Contrastive apical post-alveolar and laminal alveolar click types in Ekoka !Xung

Ekoka !Xung has four contrastive click types—dental, alveolar, lateral, and “retroflex.” We provide acoustic and ultrasound results of five speakers’ productions of the typical alveolar click and the contrastive “retroflex” click. Ultrasound results show that the “alveolar” click is apical post-alveolar and the “retroflex” click is laminal alveolar. The burst duration of the post-alveolar click averages 12 ms which is “abrupt,” while the burst duration of the alveolar click averages 30 ms, which is “noisy.” Mixed effects logistic regression models tested the effects of rise time and burst duration. Burst duration differed significantly among the two clicks (p < 0.001), while the effect of rise time was not significant. The ratio of energy in the click noisebursts below 20 ERB to the energy above 20 ERB is between 1.0 and 1.5 for the post-alveolar click, but between 0.5 and 1.0 for the alveolar click. The ratio was a significant predictor of click type (p = 0.014). The highest concentration of energy for the post-alveolar click is between 12 and 18 ERB, while the highest concentration of energy in the alveolar click is between 25 and 30 ERB. We attribute the frequency difference to a larger lingual cavity volume in the post-alveolar click, and a smaller volume in the alveolar click.