Acoustic Variations in Interdental Fricatives /θ/ and /ð/ among Educated Hausa–English Bilinguals in Northwestern Nigeria

Abstract

Interdental fricatives /θ/ and /ð/ are typologically rare and absent from the Hausa phonemic inventory, making their production by Hausa–English bilinguals a theoretically informative test case for second-language speech acquisition and Nigerian English phonology, yet no prior study has instrumentally measured their acoustic properties in this population. This study acoustically characterises /θ/ and /ð/ production among thirty educated Hausa–English bilingual speakers (aged 15–19) in Northwestern Nigeria and evaluates the influence of age, gender, education level, and language proficiency on that variation. Participants read a word list containing /θ/ and /ð/ tokens across phonetic positions; recordings were segmented in Praat and measured for duration, spectral centre of gravity, spectral standard deviation, skewness, kurtosis, and intensity, and linear mixed-effects models tested the effects of the sociolinguistic predictors on each acoustic measure. Participants produced /θ/ and /ð/ with significantly longer durations and lower spectral centre of gravity than Standard English reference values, consistent with a more anterior place of articulation, and language proficiency emerged as the strongest predictor of acoustic variation, while age, gender, and education level were not significant predictors. These findings extend earlier auditory-impressionistic descriptions of Hausa-accented English with quantified acoustic evidence and identify bilingual proficiency as the primary driver of phonetic accuracy in interdental fricative production, with implications for pronunciation pedagogy in Nigerian English contexts.