Regional variations in pitch frequencies of Karadeniz kemenche samples. Box plots show distributions of (A) bass string open frequencies, (B) treble string open frequencies, and (C) highest fingered pitches, grouped by construction region (Rize: blue, Trabzon: orange, Giresun: red). Boxes span the 25th–75th percentiles with median lines; whiskers extend to 1.5 × IQR; individual points represent samples. Open-string frequencies were measured with a digital tuner (±1 cent) on strings tuned at time of measurement. Structural modal frequency bands (Mode 2: 253 Hz; Modes 3–4: 432–457 Hz; Mode 9: 987 Hz) are overlaid as grey bands to highlight structural-acoustic coupling. Significant regional differences were confirmed by non-parametric Kruskal–Wallis tests (p <  0.01 for all frequency ranges) with effect sizes (η²) reported in the text.