This study presents longitudinal acoustic evidence of how an adult speaker’s vowels change across his lifespan. Noam Chomsky was chosen as a speaker because he presents an excellent opportunity to study the effect of relocation to a different dialect area on adult phonology since he was born and raised in Philadelphia and moved to Boston in 1955. Two linguistic variables that have different phonemic systems in Philadelphia and Boston were examined in this study: i) /o/–/oh/ distinction in Philadelphia and /o/–/oh/ merger in Boston, ii) split short-a system (a phonemic distinction between tense and lax short-a with various phonological and lexical conditioning) in Philadelphia and nasal system (an allophonic alternation between a tense short-a before nasals and lax short-a before non-nasals) in Boston. Results based on Chomsky’s public speech in 1970 and 2009 show that his /o/ has significantly shifted along both F1 and F2 over 40 years, displaying a subphonemic shift, while /oh/ remained stable. For his short-a patterns, the 1970 pattern corresponds to neither a split nor a nasal system. In 2009, in contrast, a pattern similar to a nasal system emerged. It is suggested Chomsky was able to adopt features of a new ambient dialect over time as a result of contact with a second dialect well past the critical period.