The physical constraints of articulatory and/or auditory speech mechanism are vital to the sound change of human languages (Hombert 1977; Ohala 1974, 1993). These constraints often affect the way speech sounds are produced and perceived by listeners. In this paper, with the help of acoustic experiment (s) the phoneme inventory of a relatively less explored language ie Sylheti is examined and established. The phoneme inventory of this language is substantially reduced due to the loss of (underlying) breathiness contrast [+ spread glottis]: both voiced and voiceless aspirated stops became unaspirated ([d̪han> d̪an]“paddy,”[t̪hala> t̪ala]“plate”), and the voiceless labial and dorsal stops went one step further and spirantized to homorganic fricatives ([por]>[ɸɔr]“read,”[phul]>[ɸul]“flower,”([kali]>[xali]“ink,”[khal]>[xal]“drain/channel”). The post-alveolar affricates (both aspirated and unaspirated) also spirantized to dental fricatives ([tʃa]>[sa]“tea,”[tʃhuti]>[suti]“holiday,”[dʒal]>[zal]“net,”[dʒhal]>[zal]“spicy”). Among the voiceless stops, only the dental and retroflex stops remained stops. Two controlled production experiments have been conducted to establish the phoneme inventory of Sylheti. The first experiment is meant to explore the status of the underlying breathy voice property