in fundamental frequency when compared to oral vowels. In all age groups, nasal vowels following either voiceless or voiced consonants were found to be higher in fundamental frequency than oral vowels, except in the younger age group where the fundamental frequency of nasal vowels following voiced consonants was lower than that of the oral vowels following voiced consonants.