<![CDATA[Pronunciation difficulties in English as a Foreign Language (EFL) may stem from differences between learners’ first language (L1) phonological systems and English. However, acoustic evidence of category-specific pronunciation patterns among Indonesian EFL learners remains limited. This study examined the acoustic characteristics of English pronunciation and whether pronunciation accuracy differed across selected phonological categories. A quantitative explanatory design was employed involving 60 second-semester EFL students who produced 35 target words and three short reading passages. We analyzed recordings using Praat to measure first and second vowel formants (F1 and F2), sound duration, and voice onset time (VOT). Descriptive statistics characterized acoustic variation, while one-way analysis of variance (ANOVA) and post hoc comparisons examined differences in pronunciation accuracy across six phonological categories. The results showed significant differences across categories, F(5, 2094) = 159.73, p < .001, with an effect size of η² = .276. Long vowels demonstrated the highest mean accuracy (82.10), whereas final consonants (64.49) and consonant clusters (66.48) showed lower accuracy. Acoustic measurements further indicated variation in vowel quality, duration, and consonantal timing. This study's novelty lies in integrating multiple acoustic measures with category-level statistical comparisons, extending pronunciation research beyond conventional error counts. These findings provide evidence of systematic pronunciation variation consistent with an L1 phonological transfer interpretation. Pedagogically, they suggest that pronunciation instruction should prioritize final consonants, consonant clusters, and interdental fricatives, and incorporate acoustic feedback to support targeted, evidence-based teaching. The study also offers a category-sensitive analytical framework for future research on L1 influence in EFL pronunciation.]]>
